1
|
Ferreira JJ, Amazu C, Puga-Molina LC, Ma X, England SK, Santi CM. SLO2.1/NALCN a sodium signaling complex that regulates uterine activity. iScience 2021; 24:103210. [PMID: 34746693 PMCID: PMC8551532 DOI: 10.1016/j.isci.2021.103210] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Revised: 07/29/2021] [Accepted: 09/29/2021] [Indexed: 01/05/2023] Open
Abstract
Depolarization of the myometrial smooth muscle cell (MSMC) resting membrane potential is necessary for the uterus to transition from a quiescent state to a contractile state. The molecular mechanisms involved in this transition are not completely understood. Here, we report that a coupled system between the Na+-activated K+ channel (SLO2.1) and the non-selective Na+ leak channel (NALCN) determines the MSMC membrane potential. Our data indicate that Na+ entering through NALCN acts as an intracellular signaling molecule that activates SLO2.1. Potassium efflux through SLO2.1 hyperpolarizes the membrane. A decrease in SLO2.1/NALCN activity induces membrane depolarization, triggering Ca2+ entry through voltage-dependent Ca2+ channels and promoting contraction. Consistent with functional coupling, our data show that NALCN and SLO2.1 are in close proximity in human MSMCs. We propose that these arrangements of SLO2.1 and NALCN permit these channels to functionally regulate MSMC membrane potential and cell excitability and modulate uterine contractility.
Collapse
Affiliation(s)
- Juan J. Ferreira
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
- Department of Neuroscience, Washington University in St. Louis, School of Medicine, St. Louis, MO 63110, USA
| | - Chinwendu Amazu
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Lis C. Puga-Molina
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Xiaofeng Ma
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Sarah K. England
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Celia M. Santi
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
- Department of Neuroscience, Washington University in St. Louis, School of Medicine, St. Louis, MO 63110, USA
| |
Collapse
|
2
|
Ferreira JJ, Butler A, Stewart R, Gonzalez-Cota AL, Lybaert P, Amazu C, Reinl EL, Wakle-Prabagaran M, Salkoff L, England SK, Santi CM. Oxytocin can regulate myometrial smooth muscle excitability by inhibiting the Na + -activated K + channel, Slo2.1. J Physiol 2018; 597:137-149. [PMID: 30334255 DOI: 10.1113/jp276806] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2018] [Accepted: 10/17/2018] [Indexed: 01/05/2023] Open
Abstract
KEY POINTS At the end of pregnancy, the uterus transitions from a quiescent state to a highly contractile state. This transition requires that the uterine (myometrial) smooth muscle cells increase their excitability, although how this occurs is not fully understood. We identified SLO2.1, a potassium channel previously unknown in uterine smooth muscle, as a potential significant contributor to the electrical excitability of myometrial smooth muscle cells. We found that activity of the SLO2.1 channel is negatively regulated by oxytocin via Gαq-protein-coupled receptor activation of protein kinase C. This results in depolarization of the uterine smooth muscle cells and calcium entry, which may contribute to uterine contraction. These findings provide novel insights into a previously unknown mechanism by which oxytocin may act to modulate myometrial smooth muscle cell excitability. Our findings also reveal a new potential pharmacological target for modulating uterine excitability. ABSTRACT During pregnancy, the uterus transitions from a quiescent state to a more excitable contractile state. This is considered to be at least partly a result of changes in the myometrial smooth muscle cell (MSMC) resting membrane potential. However, the ion channels controlling the myometrial resting membrane potential and the mechanism of transition to a more excitable state have not been fully clarified. In the present study, we show that the sodium-activated, high-conductance, potassium leak channel, SLO2.1, is expressed and active at the resting membrane potential in MSMCs. Additionally, we report that SLO2.1 is inhibited by oxytocin binding to the oxytocin receptor. Inhibition of SLO2.1 leads to membrane depolarization and activation of voltage-dependent calcium channels, resulting in calcium influx. The results of the present study reveal that oxytocin may modulate MSMC electrical activity by inhibiting SLO2.1 potassium channels.
Collapse
Affiliation(s)
- Juan J Ferreira
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA
| | - Alice Butler
- Washington University School of Medicine, Department of Neuroscience, St Louis, MO, USA
| | - Richard Stewart
- Washington University School of Medicine, Department of Neuroscience, St Louis, MO, USA
| | - Ana Laura Gonzalez-Cota
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA
| | - Pascale Lybaert
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA.,Present address: Laboratoire de Physiologie et Pharmacologie (LAPP), Faculté de Médecine, Université Libre de Bruxelles, Bruxelles, Belgium
| | - Chinwendu Amazu
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA
| | - Erin L Reinl
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA.,Present address: Pharmacology Department, School of Medicine, University of Maryland, Baltimore, MD, USA
| | - Monali Wakle-Prabagaran
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA
| | - Lawrence Salkoff
- Washington University School of Medicine, Department of Neuroscience, St Louis, MO, USA
| | - Sarah K England
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA
| | - Celia M Santi
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA.,Washington University School of Medicine, Department of Neuroscience, St Louis, MO, USA
| |
Collapse
|
3
|
Lutton EJ, Lammers WJEP, James S, van den Berg HA, Blanks AM. Identification of uterine pacemaker regions at the myometrial-placental interface in the rat. J Physiol 2018; 596:2841-2852. [PMID: 29704394 PMCID: PMC6046083 DOI: 10.1113/jp275688] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2017] [Accepted: 04/19/2018] [Indexed: 12/16/2022] Open
Abstract
KEY POINTS Coordinated contraction of the uterine smooth muscle is essential to parturition. Histologically and physiologically defined pacemaker structures have not been identified in uterine smooth muscle. Here we report combined electrophysiological and histological evidence of zones associated with pacemaker activity in the rat myometrium. Our method relies crucially on the integration of histological and electrophysiological data in an in silico three-dimensional reconstruction of the rat myometrium at 10 μm resolution. We find that myometrial/placental pacemaking zones are closely related with placental sites and the area of disruptive myometrial remodelling surrounding such sites. If analogues of the myometrial/placental pacemaking zone are present in the human, defining their histology and physiology will be important steps towards treatment of pre-term birth, pre-eclampsia, and postpartum haemorrhage. ABSTRACT Coordinated uterine contractions are essential for delivering viable offspring in mammals. In contrast to other visceral smooth muscles, it is not known where excitation within the uterus is initiated, and no defined pacemaking region has hitherto been identified. Using multi-electrode array recordings and high-resolution computational reconstruction of the three-dimensional micro-structure of late pregnant rat uterus, we demonstrate that electrical potentials are initiated in distinct structures within the placental bed of individual implantation sites. These previously unidentified structures represent modified smooth muscle bundles that are derived from bridges between the longitudinal and circular layers. Coordinated implantation and encapsulation by invading trophoblast give rise to isolated placental/myometrial interface bundles that directly connect to the overlying longitudinal smooth muscle layer. Taken together, these observations imply that the anatomical structure of the uterus, combined with site-specific implantation, gives rise to emergent patterns of electrical activity that drive effective contractility during parturition.
Collapse
Affiliation(s)
- E Josiah Lutton
- Cell and Developmental Biology, Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, CV4 7AL, UK
| | - Wim J E P Lammers
- Bioengineering Institute, Auckland University, Auckland, New Zealand.,Department of Physiology, College of Medicine and Health Sciences, UAE University, Al Ain, United Arab Emirates
| | - Sean James
- Department of Pathology, University Hospitals Coventry and Warwickshire (UHCW), NHS Trust, Coventry, CV2 2DX, UK
| | | | - Andrew M Blanks
- Cell and Developmental Biology, Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, CV4 7AL, UK
| |
Collapse
|
4
|
Abstract
In the United States, the generally accepted indication for tocolytic therapy centers on suppression of preterm labor. This may be in the form of preventative therapy with progesterone in women with prior spontaneous preterm birth or as an acute intervention to suppress established uterine contractions associated with cervical change occurring at less than 37 weeks gestation. This article seeks to apply this perspective to tocolytic therapy. Here, we provide a review of current tocolytic options and what the last decade of discovery has revealed about the regulation of myometrial excitability and quiescence. Moving forward, we must incorporate the emerging molecular data that is amassing in order to develop novel and effective tocolytic therapeutic options to prevent preterm labor and spontaneous preterm birth (sPTB).
Collapse
Affiliation(s)
| | | | - George Gallos
- Department of Anesthesia, Columbia University Medical Center, New York, NY.
| |
Collapse
|
5
|
Sharma V, Nair SV, Jaitley P, Nakade UP, Sharma A, Choudhury S, Garg SK. ATP-sensitive and maxi potassium channels regulate BRL 37344-induced tocolysis in buffaloes-an in vitro study. Theriogenology 2017; 107:194-202. [PMID: 29172176 DOI: 10.1016/j.theriogenology.2017.10.044] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Revised: 10/26/2017] [Accepted: 10/30/2017] [Indexed: 11/17/2022]
Abstract
Cellular coupling of beta3-adrenoceptors (β3-ADR) to potassium channels in myometrium is largely unknown. In vitro study was undertaken to unravel the presence of β3-adrenergic receptors (ADR) and the role of K+-channels in mediating β3-ADR-induced relaxation in isolated myometrial strips from cyclic non-pregnant water buffaloes. Isometric tension was recorded in isolated myometrial strips using data acquisition system based physiograph. Compared to SR 59230A, BRL 37344 was found to be more potent in inducing β3-dependent myometrial relaxation which was significantly (p < 0.05) inhibited in the presence of β3 antagonist, SAR 150640. The immunoreactive protein to β3-ADR was also detected in membrane fraction of myometrial protein. Further, incubation with BRL 37344 (10 μM) significantly (p < 0.05) increased c-AMP accumulation (37.58 ± 9.52 pmol/mg protein; n = 4) in the myometrial strips compared to basal c-AMP level (16.85 ± 3.87 pmol/mg protein; n = 4). The concentration response curves (CRC) of BRL 37344 were significantly (p < 0.05) shifted towards right in the presence of KATP channels specific blocker, glibenclamide (10 μM) and maxi K+-channels (BKCa) specific blocker, iberiotoxin (100 nM), with decrease in both efficacy and potency as compared to control. However, 4-aminopyridine (4-AP), a specific blocker of the voltage gated K+-channels (Kv), failed to alter the CRC of BRL 37344. Existence of immunoreactive protein to Kir6.1, α-subunit of BKCa and Kv1.1 channels were also detected in the membrane fraction of myometrial protein. Based on the above findings, it can be concluded that BRL 37344 is a potent stimulator of β3-adrenoceptors in buffalo myometrium and besides mediating their effect through rise in c-AMP, they are coupled to KATP and BKCa channels in inducing tocolytic effects.
Collapse
Affiliation(s)
- Vipin Sharma
- Smooth Muscle & Molecular Pharmacology Laboratory, Department of Veterinary Pharmacology & Toxicology, College of Veterinary Science and Animal Husbandry, U.P. Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam, Go-Anusandhan Sansthan, Mathura 281001, India
| | - Sooraj V Nair
- Smooth Muscle & Molecular Pharmacology Laboratory, Department of Veterinary Pharmacology & Toxicology, College of Veterinary Science and Animal Husbandry, U.P. Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam, Go-Anusandhan Sansthan, Mathura 281001, India
| | - Pooja Jaitley
- Smooth Muscle & Molecular Pharmacology Laboratory, Department of Veterinary Pharmacology & Toxicology, College of Veterinary Science and Animal Husbandry, U.P. Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam, Go-Anusandhan Sansthan, Mathura 281001, India
| | - Udayraj P Nakade
- Smooth Muscle & Molecular Pharmacology Laboratory, Department of Veterinary Pharmacology & Toxicology, College of Veterinary Science and Animal Husbandry, U.P. Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam, Go-Anusandhan Sansthan, Mathura 281001, India
| | - Abhishek Sharma
- Smooth Muscle & Molecular Pharmacology Laboratory, Department of Veterinary Pharmacology & Toxicology, College of Veterinary Science and Animal Husbandry, U.P. Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam, Go-Anusandhan Sansthan, Mathura 281001, India
| | - Soumen Choudhury
- Smooth Muscle & Molecular Pharmacology Laboratory, Department of Veterinary Pharmacology & Toxicology, College of Veterinary Science and Animal Husbandry, U.P. Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam, Go-Anusandhan Sansthan, Mathura 281001, India.
| | - Satish Kumar Garg
- Smooth Muscle & Molecular Pharmacology Laboratory, Department of Veterinary Pharmacology & Toxicology, College of Veterinary Science and Animal Husbandry, U.P. Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam, Go-Anusandhan Sansthan, Mathura 281001, India
| |
Collapse
|
6
|
Hormones and sex differences: changes in cardiac electrophysiology with pregnancy. Clin Sci (Lond) 2017; 130:747-59. [PMID: 27128800 DOI: 10.1042/cs20150710] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2015] [Accepted: 02/01/2016] [Indexed: 11/17/2022]
Abstract
Disruption of cardiac electrical activity resulting in palpitations and syncope is often an early symptom of pregnancy. Pregnancy is a time of dramatic and dynamic physiological and hormonal changes during which numerous demands are placed on the heart. These changes result in electrical remodelling which can be detected as changes in the electrocardiogram (ECG). This gestational remodelling is a very under-researched area. There are no systematic large studies powered to determine changes in the ECG from pre-pregnancy, through gestation, and into the postpartum period. The large variability between patients and the dynamic nature of pregnancy hampers interpretation of smaller studies, but some facts are consistent. Gestational cardiac hypertrophy and a physical shift of the heart contribute to changes in the ECG. There are also electrical changes such as an increased heart rate and lengthening of the QT interval. There is an increased susceptibility to arrhythmias during pregnancy and the postpartum period. Some changes in the ECG are clearly the result of changes in ion channel expression and behaviour, but little is known about the ionic basis for this electrical remodelling. Most information comes from animal models, and implicates changes in the delayed-rectifier channels. However, it is likely that there are additional roles for sodium channels as well as changes in calcium homoeostasis. The changes in the electrical profile of the heart during pregnancy and the postpartum period have clear implications for the safety of pregnant women, but the field remains relatively undeveloped.
Collapse
|
7
|
Affiliation(s)
- Barbara M. Sanborn
- Department of Biochemistry and Molecular Biology, University of Texas Houston Medical School, PO Box 20708, Houston, TX 77225
| |
Collapse
|
8
|
McCloskey C, Rada C, Bailey E, McCavera S, van den Berg HA, Atia J, Rand DA, Shmygol A, Chan YW, Quenby S, Brosens JJ, Vatish M, Zhang J, Denton JS, Taggart MJ, Kettleborough C, Tickle D, Jerman J, Wright P, Dale T, Kanumilli S, Trezise DJ, Thornton S, Brown P, Catalano R, Lin N, England SK, Blanks AM. The inwardly rectifying K+ channel KIR7.1 controls uterine excitability throughout pregnancy. EMBO Mol Med 2015; 6:1161-74. [PMID: 25056913 PMCID: PMC4197863 DOI: 10.15252/emmm.201403944] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Abnormal uterine activity in pregnancy causes a range of important clinical disorders, including preterm birth, dysfunctional labour and post-partum haemorrhage. Uterine contractile patterns are controlled by the generation of complex electrical signals at the myometrial smooth muscle plasma membrane. To identify novel targets to treat conditions associated with uterine dysfunction, we undertook a genome-wide screen of potassium channels that are enriched in myometrial smooth muscle. Computational modelling identified Kir7.1 as potentially important in regulating uterine excitability during pregnancy. We demonstrate Kir7.1 current hyper-polarizes uterine myocytes and promotes quiescence during gestation. Labour is associated with a decline, but not loss, of Kir7.1 expression. Knockdown of Kir7.1 by lentiviral expression of miRNA was sufficient to increase uterine contractile force and duration significantly. Conversely, overexpression of Kir7.1 inhibited uterine contractility. Finally, we demonstrate that the Kir7.1 inhibitor VU590 as well as novel derivative compounds induces profound, long-lasting contractions in mouse and human myometrium; the activity of these inhibitors exceeds that of other uterotonic drugs. We conclude Kir7.1 regulates the transition from quiescence to contractions in the pregnant uterus and may be a target for therapies to control uterine contractility.
Collapse
Affiliation(s)
- Conor McCloskey
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Cara Rada
- Division of Basic Science Research, Department of Obstetrics and Gynecology, School of Medicine Washington University in St. Louis,, St. Louis, MO, USA
| | - Elizabeth Bailey
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Samantha McCavera
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Hugo A van den Berg
- Warwick Systems Biology & Mathematics Institute University of Warwick, Coventry, UK
| | - Jolene Atia
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - David A Rand
- Warwick Systems Biology & Mathematics Institute University of Warwick, Coventry, UK
| | - Anatoly Shmygol
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Yi-Wah Chan
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Siobhan Quenby
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Jan J Brosens
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Manu Vatish
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Jie Zhang
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Jerod S Denton
- Vanderbilt Institute of Chemical Biology, Vanderbilt Institute for Global Health Vanderbilt University School of Medicine Medical Center North, Nashville, TN, USA
| | - Michael J Taggart
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, UK
| | | | - David Tickle
- Centre for Therapeutics and Discovery, Medical Research Council Technologies, London, UK
| | - Jeff Jerman
- Centre for Therapeutics and Discovery, Medical Research Council Technologies, London, UK
| | - Paul Wright
- Centre for Therapeutics and Discovery, Medical Research Council Technologies, London, UK
| | - Timothy Dale
- BioPark, Essen BioScience Ltd, Welwyn Garden City, Hertfordshire, UK
| | | | - Derek J Trezise
- BioPark, Essen BioScience Ltd, Welwyn Garden City, Hertfordshire, UK
| | | | - Pamela Brown
- MRC Centre for Reproductive Health (CRH), Queen's Medical Research Institute University of Edinburgh, Edinburgh, UK
| | - Roberto Catalano
- MRC Centre for Reproductive Health (CRH), Queen's Medical Research Institute University of Edinburgh, Edinburgh, UK
| | - Nan Lin
- Department of Mathematics, Washington University, St. Louis, MO, USA
| | - Sarah K England
- Division of Basic Science Research, Department of Obstetrics and Gynecology, School of Medicine Washington University in St. Louis,, St. Louis, MO, USA
| | - Andrew M Blanks
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| |
Collapse
|
9
|
Waite SL, Gandhi SV, Khan RN, Chapman NR. The effect of trichostatin-A and tumor necrosis factor on expression of splice variants of the MaxiK and L-type channels in human myometrium. Front Physiol 2014; 5:261. [PMID: 25076912 PMCID: PMC4097961 DOI: 10.3389/fphys.2014.00261] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2014] [Accepted: 06/20/2014] [Indexed: 01/30/2023] Open
Abstract
The onset of human parturition is associated with up-regulation of pro-inflammatory cytokines including tumor necrosis factor (TNF) as well as changes in ion flux, principally Ca2+ and K+, across the myometrial myocytes membrane. Elevation of intra-cellular Ca2+ from the sarcoplasmic reticulum opens L-type Ca2+ channels (LTCCs); in turn this increased calcium level activates MaxiK channels leading to relaxation. While the nature of how this cross-talk is governed remains unclear, our previous work demonstrated that the pro-inflammatory cytokine, TNF, and the histone deacetylase inhibitor, Trichostatin-A (TSA), exerted opposing effects on the expression of the pro-quiescent Gαs gene in human myometrial cells. Consequently, in this study we demonstrate that the different channel splice variants for both MaxiK and LTCC are expressed in primary myometrial myocytes. MaxiK mRNA expression was sensitive to TSA stimulation, this causing repression of the M1, M3, and M4 splice variants. A small but not statistically significantly increase in MaxiK expression was also seen in response to TNF. In contrast to this, expression of LTCC splice variants was seen to be influenced by both TNF and TSA. TNF induced overall increase in total LTCC expression while TSA stimulated a dual effect: causing induction of LTCC exon 8 expression but repressing expression of other LTCC splice variants including that encoding exons 30, 31, 33, and 34, exons 30–34 and exons 40–43. The significance of these observations is discussed herein.
Collapse
Affiliation(s)
- Sarah L Waite
- Academic Unit of Reproductive and Developmental Medicine, Department of Human Metabolism, University of Sheffield Sheffield, UK
| | - Saurabh V Gandhi
- Department of Obstetrics and Gynaecology, Sheffield Teaching Hospitals NHS Foundation Trust Sheffield, UK
| | - Raheela N Khan
- Division of Medical Sciences and Graduate Entry Medicine, School of Medicine, Royal Derby Hospital, University of Nottingham Derby, UK
| | - Neil R Chapman
- Academic Unit of Reproductive and Developmental Medicine, Department of Human Metabolism, University of Sheffield Sheffield, UK
| |
Collapse
|
10
|
Lorca RA, Prabagaran M, England SK. Functional insights into modulation of BKCa channel activity to alter myometrial contractility. Front Physiol 2014; 5:289. [PMID: 25132821 PMCID: PMC4116789 DOI: 10.3389/fphys.2014.00289] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Accepted: 07/14/2014] [Indexed: 12/15/2022] Open
Abstract
The large-conductance voltage- and Ca(2+)-activated K(+) channel (BKCa) is an important regulator of membrane excitability in a wide variety of cells and tissues. In myometrial smooth muscle, activation of BKCa plays essential roles in buffering contractility to maintain uterine quiescence during pregnancy and in the transition to a more contractile state at the onset of labor. Multiple mechanisms of modulation have been described to alter BKCa channel activity, expression, and cellular localization. In the myometrium, BKCa is regulated by alternative splicing, protein targeting to the plasma membrane, compartmentation in membrane microdomains, and posttranslational modifications. In addition, interaction with auxiliary proteins (i.e., β1- and β2-subunits), association with G-protein coupled receptor signaling pathways, such as those activated by adrenergic and oxytocin receptors, and hormonal regulation provide further mechanisms of variable modulation of BKCa channel function in myometrial smooth muscle. Here, we provide an overview of these mechanisms of BKCa channel modulation and provide a context for them in relation to myometrial function.
Collapse
Affiliation(s)
- Ramón A Lorca
- Department of Obstetrics and Gynecology, Washington University in St. Louis School of Medicine St. Louis, MO, USA
| | - Monali Prabagaran
- Department of Obstetrics and Gynecology, Washington University in St. Louis School of Medicine St. Louis, MO, USA
| | - Sarah K England
- Department of Obstetrics and Gynecology, Washington University in St. Louis School of Medicine St. Louis, MO, USA
| |
Collapse
|
11
|
Chaemsaithong P, Madan I, Romero R, Than NG, Tarca AL, Draghici S, Bhatti G, Yeo L, Mazor M, Kim CJ, Hassan SS, Chaiworapongsa T. Characterization of the myometrial transcriptome in women with an arrest of dilatation during labor. J Perinat Med 2013; 41:665-81. [PMID: 23893668 PMCID: PMC4183453 DOI: 10.1515/jpm-2013-0086] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/16/2013] [Accepted: 05/17/2013] [Indexed: 01/28/2023]
Abstract
OBJECTIVE The molecular basis of failure to progress in labor is poorly understood. This study was undertaken to characterize the myometrial transcriptome of patients with an arrest of dilatation (AODIL). STUDY DESIGN Human myometrium was prospectively collected from women in the following groups: (1) spontaneous term labor (TL; n=29) and (2) arrest of dilatation (AODIL; n=14). Gene expression was characterized using Illumina® HumanHT-12 microarrays. A moderated Student's t-test and false discovery rate adjustment were used for analysis. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) of selected genes was performed in an independent sample set. Pathway analysis was performed on the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database using Pathway Analysis with Down-weighting of Overlapping Genes (PADOG). The MetaCore knowledge base was also searched for pathway analysis. RESULTS (1) Forty-two differentially expressed genes were identified in women with an AODIL; (2) gene ontology analysis indicated enrichment of biological processes, which included regulation of angiogenesis, response to hypoxia, inflammatory response, and chemokine-mediated signaling pathway. Enriched molecular functions included transcription repressor activity, heat shock protein (Hsp) 90 binding, and nitric oxide synthase (NOS) activity; (3) MetaCore analysis identified immune response chemokine (C-C motif) ligand 2 (CCL2) signaling, muscle contraction regulation of endothelial nitric oxide synthase (eNOS) activity in endothelial cells, and triiodothyronine and thyroxine signaling as significantly overrepresented (false discovery rate <0.05); (4) qRT-PCR confirmed the overexpression of Nitric oxide synthase 3 (NOS3); hypoxic ischemic factor 1A (HIF1A); Chemokine (C-C motif) ligand 2 (CCL2); angiopoietin-like 4 (ANGPTL4); ADAM metallopeptidase with thrombospondin type 1, motif 9 (ADAMTS9); G protein-coupled receptor 4 (GPR4); metallothionein 1A (MT1A); MT2A; and selectin E (SELE) in an AODIL. CONCLUSION The myometrium of women with AODIL has a stereotypic transcriptome profile. This disorder has been associated with a pattern of gene expression involved in muscle contraction, an inflammatory response, and hypoxia. This is the first comprehensive and unbiased examination of the molecular basis of an AODIL.
Collapse
|
12
|
Malysz J, Rovner ES, Petkov GV. Single-channel biophysical and pharmacological characterizations of native human large-conductance calcium-activated potassium channels in freshly isolated detrusor smooth muscle cells. Pflugers Arch 2013; 465:965-75. [PMID: 23344746 PMCID: PMC3659209 DOI: 10.1007/s00424-012-1214-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2012] [Revised: 12/27/2012] [Accepted: 12/29/2012] [Indexed: 10/27/2022]
Abstract
Recent studies have demonstrated the importance of large-conductance Ca(2+)-activated K(+) (BK) channels in detrusor smooth muscle (DSM) function in vitro and in vivo. However, in-depth characterization of human native DSM single BK channels has not yet been provided. Here, we conducted single-channel recordings from excised patches from native human DSM cells. Inside-out and outside-out recordings in high K(+) symmetrical solution (containing 140 mM KCl and ~300 nM free Ca(2+)) showed single-channel conductance of 215-220 pS, half-maximum constant for activation of ~+75 to +80 mV, and low probability of opening (P o) at +20 mV that increased ~10-fold at +40 mV and ~60-fold at +60 mV. Using the inside-out configuration at +30 mV, reduction of intracellular [Ca(2+)] from ~300 nM to Ca(2+)-free decreased the P o by ~85 %, whereas elevation to ~800 nM increased P o by ~50-fold. The BK channel activator NS1619 (10 μM) enhanced the P o by ~10-fold at +30 mV; subsequent application of the selective BK channel inhibitor paxilline (500 nM) blocked the activity. Changes in intracellular [Ca(2+)] or the addition of NS1619 did not significantly alter the current amplitude or single-channel conductance. This is the first report to provide biophysical and pharmacological profiles of native human DSM single BK channels highlighting their importance in regulating human DSM excitability.
Collapse
Affiliation(s)
- John Malysz
- Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, SC 29208
| | - Eric S. Rovner
- Medical University of South Carolina, Charleston, SC 29425
| | - Georgi V. Petkov
- Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, SC 29208
- Medical University of South Carolina, Charleston, SC 29425
| |
Collapse
|
13
|
Corriveau S, Pasquier JC, Blouin S, Bellabarba D, Rousseau É. Chronic levothyroxine and acute T3 treatments enhance the amplitude and time course of uterine contractions in human. Am J Physiol Endocrinol Metab 2013; 304:E478-85. [PMID: 23249699 DOI: 10.1152/ajpendo.00346.2012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study compares the functional consequences of levothyroxine (T4) treatment during pregnancy as well as the acute affects of triiodothyronine (T3) on spontaneous uterine contractile activities observed in vitro. Uterine biopsies were obtained from consenting women undergoing elective caesarean at term (n = 28). Spontaneous contractile activities from T4-treated pregnant women (n = 8) were compared with control patients (n = 20) by isometric tension measurements. Effects of acute T3 and T4 on control tissues were also monitored. Area under the curve, amplitude, time to peak, duration, and frequency were quantified. In uterine strips from women treated for hypothyroidism, phasic uterine contractions of larger amplitude (+77%) were observed, with a prolonged duration at 90% relaxation (+138%) and reduced frequency (-55%) compared with values of the control group. The addition of exogenous T3 in vitro on control strips induced a significant increase in the duration of the contractions and a significant decrease in frequency (P < 0.05), which partially mimics the results obtained in strips from T4-treated women. Significant modifications of contractile properties were observed in strips from pregnant women treated with levothyroxine, consistent with those observed with the addition of exogenous T3. Clinical practices of modern obstetrics should take into account the effect of thyroid hormones on uterine contractions' time course to ensure a tighter followup at the end of pregnancy to achieve safer delivery.
Collapse
Affiliation(s)
- Stéphanie Corriveau
- Department of Obstetrics and Gynecology, Université de Sherbrooke, Sherbrooke, Quebec, Canada
| | | | | | | | | |
Collapse
|
14
|
Ehling P, Cerina M, Meuth P, Kanyshkova T, Bista P, Coulon P, Meuth SG, Pape HC, Budde T. Ca(2+)-dependent large conductance K(+) currents in thalamocortical relay neurons of different rat strains. Pflugers Arch 2012. [PMID: 23207578 DOI: 10.1007/s00424-012-1188-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Mutations in genes coding for Ca(2+) channels were found in patients with childhood absence epilepsy (CAE) indicating a contribution of Ca(2+)-dependent mechanisms to the generation of spike-wave discharges (SWD) in humans. Since the involvement of Ca(2+) signals remains unclear, the aim of the present study was to elucidate the function of a Ca(2+)-dependent K(+) channel (BKCa) under physiological conditions and in the pathophysiological state of CAE. The activation of BKCa channels is dependent on both voltage and intracellular Ca(2+) concentrations. Moreover, these channels exhibit an outstandingly high level of regulatory heterogeneity that builds the basis for the influence of BKCa channels on different aspects of neuronal activity. Here, we analyse the contribution of BKCa channels to firing of thalamocortical relay neurons, and we test the hypothesis that BKCa channel activity affects the phenotype of a genetic rat model of CAE. We found that the activation of the β2-adrenergic receptor/protein kinase A pathway resulted in BKCa channel inhibition. Furthermore, BKCa channels affect the number of action potentials fired in a burst and produced spike frequency adaptation during tonic activity. The latter result was confirmed by a computer modelling approach. We demonstrate that the β2-adrenergic inhibition of BKCa channels prevents spike frequency adaptation and, thus, might significantly support the tonic firing mode of thalamocortical relay neurons. In addition, we show that BKCa channel functioning differs in epileptic WAG/Rij and thereby likely contributes to highly synchronised, epileptic network activity.
Collapse
Affiliation(s)
- Petra Ehling
- Institute of Physiology I, University of Münster, Robert-Koch-Str. 27a, Münster, Germany.
| | | | | | | | | | | | | | | | | |
Collapse
|
15
|
Rosenbaum ST, Larsen T, Joergensen JC, Bouchelouche PN. Relaxant effect of a novel calcium-activated potassium channel modulator on human myometrial spontaneous contractility in vitro. Acta Physiol (Oxf) 2012; 205:247-54. [PMID: 22099068 DOI: 10.1111/j.1748-1716.2011.02384.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
AIM To investigate the effect of 4,5-dichloro-1,3-diethyl-1,3-dihydro-benzoimidazol-2-one (NS4591), a novel SK/IK channels positive modulator, on human myometrial activity. METHODS Organ bath studies were performed on myometrial preparations obtained from women undergoing elective caesarean section at term (N = 11) or hysterectomy (N = 11). NS4591 was added cumulatively in the concentration range of 0.3-30 μm. In separate experiments, the effects of pre-incubation of muscle preparation with the SK or IK channel blockers apamin (1 μm) and TRAM34 (10 μm) on the outcomes of NS4591 were evaluated. Simultaneous vehicle controls were performed for all experiments. The effects of drugs were studied on spontaneous contractions. RESULTS NS4591 exerted an inhibitory effect on myometrial contractions in muscle strips from non-pregnant and pregnant women. The contractility in non-pregnant and pregnant myometrium was reduced to the following values respectively: amplitude 20.65 ± 7.38% (P < 0.001) and 42.85 ± 11.04% (P < 0.05) and area under the curve 11.72 ± 7.39% (P < 0.001) and 34.84 ± 10.50% (P < 0.001) and are reflective of 30 μm NS4591 compared to vehicle control. In non-pregnant tissue, apamin partially reduced the inhibitory effects of NS4591, but we observed relaxation mediated by NS4591 despite pre-incubation with TRAM34. In contrast, in pregnant tissue, neither apamin nor TRAM34 could reverse the relaxatory effects of NS4591. CONCLUSION Our findings imply that SK/IK channels are present and functional in myometrium from pregnant and non-pregnant women. The SK/IK channel-positive modulator NS4591 exerts relaxation of human myometrium in vitro, and this may have implications for the clinical management of preterm labour.
Collapse
Affiliation(s)
- S T Rosenbaum
- Department of Gynecology and Obstetrics, Holbaek Hospital, Holbaek, Denmark.
| | | | | | | |
Collapse
|
16
|
Sadlonova V. Response to ‘Effects of potassium ion channels in term pregnant myometrium’1. J Obstet Gynaecol Res 2011. [DOI: 10.1111/j.1447-0756.2011.01732.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
17
|
Soloff MS, Jeng YJ, Izban MG, Sinha M, Luxon BA, Stamnes SJ, England SK. Effects of progesterone treatment on expression of genes involved in uterine quiescence. Reprod Sci 2011; 18:781-97. [PMID: 21795739 PMCID: PMC4051400 DOI: 10.1177/1933719111398150] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
An important action of progesterone during pregnancy is to maintain the uterus in a quiescent state and thereby prevent preterm labor. The causes of preterm labor are not well understood, so progesterone action on the myometrium can provide clues about the processes that keep the uterus from contracting prematurely. Accordingly, we have carried out Affymetrix GeneChip analysis of progesterone effects on gene expression in immortalized human myometrial cells cultured from a patient near the end of pregnancy. Progesterone appears to inhibit uterine excitability by a number of mechanisms, including increased expression of calcium and voltage-operated K(+) channels, which dampens the electrical activity of the myometrial cell, downregulation of agents, and receptors involved in myometrial contraction, reduction in cell signal components that lead to increased intracellular Ca(2+) concentrations in response to contractile stimuli, and downregulation of proteins involved in the cross-linking of actin and myosin filaments to produce uterine contractions.
Collapse
Affiliation(s)
- Melvyn S. Soloff
- Department of Obstetrics and Gynecology, University of Texas Medical Branch, Galveston, TX, USA
| | - Yow-Jiun Jeng
- Department of Obstetrics and Gynecology, University of Texas Medical Branch, Galveston, TX, USA
| | - Michael G. Izban
- Department of Obstetrics and Gynecology, Meharry Medical College, Nashville, TN, USA
| | - Mala Sinha
- Department of Biochemistry and Molecular Biology, and the Sealy Center for Molecular Medicine, University of Texas Medical Branch, Galveston, TX, USA
| | - Bruce A. Luxon
- Department of Biochemistry and Molecular Biology, and the Sealy Center for Molecular Medicine, University of Texas Medical Branch, Galveston, TX, USA
| | - Susan J. Stamnes
- Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA, USA
| | - Sarah K. England
- Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA, USA
| |
Collapse
|
18
|
Choudhury S, Garg SK, Singh TU, Mishra SK. Functional and molecular characterization of maxi K+-channels (BKCa) in buffalo myometrium. Anim Reprod Sci 2011; 126:173-8. [DOI: 10.1016/j.anireprosci.2011.05.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2010] [Revised: 05/20/2011] [Accepted: 05/30/2011] [Indexed: 11/25/2022]
|
19
|
Tong WC, Choi CY, Karche S, Holden AV, Zhang H, Taggart MJ. A computational model of the ionic currents, Ca2+ dynamics and action potentials underlying contraction of isolated uterine smooth muscle. PLoS One 2011; 6:e18685. [PMID: 21559514 PMCID: PMC3084699 DOI: 10.1371/journal.pone.0018685] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2010] [Accepted: 03/15/2011] [Indexed: 11/18/2022] Open
Abstract
Uterine contractions during labor are discretely regulated by rhythmic action potentials (AP) of varying duration and form that serve to determine calcium-dependent force production. We have employed a computational biology approach to develop a fuller understanding of the complexity of excitation-contraction (E-C) coupling of uterine smooth muscle cells (USMC). Our overall aim is to establish a mathematical platform of sufficient biophysical detail to quantitatively describe known uterine E-C coupling parameters and thereby inform future empirical investigations of physiological and pathophysiological mechanisms governing normal and dysfunctional labors. From published and unpublished data we construct mathematical models for fourteen ionic currents of USMCs: currents (L- and T-type), current, an hyperpolarization-activated current, three voltage-gated currents, two -activated current, -activated current, non-specific cation current, - exchanger, - pump and background current. The magnitudes and kinetics of each current system in a spindle shaped single cell with a specified surface area∶volume ratio is described by differential equations, in terms of maximal conductances, electrochemical gradient, voltage-dependent activation/inactivation gating variables and temporal changes in intracellular computed from known fluxes. These quantifications are validated by the reconstruction of the individual experimental ionic currents obtained under voltage-clamp. Phasic contraction is modeled in relation to the time constant of changing . This integrated model is validated by its reconstruction of the different USMC AP configurations (spikes, plateau and bursts of spikes), the change from bursting to plateau type AP produced by estradiol and of simultaneous experimental recordings of spontaneous AP, and phasic force. In summary, our advanced mathematical model provides a powerful tool to investigate the physiological ionic mechanisms underlying the genesis of uterine electrical E-C coupling of labor and parturition. This will furnish the evolution of descriptive and predictive quantitative models of myometrial electrogenesis at the whole cell and tissue levels.
Collapse
Affiliation(s)
- Wing-Chiu Tong
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
- Maternal and Fetal Health Research Centre, St. Mary's Hospital, University of Manchester, Manchester, United Kingdom
| | - Cecilia Y. Choi
- School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
| | - Sanjay Karche
- School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
| | - Arun V. Holden
- Institute of Membrane and System Biology, University of Leeds, Leeds, United Kingdom
| | - Henggui Zhang
- School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
- * E-mail: (HZ); (MT)
| | - Michael J. Taggart
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
- Maternal and Fetal Health Research Centre, St. Mary's Hospital, University of Manchester, Manchester, United Kingdom
- * E-mail: (HZ); (MT)
| |
Collapse
|
20
|
Mittal P, Romero R, Tarca AL, Draghici S, Nhan-Chang CL, Chaiworapongsa T, Hotra J, Gomez R, Kusanovic JP, Lee DC, Kim CJ, Hassan SS. A molecular signature of an arrest of descent in human parturition. Am J Obstet Gynecol 2011; 204:177.e15-33. [PMID: 21284969 DOI: 10.1016/j.ajog.2010.09.025] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2010] [Revised: 08/18/2010] [Accepted: 09/27/2010] [Indexed: 12/22/2022]
Abstract
OBJECTIVE This study was undertaken to identify the molecular basis of an arrest of descent. STUDY DESIGN Human myometrium was obtained from women in term labor (TL; n = 29) and arrest of descent (AODes; n = 21). Gene expression was characterized using Illumina HumanHT-12 microarrays. A moderated Student t test and false discovery rate adjustment were applied for analysis. Confirmatory quantitative reverse transcription-polymerase chain reaction and immunoblot were performed in an independent sample set. RESULTS Four hundred genes were differentially expressed between women with an AODes compared with those with TL. Gene Ontology analysis indicated enrichment of biological processes and molecular functions related to inflammation and muscle function. Impacted pathways included inflammation and the actin cytoskeleton. Overexpression of hypoxia inducible factor-1a, interleukin -6, and prostaglandin-endoperoxide synthase 2 in AODes was confirmed. CONCLUSION We have identified a stereotypic pattern of gene expression in the myometrium of women with an arrest of descent. This represents the first study examining the molecular basis of an arrest of descent using a genome-wide approach.
Collapse
|
21
|
Sadlonova V, Franova S, Dokus K, Janicek F, Visnovsky J, Sadlonova J. Participation of BKCa2+ and KATP potassium ion channels in the contractility of human term pregnant myometrium in in vitro conditions. J Obstet Gynaecol Res 2011; 37:215-21. [PMID: 21272145 DOI: 10.1111/j.1447-0756.2010.01340.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
AIM The aim of this study was to assess the participation of ligand-sensitive potassium large conductance calcium-activated ion channels (BK(Ca2+) ) and adenosine triphosphate (ATP)-sensitive potassium ion channels (K(ATP) ) using its openers (NS1619 and pinacidil) in the contractility of human term pregnant myometrium in in vitro conditions. METHODS Human myometrium tissue samples were collected from term pregnant laboring women who had to undergo cesarean section. The contractility of myometrium was induced by the application of oxytocin into the organ bath. Myometrial strips were incubated with the opener of BK(Ca2+) potassium ion channels NS1619 and its antagonist tetraethylammonium or with the opener of K(ATP) potassium ion channels pinacidil and its antagonist glibenclamide. RESULTS K(ATP) potassium ion channel's opener pinacidil significantly decreased amplitude of myometrial contractions (P < 0.05) as well as frequency of myometrial contractions (P < 0.05) provoked by oxytocin in human term pregnant myometrium in in vitro conditions. The inhibition of the human myometrial contractions of pinacidil was significantly antagonized by its specific antagonist glibenclamide (P < 0.05). BK(Ca2+) potassium ion channel's opener NS1619 did not significantly affect the contractile activity of human term pregnant myometrium induced by the application of oxytocin in in vitro conditions. CONCLUSION In our experimental study we found that the participation of BK(Ca2+) and K(ATP) potassium ion channels in the contractility of human term pregnant myometrium in labor is probably different.
Collapse
Affiliation(s)
- Vladimira Sadlonova
- Department of Pharmacology, Jessenius Faculty of Medicine, Comenius University, Martin, Slovakia.
| | | | | | | | | | | |
Collapse
|
22
|
Day LJ, Schaa KL, Ryckman KK, Cooper M, Dagle JM, Fong CT, Simhan HN, Merrill DC, Marazita ML, Murray JC, England SK. Single-nucleotide polymorphisms in the KCNN3 gene associate with preterm birth. Reprod Sci 2011; 18:286-95. [PMID: 21266667 DOI: 10.1177/1933719110391277] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The objectives were to determine whether single-nucleotide polymorphisms (SNPs) in KCNN3 (encodes the small conductance calcium-activated potassium channel subfamily N, member 3), associate with preterm birth (PTB). In all, 602 preterm families with at least 1 preterm (<37 weeks gestation) infant were studied: DNA from the infant and one or both parents were genotyped for 16 SNPs in KCNN3. A region of interest within KCNN3 was sequenced in 512 Caucasian non-Hispanic mothers (412 with preterm deliveries;100 who delivered at term). Family-based association testing was used for genotyping analysis; Fisher exact test was used for sequencing analysis. Six SNPs (rs1218585, rs4845396, rs12058931, rs1218568, rs6426985, and rs4845394) were associated with PTB (all Ps < .05). These variations were all located within the intronic region between exons 1 and 2. Maternal sequencing revealed an association of 3 SNPs with spontaneous PTB; rs1218585 (P = .007), rs1218584 (P = .05), and a novel SNP at chromosome1:153099353 (P = .02). Polymorphisms in KCNN3 are associated with PTB and investigation into the functional significance of these allelic changes is warranted.
Collapse
Affiliation(s)
- Lori J Day
- 1Department of Obstetrics and Gynecology, University of Iowa Carver College of Medicine, Iowa City, IA, USA
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
23
|
Ahn HS, dela Peña I, Kim YC, Cheong JH. 4-Chloro-7-Trifluoromethyl-10 H- Benzo[4,5]furo[3,2- b]Indole-1-Carboxylic Acid (TBIC), a Putative BK Ca Channel Opener with Uterine Relaxant Activities. Pharmacology 2011; 87:331-40. [DOI: 10.1159/000328141] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2011] [Accepted: 04/04/2011] [Indexed: 11/19/2022]
|
24
|
Pierce SL, England SK. SK3 channel expression during pregnancy is regulated through estrogen and Sp factor-mediated transcriptional control of the KCNN3 gene. Am J Physiol Endocrinol Metab 2010; 299:E640-6. [PMID: 20682843 PMCID: PMC2957868 DOI: 10.1152/ajpendo.00063.2010] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Overexpression of the small-conductance calcium-activated K(+) channel 3 (SK3) in transgenic mice compromises parturition, suggesting that the SK3 channel plays a role in pregnancy. In wild-type mouse myometrium, expression of SK3 transcript and protein is significantly reduced during pregnancy, but the mechanism(s) responsible for this attenuation of channel expression is unknown. The promoter region of the SK3-encoding mouse KCNN3 gene contains two binding sites for specificity protein (Sp) transcription factors, two of which are expressed in the uterus: Sp1, which enhances gene transcription in response to estrogen; and Sp3, which competes for the same binding motif as Sp1 and can repress gene expression. We investigated the hypothesis that Sp1 and Sp3 regulate SK3 channel expression during pregnancy. In mouse myometrium, Sp1 expression was reduced during late gestation, whereas Sp3 expression levels were constant throughout pregnancy. Using a reporter system, we found that Sp1 overexpression resulted in a significant increase in SK3 promoter activation and that Sp3 cotransfection reduced promoter activation to basal levels. These findings indicate that Sp3 outcompetes Sp1 to decrease SK3 transcription. To determine whether high levels of estrogen in vivo can affect the regulation of SK3 protein levels by Sp factors, ovariectomized mice were implanted with a 17β-estradiol or placebo pellet for 3 wk; estrogen-treated mice had reduced uterine SK3 protein expression compared with placebo-treated counterparts. In human myometrial cells overexpressing Sp1, estrogen treatment stimulated expression of the SK3 transcript. Overall, our findings indicate that Sp1 and Sp3 compete to regulate SK3 channel expression during pregnancy in response to stimulation by estrogen.
Collapse
Affiliation(s)
- Stephanie L Pierce
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA
| | | |
Collapse
|
25
|
CHOUDHURY S, GARG SK, SINGH TU, MISHRA SK. Cellular coupling of potassium channels with β2adrenoceptors in mediating myometrial relaxation in buffaloes (Bubalus bubalis). J Vet Pharmacol Ther 2010; 33:22-7. [DOI: 10.1111/j.1365-2885.2009.01084.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
26
|
Brainard AM, Korovkina VP, England SK. Disruption of the maxi-K-caveolin-1 interaction alters current expression in human myometrial cells. Reprod Biol Endocrinol 2009; 7:131. [PMID: 19930645 PMCID: PMC2785819 DOI: 10.1186/1477-7827-7-131] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/05/2009] [Accepted: 11/23/2009] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND One determinant of the total K+ myometrial smooth muscle cell (MSMC) current is the large conductance, calcium- and voltage-activated potassium channel (maxi-K channel). This channel provides a repolarizing current in response to excitatory stimuli, most notably in response to increases in the levels of intracellular Ca2+, and blocking the channel by pharmacological means induces the depolarization of MSMCs and also enhances contraction strength. In MSMCs, maxi-K channels can reside in the caveolae, where they associate with the scaffolding protein caveolin-1 (cav-1). The aim of this study was to investigate the consequences of this interaction - more specifically, how disruption of the association between the maxi-K channel and cav-1 may influence the current expression and excitability of myometrial cells - with the aim of better understanding the mechanisms that underlie the regulation of normal and aberrant uterine function. METHODS Myometrial biopsies were collected from women undergoing elective C-sections. From these samples, myometrial cells were isolated, cultured, infected with a virus containing either caveolin-1 (cav-1) siRNA or scrambled cav-1 siRNA, and finally subjected to patch-clamp analysis. Mutant caveolin-binding site maxi-K channel constructs were generated and transfected into mouse Ltk- fibroblasts. Channel activity, expression, association, and localization were examined by patch-clamping, Western blot, immunoprecipitation, and immunofluorescence, respectively. RESULTS The caveolin-1 siRNA suppressed the total K+ current in human myometrial smooth muscle cells (hMSMC), as evident from comparison to the currents generated by both non-infected cells and cells infected with scrambled siRNA controls. The interaction between the maxi-K channel and caveolin depends on a region in the channel's C-terminal caveolin-binding site. Mutations of aromatic residues in this site (mutant F1012A, mutant Y1007A, F1012A and mutant Y1007A, F1012A, Y1015A) resulted in a decrease in K+ current compared to that produced by wild-type channels transfected into mouse Ltk- fibroblasts. However, mutation of all three aromatic amino acids (mutant Y1007A, F1012A, Y1015A) was necessary to disrupt the association between caveolin and the maxi-K channel, as visualized by immunofluorescence and immunoprecipitation. CONCLUSION Our results suggest that disruption of the caveolin-binding site interferes with the cav-1/maxi-K channel interaction, and that lack of the cav-1/maxi-K channel interaction in MSMCs attenuates the total K+ channel current of the cell.
Collapse
Affiliation(s)
- Adam M Brainard
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, IA, USA
| | - Victoria P Korovkina
- Department of Obstetrics and Gynecology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA
| | - Sarah K England
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, IA, USA
- Department of Obstetrics and Gynecology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA
| |
Collapse
|
27
|
Pearson T, Warren AY, Barrett DA, Khan RN. Detection of EETs and HETE-generating cytochrome P-450 enzymes and the effects of their metabolites on myometrial and vascular function. Am J Physiol Endocrinol Metab 2009; 297:E647-56. [PMID: 19549792 DOI: 10.1152/ajpendo.00227.2009] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cytochrome P-450 (CYP450) enzymes of the CYP2 and -4 family in humans metabolize arachidonic acid to generate bioactive epoxyeicosatrienenoic acids (EETs) and hydroxyeicosatetrenoic acids (HETEs). We report significantly higher levels of CYP 2J2 protein expression following the onset of labor (n = 6, P < 0.05), implying increased EET-generating capacity within the uterus. Myometrial relaxation to 8,9-EET and 5,6-EET was observed, with the latter being inhibited by preincubation with 1 muM paxilline and is supported by whole cell recordings showing a modest effect of 5,6-EET on myometrial outward-current density (n = 4, P < 0.05). Only 5,6-EET of the EETs tested affected vascular reactivity (n = 6). Both 12- and 20-HETE (n = 5-6) caused vasoconstriction of partially depolarized blood vessels, with glibenclamide (n = 5) enhancing the effect of 12-HETE alone. Our findings signify a role for CYP2C9/19, -2J2, and -4A11/22 in late pregnancy, possibly related to the synthesis of lipid metabolites and downstream effects on vascular remodeling in the term pregnant uterus. The presence of CYP4A11/22 and their resultant procontractile metabolites could argue either a role in the control and initiation of labor and/or modification of the vascular delivery system to influence blood flow to the laboring uterus. The differential effects of the EETs and HETEs in the pregnant human uterus identify the CYP pathway as a novel modulator of myometrial and vascular physiology during late pregnancy.
Collapse
MESH Headings
- 8,11,14-Eicosatrienoic Acid/analogs & derivatives
- 8,11,14-Eicosatrienoic Acid/metabolism
- 8,11,14-Eicosatrienoic Acid/pharmacology
- Blood Vessels/drug effects
- Blood Vessels/metabolism
- Blood Vessels/physiology
- Cells, Cultured
- Cytochrome P-450 Enzyme System/analysis
- Cytochrome P-450 Enzyme System/metabolism
- Cytochrome P-450 Enzyme System/physiology
- Eicosanoids/metabolism
- Eicosanoids/pharmacology
- Female
- Humans
- Hydroxyeicosatetraenoic Acids/metabolism
- Hydroxyeicosatetraenoic Acids/pharmacology
- Labor, Obstetric/drug effects
- Labor, Obstetric/metabolism
- Labor, Obstetric/physiology
- Myometrium/blood supply
- Myometrium/drug effects
- Myometrium/metabolism
- Myometrium/physiology
- Pregnancy
- Uterine Contraction/drug effects
- Uterine Contraction/metabolism
Collapse
Affiliation(s)
- Timothy Pearson
- Academic Division of Obstetrics & Gynecology, Univ. of Nottingham, The Medical School, Derby City General Hospital, Derby DE22 3DT, UK
| | | | | | | |
Collapse
|
28
|
Gao L, Cong B, Zhang L, Ni X. Expression of the calcium-activated potassium channel in upper and lower segment human myometrium during pregnancy and parturition. Reprod Biol Endocrinol 2009; 7:27. [PMID: 19344525 PMCID: PMC2670306 DOI: 10.1186/1477-7827-7-27] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/13/2009] [Accepted: 04/05/2009] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND Large conductance calcium-activated potassium channel (BKCa) plays an important role in the control of uterine contractility during pregnancy. The change from uterine quiescence to enhanced contractile activity may be associated with the spatial and temporal expression of BKCa within myometrium. The objectives of this study were to examine the expression of BKCa alpha- and beta-subunit in upper segment (US) and lower segment (LS) regions of uterus, and to investigate for the possibly differential expression of these proteins in US and LS myometrium obtained from three functional states: (1) non-pregnant (NP); (2) term pregnant not in labour (TNL) and (3) term pregnant in labour (TL). METHODS Myometrial biopsies were collected from non-pregnant women at hysterectomy and pregnant women at either elective caesarean section or emergency caesarean section. Protein expression level and cellular localization of BKCa alpha- and beta-subunit in US and LS myometrium were determined by Western blot analysis and immunohistochemistry, respectively. RESULTS BKCa alpha- and beta-subunit were predominantly localized to myometrial smooth muscle in both US and LS myometrium obtained from non-pregnant and pregnant patients. The level of BKCa alpha-subunit in US but not in LS was significantly higher in NP myometrium than those measured in myometrium obtained during pregnancy. Lower expression of BKCa alpha-subunit in both US and LS was found in TL than in TNL biopsies. Expression of beta-subunit in both US and LS myometrium was significantly reduced in TL group compared with those measured in TNL group. There was no significant difference in BKCa beta-subunit expression in either US or LS between NP and TNL group. CONCLUSION Our results suggest that expression of BKCa alpha- and beta-subunit in pregnant myometrium is reduced during labour, which is consistent with the myometrial activity at the onset of parturition.
Collapse
Affiliation(s)
- Lu Gao
- Department of Physiology, Second Military Medical University, Shanghai 200433, PR China.
| | | | | | | |
Collapse
|
29
|
Abstract
With the growing frequency of preterm birth, increased effort has been made to elucidate the physiology of normal and aberrant parturition. As with many developmental processes, the study of genetically altered mice has led to an increased understanding of mechanisms controlling the maintenance and resolution of pregnancy. Studies in genetically altered mice have implicated critical roles for both prostaglandin synthesis and degradation in luteolysis and the progression of labor. The importance of local modulation of progesterone activity to cervical ripening has also been demonstrated. Although a decline in levels of serum progesterone is a part of normal labor initiation in mice but not humans, murine labor without progesterone withdrawal has been reported in some cases. These findings emphasize the importance of other components of the parturition cascade that are shared in mice and humans and highlights the importance of an increased understanding of the physiology of mouse parturition.
Collapse
Affiliation(s)
- Christine K Ratajczak
- Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri 63110, USA
| | | |
Collapse
|
30
|
Yan J, Olsen JV, Park KS, Li W, Bildl W, Schulte U, Aldrich RW, Fakler B, Trimmer JS. Profiling the phospho-status of the BKCa channel alpha subunit in rat brain reveals unexpected patterns and complexity. Mol Cell Proteomics 2008; 7:2188-98. [PMID: 18573811 DOI: 10.1074/mcp.m800063-mcp200] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Molecular diversity of ion channel structure and function underlies variability in electrical signaling in nerve, muscle, and non-excitable cells. Protein phosphorylation and alternative splicing of pre-mRNA are two important mechanisms to generate structural and functional diversity of ion channels. However, systematic mass spectrometric analyses of in vivo phosphorylation and splice variants of ion channels in native tissues are largely lacking. Mammalian large-conductance calcium-activated potassium (BK(Ca)) channels are tetramers of alpha subunits (BKalpha) either alone or together with beta subunits, exhibit exceptionally large single channel conductance, and are dually activated by membrane depolarization and intracellular Ca(2+). The cytoplasmic C terminus of BKalpha is subjected to extensive pre-mRNA splicing and, as predicted by several algorithms, offers numerous phospho-acceptor amino acids. Here we use nanoflow liquid chromatography tandem mass spectrometry on BK(Ca) channels affinity-purified from rat brain to analyze in vivo BKalpha phosphorylation and splicing. We found 7 splice variations and identified as many as 30 Ser/Thr in vivo phosphorylation sites; most of which were not predicted by commonly used algorithms. Of the identified phosphosites 23 are located in the C terminus, four were found on splice insertions. Electrophysiological analyses of phospho- and dephosphomimetic mutants transiently expressed in HEK-293 cells suggest that phosphorylation of BKalpha differentially modulates the voltage- and Ca(2+)-dependence of channel activation. These results demonstrate that the pore-forming subunit of BK(Ca) channels is extensively phosphorylated in the mammalian brain providing a molecular basis for the regulation of firing pattern and excitability through dynamic modification of BKalpha structure and function.
Collapse
Affiliation(s)
- Jiusheng Yan
- Department of Neurobiology, Physiology and Behavior, College of Biological Sciences, University of California, Davis, California 95616, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
31
|
Subunit-specific effect of the voltage sensor domain on Ca2+ sensitivity of BK channels. Biophys J 2008; 94:4678-87. [PMID: 18339745 DOI: 10.1529/biophysj.107.121590] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Large conductance Ca(2+)- and voltage-activated K(+) (BK) channels, composed of pore-forming alpha-subunits and auxiliary beta-subunits, play important roles in diverse physiological processes. The differences in BK channel phenotypes are primarily due to the tissue-specific expression of beta-subunits (beta1-beta4) that modulate channel function differently. Yet, the molecular basis of the subunit-specific regulation is not clear. In our study, we demonstrate that perturbation of the voltage sensor in BK channels by mutations selectively disrupts the ability of the beta1-subunit--but not that of the beta2-subunit--to enhance apparent Ca(2+) sensitivity. These mutations change the number of equivalent gating charges, the voltage dependence of voltage sensor movements, the open-close equilibrium of the channel, and the allosteric coupling between voltage sensor movements and channel opening to various degrees, indicating that they alter the conformation and movements of the voltage sensor and the activation gate. Similarly, the ability of the beta1-subunit to enhance apparent Ca(2+) sensitivity is diminished to various degrees, correlating quantitatively with the shift of voltage dependence of voltage sensor movements. In contrast, none of these mutations significantly reduces the ability of the beta2-subunit to enhance Ca(2+) sensitivity. These results suggest that the beta1-subunit enhances Ca(2+) sensitivity by altering the conformation and movements of the voltage sensor, whereas the similar function of the beta2-subunit is governed by a distinct mechanism.
Collapse
|
32
|
Pierce SL, Kresowik JDK, Lamping KG, England SK. Overexpression of SK3 channels dampens uterine contractility to prevent preterm labor in mice. Biol Reprod 2008; 78:1058-63. [PMID: 18305226 DOI: 10.1095/biolreprod.107.066423] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
The mechanisms that control the timing of labor have yet to be fully characterized. In a previous study, the overexpression of small conductance calcium-activated K(+) channel isoform 3 in transgenic mice, Kcnn3(tm1Jpad)/Kcnn3(tm1Jpad) (also known as SK3(T/T)), led to compromised parturition, which indicates that KCNN3 (also known as SK3) plays an important role in the delivery process. Based on these findings, we hypothesized that SK3 channel expression must be downregulated late in pregnancy to enable the uterus to produce the forceful contractions required for parturition. Thus, we investigated the effects of SK3 channel expression on gestation and parturition, comparing SK3(T/T) mice to wild type (WT) mice. Here, we show in WT mice that SK3 transcript and protein are significantly reduced during pregnancy. We also found the force produced by uterine strips from Pregnancy Day 19 (P19) SK3(T/T) mice was significantly less than that measured in WT or SK3 knockout control (SK3(DOX)) uterine strips, and this effect was reversed by application of the SK3 channel inhibitor apamin. Moreover, two treatments that induce labor in mice failed to result in complete delivery in SK3(T/T) mice within 48 h after injection. Thus, stimuli that initiate parturition under normal circumstances are insufficient to coordinate the uterine contractions needed for the completion of delivery when SK3 channel activity is in excess. Our data indicate that SK3 channels must be downregulated for the gravid uterus to generate labor contractions sufficient for delivery in both term and preterm mice.
Collapse
Affiliation(s)
- Stephanie L Pierce
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA 52242, USA
| | | | | | | |
Collapse
|
33
|
Smith RC, McClure MC, Smith MA, Abel PW, Bradley ME. The role of voltage-gated potassium channels in the regulation of mouse uterine contractility. Reprod Biol Endocrinol 2007; 5:41. [PMID: 17980032 PMCID: PMC2186335 DOI: 10.1186/1477-7827-5-41] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/21/2007] [Accepted: 11/02/2007] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Uterine smooth muscle cells exhibit ionic currents that appear to be important in the control of uterine contractility, but how these currents might produce the changes in contractile activity seen in pregnant myometrium has not been established. There are conflicting reports concerning the role of voltage-gated potassium (Kv) channels and large-conductance, calcium-activated potassium (BK) channels in the regulation of uterine contractility. In this study we provide molecular and functional evidence for a role for Kv channels in the regulation of spontaneous contractile activity in mouse myometrium, and also demonstrate a change in Kv channel regulation of contractility in pregnant mouse myometrium. METHODS Functional assays which evaluated the effects of channel blockers and various contractile agonists were accomplished by quantifying contractility of isolated uterine smooth muscle obtained from nonpregnant mice as well as mice at various stages of pregnancy. Expression of Kv channel proteins in isolated uterine smooth muscle was evaluated by Western blots. RESULTS The Kv channel blocker 4-aminopyridine (4-AP) caused contractions in nonpregnant mouse myometrium (EC50 = 54 micromolar, maximal effect at 300 micromolar) but this effect disappeared in pregnant mice; similarly, the Kv4.2/Kv4.3 blocker phrixotoxin-2 caused contractions in nonpregnant, but not pregnant, myometrium. Contractile responses to 4-AP were not dependent upon nerves, as neither tetrodotoxin nor storage of tissues at room temperature significantly altered these responses, nor were responses dependent upon the presence of the endometrium. Spontaneous contractions and contractions in response to 4-AP did not appear to be mediated by BK, as the BK channel-selective blockers iberiotoxin, verruculogen, or tetraethylammonium failed to affect either spontaneous contractions or 4-AP-elicited responses. A number of different Kv channel alpha subunit proteins were found in isolated myometrium from both nonpregnant and term-pregnant mice, and one of these proteins - Kv4.3 - was found to disappear in term-pregnant tissues. CONCLUSION These findings suggest a role for Kv channels in the regulation of uterine contractility, and that changes in the expression and/or function of specific Kv channels may account for the functional changes seen in pregnant myometrium.
Collapse
Affiliation(s)
- Ryan C Smith
- Department of Pharmacology, Creighton University Medical Center, Omaha, USA, NE 68178
| | - Marisa C McClure
- Department of Pharmacology, Creighton University Medical Center, Omaha, USA, NE 68178
| | - Margaret A Smith
- Department of Pharmacology, Creighton University Medical Center, Omaha, USA, NE 68178
| | - Peter W Abel
- Department of Pharmacology, Creighton University Medical Center, Omaha, USA, NE 68178
| | - Michael E Bradley
- Department of Pharmacology, Creighton University Medical Center, Omaha, USA, NE 68178
| |
Collapse
|
34
|
Blanks AM, Zhao ZH, Shmygol A, Bru-Mercier G, Astle S, Thornton S. Characterization of the molecular and electrophysiological properties of the T-type calcium channel in human myometrium. J Physiol 2007; 581:915-26. [PMID: 17446221 PMCID: PMC1976399 DOI: 10.1113/jphysiol.2007.132126] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Rises in intracellular calcium are essential for contraction of human myometrial smooth muscle (HMSM) and hence parturition. The T-type calcium channel may play a role in this process. The aim was to investigate the role of the T-type calcium channel in HMSM by characterizing mRNA expression, protein localization, electrophysiological properties and function of the channel subunits Cav3.1(alpha1G), Cav3.2(alpha1H), and Cav3.3(alpha1I). QRT-PCR, immunohistochemistry, electrophysiology and invitro contractility were performed on human myometrial samples from term, preterm, labour and not in labour. QRT-PCR analysis of Cav3.1, Cav3.2 and Cav3.3 demonstrated expression of Cav3.1 and Cav3.2 with no significant change (P>0.05) associated with gestation or labour status. Immunohistochemistry localized Cav3.1 to myometrial and vascular smooth muscle cells whilst Cav3.2 localized to vascular endothelial cells and invading leucocytes. Voltage clamp studies demonstrated a T-type current in 55% of cells. Nickel block of T-type current was voltage sensitive (IC50 of 118.57+/-68.9 microM at -30 mV). Activation and inactivation curves of ICa currents in cells expressing T-type channels overlapped demonstrating steady state window currents at the resting membrane potential of myometrium at term. Current clamp analysis demonstrated that hyperpolarizing pulses to a membrane potential greater than -80 mV elicited rebound calcium spikes that were blocked reversibly by 100 microM nickel. Contractility studies demonstrated a reversible decrease in contraction frequency during application of 100 microM nickel (P<0.05). We conclude that the primary T-type subunit expressed in some MSMCs is Cav3.1. We found that application of 100 microM nickel to spontaneously contracting human myometrium reversibly slows contraction frequency.
Collapse
Affiliation(s)
- Andrew M Blanks
- Clinical Science Research Institute, Division of Clinical Sciences, Warwick Medical School, Coventry CV4 7AL, UK.
| | | | | | | | | | | |
Collapse
|
35
|
Abstract
The excitability of smooth muscle cells is regulated, in part, by stretch-activated ion channels in the plasma membrane. The response to stretch of a particular muscle or organ is tuned to specific functional needs by the types of ion channels expressed. Mechanosensitive ionic conductances that yield either inward or outward currents have been observed in and characterized in studies of smooth muscles. In vascular muscles, the dominant response to stretch is muscle contraction (the myogenic response). This chapter proposes several mechanisms for the myogenic response; one of these hypotheses involves stretch-dependent activation of nonselective cation channels. The inward current resulting from an activation of these channels causes plasma membrane depolarization, activation of voltage-gated Ca(2+) channels, Ca(2+) entry, and excitation-contraction coupling. Thus, increasing the vascular pressure and distension of blood vessels cause responsive vasoconstriction. Other conductances are also proposed as participants in the myogenic response, and progress characterizing the inward current channels responsive to stretch is summarized. Outward currents responding to muscle stretch are also present in smooth muscles. For example, expression of stretch-sensitive two-pore domain K(+) (K2P) channels has been reported in visceral smooth muscles. These organs resist contraction on filling and provide a reservoir function. Stretch-dependent outward current channels are hypothesized to help stabilize membrane potential until it becomes desirable to empty the stored contents. Mechanosensitive conductances participate in the integrated responses of smooth muscle tissues. The chapter summarizes the class of channels found in smooth muscles.
Collapse
|
36
|
Doheny HC, O'Reilly MJ, Sexton DJ, Morrison JJ. THG113.31, a specific PGF2alpha receptor antagonist, induces human myometrial relaxation and BKCa channel activation. Reprod Biol Endocrinol 2007; 5:10. [PMID: 17367527 PMCID: PMC1831777 DOI: 10.1186/1477-7827-5-10] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/19/2007] [Accepted: 03/16/2007] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND PGF2alpha exerts a significant contractile effect on myometrium and is central to human labour. THG113.31, a specific non-competitive PGF2alpha receptor (FP) antagonist, exerts an inhibitory effect on myometrial contractility. The BKCa channel is ubiquitously encountered in human uterine tissue and plays a significant role in modulating myometrial cell membrane potential and excitability. The objective of this study was to investigate potential BKCa channel involvement in the response of human myometrium to THG113.31. METHODS Single and whole-cell electrophysiological BKCa channel recordings from freshly dispersed myocytes, were investigated in the presence and absence of THG113.31. Functional studies investigated the effects of THG113.31 on isolated spontaneous myometrial contractions, in the presence and absence of the BKCa channel blocker, iberiotoxin. RESULTS Single channel recordings identified the BKCa channel as a target of THG113.31. THG113.31 significantly increased the open state probability of these channels [control 0.023+/-0.006; 10 microM THG113.31 0.087+/-0.012 (P = 0.009); and 50 microM THG113.31 0.1356+/-0.018 (P = 0.001)]. In addition, THG113.31 increased whole-cell BKCa currents over a range of membrane potentials, and this effect was reversed by 100 nanoM IbTX. Isometric tension studies demonstrated that THG113.31 exerted a significant concentration-dependent relaxant effect on human myometrial tissue and pre-incubation of strips with IbTX abolished this effect on spontaneously occurring contractions. CONCLUSION These data suggests that activation of the BKCa channel may contribute, at least partially, to the uterorelaxant effect of THG113.31.
Collapse
Affiliation(s)
- Helen C Doheny
- Department of Obstetrics & Gynaecology, National University of Ireland Galway, Clinical Science Institute, University College Hospital Galway, Newcastle Road, Galway, Ireland
| | - Michael J O'Reilly
- Department of Obstetrics & Gynaecology, National University of Ireland Galway, Clinical Science Institute, University College Hospital Galway, Newcastle Road, Galway, Ireland
| | - Donal J Sexton
- Department of Obstetrics & Gynaecology, National University of Ireland Galway, Clinical Science Institute, University College Hospital Galway, Newcastle Road, Galway, Ireland
| | - John J Morrison
- Department of Obstetrics & Gynaecology, National University of Ireland Galway, Clinical Science Institute, University College Hospital Galway, Newcastle Road, Galway, Ireland
| |
Collapse
|
37
|
Shmygol A, Noble K, Wray S. Depletion of membrane cholesterol eliminates the Ca2+-activated component of outward potassium current and decreases membrane capacitance in rat uterine myocytes. J Physiol 2007; 581:445-56. [PMID: 17331986 PMCID: PMC2075177 DOI: 10.1113/jphysiol.2007.129452] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Changes in membrane cholesterol content have potent effects on cell signalling and contractility in rat myometrium and other smooth muscles. We have previously shown that depletion of cholesterol with methyl-beta-cyclodextrin (MCD) disrupts caveolar microdomains. The aim of this work was to determine the mechanism underlying the increase in Ca(2+) signalling and contractility occurring in the myometrium with MCD. Patch clamp data obtained on freshly isolated myocytes from the uterus of day 19-21 rats showed that outward K(+) current was significantly reduced by MCD. Membrane capacitance was also reduced. Cholesterol-saturated MCD had no effect on the amplitude of outward current suggesting that the reduction in the outward current was due to cholesterol depletion induced by MCD rather than a direct inhibitory action of MCD on the K(+) channels. Confocal visualization of the membrane bound indicator Calcium Green C18, revealed internalization of the surface membrane with MCD treatment. Large conductance, Ca(2+)-sensitive K(+) channel proteins have been shown to localize to caveolae. When these channels were blocked by iberiotoxin outward current was significantly reduced in the uterine myocytes; MCD treatment reduced the density of outward current. Following reduction of outward current by MCD pretreatment, iberiotoxin was unable to produce any additional decrease in the current, suggesting a common target. MCD treatment also increased the amplitude and frequency of spontaneous rises in cytosolic Ca(2+) level ([Ca(2+)](i) transients) in isolated myocytes. In intact rat myometrium, MCD treatment increased Ca(2+) signalling and contractility, consistent with previous findings, and this effect was also found to be reduced by BK channel inhibition. These data suggest that (1) disruption of cholesterol-rich microdomains and caveolae by MCD leads to a decrease in the BK channel current thus increasing cell excitability, and (2) the changes in membrane excitability produced by MCD underlie the changes found in Ca(2+) signalling and uterine contractility.
Collapse
Affiliation(s)
- A Shmygol
- Clinical Sciences Research Institute, Warwick Medical School, University of Warwick, Coventry CV2 2DX, UK
| | | | | |
Collapse
|
38
|
Carvajal JA, Vidal RJ, Cuello MA, Poblete JA, Weiner CP. Mechanisms of paracrine regulation by fetal membranes of human uterine quiescence. ACTA ACUST UNITED AC 2006; 13:343-9. [PMID: 16814163 DOI: 10.1016/j.jsgi.2006.04.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2006] [Indexed: 11/23/2022]
Abstract
OBJECTIVE To test the hypothesis that fetal membranes (chorion or amnion) release one or more factors responsible for myometrial quiescence. METHODS Myometrial samples were excised from women at elective term cesarean delivery prior to the onset of labor. Fetal membranes were obtained after cesarean delivery either before or during labor, and either term (greater than 37 weeks) or preterm (less than or equal to 36 weeks). Myometrial strips were placed in organ baths and contractions stimulated by oxytocin (10(-8) M). Contractility was measured under isometric conditions before and after exposure to fetal membranes or conditioned medium. The impact of either membrane or conditioned media on contractility was determined before and after myometrial K+ channel blockade. RESULTS Both chorion and amnion and their respective conditioned mediums decrease oxytocin-stimulated myometrial contraction. The inhibitory effect was greatest with membranes from preterm pregnancies (mean gestation 32 weeks, P <.05). The inhibitory effect was detectable in the presence of term labor, but was absent when the fetal membranes were obtained after preterm labor. Iberiotoxin, an inhibitor of large conductance Ca2+-activated K+ channels (BK(Ca)) reduced the effect of fetal membranes by 50% (P <.05). CONCLUSION We conclude that human fetal membranes release one or more factors that inhibit oxytocin-induced myometrial contractility. We suggest this factor (or factors) acts mainly by opening myometrial BK(Ca). The findings further support our hypothesis that the fetal membranes release a factor (or factors) that is central to myometrial quiescence and its premature loss leads to preterm delivery.
Collapse
Affiliation(s)
- Jorge A Carvajal
- Departmento de Obstetricia y Ginecología, Unidad de Medicina Materno Fetal, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile.
| | | | | | | | | |
Collapse
|
39
|
Yoo KY, Lee JC, Yoon MH, Shin MH, Kim SJ, Kim YH, Song TB, Lee J. The Effects of Volatile Anesthetics on Spontaneous Contractility of Isolated Human Pregnant Uterine Muscle: A Comparison Among Sevoflurane, Desflurane, Isoflurane, and Halothane. Anesth Analg 2006; 103:443-7, table of contents. [PMID: 16861431 DOI: 10.1213/01.ane.0000236785.17606.58] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
We examined the effects of equianesthetic concentrations of sevoflurane, desflurane, isoflurane, and halothane on the spontaneous contractility of isolated human pregnant uterine muscles. We also determined if their action was related to potassium channels. Uterine specimens were obtained from normal full-term pregnant women undergoing elective lower-segment cesarean delivery. Longitudinal muscle strips were mounted vertically in tissue chambers. Their isometric tension was recorded while they were exposed to 0.5-3 minimum alveolar concentration (MAC) of volatile anesthetics in the absence and presence of the high conductance calcium-activated potassium channel blocker, tetraethylammonium, or the adenosine triphosphate-sensitive potassium channel (K(ATP))-blocker, glibenclamide. The anesthetics examined produced a dose-dependent depression of contractility. The inhibitory potency of sevoflurane and desflurane was comparable to, whereas that of isoflurane was smaller than, that of halothane: concentrations causing 50% inhibition of the contractile amplitude (ED(50)) were 1.72, 1.44, 2.35, and 1.66 MAC (P < 0.05), respectively. Tetraethylammonium and glibenclamide did not affect the uterine response to the anesthetics, except for glibenclamide, which attenuated the response to isoflurane. These results indicate that the volatile anesthetics have inhibitory effects on the contractility of the human uterus. The inhibitory effect of isoflurane may in part be mediated through activation of K(ATP) channels.
Collapse
Affiliation(s)
- Kyung Y Yoo
- Department of Anesthesiology, Chonnam National University Medical School, 5 Hak-dong, Gwangju 501-746, Korea.
| | | | | | | | | | | | | | | |
Collapse
|
40
|
Aaronson PI, Sarwar U, Gin S, Rockenbauch U, Connolly M, Tillet A, Watson S, Liu B, Tribe RM. A role for voltage-gated, but not Ca2+-activated, K+ channels in regulating spontaneous contractile activity in myometrium from virgin and pregnant rats. Br J Pharmacol 2006; 147:815-24. [PMID: 16415906 PMCID: PMC1751504 DOI: 10.1038/sj.bjp.0706644] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The roles of voltage-gated (K(V)) and large conductance Ca2+-activated K+ (BK(Ca)) channels in regulating basal contractility in myometrial smooth muscle are unresolved. The aim of this study was to determine the effects of inhibition of these channels on spontaneous rhythmic contraction in myometrial strips from four groups of rats: nonpregnant and during early (day 7), mid- (day 14), and late (day 21) pregnancy. BK(Ca) channels were inhibited using iberiotoxin (1-100 nM), paxilline (1-10 microM) or penitrem A (1-500, or 3000 nM); K(V) channels were inhibited using tetraethylammonium (TEA; 1-10 mM) and/or 4-aminopyridine (4-AP; 1-5 mM). Contractility was assessed as mean integral tension (MIT). Time/vehicle controls were also performed. None of the selective BK(Ca) channel inhibitors significantly affected contractility in myometrial strips from either nonpregnant or pregnant animals. 4-AP caused concentration-dependent increases in MIT in myometrium in all four groups. TEA (5 and 10 mM) significantly increased MIT in myometrium from nonpregnant, and mid- and late pregnant rats, but not in myometrium from early pregnant rats. TEA and 4-AP still caused an increase in MIT following treatment with 3000 nM penitrem A or a combination of propranolol, phentolamine, atropine (all 1 microM) and capsaicin (10 microM) in myometrial strips from nonpregnant rats. These results indicate that whereas BK(Ca) channels play little or no part in controlling basal rhythmicity in rat myometrium, K(V) channels appear to play a crucial role in this regard, especially during mid- and late pregnancy.
Collapse
Affiliation(s)
| | - Uzma Sarwar
- Division of Reproductive Health, Endocrinology and Development, King's College London, MFRU, 10th Floor NW, St Thomas' Hospital Campus, Lambeth Palace Road, London SE1 7EH
| | - Stephanie Gin
- Division of Reproductive Health, Endocrinology and Development, King's College London, MFRU, 10th Floor NW, St Thomas' Hospital Campus, Lambeth Palace Road, London SE1 7EH
| | - Uli Rockenbauch
- Division of Asthma, Allergy and Lung Biology, King's College London, London
| | - Michelle Connolly
- Division of Asthma, Allergy and Lung Biology, King's College London, London
| | - Alexandra Tillet
- Division of Reproductive Health, Endocrinology and Development, King's College London, MFRU, 10th Floor NW, St Thomas' Hospital Campus, Lambeth Palace Road, London SE1 7EH
| | - Sarah Watson
- Division of Reproductive Health, Endocrinology and Development, King's College London, MFRU, 10th Floor NW, St Thomas' Hospital Campus, Lambeth Palace Road, London SE1 7EH
| | - Bing Liu
- Division of Reproductive Health, Endocrinology and Development, King's College London, MFRU, 10th Floor NW, St Thomas' Hospital Campus, Lambeth Palace Road, London SE1 7EH
| | - Rachel Marie Tribe
- Division of Reproductive Health, Endocrinology and Development, King's College London, MFRU, 10th Floor NW, St Thomas' Hospital Campus, Lambeth Palace Road, London SE1 7EH
- Author for correspondence:
| |
Collapse
|
41
|
Noble K, Zhang J, Wray S. Lipid rafts, the sarcoplasmic reticulum and uterine calcium signalling: an integrated approach. J Physiol 2005; 570:29-35. [PMID: 16239270 PMCID: PMC1464295 DOI: 10.1113/jphysiol.2005.098475] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The pathways involved in Ca2+ signalling in the uterus remain incompletely understood, impairing our ability to prevent preterm and difficult labours. In this review we focus on two elements in the pathway of Ca2+ signalling that have recently emerged as playing important roles: membrane lipid rafts and the sarcoplasmic reticulum. We examine the evidence for lipid rafts in the uterus and discuss their functional role. We suggest that the increases in cytosolic [Ca2+] and contractility that occur with raft disruption are due, at least in part, to effects on large conductance Ca2+-activated K+ (BK) channels that are localized to rafts. The role of the SR in contributing to subsarcolemmal cytosolic microdomains in uterus is evaluated, along with its interactions with ion channels on the plasma membrane. Thus, signalling microdomains play an important, but incompletely understood, role in the uterus, and integrating them into other Ca2+ signalling pathways is a challenge for further research. We suggest that the role of the SR changes in pregnancy, from promoting quiescence via BK channels or SR Ca2+ uptake, to promoting Ca2+ entry and contractility at term, and relate data on lipid rafts to clinical outcome in obese pregnant women.
Collapse
Affiliation(s)
- Karen Noble
- Department of Physiology, University of Liverpool, Crown Street, Liverpool, L69 3BX, UK
| | | | | |
Collapse
|
42
|
Warren AY, Matharoo-Ball B, Shaw RW, Khan RN. Hydrogen peroxide and superoxide anion modulate pregnant human myometrial contractility. Reproduction 2005; 130:539-44. [PMID: 16183871 DOI: 10.1530/rep.1.00437] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Reactive oxygen species (ROS) have the propensity to cause macromolecular damage with consequent modification of cellular function. We investigated the effects of two particular oxidants, superoxide (O2−) anions and hydrogen peroxide (H2O2), on oxytocin-induced myometrial contractility using biopsies from women undergoing Caesarean section at term gestation. Isometric tension recordings were performed and concentration–response curves derived after addition of test agents. A maximal reduction in myometrial contractility to 27.2 ± 4.5% of control was observed followed application of H2O2. The enzyme scavenger catalase (CAT) reduced the inhibitory effect of H2O2but had little effect at 10-fold lower concentrations. Addition of dialysed xanthine oxidase ± hypoxanthine significantly inhibited contractility to 23.8.0 ± 4.2% compared with control. Pre-incubation with superoxide dismutase and CAT diminished this effect. The non-specific potassium channel blocker, tetraethylammonium chloride (1 mM), had no effect on myometrial contractility. We conclude that human myometrium is susceptible to the effects of ROS, which may be produced by reperfusion–ischaemic episodes during labour. Our findings could, in part, explain the weak or prolonged depression of contractions characteristic of myometrial dysfunction culminating in difficult labours.
Collapse
Affiliation(s)
- Averil Y Warren
- Centre for Reproduction and Early Life, Institute of Clinical Research, University of Nottingham, The Medical School, Derby DE22 3DT, UK
| | | | | | | |
Collapse
|
43
|
Doheny HC, Lynch CM, Smith TJ, Morrison JJ. Functional coupling of beta3-adrenoceptors and large conductance calcium-activated potassium channels in human uterine myocytes. J Clin Endocrinol Metab 2005; 90:5786-96. [PMID: 16014404 DOI: 10.1210/jc.2005-0574] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
CONTEXT Beta3-adrenoreceptor modulation in human myometrium during pregnancy is linked functionally to myometrial inhibition. Maxi-K+ channels (BK(Ca)) play a significant role in modulating cell membrane potential and excitability. OBJECTIVE This study was designed to investigate the potential involvement of BK(Ca) channel function in the response of human myometrium to beta3-adrenoceptor activation. DESIGN Single and whole-cell electrophysiological BK(Ca) channel recordings from freshly dispersed myocytes were obtained in the presence and absence of BRL37344, a specific beta3-adrenoreceptor agonist. The in vitro effects of BRL37344 on isolated myometrial contractions, in the presence and absence of the specific BK(Ca) channel blocker, iberiotoxin (IbTX), were investigated. SETTING The study was carried out at the Clinical Science Institute. PATIENTS OR OTHER PARTICIPANTS Myometrial biopsies were obtained at elective cesarean delivery. INTERVENTION No intervention was applied. MAIN OUTCOME MEASURES Open state probability of single channel recordings, whole cell currents, and myometrial contractile activity were measured. RESULTS Single-channel recordings identified the BK(Ca) channel as a target of BRL37344. BRL37344 significantly increased the open state probability of this channel in a concentration-dependent manner (control 0.031 +/- 0.004; 50 microM BRL37344 0.073 +/- 0.005 (P < 0.001); and 100 microM BRL37344 0.101 +/- 0.005 (P < 0.001). This effect was completely blocked after preincubation of the cells with 1 microM bupranolol, a nonspecific beta-adrenoreceptor blocker, or 100 nM SR59230a, a specific beta3-adrenoreceptor antagonist. In addition, BRL37344 increased whole-cell currents over a range of membrane potentials, and this effect was reversed by 100 nM IbTX. In vitro isometric tension studies demonstrated that BRL37344 exerted a significant concentration-dependent relaxant effect on human myometrial tissue (P < 0.05), and preincubation of these strips with IbTX attenuated this effect on both spontaneous and oxytocin-induced contractions (44.44 and 57.84% at 10(-5) M, respectively). CONCLUSIONS These findings outline that activation of the BK(Ca) channel may explain the potent uterorelaxant effect of beta3-adrenoreceptor agonists.
Collapse
Affiliation(s)
- Helen C Doheny
- Department of Obstetrics and Gynecology, National University of Ireland Galway, Clinical Science Institute, University College Hospital Galway, Galway, Ireland.
| | | | | | | |
Collapse
|
44
|
Sawada K, Morishige KI, Hashimoto K, Tasaka K, Kurachi H, Murata Y, Kurachi Y. Gestational change of K+ channel opener effect is correlated with the expression of uterine KATP channel subunits. Eur J Obstet Gynecol Reprod Biol 2005; 122:49-56. [PMID: 16154039 DOI: 10.1016/j.ejogrb.2004.11.026] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2004] [Revised: 11/10/2004] [Accepted: 11/25/2004] [Indexed: 11/20/2022]
Abstract
OBJECTIVE We analyzed the gestational changes of pharmacological activity and molecular levels of KATP channels in rat myometrium. STUDY DESIGN Using rat myometrium, the effects of K+ channel openers (KCOs) were examined in an isometric tension study of oxytocin-induced contraction. We also examined the effects of KCOs on the intracellular Ca2+ levels of cultured myometrial cells. The expression of myometrial KATP channels was assessed by RT-PCR and Northern blot analysis. RESULTS The effect of KCOs were altered during pregnancy, with a significant increase of their potency at day 18 of pregnancy followed by a decline towards the non-pregnant level at the day of delivery. KCOs suppressed the Ca2+ influx across the cell membrane. The mRNAs encoding each component of myometrial KATP channels, Kir6.1 and SUR2B, exhibited gestational stage-dependent alterations similar to those of the effects of KCOs. CONCLUSION These findings suggest that KCOs inhibit uterine myometrial contraction more effectively during pregnancy than in the non-pregnant state due to gestation-enhanced expression of KATP channels, implying that KCOs might be useful for preventing premature delivery.
Collapse
Affiliation(s)
- Kenjiro Sawada
- Department of Obstetrics and Gynecology, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871, Japan
| | | | | | | | | | | | | |
Collapse
|
45
|
Brainard AM, Miller AJ, Martens JR, England SK. Maxi-K channels localize to caveolae in human myometrium: a role for an actin-channel-caveolin complex in the regulation of myometrial smooth muscle K+ current. Am J Physiol Cell Physiol 2005; 289:C49-57. [PMID: 15703204 DOI: 10.1152/ajpcell.00399.2004] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Multiple cell-signaling pathways converge to modulate large-conductance, voltage- and Ca2+-sensitive K+ channel (maxi-K channel) activity and buffer cell excitability in human myometrial smooth muscle cells (hMSMCs). Recent evidence indicates that maxi-K channel proteins can target to membrane microdomains; however, their association with other proteins within these macromolecular complexes has not been elucidated. Biochemical isolation of detergent-resistant membrane fractions from human myometrium demonstrates the presence of maxi-K channels in lipid raft microdomains, which cofractionate with caveolins. In both nonpregnant and late-pregnant myometrium, maxi-K channels associate and colocalize with caveolar scaffolding proteins caveolin-1 and caveolin-2, but not caveolin-3. Disruption of cultured hMSMC caveolar complexes by cholesterol depletion with cyclodextrin increases an iberiotoxin-sensitive K+ current. Coimmunoprecipitations have indicated that the maxi-K channel also is associated with both α- and γ-actin. Immunocytochemical analysis indicates colocalization of maxi-K channels, actin, and caveolin-1 in primary cultures of hMSMCs. Further experiments using immunoelectron microscopy have shown the proximity of both actin and the maxi-K channel within the same cell surface caveolar structures. Functionally, disruption of the actin cytoskeleton in cultured hMSMCs by cytochalasin D and latrunculin A greatly increased the open-state probability of the channel, while stabilization of actin cytoskeleton with jasplakinolide abolished the effect of latrunculin A. These data indicate that the actin cytoskeleton is involved as part of a caveolar complex in the regulation of myometrial maxi-K channel function.
Collapse
Affiliation(s)
- Adam M Brainard
- Department of Physiology and Biophysics, Carver College of Medicine, University of Iowa, 5-660 Bowen Science Bldg., Iowa City, Iowa 52242, USA
| | | | | | | |
Collapse
|
46
|
Analysis of Maxi-K alpha subunit splice variants in human myometrium. Reprod Biol Endocrinol 2004; 2:67. [PMID: 15383146 PMCID: PMC524189 DOI: 10.1186/1477-7827-2-67] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/25/2004] [Accepted: 09/21/2004] [Indexed: 11/25/2022] Open
Abstract
Background Large-conductance, calcium-activated potassium (Maxi-K) channels are implicated in the modulation of human uterine contractions and myometrial Ca2+ homeostasis. However, the regulatory mechanism(s) governing the expression of Maxi-K channels with decreased calcium sensitivity at parturition are unclear. The objectives of this study were to investigate mRNA expression of the Maxi-K alpha subunit, and that of its splice variants, in human non-pregnant and pregnant myometrium, prior to and after labour onset, to determine whether altered expression of these splice variants is associated with decreased calcium sensitivity observed at labour onset. Methods Myometrial biopsies were obtained at hysterectomy (non-pregnant, NP), and at Caesarean section, at elective (pregnant not-in-labour, PNL) and intrapartum (pregnant in-labour, PL) procedures. RNA was extracted from all biopsies and quantitative real-time RT-PCR was used to investigate for possible differential expression of the Maxi-K alpha subunit, and that of its splice variants, between these functionally-distinct myometrial tissue sets. Results RT-PCR analysis identified the presence of a 132 bp and an 87 bp spliced exon of the Maxi-K alpha subunit in all three myometrial tissue sets. Quantitative real-time PCR indicated a decrease in the expression of the Maxi-K alpha subunit with labour onset. While there was no change in the proportion of Maxi-K alpha subunits expressing the 87 bp spliced exon, the proportion of alpha subunits expressing the 132 bp spliced exon was significantly increased with labour onset, compared to both non-pregnant and pregnant not-in-labour tissues. An increased proportion of 132 bp exon-containing alpha subunit variants with labour onset is of interest, as channels expressing this spliced exon have decreased calcium and voltage sensitivities. Conclusions Our findings suggest that decreased Maxi-K alpha subunit mRNA expression in human myometrium at labour onset, coupled to an increased proportion of Maxi-K channels expressing the 132 bp spliced exon, may be linked to decreased Maxi-K channel calcium and voltage sensitivity, thereby promoting enhanced uterine activity at the time of labour.
Collapse
|
47
|
Chanrachakul B, Broughton Pipkin F, Khan RN. Contribution of coupling between human myometrial beta2-adrenoreceptor and the BK(Ca) channel to uterine quiescence. Am J Physiol Cell Physiol 2004; 287:C1747-52. [PMID: 15329337 DOI: 10.1152/ajpcell.00236.2004] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The beta(2)-adrenergic receptor (beta(2)-AR) and the large-conductance Ca(2+)-activated K(+) (BK(Ca)) channel have been shown, separately, to be involved in mediating uterine relaxation. Our recent studies reveal that the levels of both beta(2)-AR and BK(Ca) channel proteins in pregnant human myometrium decrease by approximately 50% after the onset of labor. We present direct evidence in support of a structural and functional association between the beta(2)-AR and the BK(Ca) channel in pregnant human myometrium. Localization of both proteins is predominantly plasmalemmal, with 60% of beta(2)-AR colocalizing with the BK(Ca) channel. Coimmunoprecipitation studies indicate that BK(Ca) and beta(2)-AR are structurally linked by direct protein-protein interactions. Functional correlation was confirmed by experiments of human myometrial contractility in which the BK(Ca) channel blocker, paxilline, significantly antagonized the relaxant effect of the beta(2)-AR agonist ritodrine. These novel findings provide an insight into the coupling between the beta(2)-AR and BK(Ca) channel and may have utility in the application of this signaling cascade for therapeutic potential in the management of preterm labor.
Collapse
Affiliation(s)
- Boonsri Chanrachakul
- Center for Reproduction and Early Life, Institute of Clinical Research, University of Nottingham, Academic Division of Obstetrics and Gynaecology, The Medical School, Derby City General Hospital, Uttoxeter New Road, Derby DE22 3DT, UK
| | | | | |
Collapse
|
48
|
Khan RN, Hamoud H, Warren A, Wong LF, Arulkumaran S. Relaxant action of sildenafil citrate (Viagra) on human myometrium of pregnancy. Am J Obstet Gynecol 2004; 191:315-21. [PMID: 15295385 DOI: 10.1016/j.ajog.2003.11.005] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
OBJECTIVE The purpose of this study was to investigate the effect of the cyclic guanosine monophosphate phosphodiesterase 5-specific inhibitor, sildenafil citrate, on the contractions of isolated pregnant human myometrium. STUDY DESIGN Myometrial samples were obtained from women who underwent elective cesarean delivery. Myometrial contractions that were recorded in response to sildenafil in the absence and presence of the potassium channel blocker, tetraethylammonium or the guanylate cyclase inhibitor, methylene blue (10 micromol/L) were studied. One-way analysis of variance with post-hoc analysis was used to test differences among groups. RESULTS Sildenafil caused relaxation of myometrium in a concentration-dependent manner. The log(10) EC(50) value for this relaxation in the presence of 20 mmol/L tetraethylammonium was significantly different (P<.01) than values that were obtained with sildenafil alone or sildenafil in the presence of either methylene blue or 5 and 10 mmol/L tetraethylammonium. CONCLUSION Myometrial relaxation that is evoked by the direct application of sildenafil occurs independently of cyclic guanosine monophosphate. Potassium channels appear to be the likely candidates in mediating this response.
Collapse
Affiliation(s)
- Raheela N Khan
- Academic Division of Obstetrics and Gynaecology, University of Nottingham, The Medical School, Derby City General Hospital, Derby, United Kingdom.
| | | | | | | | | |
Collapse
|
49
|
Buxton ILO. Regulation of uterine function: a biochemical conundrum in the regulation of smooth muscle relaxation. Mol Pharmacol 2004; 65:1051-9. [PMID: 15102932 DOI: 10.1124/mol.65.5.1051] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Premature birth accounts for the majority of fetal morbidity and mortality in the developed world and is disproportionately represented in some populations, such as African Americans in the United States. The costs associated with prematurity are staggering in both monetary and human terms. Present therapeutic approaches for the treatment of labor leading to preterm delivery are inadequate and our understanding of the regulation of myometrial smooth muscle contraction-relaxation is incomplete. The ability of nitric oxide to relax smooth muscle has led to an interest in employing nitric oxide-donors in the treatment of preterm labor. Fundamental differences exist, however, in the regulation of uterine smooth muscle relaxation and that of other smooth muscles and constitute a conundrum in our understanding. We review the evidence that nitric oxide-mediated relaxation of myometrial smooth muscle, unlike vascular or gastrointestinal smooth muscle, is independent of global elevation of cyclic guanosine 5'-monophosphate. Applying our current understanding of microdomain signaling and taking clues from genomic studies of pregnancy, we offer a framework in which to view the apparent conundrum and suggest testable hypotheses of uterine relaxation signaling that can explain the mechanistic distinctions. We propose that understanding these mechanistic distinctions in myometrium will reveal molecular targets that are unique and thus may be explored as therapeutic targets in the development of new uterine smooth muscle-specific tocolytics.
Collapse
Affiliation(s)
- Iain L O Buxton
- Department of Pharmacology, University of Nevada School of Medicine, Reno, NV 89557, USA.
| |
Collapse
|
50
|
Arakawa TK, Mlynarczyk M, Kaushal KM, Zhang L, Ducsay CA. Long-term hypoxia alters calcium regulation in near-term ovine myometrium. Biol Reprod 2004; 71:156-62. [PMID: 14985251 DOI: 10.1095/biolreprod.103.026708] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
Previous studies showed that long-term hypoxia (LTH) during pregnancy alters myometrial contractility. The present study was designed to test the hypothesis that LTH during pregnancy suppresses myometrial contractility in sheep by affecting the calcium signaling cascade. Pregnant sheep were maintained at high altitude (3820 m) from Day 30 to Day 139 of gestation, when the animals were killed for collection of myometrial tissue. Tissue was also collected from age-matched, normoxic controls. Circular and longitudinal layers were separated, and strips from each layer were mounted in a muscle bath. After pretreatment with 10(-8) M oxytocin, the strips were exposed to increasing half- or quarter-log doses of nifedipine (L-type calcium-channel blocker), ruthenium red, ryanodine (blockers of inositol 1,4,5-trisphosphate-insensitive calcium stores), or 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (NCDC; phospholipase C inhibitor). Area under the contraction curve was analyzed, and pD(2) (log of concentration yielding 50% of maximum response) values and maximum relaxation responses were calculated. The maximum relaxation response to nifedipine was increased in both longitudinal (P < 0.01) and circular (P < 0.05) myometrial layers from LTH compared to control tissue, whereas no difference was observed in response to ruthenium red or ryanodine. The maximum relaxation response to NCDC was lower in the LTH circular layer (P < 0.05). Together, these data are indicative of an increase in the dependence of ovine uterine smooth muscle on extracellular calcium influx through the L-type, voltage-gated calcium channels following LTH. This appears to occur not through an increase in L-type calcium channels but, rather, through a possible decline in importance of the oxytocin-induced, phospholipase C-mediated pathway, resulting in a greater proportion of extracellular calcium contributing to contraction. Layer-dependent differences also exist between the circular and longitudinal myometrium in response to phospholipase C inhibition.
Collapse
Affiliation(s)
- T K Arakawa
- Center for Perinatal Biology, Departments of Physiology/Pharmacology and Pediatrics, Loma Linda University School of Medicine, Loma Linda, California 92350, USA
| | | | | | | | | |
Collapse
|