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Large RJ, Kshatri A, Webb TI, Roy S, Akande A, Bradley E, Sergeant GP, Thornbury KD, McHale NG, Hollywood MA. Effects of the novel BK (KCa 1.1) channel opener GoSlo-SR-5-130 are dependent on the presence of BKβ subunits. Br J Pharmacol 2015; 172:2544-56. [PMID: 25598230 DOI: 10.1111/bph.13085] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Revised: 12/12/2014] [Accepted: 01/02/2015] [Indexed: 01/12/2023] Open
Abstract
BACKGROUND AND PURPOSE GoSlo-SR compounds are efficacious BK (KCa 1.1) channel openers, but little is known about their mechanism of action or effect on bladder contractility. We examined the effects of two closely related compounds on BK currents and bladder contractions. EXPERIMENTAL APPROACH A combination of electrophysiology, molecular biology and synthetic chemistry was used to examine the effects of two novel channel agonists on BK channels from bladder smooth muscle cells and in HEK cells expressing BKα alone or in combination with either β1 or β4 subunits. KEY RESULTS GoSlo-SR-5-6 shifted the voltage required for half maximal activation (V1/2 ) of BK channels approximately -100 mV, irrespective of the presence of regulatory β subunits. The deaminated derivative, GoSlo-SR-5-130, also shifted the activation V1/2 in smooth muscle cells by approximately -100 mV; however, this was reduced by ∼80% in HEK cells expressing only BKα subunits. When β1 or β4 subunits were co-expressed with BKα, efficacy was restored. GoSlo-SR-5-130 caused a concentration-dependent reduction in spontaneous bladder contraction amplitude and this was abolished by iberiotoxin, consistent with an effect on BK channels. CONCLUSIONS AND IMPLICATIONS GoSlo-SR-5-130 required β1 or β4 subunits to mediate its full effects, whereas GoSlo-SR-5-6 worked equally well in the absence or presence of β subunits. GoSlo-SR-5-130 inhibited spontaneous bladder contractions by activating BK channels. The novel BK channel opener, GoSlo-SR-5-130, is approximately fivefold more efficacious on BK channels with regulatory β subunits and may be a useful scaffold in the development of drugs to treat diseases such as overactive bladder.
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Affiliation(s)
- R J Large
- The Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Co. Louth, Ireland
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Roy S, Large RJ, Akande AM, Kshatri A, Webb TI, Domene C, Sergeant GP, McHale NG, Thornbury KD, Hollywood MA. Development of GoSlo-SR-5-69, a potent activator of large conductance Ca2+-activated K+ (BK) channels. Eur J Med Chem 2014; 75:426-37. [PMID: 24561672 DOI: 10.1016/j.ejmech.2014.01.035] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2013] [Revised: 01/13/2014] [Accepted: 01/16/2014] [Indexed: 10/25/2022]
Abstract
We have designed, synthesised and characterised the effects of a number of novel anthraquinone derivatives and assessed their effects on large conductance, Ca(2+) activated K(+) (BK) channels recorded from rabbit bladder smooth muscle cells using the excised, inside/out configuration of the patch clamp technique. These compounds are members of the GoSlo-SR family of compounds, which potently open BK channels and shift the voltage required for half maximal activation (V1/2) negatively. The efficacy of the anilinoanthraquinone derivatives was enhanced when the size of ring D was increased, since the cyclopentane and cyclohexane derivatives shifted the V1/2, by -24 ± 6 mV and -54 ± 8 mV, respectively, whereas the cycloheptane and cyclooctane derivatives shifted the V1/2 by -61 ± 6 mV and -106 ± 6 mV. To examine if a combination of hydrophobicity and steric bulking of this region further enhanced their ability to open BK channels, we synthesised a number of naphthalene and tetrahydro-naphthalene derivatives. The tetrahydro-2-naphthalene derivative GoSlo-SR-5-69 was the most potent and efficacious of the series since it was able to shift the activation V1/2 by greater than -100 mV when applied at a concentration of 1 μM and had an EC50 of 251 nM, making it one of the most potent and efficacious BK channel openers synthesised to date.
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Affiliation(s)
- Subhrangsu Roy
- Ion Channel Biotechnology Centre, Dundalk Institute of Technology, Dublin Road, Dundalk, County Louth, Ireland
| | - Roddy J Large
- Ion Channel Biotechnology Centre, Dundalk Institute of Technology, Dublin Road, Dundalk, County Louth, Ireland
| | - Adebola Morayo Akande
- The Smooth Muscle Research Centre, Dundalk Institute of Technology, Dublin Road, Dundalk, County Louth, Ireland
| | - Aravind Kshatri
- The Smooth Muscle Research Centre, Dundalk Institute of Technology, Dublin Road, Dundalk, County Louth, Ireland
| | - Tim I Webb
- Ion Channel Biotechnology Centre, Dundalk Institute of Technology, Dublin Road, Dundalk, County Louth, Ireland
| | - Carmen Domene
- Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK; Department of Chemistry, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, UK
| | - Gerard P Sergeant
- The Smooth Muscle Research Centre, Dundalk Institute of Technology, Dublin Road, Dundalk, County Louth, Ireland; Ion Channel Biotechnology Centre, Dundalk Institute of Technology, Dublin Road, Dundalk, County Louth, Ireland
| | - Noel G McHale
- The Smooth Muscle Research Centre, Dundalk Institute of Technology, Dublin Road, Dundalk, County Louth, Ireland; Ion Channel Biotechnology Centre, Dundalk Institute of Technology, Dublin Road, Dundalk, County Louth, Ireland
| | - Keith D Thornbury
- The Smooth Muscle Research Centre, Dundalk Institute of Technology, Dublin Road, Dundalk, County Louth, Ireland; Ion Channel Biotechnology Centre, Dundalk Institute of Technology, Dublin Road, Dundalk, County Louth, Ireland
| | - Mark A Hollywood
- The Smooth Muscle Research Centre, Dundalk Institute of Technology, Dublin Road, Dundalk, County Louth, Ireland; Ion Channel Biotechnology Centre, Dundalk Institute of Technology, Dublin Road, Dundalk, County Louth, Ireland.
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Roy S, Morayo Akande A, Large RJ, Webb TI, Camarasu C, Sergeant GP, McHale NG, Thornbury KD, Hollywood MA. Structure-activity relationships of a novel group of large-conductance Ca(2+)-activated K(+) (BK) channel modulators: the GoSlo-SR family. ChemMedChem 2012; 7:1763-9. [PMID: 22930560 DOI: 10.1002/cmdc.201200321] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2012] [Indexed: 01/20/2023]
Abstract
Opening up ion channels: We synthesised a series of anthraquinone analogues, called the GoSlo-SR family. Their effects on bladder smooth muscle BK channels were examined and, as shown, shifted voltage dependent activation >-100 mV (at 10 μM). They were more efficacious than NS11021 and could provide a new scaffold for the design of efficacious BK openers.
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Affiliation(s)
- Subhrangsu Roy
- Ion Channel Biotechnology Centre, Dundalk Institute of Technology, Dublin Road, Dundalk, Co. Louth, Ireland
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4
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Niwa S, Ohya S, Kojima Y, Sasaki S, Yamamura H, Sakuragi M, Kohri K, Imaizumi Y. Down-Regulation of the Large-Conductance Ca 2+-Activated K + Channel, K Ca1.1 in the Prostatic Stromal Cells of Benign Prostate Hyperplasia. Biol Pharm Bull 2012; 35:737-44. [DOI: 10.1248/bpb.35.737] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Satomi Niwa
- Department of Molecular & Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University
| | - Susumu Ohya
- Department of Molecular & Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University
| | - Yoshiyuki Kojima
- Department of Nephro-urology, Graduate School of Medical Sciences, Nagoya City University
| | - Shoichi Sasaki
- Department of Nephro-urology, Graduate School of Medical Sciences, Nagoya City University
| | - Hisao Yamamura
- Department of Molecular & Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University
| | | | - Kenjiro Kohri
- Department of Nephro-urology, Graduate School of Medical Sciences, Nagoya City University
| | - Yuji Imaizumi
- Department of Molecular & Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University
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5
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Hristov KL, Chen M, Kellett WF, Rovner ES, Petkov GV. Large-conductance voltage- and Ca2+-activated K+ channels regulate human detrusor smooth muscle function. Am J Physiol Cell Physiol 2011; 301:C903-12. [PMID: 21697543 DOI: 10.1152/ajpcell.00495.2010] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The large-conductance voltage- and Ca(2+)-activated K(+) (BK) channel is expressed in many smooth muscle types, but its role in human detrusor smooth muscle (DSM) is unclear. With a multidisciplinary approach spanning channel molecules, single-channel activity, freshly isolated human DSM cells, intact DSM preparations, and the BK channel specific inhibitor iberiotoxin, we elucidated human DSM BK channel function and regulation. Native human DSM tissues were obtained during open surgeries from patients with no preoperative history of overactive bladder. RT-PCR experiments on single human DSM cells showed mRNA expression of BK channel α-, β(1)-, and β(4)-subunits. Western blot and immunocytochemistry confirmed BK channel α, β(1), and β(4) protein expression. Native human BK channel properties were described using the perforated whole cell configuration of the patch-clamp technique. In freshly isolated human DSM cells, BK channel blockade with iberiotoxin inhibited a significant portion of the total voltage step-induced whole cell K(+) current. From single BK channel recordings, human BK channel conductance was calculated to be 136 pS. Voltage-dependent iberiotoxin- and ryanodine-sensitive transient BK currents were identified in human DSM cells. In current-clamp mode, iberiotoxin inhibited the hyperpolarizing membrane potential transients and depolarized the cell resting membrane potential. Isometric DSM tension recordings revealed that BK channels principally control the contractions of isolated human DSM strips. Collectively, our results indicate that BK channels are fundamental regulators of DSM excitability and contractility and may represent new targets for pharmacological or genetic control of urinary bladder function in humans.
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Affiliation(s)
- Kiril L Hristov
- Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, 29208, USA
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6
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Hotta S, Morimura K, Ohya S, Muraki K, Takeshima H, Imaizumi Y. Ryanodine receptor type 2 deficiency changes excitation-contraction coupling and membrane potential in urinary bladder smooth muscle. J Physiol 2007; 582:489-506. [PMID: 17363382 PMCID: PMC2075324 DOI: 10.1113/jphysiol.2007.130302] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The possibility that the ryanodine receptor type 2 (RyR2) can function as the major Ca(2+)-induced Ca(2+) release (CICR) channel in excitation-contraction (E-C) coupling was examined in smooth muscle cells (SMCs) isolated from urinary bladder (UB) of RyR2 heterozygous KO mice (RyR2+/-). RyR2 mRNA expression in UB from RyR2+/- was much lower than that in wild-type (RyR2+/+. In single UBSMCs from RyR2+/+, membrane depolarization under voltage clamp initially induced several local Ca(2+) transients (hot spots) in peripheral areas of the cell. Then, Ca(2+) waves spread from Ca(2+) hot spots to other areas of the myocyte. The number of Ca(2+) hot spots elicited by a short depolarization (< 20 ms) in UBSMCs of RyR2+/- was significantly smaller than in those of RyR2+/+. The force development induced either by direct electrical stimulation or by 10 microm acetylcholine in tissue segments of RyR2+/- was smaller than and comparable to those in RyR2+/+, respectively. The frequency of spontaneous transient outward currents in single myocytes and the membrane depolarization by 1 microm paxilline in tissue segments from RyR2+/- were significantly lower and smaller than those in RyR2+/+, respectively. The urination frequency and volume per voiding in RyR2+/- were significantly increased and reduced, respectively, compared with RyR2+/+. In conclusion, RyR2 plays a crucial role in the regulation of CICR during E-C coupling and also in the regulation of resting membrane potential, presumably via the modulation of Ca(2+)-dependent K(+) channel activity in UBSMCs and, thereby, has a pivotal role in the control of bladder activity.
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Affiliation(s)
- Shingo Hotta
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Science, Nagoya City University, 3-1 Tanabedori, Mizuhoku, Nagoya 467-8603, Japan
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Kiyoshi H, Yamazaki D, Ohya S, Kitsukawa M, Muraki K, Saito SY, Ohizumi Y, Imaizumi Y. Molecular and electrophysiological characteristics of K+ conductance sensitive to acidic pH in aortic smooth muscle cells of WKY and SHR. Am J Physiol Heart Circ Physiol 2006; 291:H2723-34. [PMID: 16815980 DOI: 10.1152/ajpheart.00894.2005] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Changes in K(+) conductances and their contribution to membrane depolarization in the setting of an acidic pH environment have been studied in myocytes from aortic smooth muscle cells of spontaneously hypertensive rats (SHR) compared with those from Wistar-Kyoto (WKY) rats. The resting membrane potential (RMP) of aortic smooth muscle at extracellular pH (pH(o)) of 7.4 was significantly more depolarized in SHR than in WKY rats. Acidification to pH(o) 6.5 made this difference in RMP between SHR and WKY rats more significant by further depolarizing the SHR myocytes. Large-conductance Ca(2+)-activated K(+) (BK) currents, which were markedly suppressed by acidification, were larger in aortic myocytes of SHR than in those of WKY rats. In contrast, acid-sensitive, non-BK currents were smaller in SHR. Western blot analyses showed that expression of BK-alpha- and -beta(1) subunits in SHR aortas was upregulated and comparable with those in WKY rats, respectively. Additional electrophysiological and molecular studies showed that pH- and halothane-sensitive two-pore domain weakly inward rectifying K(+) channel (TWIK)-like acid-sensitive K(+) (TASK) channel subtypes were functionally expressed in aortas, and TASK1 expression was significantly higher in WKY than in SHR. Although the background current through TASK channels at normal pH(o) (7.4) was small and may not contribute significantly to the regulation of RMP, TASK channel activation by halothane or alkalization (pH(o) 8.0) induced significant hyperpolarization in WKY but not in SHR. In conclusion, the larger depolarization and subsequent abnormal contractions after acidification in aortic myocytes in the setting of SHR hypertension are mainly attributable to the larger contribution of BK current to the total membrane conductance than in WKY aortas.
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MESH Headings
- Animals
- Aorta/metabolism
- Aorta/pathology
- Aorta/physiopathology
- Down-Regulation/physiology
- Electrophysiology
- Halothane/pharmacology
- Hydrogen-Ion Concentration
- Hypertension/pathology
- Hypertension/physiopathology
- Male
- Membrane Potentials/genetics
- Membrane Potentials/physiology
- Muscle, Smooth, Vascular/metabolism
- Muscle, Smooth, Vascular/pathology
- Muscle, Smooth, Vascular/physiopathology
- Myocardial Contraction/physiology
- Myocytes, Cardiac/metabolism
- Myocytes, Cardiac/pathology
- Nerve Tissue Proteins
- Potassium Channels, Calcium-Activated/genetics
- Potassium Channels, Calcium-Activated/metabolism
- Potassium Channels, Tandem Pore Domain/genetics
- Potassium Channels, Tandem Pore Domain/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Rats
- Rats, Inbred SHR
- Rats, Inbred WKY
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Affiliation(s)
- Hidekazu Kiyoshi
- Dept. of Molecular & Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Mizuhoku, Nagoya 467-8603, Japan
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8
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Laporte R, Hui A, Laher I. Pharmacological modulation of sarcoplasmic reticulum function in smooth muscle. Pharmacol Rev 2005; 56:439-513. [PMID: 15602008 DOI: 10.1124/pr.56.4.1] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The sarco/endoplasmic reticulum (SR/ER) is the primary storage and release site of intracellular calcium (Ca2+) in many excitable cells. The SR is a tubular network, which in smooth muscle (SM) cells distributes close to cellular periphery (superficial SR) and in deeper aspects of the cell (deep SR). Recent attention has focused on the regulation of cell function by the superficial SR, which can act as a buffer and also as a regulator of membrane channels and transporters. Ca2+ is released from the SR via two types of ionic channels [ryanodine- and inositol 1,4,5-trisphosphate-gated], whereas accumulation from thecytoplasm occurs exclusively by an energy-dependent sarco-endoplasmic reticulum Ca2+-ATPase pump (SERCA). Within the SR, Ca2+ is bound to various storage proteins. Emerging evidence also suggests that the perinuclear portion of the SR may play an important role in nuclear transcription. In this review, we detail the pharmacology of agents that alter the functions of Ca2+ release channels and of SERCA. We describe their use and selectivity and indicate the concentrations used in investigating various SM preparations. Important aspects of cell regulation and excitation-contractile activity coupling in SM have been uncovered through the use of such activators and inhibitors of processes that determine SR function. Likewise, they were instrumental in the recent finding of an interaction of the SR with other cellular organelles such as mitochondria. Thus, an appreciation of the pharmacology and selectivity of agents that interfere with SR function in SM has greatly assisted in unveiling the multifaceted nature of the SR.
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Affiliation(s)
- Régent Laporte
- Ferring Research Institute, Inc., Ferring Pharmaceuticals, San Diego, California, USA
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Meredith AL, Thorneloe KS, Werner ME, Nelson MT, Aldrich RW. Overactive bladder and incontinence in the absence of the BK large conductance Ca2+-activated K+ channel. J Biol Chem 2004; 279:36746-52. [PMID: 15184377 DOI: 10.1074/jbc.m405621200] [Citation(s) in RCA: 287] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
BK large conductance voltage- and calcium-activated potassium channels respond to elevations in intracellular calcium and membrane potential depolarization, braking excitability of smooth muscle. BK channels are thought to have a particularly prominent role in urinary bladder smooth muscle function and therefore are candidate targets for overactive bladder therapy. To address the role of the BK channel in urinary bladder function, the gene mSlo1 for the pore-forming subunit of the BK channel was deleted. Slo(-/-) mice were viable but exhibited moderate ataxia. Urinary bladder smooth muscle cells of Slo(-/-) mice lacked calcium- and voltage-activated BK currents, whereas local calcium transients ("calcium sparks") and voltage-dependent potassium currents were unaffected. In the absence of BK channels, urinary bladder spontaneous and nerve-evoked contractions were greatly enhanced. Consistent with increased urinary bladder contractility caused by the absence of BK currents, Slo(-/-) mice demonstrate a marked elevation in urination frequency. These results reveal a central role for BK channels in urinary bladder function and indicate that BK channel dysfunction leads to overactive bladder and urinary incontinence.
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Affiliation(s)
- Andrea L Meredith
- Department of Molecular and Cellular Physiology and the Howard Hughes Medical Institute, 279 Campus Drive, Stanford University, Stanford, CA 94305, USA
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10
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Petrova R, Yamamoto Y, Muraki K, Yonekura H, Sakurai S, Watanabe T, Li H, Takeuchi M, Makita Z, Kato I, Takasawa S, Okamoto H, Imaizumi Y, Yamamoto H. Advanced glycation endproduct-induced calcium handling impairment in mouse cardiac myocytes. J Mol Cell Cardiol 2002; 34:1425-31. [PMID: 12393002 DOI: 10.1006/jmcc.2002.2084] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Long-standing diabetes causes cardiovascular complications including direct cardiac muscle weakening known as diabetic cardiomyopathy. This is characterized by disturbances in both cardiac contraction and relaxation, which are maintained by calcium homeostasis in cardiac cells. Our recent in vitro and in vivo studies have shown that advanced glycation endproducts (AGE) account for diabetic vasculopathy through their engagement of the receptor for AGE (RAGE). Here we show that AGE and RAGE may directly affect the myocardial Ca(2+) homeostasis. We created transgenic mice that overexpressed human RAGE in the heart and analyzed the Ca(2+) transients in cultivated cardiac myocytes (CM) from the RAGE-transgenic and non-transgenic control fetuses. RAGE overexpression was found to reduce the systolic and diastolic intracellular calcium concentration ([Ca(2+)](i)). Exposure to AGE caused a significant prolongation of the decay time of [Ca(2+)](i) in CM from control mice, and this response was augmented in CM from the RAGE transgenic mice. The results suggest that the AGE and RAGE could play an active role in the development of diabetes-induced cardiac dysfunction.
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Affiliation(s)
- Ralica Petrova
- Department of Biochemistry and Molecular Vascular Biology, Kanazawa University Graduate School of Medical Science, 13-1 Takara-machi, Kanazawa 920-8640, Japan
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Imaizumi Y, Sakamoto K, Yamada A, Hotta A, Ohya S, Muraki K, Uchiyama M, Ohwada T. Molecular basis of pimarane compounds as novel activators of large-conductance Ca(2+)-activated K(+) channel alpha-subunit. Mol Pharmacol 2002; 62:836-46. [PMID: 12237330 DOI: 10.1124/mol.62.4.836] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Effects of pimaric acid (PiMA) and eight closely related compounds on large-conductance K(+) (BK) channels were examined using human embryonic kidney (HEK) 293 cells, in which either the alpha subunit of BK channel (HEKBKalpha) or both alpha and beta1 (HEKBKalphabeta1) subunits were heterologously expressed. Effects of these compounds (10 microM) on the membrane potential of HEKBKalphabeta1 were monitored by use of DiBAC(4)(3), a voltage-sensitive dye. PiMA, isopimaric acid, sandaracoisopimaric acid, dihydropimaric acid, dihydroisopimaric acid, and dihydroisopimarinol induced substantial membrane hyperpolarization. The direct measurement of BKalphabeta1 opening under whole-cell voltage clamp showed that these six compounds activated BKalphabeta1 in a very similar concentration range (1-10 microM); in contrast, abietic acid, sclareol, and methyl pimarate had no effect. PiMA did not affect the charybdotoxin-induced block of macroscopic BKalphabeta1 current. Single channel recordings of BKalphabeta1 in inside-out patches showed that 10 microM PiMA did not change channel conductance but significantly increased its open probability as a result of increase in sensitivity to Ca(2+) and voltage. Because coexpression of the beta1 subunit did not affect PiMA-induced potentiation, the site of action for PiMA is suggested to be BKalpha subunit. PiMA was selective to BK over cloned small and intermediate Ca(2+) activated K(+) channels. In conclusion, PiMA (>1 microM) increases Ca(2+) and voltage-sensitivity of BKalpha when applied from either side of the cell membrane. The marked difference in potency as BK channel openers between PiMA and abietic acid, despite only very small differences in their chemical structures, may provide insight into the fundamental structure-activity relationship governing BKalpha activation.
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Affiliation(s)
- Yuji Imaizumi
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan.
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12
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Ohi Y, Yamamura H, Nagano N, Ohya S, Muraki K, Watanabe M, Imaizumi Y. Local Ca(2+) transients and distribution of BK channels and ryanodine receptors in smooth muscle cells of guinea-pig vas deferens and urinary bladder. J Physiol 2001; 534:313-26. [PMID: 11454953 PMCID: PMC2278703 DOI: 10.1111/j.1469-7793.2001.t01-3-00313.x] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
1. The relationship between Ca(2+) sparks spontaneously occurring at rest and local Ca(2+) transients elicited by depolarization was analysed using two-dimensional confocal Ca(2+) images of single smooth muscle cells isolated from guinea-pig vas deferens and urinary bladder. The current activation by these Ca(2+) events was also recorded simultaneously under whole-cell voltage clamp. 2. Spontaneous transient outward currents (STOCs) and Ca(2+) sparks were simultaneously detected at -40 mV in approximately 50 % of myocytes of either type. Ca(2+) sparks and corresponding STOCs occurred repetitively in several discrete sites in the subplasmalemmal area. Large conductance Ca(2+)-dependent K(+) (BK) channel density in the plasmalemma near the Ca(2+) spark sites generating STOCs was calculated to be 21 channels microm(-2). 3. When myocytes were depolarized from -60 to 0 mV, several local Ca(2+) transients were elicited within 20 ms in exactly the same peripheral sites where sparks occurred at rest. The local Ca(2+) transients often lasted over 300 ms and spread into other areas. The appearance of local Ca(2+) transients occurred synchronously with the activation of Ca(2+)-dependent K(+) current (I(K,Ca)). 4. Immunofluorescence staining of the BK channel alpha-subunit (BKalpha) revealed a spot-like pattern on the plasmalemma, in contrast to the uniform staining of voltage-dependent Ca(2+) channel alpha1C subunits along the plasmalemma. Ryanodine receptor (RyR) immunostaining also suggested punctate localization predominantly in the periphery. Double staining of BKalpha and RyRs revealed spot-like co-localization on/beneath the plasmalemma. 5. Using pipettes of relatively low resistance, inside-out patches that included both clustered BK channels at a density of over 20 channels microm(-2) and functional Ca(2+) storage sites were obtained at a low probability of approximately 5%. The averaged BK channel density was 3-4 channels microm(-2) in both types of myocyte. 6. These results support the idea that a limited number of discrete sarcoplasmic reticulum (SR) fragments in the subplasmalemmal area play key roles in the control of BK channel activity in two ways: (i) by generating Ca(2+) sparks at rest to activate STOCs and (ii) by generating Ca(2+) transients presumably triggered by sparks during an action potential to activate a large I(K,Ca) and also induce a contraction. BK channels and RyRs may co-localize densely at the junctional areas of plasmalemma and SR fragments, where Ca(2+) sparks occur to elicit STOCs.
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Affiliation(s)
- Y Ohi
- Department of Molecular and Cellular Pharmacology, Faculty of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabedori, Mizuhoku, Nagoya 467-8603, Japan
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Yamada A, Gaja N, Ohya S, Muraki K, Narita H, Ohwada T, Imaizumi Y. Usefulness and limitation of DiBAC4(3), a voltage-sensitive fluorescent dye, for the measurement of membrane potentials regulated by recombinant large conductance Ca2+-activated K+ channels in HEK293 cells. JAPANESE JOURNAL OF PHARMACOLOGY 2001; 86:342-50. [PMID: 11488436 DOI: 10.1254/jjp.86.342] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The usefulness of bis-(1,3-dibutylbarbituric acid)-trimethine oxonol (DiBAC4(3)), a voltage-sensitive fluorescent dye, for the measurement of membrane potentials (MPs) was evaluated in HEK293 cells, where alpha or alpha plus beta1 subunits of large conductance Ca2+-activated K+ (BK) channels were expressed (HEKBK alpha and HEKBK alphabeta). The fluorescent intensity of DiBAC4(3) was measured at various potentials under voltage-clamp for calibration to estimate the absolute MP semi-quantitatively. The resting MPs measured with DiBAC4(3) were roughly comparable to those recorded with a microelectrode; the MP in HEKBK alphabeta was 10-20 mV more negative than that in native HEK. In HEKBK alpha, the membrane hyperpolarization induced by 10 microM Evans blue, a BK channel opener, was detected with DiBAC4(3). NS-1619, another BK channel opener, induced gradual but substantial change in F/F(K) even in native HEK, while the BK channel opening effect was detected. Oscillatory membrane hyperpolarization was induced in HEKBK alphabeta by application of 10 microM acetylcholine via increase in intracellular Ca2+ concentration. The oscillatory hyperpolarization was, however, detected only as a slow hyperpolarization with DiBAC4(3). It can be concluded that relatively slow effects of BK channel modulators can be semi-quantitatively measured by use of DiBAC4(3) in HEKBK, while the limited temporal resolution and possible artifacts should be taken into account.
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Affiliation(s)
- A Yamada
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
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14
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Ohi Y, Takai N, Muraki K, Watanabe M, Imaizumi Y. Ca2+-images of smooth muscle cells and endothelial cells in one confocal plane in femoral artery segments of the rat. JAPANESE JOURNAL OF PHARMACOLOGY 2001; 86:106-13. [PMID: 11430461 DOI: 10.1254/jjp.86.106] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Simultaneous recording of Ca2+-images in one confocal plane from vascular smooth muscle cells (SMCs) and endothelial cells (ECs) of an intact rat femoral artery segment was performed using indo-1 and a confocal microscope. During application of 10 microM acetylcholine (ACh), elevation and oscillation of intracellular Ca2+ concentration ([Ca2+]i) were observed in ECs but not in SMCs. Sequential conduction of Ca2+ oscillation from an EC to the neighboring ECs in one longitudinal direction was often observed in the presence of ACh. On the other hand, the activation of voltage-dependent Ca2+ channels by external 30 mM K+ resulted in the elevation of [Ca2+]i only in SMCs. When 10 microM ACh was added in the presence of 30 mM K+, it was observed in one confocal plane that [Ca2+]i in ECs and SMCs was almost simultaneously increased and decreased, respectively. The simultaneous recording method in this intact preparation will provide a line of valuable information about the interactions between SMCs and ECs, based on spatio-temporal analyses of absolute values of [Ca2+]i in individual cells.
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MESH Headings
- Acetylcholine/metabolism
- Animals
- Calcium/metabolism
- Endothelium, Vascular/metabolism
- Endothelium, Vascular/ultrastructure
- Femoral Artery/metabolism
- Femoral Artery/ultrastructure
- Image Processing, Computer-Assisted
- Male
- Microscopy, Confocal
- Microscopy, Fluorescence
- Muscle, Smooth, Vascular/metabolism
- Muscle, Smooth, Vascular/ultrastructure
- Rats
- Rats, Wistar
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Affiliation(s)
- Y Ohi
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
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15
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Ohi Y, Atsuki K, Tori Y, Ohizumi Y, Watanabe M, Imaizumi Y. Imaging of Ca2+ release by caffeine and 9-methyl-7-bromoeudistomin D and the associated activation of large conductance Ca2+-dependent K+ channels in urinary bladder smooth muscle cells of the guinea pig. JAPANESE JOURNAL OF PHARMACOLOGY 2001; 85:382-90. [PMID: 11388642 DOI: 10.1254/jjp.85.382] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Ca2+ release by caffeine and 9-methyl-7-bromoeudistomin D (MBED) and the concomitant activation of large conductance Ca2+-dependent K+ (BK) channels were analyzed using confocal Ca2+ imaging and whole cell voltage-clamp methods in guinea pig urinary bladder smooth muscle cells. Puff application of 3 or 10 mM caffeine for several seconds (2 - 5 s) elicited a large increase in intracellular Ca2+ concentration ([Ca2+]i) and induced a phasic outward current at a holding potential of -40 mV. The phasic outward current was the summation of spontaneous transient outward currents (STOCs) due to marked activation of BK channels and was followed by a short cessation of STOCs. Although the increase in superficial [Ca2+]i by caffeine was faster than that in global [Ca2+]i, the peak [Ca2+]i was identical in these areas. Puff application of 100 microM MBED also markedly enhanced STOCs for a few seconds. This response to MBED was not observed when stored Ca2+ was depleted by caffeine. The increase in [Ca2+]i by MBED occurred mainly in superficial areas. Longer application of 100 microM MBED for 2 min did not induce significant global [Ca2+]i increase but decreased the amount of Ca2+ release and cell shortening during the subsequent application of 10 mM caffeine. These results indicate that short application of MBED releases Ca2+ preferentially from superficial storage sites, presumably due to its slow approach to deeper sites. MBED may be a good pharmacological tool to manipulate selectively the superficial Ca2+ stores related to STOCs.
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Affiliation(s)
- Y Ohi
- Department of Molecular and Cellular Pharmacology, Faculty of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
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16
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Herrera GM, Heppner TJ, Nelson MT. Voltage dependence of the coupling of Ca(2+) sparks to BK(Ca) channels in urinary bladder smooth muscle. Am J Physiol Cell Physiol 2001; 280:C481-90. [PMID: 11171567 DOI: 10.1152/ajpcell.2001.280.3.c481] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Large-conductance Ca(2+)-dependent K(+) (BK(Ca)) channels play a critical role in regulating urinary bladder smooth muscle (UBSM) excitability and contractility. Measurements of BK(Ca) currents and intracellular Ca(2+) revealed that BK(Ca) currents are activated by Ca(2+) release events (Ca(2+) sparks) from ryanodine receptors (RyRs) in the sarcoplasmic reticulum. The goals of this project were to characterize Ca(2+) sparks and BK(Ca) currents and to determine the voltage dependence of the coupling of RyRs (Ca(2+) sparks) to BK(Ca) channels in UBSM. Ca(2+) sparks in UBSM had properties similar to those described in arterial smooth muscle. Most Ca(2+) sparks caused BK(Ca) currents at all voltages tested, consistent with the BK(Ca) channels sensing approximately 10 microM Ca(2+). Membrane potential depolarization from -50 to -20 mV increased Ca(2+) spark and BK(Ca) current frequency threefold. However, membrane depolarization over this range had a differential effect on spark and current amplitude, with Ca(2+) spark amplitude increasing by only 30% and BK(Ca) current amplitude increasing 16-fold. A major component of the amplitude modulation of spark-activated BK(Ca) current was quantitatively explained by the known voltage dependence of the Ca(2+) sensitivity of BK(Ca) channels. We, therefore, propose that membrane potential, or any other agent that modulates the Ca(2+) sensitivity of BK(Ca) channels, profoundly alters the coupling strength of Ca(2+) sparks to BK(Ca) channels.
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Affiliation(s)
- G M Herrera
- Department of Molecular Physiology and Biophysics, University of Vermont College of Medicine, Burlington, Vermont 05405, USA
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17
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Abstract
Iron homeostasis is maintained by regulating its absorption: Under conditions of deficiency, assimilation is enhanced but iron uptake is otherwise limited to prevent toxicity due to overload. Iron deficiency remains the most important micronutrient deficiency worldwide, but increasing awareness of the genetic basis for iron-loading diseases points to iron overload as a major public health issue as well. Recent identification of mutant alleles causing iron uptake disorders in mice and humans provides new insights into the mechanisms involved in iron transport and its regulation. This article summarizes these discoveries and discusses their impact on our current understanding of iron transport and its regulation.
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Affiliation(s)
- M Wessling-Resnick
- Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts 02115, USA.
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18
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Tokuno T, Muraki K, Watanabe M, Imaizumi Y. Effects of K+ channel modulators on the relationship between action potential duration and Ca2+ transients in single ventricular myocytes of the guinea pig. JAPANESE JOURNAL OF PHARMACOLOGY 1999; 80:243-53. [PMID: 10461770 DOI: 10.1254/jjp.80.243] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Effects of K+ channel modulators, cromakalim and E4031 [1-[2-(6-methyl-2-pyridyl)-ethyl]-4-(4-methylsulfonylaminobenzoyl) piperidine], on the relationship between the action potential duration (APD) and Ca2+ transients were examined in single myocytes isolated from guinea pig cardiac left ventricle. Application of cromakalim decreased APD at 90% repolarization (APD90) and Ca2+ transient elicited at 0.5 Hz (IC50s=0.6 and 3 microM, respectively). Application of 0.3 microM E4031 increased these parameters by 110% and 45%, respectively. Under voltage-clamp, the relation between the duration of depolarization to 0 mV and Ca2+ transients could be described by the sum of two exponential components; the time constants were approximately 5 and 280 msec, respectively. The first component was abolished by 10 microM ryanodine, suggesting the involvement of Ca2+-induced Ca2+ release (CICR). Neither cromakalim nor E4031 directly affected Ca2+ current and Ca2+ transients under voltage clamp. When APD was changed by K+ channel modulators, the relation between APD90 and Ca2+-transients was almost similar to that obtained by changing the depolarization duration under voltage-clamp. CICR was changed significantly only when APD90 was markedly shortened by cromakalim. The extensively prolonged AP and Ca2+ transient in the presence of E4031 were reduced by an addition of cromakalim. It is concluded that these two K+ channel modulators can significantly alter the AP-induced Ca2+ transient mainly by changing APD, which regulates both Ca2+ influx and extrusion.
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Affiliation(s)
- T Tokuno
- Department of Pharmacology & Therapeutics, Faculty of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
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19
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Imaizumi Y, Ohi Y, Yamamura H, Ohya S, Muraki K, Watanabe M. Ca2+ spark as a regulator of ion channel activity. JAPANESE JOURNAL OF PHARMACOLOGY 1999; 80:1-8. [PMID: 10446750 DOI: 10.1254/jjp.80.1] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Ca2+ spark is a local and transient Ca2+ release from sarcoplasmic reticulum (SR) through the ryanodine receptor Ca2+-releasing channel (RyR). In cardiac myocytes, Ca2+ spark is an elementary unit of Ca2+-induced Ca2+ release (CICR) by opening of RyR(s) in junctional SR (jSR), which is triggered by Ca2+-influx through L-type Ca2+ channels to the narrow space between a transverse tubule and jSR. Ca2+ spark has, therefore, been described as the evidence for "the local control of excitation-contraction coupling". In contrast, Ca2+ sparks in smooth muscle have been reported in relation to Ca2+-dependent K+ (K(Ca)) channel activation and muscle relaxation. A spontaneous Ca2+ spark in a superficial area activates 10-100 K(Ca) channels nearby and induces membrane hyperpolarization, which reduces Ca2+ channel activity. In several types of smooth muscle cells, which have relatively high membrane excitability, an action potential (AP) elicits 5-20 Ca2+ hot spots (evoked sparks with long life) in the early stage via CICR in discrete superficial SR elements and activates K(Ca)-channel current highly responsible for AP repolarization and afterhyperpolarization. CICR available for contraction may occur more slowly by the propagation of CICR from superficial SR to deeper ones. The regulatory mechanism of ion channel activity on plasma membrane by superficial SR via Ca2+ spark generation in smooth muscle cells may be analogously common in several types of cells including neurons.
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Affiliation(s)
- Y Imaizumi
- Department of Pharmacology & Therapeutics, Faculty of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
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20
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Abstract
The electrophysiological properties of detrusor smooth muscle are described, in particular with regard to their influence on the contractile properties of the tissue. The Ca2+ and K+ channel activities are most important in generating action potentials, but the role of several other ionic currents is described, including Cl-, Ca2+-activated, stretch-activated and ligand-gated channels. The variable appearance and functions of different ionic currents in disease states is discussed, as well as the question of whether electrical activity can transmit between adjacent smooth muscle cells. In addition, the precise role that electrophysiological phenomena play in the regulation of the contractile state of the smooth muscle cells, as well as the generation of bladder electromyograms, is discussed.
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Affiliation(s)
- C H Fry
- Institute of Urology and Nephrology, University College, London, UK
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21
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Seino-Umeda A, Fang YI, Ishibashi M, Kobayashi J, Ohizumi Y. 9-Methyl-7-bromoeudistomin D induces Ca2+ release from cardiac sarcoplasmic reticulum. Eur J Pharmacol 1998; 357:261-5. [PMID: 9797046 DOI: 10.1016/s0014-2999(98)00589-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
9-Methyl-7-bromoeudistomin D (MBED), the most powerful caffeine-like releaser of Ca2+ from skeletal muscle sarcoplasmic reticulum, induced Ca2+ release from the cardiac sarcoplasmic reticulum. MBED (5 microM) and caffeine (1 mM) caused rapid Ca2+ release from the fragmented cardiac sarcoplasmic reticulum in a Ca2+ electrode experiment. [3H]MBED bound to a single class of high-affinity binding sites in cardiac sarcoplasmic reticulum membranes (Kd = 150 nM). These results suggest that MBED binds to a specific binding site on cardiac sarcoplasmic reticulum membranes to induce Ca2+ release from the cardiac sarcoplasmic reticulum. Thus, MBED is a useful probe for characterizing Ca2+ release the channels not only in skeletal sarcoplasmic reticulum but also in cardiac sarcoplasmic reticulum.
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Affiliation(s)
- A Seino-Umeda
- Yokohama Research Center, Mitsubishi Chemical, Japan
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22
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Imaizumi Y, Torii Y, Ohi Y, Nagano N, Atsuki K, Yamamura H, Muraki K, Watanabe M, Bolton TB. Ca2+ images and K+ current during depolarization in smooth muscle cells of the guinea-pig vas deferens and urinary bladder. J Physiol 1998; 510 ( Pt 3):705-19. [PMID: 9660887 PMCID: PMC2231067 DOI: 10.1111/j.1469-7793.1998.705bj.x] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. Electrical events and intracellular calcium concentration ([Ca2+]) imaged using fluo-3 and laser scanning confocal microscopy were simultaneously monitored in single smooth muscle cells freshly isolated from guinea-pig vas deferens or urinary bladder. 2. Images obtained every 8 ms, during stepping from -60 to 0 or +10 mV for 50 ms under voltage clamp, showed that a rise in [Ca2+] could be detected within 20 ms of depolarization in five to twenty small (< 2 micrometer diameter) 'hot spots', over 95 % of which were located within 1.5 micrometer of the cell membrane. Depolarization at 30 s intervals activated hot spots at the same places. 3. Cd2+ or verapamil abolished both hot spots and Ca2+-activated K+ current (IK,Ca). Caffeine almost abolished hot spots and markedly reduced IK,Ca. Cyclopiazonic acid, which raised basal global [Ca2+], decreased the rise in hot spot [Ca2+] and IK,Ca amplitude during depolarization. These results suggest that Ca2+ entry caused Ca2+-induced Ca2+ release (CICR). 4. Under voltage clamp, hot spot [Ca2+] closely paralleled the rise in IK,Ca and reached a peak within 20 ms of the start of depolarization, but the rise in global [Ca2+] over the whole cell area was much slower. Step depolarization to potentials positive to -20 mV caused hot spots to grow in size and coalesce, leading to a rise in global [Ca2+] and contraction. Ca2+ hot spots also occurred during the up-stroke of an evoked action potential under current clamp. 5. It is concluded that the entry of Ca2+ in the early stages of an action potential evokes CICR from discrete subplasmalemma Ca2+ storage sites and generates hot spots that spread to initiate a contraction. The activation of Ca2+-dependent K+ channels in the plasmalemma over hot spots initiates IK,Ca and action potential repolarization.
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Affiliation(s)
- Y Imaizumi
- Department of Pharmacology and Therapeutics, Faculty of Pharmaceutical Sciences, Nagoya City University, Nagoya 467-8603, Japan.
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23
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van Breemen C, Skarsgard P, Laher I, McManus B, Wang X. Endothelium-smooth muscle interactions in blood vessels. Clin Exp Pharmacol Physiol 1997; 24:989-92. [PMID: 9406674 DOI: 10.1111/j.1440-1681.1997.tb02737.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
1. Blood vessel tone is determined both by smooth muscle and endothelial functions. In coronary arteries taken from rat (Fisher-Lewis) cardiac transplanted hearts, the inducible form of NOS (iNOS) in smooth muscle is more active, while acetylcholine-induced nitric oxide production in the endothelium is greatly diminished. This causes a greatly reduced myogenic constriction, in pressurized septal arteries taken from immunologically challenged transplanted hearts. 2. The sarcoplasmic reticulum (SR) of smooth muscle and the endoplasmic reticulum (ER) of endothelial cells sequester Ca2+ from the cytoplasm. This reduces the intracellular concentration of free Ca2+, which is necessary for the activation of cellular processes. The release of Ca2+ from internal stores occurs through ryanodine and IP3 recoptors located on the SR membrane. 3. The superficial SR/ER also interacts with ion exchangers and pumps in the plasma membrane. This allows for the superficial SR/ER to function in Ca2+ extrusion; for example, inhibition of the SR/ER Ca(2+)-ATPase (SERCA) partially inhibits the rate of loss Ca2+ from the cell. Recent data suggest that the SR Ca(2+)-ATPase and the Na(+)-Ca2+ exchanger of smooth muscle cells function in series; that is, Ca2+ uptake by the SR followed by release towards the exchanger to mediate extrusion. This interaction between the SERCA of the superficial SR and ion exchangers and pumps creates intracellular Ca2+ gradients. 4. The SERCA of the superficial, peripherally distributed SR/ER also serves to regulate Ca2+ entry from the extracellular space. This occurs in part by inhibition of the superficial buffer barrier function of the SR as well as by depletion of stimulated Ca2+ entry. 5. Ca2+ entry is also regulated in endothelial and smooth muscle cells by the membrane potential. Membrane hyperpolarization increases the driving force for Ca2+ entry into endothelial cells, which lack voltage-gated Ca2+ channels, and reduces open state probability of voltage-gated Ca2+ channels in vascular smooth muscle cells. The two cell types have electrical contact and interact in a dynamic manner to regulate blood vessel diameter.
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Affiliation(s)
- C van Breemen
- Department of Pharmacology, Faculty of Medicine, University of British Columbia, Vancouver, Canada
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24
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Hashitani H, Suzuki H. K+ channels which contribute to the acetylcholine-induced hyperpolarization in smooth muscle of the guinea-pig submucosal arteriole. J Physiol 1997; 501 ( Pt 2):319-29. [PMID: 9192304 PMCID: PMC1159480 DOI: 10.1111/j.1469-7793.1997.319bn.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
1. Membrane potentials were recorded from submucosal arterioles (diameter, 30-80 microns) of the guinea-pig small intestine, using conventional microelectrode techniques. In control solution the resting membrane potential was about -73 mV, and the addition of 0.5 mM Ba2+ depolarized the membrane to about -43 mV. 2. ACh (10 nM to 10 microM), or substance P (0.1 microM), caused a membrane hyperpolarization in preparations which had been depolarized by Ba2+ but not in control preparations. ACh produced a sustained hyperpolarization, whereas substance P produced a transient hyperpolarization, without being affected by either nitroarginine (0.1 mM) or indomethacin (10 microM). 3. In the presence of 50 microM BAPTA (acetoxymethyl ester form), the membrane potentials were not altered in the control solution or in the presence of Ba2+, but Ba2+ caused a smooth depolarization of the membrane. Following this procedure, both ACh and substance P caused membrane depolarization instead of hyperpolarization, suggesting that the ACh- and substance P-induced hyperpolarization in arteriolar smooth muscle are intracellular [Ca2+] dependent. 4. In short segments (200-500 microns) of arteriole, the time constant of electrotonic potentials produced by passing current pulses through the recording electrode was about 75 ms. The addition of Ba2+ increased both the input resistance and the time constant. 5. The hyperpolarizations produced by ACh or substance P were associated with a reduction in the amplitude and the time constant of electrotonic potential. 6. The reversal potential for the ACh-induced hyperpolarization, estimated from the current-voltage relationship, was about -86 mV, a value close to the equilibrium potential for K+. 7. In the presence of 50 nM charybdotoxin the hyperpolarization produced by ACh became transient and was reduced in amplitude: the residual response was further reduced by apamin (0.1 microM). The response produced by substance P was also reduced by 50 nM charybdotoxin: again the residual response was sensitive to 0.1 microM apamin. The hyperpolarizations produced by either ACh or substance P were insensitive to glibenclamide (10 microM) and 4-aminopyridine (1 mM). 8. It is suggested that in submucosal arterioles of the guinea-pig ileum, ACh- or substance P-induced hyperpolarizations of smooth muscle result from activation of both charybdotoxin-sensitive and apamin-sensitive K+ channels, with the former being predominant. The results are discussed in relation to the possible involvement of one or more endothelium-dependent hyperpolarizing factors in ACh- and substance P-induced hyperpolarization.
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Affiliation(s)
- H Hashitani
- Department of Physiology, Nagoya City University Medical School, Japan
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25
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Ohizumi Y. Application of Physiologically Active Substances Isolated from Natural Resources to Pharmacological Studies. ACTA ACUST UNITED AC 1997. [DOI: 10.1254/jjp.60.263] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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26
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Abstract
Spontaneous transient outward currents (STOCs) lasting about 100 ms occur in single smooth muscle cells and represent the simultaneous opening of up to a hundred calcium-activated potassium (BK) channels. The recent observation of brief focal releases of sarcoplasmic reticulum (SR) calcium ('sparks') in smooth muscle cells has provided support for the original suggestion that STOCs arise due to the spontaneous releases of calcium from the SR close to the sarcolemma. However, it is possible that such releases occur in a region of close apposition of SR membrane and sarcolemma about 0.1 microns wide ('junctional space') in which case they would be detectable by endogenous calcium-sensitive molecules such as BK channels but, using present confocal microscopy technique, not by calcium-indicator dyes introduced into the cell; should calcium escape from the junctional space then it may be visualised as 'sparks' by the fluorescent emission from calcium-indicator dyes using confocal microscopy. Some STOCs seem too large to represent the effect of a single 'spark' and some form of calcium-induced calcium release or 'macrospark' may be involved in their generation. Depletion of calcium stores by caffeine, ryanodine, or by activation of receptors linked to the phospholipase C/inositol trisphosphate system abolishes STOCs. However, low concentrations of caffeine or inositol trisphosphate accelerate STOC discharge by an unknown mechanism and often decrease STOC size presumably by depleting store calcium; similar effects are produced by agents such as cyclopiazonic acid and thapsigargin which inhibit calcium storage mechanisms (largely the SR calcium pump).
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Affiliation(s)
- T B Bolton
- Department of Pharmacology and Clinical Pharmacology, St George's Hospital Medical School, London, UK.
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