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Myosin light chain phosphorylation exhibits a gradient across the wall of cerebellar arteries under sustained ex vivo vascular tone. Sci Rep 2023; 13:909. [PMID: 36650375 PMCID: PMC9845333 DOI: 10.1038/s41598-023-28092-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Accepted: 01/12/2023] [Indexed: 01/18/2023] Open
Abstract
Small blood vessel diseases are often associated with impaired regulation of vascular tone. The current understanding of resistance arteries often focuses on how a level of vascular tone is achieved in the acute phase, while less emphasis is placed on mechanisms that maintain vascular tone. In this study, cannulated rat superior cerebellar arteries (SCA) developed spontaneous myogenic tone and showed a marked and sustained constriction in the presence of diluted serum (10%), a stimulus relevant to cerebrovascular disease. Both phosphorylated myosin light chain (MLC-p) and smooth muscle alpha actin (SM-α-actin) aligned with phalloidin-stained actin filaments in the vessel wall, while exhibiting a 'high to low' gradient across the layers of vascular smooth muscle cells (VSMC), peaking in the outer layer. The MLC-p distribution profile shifted towards the adventitia in serum treated vessels, while removal of the serum reversed it. Furthermore, a positive correlation between the MLC-p signal and vessel wall tension was also evident. The gradients of phosphorylated MLC and SM-α-actin are consistent with a spatial regulation of the myosin-actin apparatus in the vessel wall during the maintenance of vascular tone. Further, the changing profiles of MLC-p and SM-α-actin are consistent with SCA vasoconstriction being accompanied by VSMC cytoskeletal reorganization.
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2
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Duffin J, Mikulis DJ, Fisher JA. Control of Cerebral Blood Flow by Blood Gases. Front Physiol 2021; 12:640075. [PMID: 33679453 PMCID: PMC7930328 DOI: 10.3389/fphys.2021.640075] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Accepted: 01/25/2021] [Indexed: 12/19/2022] Open
Abstract
Cerebrovascular reactivity can be measured as the cerebrovascular flow response to a hypercapnic challenge. The many faceted responses of cerebral blood flow to combinations of blood gas challenges are mediated by its vasculature's smooth muscle and can be comprehensively described by a simple mathematical model. The model accounts for the blood flow during hypoxia, anemia, hypocapnia, and hypercapnia. The main hypothetical basis of the model is that these various challenges, singly or in combination, act via a common regulatory pathway: the regulation of intracellular hydrogen ion concentration. This regulation is achieved by membrane transport of strongly dissociated ions to control their intracellular concentrations. The model assumes that smooth muscle vasoconstriction and vasodilation and hence cerebral blood flow, are proportional to the intracellular hydrogen ion concentration. Model predictions of the cerebral blood flow responses to hypoxia, anemia, hypocapnia, and hypercapnia match the form of observed responses, providing some confidence that the theories on which the model is based have some merit.
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Affiliation(s)
- James Duffin
- Department of Anesthesia and Pain Management, University of Toronto, Toronto, ON, Canada
- Department of Physiology, University of Toronto, Toronto, ON, Canada
- Thornhill Research Inc., Toronto, ON, Canada
- University Health Network, Toronto, ON, Canada
| | - David J. Mikulis
- Division of Neuroradiology Imaging, Joint Department of Medical Imaging, University Health Network, Toronto, ON, Canada
| | - Joseph A. Fisher
- Department of Anesthesia and Pain Management, University of Toronto, Toronto, ON, Canada
- Department of Physiology, University of Toronto, Toronto, ON, Canada
- Thornhill Research Inc., Toronto, ON, Canada
- University Health Network, Toronto, ON, Canada
- Faculty of Medicine, Institute of Medical Science, University of Toronto, Toronto, ON, Canada
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Boedtkjer E. Acid-base regulation and sensing: Accelerators and brakes in metabolic regulation of cerebrovascular tone. J Cereb Blood Flow Metab 2018; 38:588-602. [PMID: 28984162 PMCID: PMC5888856 DOI: 10.1177/0271678x17733868] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/08/2017] [Revised: 08/10/2017] [Accepted: 09/06/2017] [Indexed: 12/29/2022]
Abstract
Metabolic regulation of cerebrovascular tone directs blood flow to areas of increased neuronal activity and during disease states partially compensates for insufficient perfusion by enhancing blood flow in collateral blood vessels. Acid-base disturbances frequently occur as result of enhanced metabolism or insufficient blood supply, but despite definitive evidence that acid-base disturbances alter arterial tone, effects of individual acid-base equivalents and the underlying signaling mechanisms are still being debated. H+ is an important intra- and extracellular messenger that modifies cerebrovascular tone. In addition, low extracellular [HCO3-] promotes cerebrovascular contraction through an endothelium-dependent mechanism. CO2 alters arterial tone development via changes in intra- and extracellular pH but it is still controversial whether CO2 also has direct vasomotor effects. Vasocontractile responses to low extracellular [HCO3-] and acute CO2-induced decreases in intracellular pH can counteract H+-mediated vasorelaxation during metabolic and respiratory acidosis, respectively, and may thereby reduce the risk of capillary damage and cerebral edema that could be consequences of unopposed vasodilation. In this review, the signaling mechanisms for acid-base equivalents in cerebral arteries and the mechanisms of intracellular pH control in the arterial wall are discussed in the context of metabolic regulation of cerebrovascular tone and local perfusion.
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Affiliation(s)
- Ebbe Boedtkjer
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
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4
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Boedtkjer E, Matchkov VV, Boedtkjer DMB, Aalkjaer C. Negative News: Cl− and HCO3− in the Vascular Wall. Physiology (Bethesda) 2016; 31:370-83. [DOI: 10.1152/physiol.00001.2016] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Cl− and HCO3− are the most prevalent membrane-permeable anions in the intra- and extracellular spaces of the vascular wall. Outwardly directed electrochemical gradients for Cl− and HCO3− permit anion channel opening to depolarize vascular smooth muscle and endothelial cells. Transporters and channels for Cl− and HCO3− also modify vascular contractility and structure independently of membrane potential. Transport of HCO3− regulates intracellular pH and thereby modifies the activity of enzymes, ion channels, and receptors. There is also evidence that Cl− and HCO3− transport proteins affect gene expression and protein trafficking. Considering the extensive implications of Cl− and HCO3− in the vascular wall, it is critical to understand how these ions are transported under physiological conditions and how disturbances in their transport can contribute to disease development. Recently, sensing mechanisms for Cl− and HCO3− have been identified in the vascular wall where they modify ion transport and vasomotor function, for instance, during metabolic disturbances. This review discusses current evidence that transport (e.g., via NKCC1, NBCn1, Ca2+-activated Cl− channels, volume-regulated anion channels, and CFTR) and sensing (e.g., via WNK and RPTPγ) of Cl− and HCO3− influence cardiovascular health and disease.
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Affiliation(s)
| | | | - Donna M. B. Boedtkjer
- Department of Biomedicine, Aarhus University, Denmark
- Department of Clinical Medicine, Aarhus University, Denmark; and
| | - Christian Aalkjaer
- Department of Biomedicine, Aarhus University, Denmark
- Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark
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Telinius N, Mohanakumar S, Majgaard J, Kim S, Pilegaard H, Pahle E, Nielsen J, de Leval M, Aalkjaer C, Hjortdal V, Boedtkjer DB. Human lymphatic vessel contractile activity is inhibited in vitro but not in vivo by the calcium channel blocker nifedipine. J Physiol 2014; 592:4697-714. [PMID: 25172950 DOI: 10.1113/jphysiol.2014.276683] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Calcium channel blockers (CCB) are widely prescribed anti-hypertensive agents. The commonest side-effect, peripheral oedema, is attributed to a larger arterial than venous dilatation causing increased fluid filtration. Whether CCB treatment is detrimental to human lymphatic vessel function and thereby exacerbates oedema formation is unknown. We observed that spontaneous lymphatic contractions in isolated human vessels (thoracic duct and mesenteric lymphatics) maintained under isometric conditions were inhibited by therapeutic concentrations (nanomolar) of the CCB nifedipine while higher than therapeutic concentrations of verapamil (micromolar) were necessary to inhibit activity. Nifedipine also inhibited spontaneous action potentials measured by sharp microelectrodes. Furthermore, noradrenaline did not elicit normal increases in lymphatic vessel tone when maximal constriction was reduced to 29.4 ± 4.9% of control in the presence of 20 nmol l(-1) nifedipine. Transcripts for the L-type calcium channel gene CACNA1C were consistently detected from human thoracic duct samples examined and the CaV1.2 protein was localized by immunoreactivity to lymphatic smooth muscle cells. While human lymphatics ex vivo were highly sensitive to nifedipine, this was not apparent in vivo when nifedipine was compared to placebo in a randomized, double-blinded clinical trial: conversely, lymphatic vessel contraction frequency was increased and refill time was faster despite all subjects achieving target nifedipine plasma concentrations. We conclude that human lymphatic vessels are highly sensitive to nifedipine in vitro but that care must be taken when extrapolating in vitro observations of lymphatic vessel function to the clinical situation, as similar changes in lymphatic function were not evident in our clinical trial comparing nifedipine treatment to placebo.
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Affiliation(s)
- Niklas Telinius
- Department of Biomedicine, Aarhus University, Aarhus, Denmark Department of Cardiothoracic Surgery, Aarhus University Hospital, Aarhus, Denmark
| | - Sheyanth Mohanakumar
- Department of Biomedicine, Aarhus University, Aarhus, Denmark Department of Cardiothoracic Surgery, Aarhus University Hospital, Aarhus, Denmark
| | - Jens Majgaard
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Sukhan Kim
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Hans Pilegaard
- Department of Cardiothoracic Surgery, Aarhus University Hospital, Aarhus, Denmark
| | - Einar Pahle
- Department of Surgery, Viborg Hospital, Viborg, Denmark
| | - Jørn Nielsen
- Department of Surgery, Viborg Hospital, Viborg, Denmark
| | - Marc de Leval
- International Congenital Cardiac Centre, Harley Street Clinic, London, UK
| | | | - Vibeke Hjortdal
- Department of Cardiothoracic Surgery, Aarhus University Hospital, Aarhus, Denmark
| | - Donna Briggs Boedtkjer
- Department of Biomedicine, Aarhus University, Aarhus, Denmark Department of Cardiothoracic Surgery, Aarhus University Hospital, Aarhus, Denmark
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6
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Telinius N, Kim S, Pilegaard H, Pahle E, Nielsen J, Hjortdal V, Aalkjaer C, Boedtkjer DB. The contribution of K(+) channels to human thoracic duct contractility. Am J Physiol Heart Circ Physiol 2014; 307:H33-43. [PMID: 24778167 DOI: 10.1152/ajpheart.00921.2013] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In smooth muscle cells, K(+) permeability is high, and this highly influences the resting membrane potential. Lymph propulsion is dependent on phasic contractions generated by smooth muscle cells of lymphatic vessels, and it is likely that K(+) channels play a critical role in regulating contractility in this tissue. The aim of this study was to investigate the contribution of distinct K(+) channels to human lymphatic vessel contractility. Thoracic ducts were harvested from 43 patients and mounted in a wire myograph for isometric force measurements or membrane potential recordings with an intracellular microelectrode. Using K(+) channel blockers and activators, we demonstrate a functional contribution to human lymphatic vessel contractility from all the major classes of K(+) channels [ATP-sensitive K(+) (KATP), Ca(2+)-activated K(+), inward rectifier K(+), and voltage-dependent K(+) channels], and this was confirmed at the mRNA level. Contraction amplitude, frequency, and baseline tension were altered depending on which channel was blocked or activated. Microelectrode impalements of lymphatic vessels determined an average resting membrane potential of -43.1 ± 3.7 mV. We observed that membrane potential changes of <5 mV could have large functional effects with contraction frequencies increasing threefold. In general, KATP channels appeared to be constitutively open since incubation with glibenclamide increased contraction frequency in spontaneously active vessels and depolarized and initiated contractions in previously quiescent vessels. The largest change in membrane voltage was observed with the KATP opener pinacidil, which caused 24 ± 3 mV hyperpolarization. We conclude that K(+) channels are important modulators of human lymphatic contractility.
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7
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Boedtkjer E, Aalkjaer C. Intracellular pH in the resistance vasculature: regulation and functional implications. J Vasc Res 2012; 49:479-96. [PMID: 22907294 DOI: 10.1159/000341235] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2012] [Accepted: 06/20/2012] [Indexed: 12/18/2022] Open
Abstract
Net acid extrusion from vascular smooth muscle (VSMCs) and endothelial cells (ECs) in the wall of resistance arteries is mediated by the Na(+),HCO(3)(-) cotransporter NBCn1 (SLC4A7) and the Na(+)/H(+) exchanger NHE1 (SLC9A1) and is essential for intracellular pH (pH(i)) control. Experimental evidence suggests that the pH(i) of VSMCs and ECs modulates both vasocontractile and vasodilatory functions in resistance arteries with implications for blood pressure regulation. The connection between disturbed pH(i) and altered cardiovascular function has been substantiated by a genome-wide association study showing a link between NBCn1 and human hypertension. On this basis, we here review the current evidence regarding (a) molecular mechanisms involved in pH(i) control in VSMCs and ECs of resistance arteries at rest and during contractions, (b) implications of disturbed pH(i) for resistance artery function, and (c) involvement of disturbed pH(i) in the pathogenesis of vascular disease. The current evidence clearly implies that pH(i) of VSMCs and ECs modulates vascular function and suggests that disturbed pH(i) either consequent to disturbed regulation or due to metabolic challenges needs to be taken into consideration as a mechanistic component of artery dysfunction and disturbed blood pressure regulation.
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Affiliation(s)
- Ebbe Boedtkjer
- Department of Biomedicine and Water and Salt Research Center, Aarhus University, Aarhus, Denmark.
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8
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Chin LMK, Heigenhauser GJF, Paterson DH, Kowalchuk JM. Pulmonary O2 uptake and leg blood flow kinetics during moderate exercise are slowed by hyperventilation-induced hypocapnic alkalosis. J Appl Physiol (1985) 2010; 108:1641-50. [PMID: 20339012 PMCID: PMC2886676 DOI: 10.1152/japplphysiol.01346.2009] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2009] [Accepted: 03/23/2010] [Indexed: 11/22/2022] Open
Abstract
The effect of hyperventilation-induced hypocapnic alkalosis (Hypo) on the adjustment of pulmonary O2 uptake (VO2p) and leg femoral conduit artery ("bulk") blood flow (LBF) during moderate-intensity exercise (Mod) was examined in eight young male adults. Subjects completed four to six repetitions of alternate-leg knee-extension exercise during normal breathing [Con; end-tidal partial pressure of CO2 (PetCO2) approximately 40 mmHg] and sustained hyperventilation (Hypo; PetCO2 approximately 20 mmHg). Increases in work rate were made instantaneously from baseline (3 W) to Mod (80% estimated lactate threshold). VO2p was measured breath by breath by mass spectrometry and volume turbine, and LBF (calculated from mean femoral artery blood velocity and femoral artery diameter) was measured simultaneously by Doppler ultrasound. Concentration changes of deoxy (Delta[HHb])-, oxy (Delta[O2Hb])-, and total hemoglobin-myoglobin (Delta[HbTot]) of the vastus lateralis muscle were measured continuously by near-infrared spectroscopy (NIRS). The kinetics of VO2p, LBF, and Delta[HHb] were modeled using a monoexponential equation by nonlinear regression. The time constants for the phase 2 VO2p (Hypo, 49+/-26 s; Con, 28+/-8 s) and LBF (Hypo, 46+/-16 s; Con, 23+/-6 s) were greater (P<0.05) in Hypo compared with Con. However, the mean response time for the overall Delta[HHb] response was not different between conditions (Hypo, 23+/-5 s; Con, 24+/-3 s), whereas the Delta[HHb] amplitude was greater (P<0.05) in Hypo (8.05+/-7.47 a.u.) compared with Con (6.69+/-6.31 a.u.). Combined, these results suggest that hyperventilation-induced hypocapnic alkalosis is associated with slower convective (i.e., slowed femoral artery and microvascular blood flow) and diffusive (i.e., greater fractional O2 extraction for a given DeltaVO2p) O2 delivery, which may contribute to the hyperventilation-induced slowing of VO2p (and muscle O2 utilization) kinetics.
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Affiliation(s)
- Lisa M K Chin
- Canadian Centre for Activity and Aging, School of Kinesiology, Department of Physiology and Pharmacology, Arthur and Sonia Labatt Health Sciences Bldg., Rm. 411C, The University of Western Ontario, London, ON, Canada N6A 5B9
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9
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Cho YE, Ahn DS, Kim YH, Taggart MJ, Lee YH. Changes in stretch-induced tone induced by intracellular acidosis in rabbit basilar artery: effects on BKCa channel activity. Vascul Pharmacol 2007; 47:74-82. [PMID: 17521967 DOI: 10.1016/j.vph.2007.04.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2007] [Revised: 04/11/2007] [Accepted: 04/16/2007] [Indexed: 11/29/2022]
Abstract
It is known that myogenic reactivity is a fundamental determinant of the relative constancy of blood flow through the cerebral artery. It is also known that acute alteration of pH significantly affects the cerebral circulation and, therefore, we investigated the effect of mechanism of action of intracellular acidosis on myogenic tone in rabbit basilar artery. Myogenic tone was developed by imposed stretch of basilar artery and intracellular acidosis induced by the bath application of 20 mmol/L sodium acetate. Sodium acetate caused a biphasic increase in myogenic tone. The initial component reached a peak quickly and then fell slowly to a lower steady-state significantly above basal tone. The sodium acetate-induced increase in myogenic tone was completely inhibited by elimination of external Ca2+, or treatment of nifedipine, but not with gadolinium or NPPB. TEA (5 mmol/L) and iberiotoxin (100 nmol/L) inhibited the sodium acetate-induced increase in myogenic tone. In inside-out patch-clamp recordings, decreasing pH of the mock intracellular solution from 7.4 to 6.9 markedly inhibited BKCa currents. Several inhibitors involved in Ca2+ sensitization pathways, 10(-6) mol/L Y-27632, 5 x 10(-7) mol/L calphostin C and 10(-5) mol/L PD98059 had no effect on the sodium acetate-induced increase in myogenic tone. These results suggest that intracellular acidosis increases stretch-induced myogenic tone in rabbit basilar artery. Furthermore, voltage-dependent Ca2+ influx plays a key role in intracellular acidosis-induced increase in myogenic tone and may be mediated, at least in part, by inhibition of BKCa.
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Affiliation(s)
- Young-Eun Cho
- BK 21 Project for Medical Sciences, College of Medicine Yonsei University, Seoul, 120-752, South Korea
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10
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Park JK, Kim YC, Sim JH, Choi MY, Choi W, Hwang KK, Cho MC, Kim KW, Lim SW, Lee SJ. Regulation of membrane excitability by intracellular pH (pHi) changers through Ca2+-activated K+ current (BK channel) in single smooth muscle cells from rabbit basilar artery. Pflugers Arch 2007; 454:307-19. [PMID: 17285302 DOI: 10.1007/s00424-007-0204-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2006] [Accepted: 12/31/2006] [Indexed: 01/12/2023]
Abstract
Employing microfluorometric system and patch clamp technique in rabbit basilar arterial myocytes, regulation mechanisms of vascular excitability were investigated by applying intracellular pH (pH(i)) changers such as sodium acetate (SA) and NH(4)Cl. Applications of caffeine produced transient phasic contractions in a reversible manner. These caffeine-induced contractions were significantly enhanced by SA and suppressed by NH(4)Cl. Intracellular Ca(2+) concentration ([Ca(2+)](i)) was monitored in a single isolated myocyte and based the ratio of fluorescence using Fura-2 AM (R (340/380)). SA (20 mM) increased and NH(4)Cl (20 mM) decreased R (340/380) by 0.2 +/- 0.03 and 0.1 +/- 0.02, respectively, in a reversible manner. Caffeine (10 mM) transiently increased R (340/380) by 0.9 +/- 0.07, and the ratio increment was significantly enhanced by SA and suppressed by NH(4)Cl, implying that SA and NH(4)Cl may affect [Ca(2+)](i) (p < 0.05). Accordingly, we studied the effects of SA and NH(4)Cl on Ca(2+)-activated K(+) current (IK(Ca)) under patch clamp technique. Caffeine produced transient outward current at holding potential (V (h)) of 0 mV, caffeine induced transient outward K(+) current, and the spontaneous transient outward currents were significantly enhanced by SA and suppressed by NH(4)Cl. In addition, IK(Ca) was significantly increased by acidotic condition when pH(i) was lowered by altering the NH(4)Cl gradient across the cell membrane. Finally, the effects of SA and NH(4)Cl on the membrane excitability and basal tension were studied: Under current clamp mode, resting membrane potential (RMP) was -28 +/- 2.3 mV in a single cell level and was depolarized by 13 +/- 2.4 mV with 2 mM tetraethylammonium (TEA). SA hyperpolarized and NH(4)Cl depolarized RMP by 10 +/- 1.9 and 16 +/- 4.7 mV, respectively. SA-induced hyperpolarization and relaxation of basal tension was significantly inhibited by TEA. These results suggest that SA and NH(4)Cl might regulate vascular tone by altering membrane excitability through modulation of [Ca(2+)](i) and Ca(2+)-activated K channels in rabbit basilar artery.
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Affiliation(s)
- Jong Kook Park
- Department of Anesthesiology and Pain Medicine, College of Medicine, Cheju National University, 66 Jejudaehakno, Jeju, Jeju Special Self-Governing Province 690-756, South Korea
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11
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Liu G, Daneshgari F. Effects of cold storage on the function and morphology of isolated urinary bladder in rat. Neurourol Urodyn 2006; 25:381-7. [PMID: 16710851 DOI: 10.1002/nau.20169] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AIMS We investigated the effects of 24- and 48-hr storage at 4 degrees C in Krebs solution on the function and morphology of isolated, rat urinary bladders. METHODS Strips of bladder were obtained from eight male Sprague-Dawley rats. Six strips were harvested from each bladder and randomized to storage for 24 or 48 hr at 4 degrees C in Krebs solution or examination immediately after harvest. Contractile responses of the strips to potassium chloride (KCl), electric field stimulation (EFS), adenosine 5'-triphosphate (ATP) and carbamylcholine (CCh) were assessed. Histological examination of the bladder strips was performed. The pO(2), pCO(2), and pH of the solution in each storage container were measured at each storage time point. RESULTS Cold storage induced a significant decrease in the amplitude of contraction in response to KCl and EFS after 24 or 48 hr of storage compared with control. The response of the bladder strips to ATP and CCh was significantly reduced after 48-hr storage compared with control, but not 24-hr storage. The pO(2) and pCO(2) decreased after cold storage. The pH increased after 24 hr of storage and remained stable between 24 and 48 hr of storage. Histological evaluation of the strips showed tissue swelling after 24 and 48 hr of storage. CONCLUSIONS These results suggest that the morphology and function of bladder strips stored for 24 to 48 hr at 4 degrees C in Krebs solution undergo significant changes. Further studies are needed to assess the allowable time for storage of bladder tissue.
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Affiliation(s)
- Guiming Liu
- Glickman Urological Institute and Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA
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Baxter KA, Laher I, Church J, Hsiang YN. Acidosis Augments Myogenic Constriction in Rat Coronary Arteries. Ann Vasc Surg 2006; 20:630-7. [PMID: 17013684 DOI: 10.1007/s10016-006-9109-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The myogenic response is a process by which blood vessels autoregulate vascular smooth muscle tone in response to changes in transmural pressure. It is characterized by vessel contraction or dilation with increased or decreased pressure, respectively. We sought to identify whether acidosis impacts the myogenic response in rat coronary resistance arteries. Ventricular septal arteries were isolated from male Sprague-Dawley rats and mounted on a pressure myograph. The myogenic response was assessed by measuring the arterial diameter at pressures of 10-120 mm Hg. The fluorescence indicators 2',7'-bis-(carboxyethyl)-5(and-6)-carboxyfluorescein and Fura-2 were utilized to measure intracellular pH (pH(i)) and intracellular free calcium concentration ([Ca(2+)](i)), respectively. A decrease in the extracellular pH (pH(o)) from 7.4 to 6.9 produced a fall in pH(i) and an increase in the myogenic response. Under nominally HCO (3) (-) /CO(2)-free conditions at a constant pH(o), blockade of the sodium-hydrogen exchanger with HOE694 also resulted in a fall in pH(i) and a similar enhancement of myogenic activity. Concentration response curves were constructed to measure the potencies of the HOE694 effects: the EC(50) was 34 microM for the pH(i) change and 19 microM for vessel constriction. Apparent [Ca(2+)](i) remained unchanged during HOE694-induced intracellular acidification. Furthermore, in the presence of HCO (3) (-) , HOE694 did not markedly affect pH(i) and vascular tone remained unaltered. Our data demonstrate that acidosis augments myogenic constriction of rat coronary arteries. These effects are due to a fall in pH(i) consequent upon the reduction in pH(o) and may reflect an increased myofilament [Ca(2+)](i) sensitivity within vascular smooth muscle cells.
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Affiliation(s)
- Keith A Baxter
- Department of Surgery, University of British Columbia, Vancouver, British Columbia, Canada
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Wakabayashi I, Poteser M, Groschner K. Intracellular pH as a determinant of vascular smooth muscle function. J Vasc Res 2006; 43:238-50. [PMID: 16449818 DOI: 10.1159/000091235] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2005] [Accepted: 11/20/2005] [Indexed: 11/19/2022] Open
Abstract
Intracellular pH (pHi) is a physiological parameter that is intimately linked to contractility, growth and proliferation of vascular smooth muscle (VSM). Regarding contractility, no general unifying concept of pHi regulation but a rather complex relation between pHi signals and vascular tone has been revealed so far. The modulation of vasotone by pHi depends on the type of blood vessel as well as on the pattern of regulatory input signals. In addition, changes in pHi have been recognized as an important cellular signal to determine the fate of cells in terms of proliferation or apoptosis. Cellular sensors for pHi include a variety of ion transport systems which control intracellular Ca2+ gradients and are likely to serve as a link between pHi and cell functions. Here we provide an overview on the potential targets and mechanisms that transduce pHi signals in VSM. The role of pHi-sensing signaling complexes and localized pHi signaling as the basis of diversity of pHi regulation of VSM function is discussed.
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Affiliation(s)
- Ichiro Wakabayashi
- Department of Hygiene and Preventive Medicine, Yamagata University School of Medicine, Yamagata, Japan.
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14
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Fellner SK, Arendshorst WJ. Store-operated Ca2+ entry is exaggerated in fresh preglomerular vascular smooth muscle cells of SHR. Kidney Int 2002; 61:2132-41. [PMID: 12028453 DOI: 10.1046/j.1523-1755.2002.00383.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Regulation of preglomerular vasomotor tone vessels ultimately control glomerular filtration rate, sodium reabsorption and systemic blood pressure. To gain insight into the complex renal hemodynamic factors that may result in hypertension, we studied calcium signaling pathways. METHODS Fresh, single, preglomerular vascular smooth muscle cells (VSMC) were isolated from 5- to 6-week-old SHR and WKY utilizing a magnetized microsphere/sieving technique. Cytosolic Ca2+ ([Ca2+]i) was measured with fura-2 ratiometric fluorescence. To examine store-operated calcium entry (SOC), VSMC were activated in calcium-free buffer containing nifedipine. To deplete the sarcoplasmic reticulum (SR) of Ca2+, vasopressin-1 receptor agonist [V1R; inositol trisphosphate (IP3)-mediated mobilization], ryanodine (non-IP3 induced mobilization), and cyclopiazonic acid (CPA; Ca2+-ATPase inhibition) were utilized. Addition of external calcium followed by quenching of the fura/Ca2+ signal with Mn2+ permitted assessment of divalent cation entry via SOC. RESULTS V1R caused greater mobilization in SHR than WKY (P < 0.01) as well as greater calcium entry (P < 0.001). Ryanodine and CPA both caused SR calcium depletion that was not statistically different between strains, but absolute calcium entry through SOC was more than double in SHR following either maneuver (P < 0.001). 2-Amino-ethoxybiphenyl borane (2-APB), an inhibitor not only of IP3 receptors, but also of SOC, blocked calcium entry in the ryanodine and CPA experiments independent of IP3. As well, Gd3+, a selective inhibitor of SOC, inhibited the Ca2+ response. We also studied L-channel calcium entry stimulated by V1R. The total calcium response was greater in SHR as was the absolute inhibition by nifedipine. As a percent of the total response, participation of L-type channels sensitive to nifedipine was about 45% in both strains of rat. CONCLUSION Utilizing three separate mechanisms to deplete the SR of Ca2+ in order to activate SOC, we show for the first time, that SOC is exaggerated in preglomerular VSMC of young SHR.
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MESH Headings
- Animals
- Animals, Newborn/metabolism
- Arginine Vasopressin/pharmacology
- Arterioles
- Calcium/metabolism
- Calcium Channels/drug effects
- Calcium Channels/metabolism
- Calcium Channels, L-Type/metabolism
- Calcium-Transporting ATPases/antagonists & inhibitors
- Indoles/pharmacology
- Inositol 1,4,5-Trisphosphate Receptors
- Kidney Glomerulus/blood supply
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/metabolism
- Protein Isoforms/metabolism
- Rats
- Rats, Inbred SHR/metabolism
- Rats, Inbred WKY
- Receptors, Cytoplasmic and Nuclear/drug effects
- Receptors, Cytoplasmic and Nuclear/metabolism
- Receptors, Vasopressin/agonists
- Ryanodine/pharmacology
- Ryanodine Receptor Calcium Release Channel/drug effects
- Ryanodine Receptor Calcium Release Channel/metabolism
- Sarcoplasmic Reticulum/enzymology
- Vasopressins/metabolism
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Affiliation(s)
- Susan K Fellner
- Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, 27599-7545, USA.
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15
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Yartsev VN, Karachentseva OV, Dvoretsky DP. Effect of pH changes on reactivity of rat mesenteric artery segments at different magnitude of stretch. ACTA PHYSIOLOGICA SCANDINAVICA 2002; 174:1-7. [PMID: 11851591 DOI: 10.1046/j.1365-201x.2002.00923.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The reaction to noradrenaline (NA) (10 microM) and electrical field stimulation (EFS) was studied in rat mesenteric artery segments at different magnitude of stretch and the solution pH. Alkaline solution (pH 7.8) potentiated and acidic solution (pH 7.0 or 6.6) inhibited the EFS-evoked response of segments stretched to values corresponding to arterial pressure of 5-200 mmHg. These pH changes failed to alter resting tension at any magnitude of stretch. Acedic solution of pH 6.6 caused 2-fold decrease in noradrenaline- and 5-15-fold decrease in the EFS-evoked response of segments stretched to values corresponding to arterial pressure of 50, 125, and 200 mmHg. In segments pre-contracted with noradrenaline (10 microM) acidification caused the decrease of the dilation and appearance of the constriction induced by the EFS. The effect of acidosis on the EFS-evoked response was diminished and the effect on noradrenaline-evoked response was abolished in the presence of nitric oxide synthase blocker, NG-nitro-L-arginine (100 microM). These results suggest that acidosis effectively impairs reactivity of the rat mesenteric artery in a wide range of its stretch, and the inhibition of the response to noradrenaline occurs completely, while to EFS only partially due to nitric oxide (NO) release, presumably by the endothelium. In addition, it was shown that acidosis is able to act not only as the commonly known dilator agent, but also as an agent potentiating constriction in case of the high noradrenaline-induced tone.
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Affiliation(s)
- V N Yartsev
- Laboratory of Circulation, Pavlov Institute of Physiology, Nab. Makarova 6, St Petersburg, 199034, Russia
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16
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Pickkers P, Hughes AD, Russel FGM, Thien T, Smits P. In vivo evidence for K(Ca) channel opening properties of acetazolamide in the human vasculature. Br J Pharmacol 2001; 132:443-50. [PMID: 11159693 PMCID: PMC1572572 DOI: 10.1038/sj.bjp.0703825] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. The selective carbonic anhydrase inhibitor acetazolamide is known to increase blood flow in several organs. Acetazolamide directly dilates isolated resistance arteries associated with activation of calcium-activated potassium (K(Ca)) channels. We examined both the presence and mechanism of the direct vascular action of acetazolamide in vivo in humans. 2. Forearm vasodilator responses of 30 healthy volunteers to infusion of placebo and increasing doses of acetazolamide (1-3-10 mg min(-1) dl(-1)) into the brachial artery were recorded by venous occlusion plethysmography, before and after local administration of L-NMMA (0.2 mg min(-1) dl(-1), an inhibitor of NO-synthase, n=6), indomethacin (5.0 microg min(-1) dl(-1), an inhibitor of prostaglandin synthesis, n=6), glibenclamide (10 microg min(-1) dl(-1), an inhibitor of K(ATP) channels, n=6), tetraethylammonium (0.1 mg min(-1) dl(-1), an inhibitor of K(Ca) channels, n=6) or placebo (NaCl 0.9%, n=6). Lower dosages of acetazolamide did not affect vascular tone (n=6). 3. Acetazolamide infusions increased forearm blood flow from 2.41+/-0.17 to 2.99+/-0.18, 4.09+/-0.26 and 6.77+/-0.49 ml min(-1) dl(-1) in the infused forearm (P:<0.001), with no significant changes in the non-infused forearm, blood pressure or heart rate. Acetazolamide-induced vasodilation was not inhibited by L-NMMA, indomethacin, or glibenclamide but was significantly attenuated by TEA (vasodilation: 23+/-6, 82+/-19, 241+/-38% versus 27+/-8, 44+/-22, 42+/-35%). 4. We conclude that acetazolamide exerts a direct vasodilator effect in vivo in humans mediated by vascular K(Ca) channel activation. This makes acetazolamide the first drug known that specifically modulates this channel.
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Affiliation(s)
- Peter Pickkers
- Division of General Internal Medicine, Department of Medicine, University Medical Centre Nijmegen, The Netherlands
- Department of Pharmacology and Toxicology, University Medical Centre Nijmegen, The Netherlands
| | - Alun D Hughes
- Department of Clinical Pharmacology, St. Mary's Hospital Medical School, Imperial College of Science, Technology and Medicine, London
| | - Frans G M Russel
- Department of Pharmacology and Toxicology, University Medical Centre Nijmegen, The Netherlands
| | - Theo Thien
- Division of General Internal Medicine, Department of Medicine, University Medical Centre Nijmegen, The Netherlands
| | - Paul Smits
- Division of General Internal Medicine, Department of Medicine, University Medical Centre Nijmegen, The Netherlands
- Department of Pharmacology and Toxicology, University Medical Centre Nijmegen, The Netherlands
- Author for correspondence:
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17
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Fellner SK, Arendshorst WJ. Ryanodine receptor and capacitative Ca2+ entry in fresh preglomerular vascular smooth muscle cells. Kidney Int 2000; 58:1686-94. [PMID: 11012902 DOI: 10.1046/j.1523-1755.2000.00329.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND A multiplicity of hormonal, neural, and paracrine factors regulates preglomerular arterial tone by stimulating calcium entry or mobilization. We have previously provided evidence for capacitative (store-operated) Ca2+ entry in fresh renal vascular smooth muscle cells (VSMCs). Ryanodine-sensitive receptors (RyRs) have recently been identified in a variety of nonrenal vascular beds. METHODS We isolated fresh rat preglomerular VSMCs with a magnetized microsphere/sieving technique; cytosolic Ca2+ ([Ca2+]i) was measured with fura-2 ratiometric fluorescence. RESULTS Ryanodine (3 micromol/L) increased [Ca2+]i from 79 to 138 nmol/L (P = 0.01). Nifedipine (Nif), given before or after ryanodine, was without effect. The addition of calcium (1 mmol/L) to VSMCs in calcium-free buffer did not alter resting [Ca2+]i. In Ca-free buffer containing Nif, [Ca2+]i rose from 61 to 88 nmol/L after the addition of the Ca2+-ATPase inhibitor cyclopiazonic acid and to 159 nmol/L after the addition of Ca2+ (1 mmol/L). Mn2+ quenched the Ca/fura signal, confirming divalent cation entry. In Ca-free buffer with Nif, [Ca2+]i increased from 80 to 94 nmol/L with the addition of ryanodine and further to 166 nmol/L after the addition of Ca2+ (1 mmol/L). Mn2+ quenching was again shown. Thus, emptying of the sarcoplasmic reticulum (SR) with ryanodine stimulated capacitative Ca2+ entry. CONCLUSION Preglomerular VSMCs have functional RyR, and a capacitative (store-operated) entry mechanism is activated by the depletion of SR Ca2+ with ryanodine, as is the case with inhibitors of SR Ca2+-ATPase.
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Affiliation(s)
- S K Fellner
- Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7545, USA.
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18
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Lynch F, Sweeney M, O'Regan RG, McLoughlin P. Hypercapnia-induced contraction in isolated pulmonary arteries is endothelium-dependent. RESPIRATION PHYSIOLOGY 2000; 121:65-74. [PMID: 10854624 DOI: 10.1016/s0034-5687(00)00106-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
It has been demonstrated previously that isohydric hypercapnia (IH) does not affect agonist-induced tension development in pulmonary arteries. The aim of the present study was to examine the effects of IH on depolarisation-induced, steady state tension in the isolated rat pulmonary artery. Rings were submaximally contracted with high KCl under control conditions (5% CO(2)-95% air). IH was achieved by switching to a modified PSS (isosmotic substitution of NaHCO(3) for NaCl), equilibrated with 10% CO(2) in air. On switching to IH, a significant increase in mean (+/-SEM) tension (25.3+/-6.3% Tmax) was observed in endothelium intact rings (n=6). Endothelial removal significantly reduced this response. Non-specific inhibition of nitric oxide synthase (NOS) isoenzymes (L-NAME, 10(-3) M) abolished the IH-induced increase in tension while inhibition of neuronal NOS (TRIM, 10(-5) M) was without effect. The relaxant response to the nitric oxide donor sodium nitroprusside was similar in IH and control conditions. These results suggest that IH caused an endothelium-dependent increase in depolarisation-induced tension by reducing NO production.
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Affiliation(s)
- F Lynch
- Department of Human Anatomy and Physiology, University College Dublin, Earlsfort Terrace, 2, Dublin, Ireland
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19
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Abstract
Angiotensin II activates multiple signalling pathways in vascular smooth muscle. The precise pattern of signals and their relative importance to a particular functional response depends on both cell type and differentiation state. Although the contractile and trophic effects of Ang II are often thought of as distinct responses it is increasingly difficult to differentiate them in terms of signalling pathways. Since vasoconstriction and abnormal growth are both features of circulatory diseases such as hypertension and atherosclerosis a better understanding of the signalling pathways responsible for the vasoconstrictor and trophic actions of this peptide may help define novel therapeutic targets in cardiovascular disease.
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20
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Hill PB, Dora KA, Hughes AD, Garland CJ. The involvement of intracellular Ca(2+) in 5-HT(1B/1D) receptor-mediated contraction of the rabbit isolated renal artery. Br J Pharmacol 2000; 130:835-42. [PMID: 10864890 PMCID: PMC1572141 DOI: 10.1038/sj.bjp.0703387] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
5-Hydroxytryptamine(1B/1D) (5-HT(1B/1D)) receptor coupling to contraction was investigated in endothelium-denuded rabbit isolated renal arteries, by simultaneously measuring tension and intracellular [Ca(2+)], and tension in permeabilized smooth muscle cells. In intact arterial segments, 1 nM - 10 microM 5-HT failed to induce contraction or increase the fura-2 fluorescence ratio (in the presence of 1 microM ketanserin and prazosin to block 5-HT(2) and alpha(1)-adrenergic receptors, respectively). However, in vessels pre-exposed to either 20 mM K(+) or 30 nM U46619, 5-HT stimulated concentration-dependent increases in both tension and intracellular [Ca(2+)]. 1 nM - 10 microM U46619 induced concentration-dependent contractions. In the presence of nifedipine (0.3 and 1 microM) the maximal contraction to U46619 (10 microM) was reduced by around 70%. The residual contraction was abolished by the putative receptor operated channel inhibitor, SKF 96365 (2 microM). With 0.3 microM nifedipine present, 100 nM U46619 evoked similar contraction to 30 nM U46619 in the absence of nifedipine, but contraction to 5-HT (1 nM - 10 microM) was abolished. In permeabilized arterial segments, 10 mM caffeine, 1 microM IP(3) or 100 microM phenylephrine, each evoked transient contractions by releasing Ca(2+) from intracellular stores, whereas 5-HT had no effect. In intact arterial segments pre-stimulated with 20 mM K(+), 5-HT-evoked contractions were unaffected by 1 microM thapsigargin, which inhibits sarco- and endoplasmic reticulum calcium-ATPases. In vessels permeabilized with alpha-toxin and then pre-contracted with Ca(2+) and GTP, 5-HT evoked further contraction, reflecting increased myofilament Ca(2+)-sensitivity. Contraction linked to 5-HT(1B/1D) receptor stimulation in the rabbit renal artery can be explained by an influx of external Ca(2+) through voltage-dependent Ca(2+) channels and sensitization of the contractile myofilaments to existing levels of Ca(2+), with no release of Ca(2+) from intracellular stores.
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MESH Headings
- 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid/pharmacology
- Actin Cytoskeleton/drug effects
- Actin Cytoskeleton/physiology
- Animals
- Caffeine/pharmacology
- Calcium/metabolism
- Calcium Channel Blockers/pharmacology
- Capillary Permeability
- Dose-Response Relationship, Drug
- Female
- Fluorescence
- Fura-2
- Imidazoles/pharmacology
- In Vitro Techniques
- Inositol 1,4,5-Trisphosphate/pharmacology
- Muscle Contraction/drug effects
- Muscle Contraction/physiology
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- Muscle, Smooth, Vascular/physiology
- Nifedipine/pharmacology
- Phenylephrine/pharmacology
- Potassium/pharmacology
- Rabbits
- Receptor, Serotonin, 5-HT1B
- Receptor, Serotonin, 5-HT1D
- Receptors, Serotonin/physiology
- Renal Artery/drug effects
- Renal Artery/physiology
- Serotonin/pharmacology
- Thapsigargin/pharmacology
- Vasoconstrictor Agents/pharmacology
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Affiliation(s)
- P B Hill
- Cardiovascular Research Laboratories, University Walk, University of Bristol, Bristol, BS8 1TD
| | - K A Dora
- Cardiovascular Research Laboratories, University Walk, University of Bristol, Bristol, BS8 1TD
| | - A D Hughes
- Clinical Pharmacology, Imperial College of Science, Technology & Medicine, St Mary's Hospital, London W2 1NY
| | - C J Garland
- Cardiovascular Research Laboratories, University Walk, University of Bristol, Bristol, BS8 1TD
- Author for correspondence:
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21
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Okazaki K, Endou M, Okumura F. Involvement of barium-sensitive K+ channels in endothelium-dependent vasodilation produced by hypercapnia in rat mesenteric vascular beds. Br J Pharmacol 1998; 125:168-74. [PMID: 9776357 PMCID: PMC1565600 DOI: 10.1038/sj.bjp.0702048] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. We examined the vasodilatory effect of hypercapnia in the rat isolated mesenteric vascular bed. The preparation was perfused constantly (5 ml min(-1) with oxygenated Krebs-Ringer solution, and the perfusion pressure was measured. In order to keep the extracellular pH (pHe) constant (around 7.35) against a change in CO2, adequate amounts of NaHCO3 were added to Krebs-Ringer solution. 2. In the endothelium intact preparations, an increase in CO2 from 2.5% to 10% in increments of 2.5% decreased the 10 microM phenylephrine (PE)-produced increase in the perfusion pressure in a concentration-dependent manner. Denudation of the endothelium by CHAPS (3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulphonate) (5 mg l(-1), 90 s perfusion) abolished the vasodilatory effect of hypercapnia. 3. An increase in CO2 from 5% to 10% reduced the increases in the perfusion pressure produced by 10 microM PE and 400 nM U-46619 by 48% and 44%, respectively. NG-monomethyl-L-arginine (100 microM) and indomethacin (10 microM) did not affect the vasodilatory effect of hypercapnia, whereas the vasodilatory response of the preparation to hypercapnia disappeared when the preparation was contracted by 60 mM K+ instead of PE or U-46619. 4. The vasodilatory effect of hypercapnia observed in the PE- or U-46619-precontracted preparation was affected by neither tetraethylammonium (1 mM), apamin (500 microM), glibenclamide (10 microM), nor 4-aminopyridine (1.5 mM). On the other hand, pretreatment with Ba2+ at a concentration of 0.3 mM abolished the hypercapnia-produced vasodilation. 5. An increase in the concentration of K+ in Krebs-Ringer solution from 4.5 mM to 12.5 mM in increments of 2 mM reduced the PE-produced increase in the perfusion pressure in a concentration-dependent manner. Pretreatment of the preparations with not only Ba2+ (0.3 mM) but also CHAPS abolished the vasodilatory effect of K+. 6. The results suggest that an increase in CO2 produces vasodilation by an endothelium-dependent mechanism in the rat mesenteric vascular bed. The membrane hyperpolarization of the endothelial cell by an activation of the inward rectifier K+ channel seems to be the mechanism underlying the hypercapnia-produced vasodilation. Neither nitric oxide nor prostaglandins are involved in this response.
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Affiliation(s)
- K Okazaki
- Department of Anesthesiology, Yokohama City University School of Medicine, Japan
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22
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Bondarenko AI, Sagach VF. Modulation of the membrane potential of endothelial cells from the guinea pig aorta by intracellular alkalinization. NEUROPHYSIOLOGY+ 1998. [DOI: 10.1007/bf02463058] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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23
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Peng HL, Jensen PE, Nilsson H, Aalkjaer C. Effect of acidosis on tension and [Ca2+]i in rat cerebral arteries: is there a role for membrane potential? THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:H655-62. [PMID: 9486271 DOI: 10.1152/ajpheart.1998.274.2.h655] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The cellular mechanism responsible for the reduction of tension in cerebral small arteries to acidosis is not known. In this study the role of smooth muscle intracellular Ca2+ concentration ([Ca2+]i) and membrane potential for the relaxation to acidosis was investigated in isolated rat cerebral small arteries. Isometric force was measured simultaneously with [Ca2+]i (fura 2) or with membrane potential (intracellular microelectrodes), and acidosis was induced by increasing PCO2 or reducing HCO3- of the bathing solution. Both hypercapnic and normocapnic acidosis were associated with a reduction of intracellular pH [measured with 2',7'-bis-(carboxyethyl)-5 (and -6)-carboxyfluorescein], caused relaxation, and reduced [Ca2+]i. However, whereas hypercapnic acidosis caused hyperpolarization, normocapnic acidosis was associated with depolarization. It is concluded that a reduction of [Ca2+]i is in part responsible for the direct effect of the acidosis on the vascular smooth muscle both during normo- and hypercapnia. The mechanism responsible for the reduction of [Ca2+]i differs between the hypercapnic and normocapnic acidosis, being partly explained by hyperpolarization during hypercapnic acidosis, whereas it is seen despite depolarization during normocapnic acidosis.
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Affiliation(s)
- H L Peng
- Department of Pharmacology, University of Aarhus, Denmark
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24
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Nakanishi T, Gu H, Momma K. Developmental changes in the effect of acidosis on contraction, intracellular pH, and calcium in the rabbit mesenteric small artery. Pediatr Res 1997; 42:750-7. [PMID: 9396553 DOI: 10.1203/00006450-199712000-00006] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The purpose of the present study was to determine developmental changes in the effect of respiratory acidosis on vascular smooth muscle contraction. Vessel diameter, intracellular pH (pHi), and calcium concentration ([Ca]i) were measured in a cannulated preparation of the small mesenteric artery of newborn and adult rabbits. In the artery precontracted by high KCl, acidosis caused a vasorelaxation both in the newborn and the adult; the vasorelaxation was greater in the newborn than in the adult. The fura-2 fluorescence ratio, an indicator of [Ca]i, decreased transiently during acidosis and the decrease was similar in the two age groups. In the artery precontracted by norepinephrine, acidosis caused a transient vasoconstriction in the adult and a vasorelaxation in the newborn. In these vessels, the fura-2 fluorescence ratio increased transiently during acidosis; the increase was similar in the two groups. Upon induction of acidosis, pHi fell rapidly in the artery precontracted by norepinephrine or high KCl, and the depression of pHi was similar in the two groups. In the skinned smooth muscle preparation, a tension-[Ca] relationship curve at pH 7.1 was not significantly different from that at pH 6.8 in the adult. In the newborn, the tension-[Ca] curve at pH 6.8 was shifted to the right, compared with that at pH 7.1. These data suggest that the vasorelaxant effect of respiratory acidosis in the premature vessel is greater than in the adult. The greater vasorelaxation in the newborn cannot be explained by the age-related difference in pHi or [Ca]i during acidosis. The greater sensitivity of myofibrils to low pHi in the newborn may, at least in part, be responsible for the greater vasorelaxation in this age group.
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Affiliation(s)
- T Nakanishi
- Department of Pediatric Cardiology, The Heart Institute of Japan, Tokyo Women's Medical College, Japan
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25
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Achike FI, Mohamad R, Dai S, Ogle CW. Effects of acidosis or alkalosis on the actions of nifedipine on excitation-contraction coupling in the rat tail artery. Clin Exp Pharmacol Physiol 1997; 24:692-6. [PMID: 9315371 DOI: 10.1111/j.1440-1681.1997.tb02114.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
1. The clinical success of calcium channel blockers in the management of organ ischaemia is less than theoretically anticipated. Blood gas/pH changes are associated with organ ischaemia; therefore, we studied the possibility that pH changes could alter the pharmacological effects of the calcium channel blocker nifedipine on rat tail artery contracted by either noradrenaline (NA) or potassium. 2. Segments (2-2.5 cm) of the proximal third of the male Sprague-Dawley rat tail ventral artery were initially bathed and perfused with a physiological salt solution (PSS; pH 7.48) for 25-30 min, after which time bathing/perfusion was continued with a nominally calcium-free PSS made acidotic (pH 7.20), alkalotic (pH 7.67) or unaltered (control). After equilibration, the perfusion pressure (PP) responses to increasing concentrations of calcium in the presence of NA (3.0 mumol/L) or potassium (100 mmol/L) with nifedipine or its vehicle were recorded. 3. The calcium sensitivity of potassium- or NA-stimulated rat tail arteries was reduced during acidosis, as was the maximum PP in potassium- but not NA-stimulated tissues. Alkalosis reduced the calcium sensitivity in potassium- but not NA-stimulated contraction and had no effect on maximum PP. 4. The inhibitory effect of nifedipine (0.6 mumol/L) on contraction was enhanced during acidosis in either NA- or potassium-stimulated arteries and also during alkalosis in NA-treated arteries, although it had little effect during normal conditions. 5. The results indicate that changes in pH alter the vascular contractility profile in a manner dependent on the excitation-contraction coupling mode. The calcium antagonistic effect of nifedipine is pH dependent and it is suggested that pH changes associated with ischaemic conditions may alter the therapeutic profile of nifedipine.
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Affiliation(s)
- F I Achike
- Department of Pharmacology, Faculty of Medicine, University of Hong Kong, Hong Kong.
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26
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Nakanishi T, Gu H, Momma K. Effect of acidosis on contraction, intracellular pH, and calcium in the newborn and adult rabbit aorta. Heart Vessels 1997; 12:207-15. [PMID: 9846805 DOI: 10.1007/bf02766785] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
This study investigated the effect of acidosis on intracellular pH (pHi), intracellular calcium concentration ([Ca]i), and vascular contraction in the aorta of the newborn and adult rabbit. Isometric tension, pHi, and [Ca]i were measured in an isolated ring preparation. After the vascular contraction was induced with 50mM KC1, the effect of respiratory acidosis produced by elevation of PCO2 was studied. Respiratory acidosis caused a transient depression followed by a recovery of contractile tension. The decrease in developed tension was greater in the newborn than in the adult. The decrease in pHi during acidosis was similar in the two age groups. [Ca]i increased during acidosis and the increase was greater in the newborn than in the adult. These data show that the vasorelaxant effect of acidosis in the newborn aorta is greater than that in the adult aorta. The greater vasodilation in the newborn cannot be explained by the difference in pHi or [Ca]i.
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Affiliation(s)
- T Nakanishi
- Department of Pediatric Cardiology, Heart Institute of Japan, Tokyo Women's Medical College, Japan
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27
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Jensen PE. Calphostin C-sensitive enhancements of force by lysophosphatidylinositol and diacylglycerols in mesenteric arteries from the rat. Br J Pharmacol 1996; 119:15-22. [PMID: 8872351 PMCID: PMC1915738 DOI: 10.1111/j.1476-5381.1996.tb15671.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. A pharmacological characterization was made of the effects of lysophosphatidyl-inositol (lysoPI) and -ethanolamine (lysoPE) on the Ca(2+)-sensitivity of contraction in alpha-toxin permeabilized rat mesenteric arteries. The effect of GTP gamma S (G-protein activator), diacylglycerols (DAGs, dioctanoyl glycerol (diC8) and 1-stearoyl-2-arachidonoyl-sn-glycerol) and phorbol myristate acetate (PMA, protein kinase C (PKC) activator) on Ca(2+)-sensitivity was also assessed. 2. LysoPI increased the Ca(2+)-sensitivity, demonstrated by both an increase in tension induced by 1 microM [Ca2+]free and an increase in the Ca(2+)-sensitivity of Ca2+ concentration-tension curves. LysoPE did not enhance force or Ca(2+)-sensitivity. 3. GTP gamma S enhanced force at constant Ca2+, increased the Ca(2+)-sensitivity, and increased force under Ca(2+)-free conditions. PMA also increased force at constant Ca2+ and increased Ca(2+)-sensitivity, but caused no force development under Ca(2+)-free conditions. 4. DAGs, both diC8 and the more physiological relevant DAG, 1-stearoyl-2-arachidonoyl-sn-glycerol, enhanced force at constant Ca2+ and increased the Ca(2+)-sensitivity. DiC8, in contrast to 1-stearoyl-2-arachidonoyl-sn-glycerol, caused force development under Ca(2+)-free conditions and substantially enhanced force at maximal Ca(2+)-induced contraction. GDP-beta-S abolished the increased Ca(2+)-sensitization induced by noradrenaline, but not that by DAGs. 5. The PKC inhibitor calphostin C completely abolished Ca(2+)-sensitization induced by all of the Ca(2+)-sensitizing agents. 6. These results show that lysoPI can increase the Ca(2+)-sensitivity of smooth muscle contraction, and the Ca(2+)-sensitization induced by DAGs was not completely G-protein mediated, because it was not inhibited by GDP-beta-S. A central role for PKC in regulation of Ca(2+)-sensitization in rat mesenteric small arteries was indicated by the abolishment of Ca(2+)-sensitization by calphostin C.
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Affiliation(s)
- P E Jensen
- Institute of Pharmacology, University of Aarhus, Denmark
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Burdyga TV, Taggart MJ, Wray S. An investigation into the mechanism whereby pH affects tension in guinea-pig ureteric smooth muscle. J Physiol 1996; 493 ( Pt 3):865-76. [PMID: 8799906 PMCID: PMC1159032 DOI: 10.1113/jphysiol.1996.sp021429] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. We have altered intracellular (pHi) and extracellular pH (pHo) in the smooth muscle of guinea-pig ureter and determined the effects on evoked phasic contractions. In order to investigate the mechanisms underlying the effects of pH alteration, intracellular Ca2+ ([Ca2+]i), pHi, electrical activity and force were measured. 2. Intracellular acidification, produced by the weak acid butyrate, application of CO2 at constant pHo or removal of weak bases, greatly increased phasic contractions. Alkalinization with weak bases or by removal of CO2 inhibited contractions. The results were similar whether Hepes or CO2-HCO3-buffered the solutions. 3. Phasic contractions were preceded by intracellular Ca2+ transients in the ureter. Acidification of the cytoplasm led to an increase in the amplitude of the Ca2+ transient, and alkalinization decreased its magnitude. 4. In the ureter the action potential leads to Ca2+ influx, therefore electrophysiological recordings of its configuration were made during alteration of pHi. Acidification led to the action potential duration and amplitude being increased, whereas alkalinization shortened the action potential and reduced its amplitude. 5. As the effects of acidification on the action potential resembled the effects of blocking of K+ channels, we investigated whether pHi alteration was able to alter tension when K+ channels were blocked by tetraethylammonium. Acidification was unable to potentiate force under these conditions nor did alkalinization decrease force. 6. External pH over the range 6.8-8.0 had little or no effect on pHi, phasic contractions and [Ca2+]i. Tonic contractions were enhanced, however, when pHo was increased. 7. These data suggest that pHi alteration in the guinea-pig ureter modulates the action potential, probably by alteration of K+ currents. Subsequent changes in [Ca2+]i and contraction then occur. A potentiating effect of acidic pH on force is not common in muscle, but may be a characteristic of the smooth muscle of the urinary tract. Changes of pHo had little effect on phasic force or pHi, but modulated tonic contractions. The possible physiological significance of these results is discussed.
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Affiliation(s)
- T V Burdyga
- Physiological Laboratory, University of Liverpool, UK
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29
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McKinnon W, Aaronson PI, Knock G, Graves J, Poston L. Mechanism of lactate-induced relaxation of isolated rat mesenteric resistance arteries. J Physiol 1996; 490 ( Pt 3):783-92. [PMID: 8683476 PMCID: PMC1158715 DOI: 10.1113/jphysiol.1996.sp021186] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
1. The effects of the sodium salt of the weak acid lactate on tension and intracellular pH (pH1) were studied in rat mesenteric small arteries mounted on a wire myograph. Sodium lactate was substituted iso-osmotically for sodium chloride. 2. At a concentration of 50 mM, both L- and D-stereoisomers of lactate markedly relaxed arteries preconstricted with noradrenaline (NA) within 10 min. The concentration-response relationship for L-lactate showed that the NA contracture was relaxed by 50% at approximately 26 mM. L-Lactate did not, however, relax arteries preconstricted with high-K+(45 mM) solution. 3. L-Lactate did not alter extracellular pH (pHo) but caused a small but significant decrease in pH1, measured using the pH-sensitive fluorochrome, 2',7'-bis(carboxyethyl)-5-(6)-carboxyfluorescein (BCECF). Relaxation to L-lactate was unaffected when this change in pHi was offset by the simultaneous addition of NH4Cl to the solution. 4. Sodium pyruvate (50 mM) caused a significant intracellular acidosis but did not relax arteries preconstricted with NA. 5. L-Lactate-induced relaxations were unaffected by removal of the endothelium or when the synthesis of nitric oxide (NO) was inhibited by 10(-4) M N omega-nitro-L-arginine methyl ester (L-NAME). 6. The potassium channel blockers glibenclamide (10 microM), 4-aminopyridine (3 mM) and tetraethylammonium chloride (10 mM) did not affect L-lactate-induced relaxation in arteries preconstricted with NA. Inhibition of guanylate cyclase with Methylene Blue, or cyclooxgenase with indomethacin, also did not affect relaxation to L-lactate. 7. The Rp stereoisomer of adenosine-3',5'-cyclic monophosphothioate (Rp-cAMPS), an analogue of cAMP which inhibits competitively stimulation of protein kinase A, reduced significantly L-lactate-induced relaxation at a concentration of 25 microM. Rp-cAMPS also significantly reduced forskolin-induced relaxation of the NA contracture. 8. It is concluded that L-lactate-induced relaxation in this vascular bed is pHi-1 endothelium-, and nitric oxide-independent. It is not mediated by inhibition of voltage-gated Ca2+ channels, opening of K+ channels, prostacylin or cyclic GMP. cAMP may however play a role in L-lactate-induced relaxation.
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Affiliation(s)
- W McKinnon
- Department of Physiology, United Medical School, Guy's Hospital, London, UK
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30
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Achike FI, Ballard HJ, Ogle CW. Influence of extracellular pH, sodium propionate and trimethylamine on excitation-contraction coupling in the rat tail artery. Clin Exp Pharmacol Physiol 1996; 23:145-9. [PMID: 8819643 DOI: 10.1111/j.1440-1681.1996.tb02586.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
1. The effects of extracellular or intracellular pH changes on agonist- or depolarization-induced contractions of the rat tail artery were investigated. 2. Vessels were perfused initially (25 min) with physiological salt solution (PSS) at a pressure of 30 mmHg. Perfusion was then continued with calcium-free PSS containing either 3.0 micromol/L noradrenaline (NA) or 100 mmol/L K+, which had been made either acidotic or alkalotic. Contractile responses to graded concentrations of calcium were assessed. 3. A reduction in the intracellular or extracellular pH was induced by the addition of a weak acid (30 mmol/L sodium propionate) or reduction of the concentration of HCO3- in the PSS, respectively; an elevation of the intracellular or extracellular pH was produced by the addition of a weak base (10 mmol/L trimethylamine) or by increasing HCO3-, respectively. The PSS was bubbled with 5% CO2/95% O2. 4. Lowered intracellular pH did not alter NA- or K+-stimulated contractions. During lowered extracellular pH, contractile responsiveness and peak response were significantly reduced in K+-stimulated arteries, but were not affected in NA-stimulated arteries. 5. Elevated intracellular pH did not alter NA-induced contraction, but reduced the sensitivity to K+-stimulated contractions. Elevated extracellular pH had little effect on the magnitude of K+-induced contractions, but slightly enhanced (although not significantly) NA-induced contractions. 6. It is concluded that reduced contractile responses to K+ during extracellular acidosis are due to the modulation of potential-operated calcium channels (POC). Alkalotic vasodilatation is mediated by intracellular events and is POC-modulated, whereas alkalotic vasoconstriction appears to be due to extracellular events and is modulated by receptor-operated calcium channels (ROC).
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Affiliation(s)
- F I Achike
- Department of Physiology, Faculty of Medicine, The University of Hong Kong
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31
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Aaronson PI, McKinnon W, Poston L. Mechanism of butyrate-induced vasorelaxation of rat mesenteric resistance artery. Br J Pharmacol 1996; 117:365-71. [PMID: 8789392 PMCID: PMC1909272 DOI: 10.1111/j.1476-5381.1996.tb15200.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. The vasorelaxant effect of the sodium salt of the short chain fatty acid, butyrate, on preconstricted rat small mesenteric arteries (mean inner diameter approximately 300 microns) was characterized. Isometric force development was measured with a myograph, and intracellular pH (pHi) was simultaneously monitored, in arteries loaded with the fluorescent dye BCECF in its acetomethoxy form. Sodium butyrate (substituted isosmotically for NaCl) was applied to arteries after noradrenaline (NA) or high K+ contractures were established. 2. Arteries preconstricted with a concentration of NA inducing an approximately half maximal contraction were relaxed by 91.5 +/- 6.3% by 50 mmol l-1 butyrate. This concentration of butyrate did not, however, cause a significant relaxation of contractures to a maximal (5 mumol l-1) NA concentration, and also failed to relax significantly contractures stimulated by high (45 and 90 mmol l-1) K+ solutions. Contractures elicited with a combination of NA (at a submaximal concentration) and 45 mmol l-1 K+ were, however, markedly relaxed by butyrate. 3. Investigation of the concentration-dependency of the butyrate-induced relaxation of the half maximal NA response revealed an EC50 for butyrate of approximately 22 mmol l-1. 4. Sodium butyrate (50 mmol l-1) caused pHi to decrease from 7.25 +/- 0.02 to 6.89 +/- 0.08 (n = 4, P < 0.001). However, the vasorelaxant effect of butyrate on the submaximal NA contracture was not significantly modified when this fall in intracellular pH was prevented by the simultaneous application of NH4Cl. 5. Butyrate-induced relaxation was also unaffected by endothelial denudation and inhibition of NO synthase with N omega-nitro-L-arginine methyl ester (100 mumol l-1). 6. The relaxation of the NA contracture by 50 mmol l-1 sodium butyrate was abolished in arteries pretreated with the cyclic AMP antagonist Rp-cAMPS (25 mumol l-1). 7. We conclude that the butyrate-induced relaxation of the NA contracture is independent of intracellular acidification. The ability of Rp-cAMPS to abolish the butyrate relaxation indicates that stimulation of the cyclic AMP second messenger system may play an important role in mediating this effect.
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Affiliation(s)
- P I Aaronson
- Department of Pharmacology, Guy's and St Thomas' Hospitals, London
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32
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Schiffrin EL, Lariviere R, Touyz RM. ETA and ETB receptors on vascular smooth muscle cells from mesenteric vessels of spontaneously hypertensive rats. CLINICAL AND EXPERIMENTAL PHARMACOLOGY & PHYSIOLOGY. SUPPLEMENT 1995; 22:S193-4. [PMID: 9072351 DOI: 10.1111/j.1440-1681.1995.tb02877.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
1. To investigate the contribution of ETA and ETB receptors, calcium responses to the ETB agonist, IRL-1620, to endothelin-1 (ET-1) and to the ETA antagonist, BQ-123, were examined in primary cultured unpassaged vascular smooth muscle cells (VSMC) from mesenteric vessels of 3, 9 and 17 week old spontaneously hypertensive rats (SHR), Wistar and Wistar-Kyoto (WKY) rats using Fura-2 methodology. 2. IRL-1620 (10(-7) mol/L) and ET-1 (10(-9) mol/L) increased [Ca2+]i in all strains and ages. Responses to ET-1 and IRL-1620 were blunted in 17 week SHR. BQ-123 significantly reduced ET-1-stimulated [Ca2+]i. In endothelium-denuded mesenteric vessels, ET-1 and IRL-1620 induced significant [Ca2+]i responses. 3. Binding of ET-1 was significantly lower in mesenteric artery membranes from 17 week SHR compared to controls. 4. Thus, ETA and ETB receptors are present in rat mesenteric VSMC. In adult SHR, a reduced density of ET receptors results in decreased responses to IRL-1620 and to ET-1.
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MESH Headings
- Animals
- Endothelin Receptor Antagonists
- Endothelins/pharmacology
- Endothelium, Vascular/metabolism
- Endothelium, Vascular/pathology
- Hypertension/metabolism
- Hypertension/pathology
- In Vitro Techniques
- Male
- Mesenteric Arteries/cytology
- Mesenteric Arteries/metabolism
- Mesenteric Arteries/pathology
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- Peptide Fragments/pharmacology
- Peptides, Cyclic/pharmacology
- Rats
- Rats, Inbred SHR
- Rats, Inbred WKY
- Rats, Wistar
- Receptors, Endothelin/metabolism
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Affiliation(s)
- E L Schiffrin
- MRC Multidisciplinary Research Group on Hypertension, Clinical Research Institute of Montreal, University of Montreal, Quebec, Canada
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Austin C, Wray S. The effects of extracellular pH and calcium change on force and intracellular calcium in rat vascular smooth muscle. J Physiol 1995; 488 ( Pt 2):281-91. [PMID: 8568670 PMCID: PMC1156670 DOI: 10.1113/jphysiol.1995.sp020966] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
1. In order to investigate the mechanism whereby changes in external pH (pHo) alter tone in rat mesenteric resistance vessels, we have made simultaneous measurements of tension and intracellular Ca2+ [Ca2+]i. Strips of mesenteric artery were loaded with the Ca(2+)-sensitive indicator indo-1 and superfused with physiological salt solution at pH 7.4 and 37 degrees C. 2. An increase of pHo from 7.4 to 7.9 produced an increase in tension. This was accompanied by an increase in [Ca2+]i in resting and high-K(+)-depolarized vessels. Acidification to 6.9 reduced tension and was associated with a fall in [Ca2+]i. Over the pHi range examined, 6.6-7.9, parallel changes in [Ca2+]i and tension were found in K(+)-activated vessels. 3. In contrast to the relatively slow change in [Ca2+]i, pHi and tension with change of pHo, depolarization produced rapid changes in [Ca2+]i and tension, consistent with a more direct action on Ca2+ mobilization. 4. Reducing the external [Ca2+] below 1 mM produced a pronounced fall in [Ca2+]i and force. Changes in [Ca2+]i, produced by alteration of external [Ca2+] (Cao2+) were used to examine the relation between [Ca2+]i and tension. A linear relation was found. Alteration of pHo to 6.9 or 7.9 did not significantly change this relation. When the tension data were normalized to their own maxima, no shift in the tension-Ca2+ relation occurred, suggesting little or no effect of pH on the Ca2+ sensitivity of force production by the contractile proteins. 5. To determine further whether the changes in [Ca2+]i produced by alteration of pHo could account for all the changes observed in tension, [Ca2+]i was restored to control levels while maintaining an altered pHo. When this was done, restoration of [Ca2+]i led to restoration of force. Thus, in this preparation, the changes in [Ca2+]i produced by altering pHo in depolarized vessels can account for the changes in vascular tone.
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Affiliation(s)
- C Austin
- Physilogical Laboratory, University of Liverpool, UK
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34
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Ward DT, Ohanian J, Heagerty AM, Ohanian V. Phospholipase D-induced phosphatidate production in intact small arteries during noradrenaline stimulation: involvement of both G-protein and tyrosine-phosphorylation-linked pathways. Biochem J 1995; 307 ( Pt 2):451-6. [PMID: 7733882 PMCID: PMC1136669 DOI: 10.1042/bj3070451] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
To investigate membrane lipid metabolism during smooth-muscle activation, the role of phospholipase D (PLD) in the production of phosphatidate (PA) was studied in rat small arteries stimulated with noradrenaline. Incubation with [3H]myristate preferentially labelled phosphatidylcholine (PtdCho), and in the presence of 0.5% ethanol [3H]phosphatidylethanol ([3H]PEt) was formed, demonstrating PLD activity. Noradrenaline (NA) stimulation resulted in an increase in PtdCho derived [3H]PA and [3H]PEt formation, indicating PLD activation. Stimulation of [14C]choline release confirmed PLD-mediated hydrolysis of PtdCho. Propranolol, an inhibitor of PA phosphohydrolase, increased [3H]PA levels in non-stimulated tissue and decreased the rate of degradation of both [3H]PA and [3H]PEt, implying that this is an active route for PA metabolism in small arteries. However, [3H]diacylglycerol levels were not increased during NA stimulation. Fluoroaluminate increased [3H]PEt formation and [14C]choline release, whereas high K+ in the presence of alpha 1-adrenoceptor blockade did not. Pervanadate increased phosphotyrosine levels in small arteries, and markedly stimulated [3H]PEt formation and [14C]choline release. The combination of pervanadate and NA stimulation resulted in a dramatic increase in [3H]PEt formation, which was greater than the sum of the individual responses to the two agonists. Pervanadate and fluoroaluminate in combination appeared to give an additive response, whereas high K+ did not alter the pervanadate-induced formation of [3H]PEt. Phosphotyrosine levels were increased by NA in the presence of tyrosine phosphatase inhibitors. This effect was blocked by genistein, a tyrosine kinase inhibitor. These data demonstrate that in NA-stimulated small arteries PLD-induced PtdCho hydrolysis contributes to accumulation of PA, but not of diacylglycerol. Furthermore, regulation of PLD activity appears to require G-protein and tyrosine-phosphorylation-linked pathways.
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Affiliation(s)
- D T Ward
- Department of Medicine, University Hospital of South Manchester, U.K
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35
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Pickkers P, Hughes AD. Relaxation and decrease in [Ca2+]i by hydrochlorothiazide in guinea-pig isolated mesenteric arteries. Br J Pharmacol 1995; 114:703-7. [PMID: 7537594 PMCID: PMC1510005 DOI: 10.1111/j.1476-5381.1995.tb17195.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
1. We examined the effect of the thiazide diuretic, hydrochlorothiazide, on on intracellular calcium concentration ([Ca2+]i) and tone in guinea-pig mesentery arteries. Vessels were mounted on a microvascular myograph and loaded with the Ca(2+)-sensitive fluorescent dye, Fura-2. 2. Hydrochlorothiazide caused relaxation of noradrenaline-precontracted arteries associated with a fall in [Ca2+]i. Preincubation of arteries with hydrochlorothiazide inhibited both contraction and rise in [Ca2+]i in response to noradrenaline. Hydrochlorothiazide did not affect tone and [Ca2+]i when this was elevated by a combination of depolarizing potassium solution and noradrenaline. 3. Hydrochlorothiazide-induced vasorelaxation and decrease of [Ca2+]i was abolished by charybdotoxin, a blocker of large conductance Ca(2+)-activated K channels. 4. The rise in [Ca2+]i elicited by caffeine in Ca(2+)-free physiological salt solution, and presumably reflecting Ca2+ release from intracellular stores, was not altered by preincubation with hydrochlorothiazide. 5. Under depolarizing conditions hydrochlorothiazide did not alter the relationship between the extracellular concentration of Ca2+ and [Ca2+]i; however, hydrochlorothiazide caused a small reduction in the contraction produced for a given rise in [Ca2+]i suggesting hydrochlorothiazide may cause a slight desensitization of the contractile machinery. 6. These findings suggest that hydrochlorothiazide opens Ca(2+)-activated K channels leading to hyperpolarization and consequent closing of voltage-operated calcium channels. The result of this is an impaired influx of extracellular Ca2+, a decrease in [Ca2+]i and vasorelaxation.
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Affiliation(s)
- P Pickkers
- Department of Clinical Pharmacology, St. Mary's Hospital Medical School, Imperial College of Science Technology and Medicine, London
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Aalkjaer C, Lombard JH. Effect of hypoxia on force, intracellular pH and Ca2+ concentration in rat cerebral and mesenteric small arteries. J Physiol 1995; 482 ( Pt 2):409-19. [PMID: 7714832 PMCID: PMC1157739 DOI: 10.1113/jphysiol.1995.sp020528] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
1. The effect of severe hypoxia on force, intracellular Ca2+ concentration ([Ca2+]i) and pHi was studied in isolated small arteries from rat brain and rat mesenterium. The arteries were mounted for isometric force recording while [Ca2+]i was measured with fura-2 or pHi was measured with bis-carboxyethylcarboxyfluorescein (BCECF). 2. Hypoxia reduced the force development in response to arginine vasopressin (AVP) while [Ca2+]i was unchanged or only slightly reduced. Inhibition of acid extrusion by omission of sodium caused no force development in mesenteric arteries, but the fall in pHi was enhanced during hypoxia. In cerebral arteries, hypoxia reduced the force development associated with omission of sodium, and the fall in pHi was less than during normoxic conditions. When acid extrusion was intact, pHi was not affected by hypoxia and the changes in pHi during activation with AVP were similar during hypoxia and in the control situation. 3. Although a decrease in smooth muscle [Ca2+]i may be partly responsible for the reduced force development during hypoxia, [Ca2+]i-independent mechanism(s) may play an even more important role. Furthermore, although hypoxia and force development are associated with enhanced acid production, acid extrusion maintains pHi near the control level and it is unlikely that a decrease in smooth muscle pHi plays any role in the reduced force development during hypoxia.
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Affiliation(s)
- C Aalkjaer
- Department of Pharmacology, University of Aarhus, Denmark
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37
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Hughes AD. Increase in tone and intracellular Ca2+ in rabbit isolated ear artery by platelet-derived growth factor. Br J Pharmacol 1995; 114:138-42. [PMID: 7712009 PMCID: PMC1510153 DOI: 10.1111/j.1476-5381.1995.tb14917.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
1. The effect of platelet-derived growth factor (PDGF-AB) on tone and intracellular Ca2+ ([Ca2+]i) was examined in rabbit isolated ear arteries. Arteries were mounted in a myograph and loaded with the Ca(2+)-sensitive fluorescent indicator, fura-2, for concurrent measurements of isometric force and [Ca2+]i. 2. PDGF-AB contracted rabbit ear artery in a concentration-dependent manner. PDGF-AB induced tone was associated with a rise in [Ca2+]i. In the presence of noradrenaline, PDGF-AB induced a similar rise in [Ca2+]i but contraction in response to PDGF-AB in the presence of noradrenaline was increased compared with PDGF-AB alone. 3. PDGF-AB-induced rise in [Ca2+]i and tone were abolished by removal of extracellular Ca2+ (with addition of BAPTA, a Ca2+ chelator), and by preincubation with a dihydropyridine calcium channel blocker, (-)-202,791. Bistyrphostin, a selective inhibitor of tyrosine kinases, also inhibited PDGF-AB-induced tone, but had no effect on noradrenaline- or potassium-induced tone. 4. PDGF-AB contracts rabbit ear artery by increasing Ca2+ entry through voltage-operated calcium channels. This effect involves activation of a tyrosine kinase.
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Affiliation(s)
- A D Hughes
- Department of Clinical Pharmacology, St. Mary's Hospital Medical School, Imperial College of Science Technology and Medicine, London
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38
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Austin C, Wray S. A quantitative study of the relation between intracellular pH and force in rat mesenteric vascular smooth muscle. Pflugers Arch 1994; 427:270-6. [PMID: 8072846 DOI: 10.1007/bf00374534] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Strips of rat mesenteric artery were loaded with carboxy-seminaphthorhodafluor (SNARF) to measure intracellular pH (pHi) and force simultaneously. pHi was altered by using weak acids and bases. Alkalinization produced an increase in force. For equal elevations of pHi a greater and faster increase of force was obtained in depolarized (high K+) than in non-depolarised preparations. Acidification produced little change in force unless the tissue was contracted (high-K+), in which case it elicited relaxation. Examination of the relationship between pHi and force in depolarized preparations showed that acidification produced a greater change in force than alkalinization. Removal of weak bases produced a transient acidification that was accompanied by a fall in force in all preparations. This was followed by a secondary contraction in depolarized preparations during the period over which pHi was acidic and being restored to resting values. Some preparations demonstrated a hysteresis in the relation between pHi and force. It is concluded that the relationship between pHi and force in mesenteric vascular smooth muscle is not constant but depends on the previous history of the preparation, and may involve differences in the interactions between H+, Ca2+ and the contractile machinery.
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Affiliation(s)
- C Austin
- Physiological Laboratory, University of Liverpool, UK
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