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Treinys R, Kanaporis G, Fischmeister R, Jurevičius J. Metabolic Inhibition Induces Transient Increase of L-type Ca 2+ Current in Human and Rat Cardiac Myocytes. Int J Mol Sci 2019; 20:ijms20061501. [PMID: 30917498 PMCID: PMC6471217 DOI: 10.3390/ijms20061501] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2019] [Revised: 03/15/2019] [Accepted: 03/23/2019] [Indexed: 01/17/2023] Open
Abstract
Metabolic inhibition is a common condition observed during ischemic heart disease and heart failure. It is usually accompanied by a reduction in L-type Ca2+ channel (LTCC) activity. In this study, however, we show that metabolic inhibition results in a biphasic effect on LTCC current (ICaL) in human and rat cardiac myocytes: an initial increase of ICaL is observed in the early phase of metabolic inhibition which is followed by the more classical and strong inhibition. We studied the mechanism of the initial increase of ICaL in cardiac myocytes during β-adrenergic stimulation by isoprenaline, a non-selective agonist of β-adrenergic receptors. The whole-cell patch⁻clamp technique was used to record the ICaL in single cardiac myocytes. The initial increase of ICaL was induced by a wide range of metabolic inhibitors (FCCP, 2,4-DNP, rotenone, antimycin A). In rat cardiomyocytes, the initial increase of ICaL was eliminated when the cells were pre-treated with thapsigargin leading to the depletion of Ca2+ from the sarcoplasmic reticulum (SR). Similar results were obtained when Ca2+ release from the SR was blocked with ryanodine. These data suggest that the increase of ICaL in the early phase of metabolic inhibition is due to a reduced calcium dependent inactivation (CDI) of LTCCs. This was further confirmed in human atrial myocytes where FCCP failed to induce the initial stimulation of ICaL when Ca2+ was replaced by Ba2+, eliminating CDI of LTCCs. We conclude that the initial increase in ICaL observed during the metabolic inhibition in human and rat cardiomyocytes is a consequence of an acute reduction of Ca2+ release from SR resulting in reduced CDI of LTCCs.
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Affiliation(s)
- Rimantas Treinys
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas LT-50162, Lithuania.
| | - Giedrius Kanaporis
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas LT-50162, Lithuania.
| | - Rodolphe Fischmeister
- INSERM UMR-S 1180, Univ Paris-Sud, Université Paris-Saclay, Châtenay-Malabry F-92296, France.
| | - Jonas Jurevičius
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas LT-50162, Lithuania.
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Curry L, Almukhtar H, Alahmed J, Roberts R, Smith PA. Simvastatin Inhibits L-Type Ca2+-Channel Activity Through Impairment of Mitochondrial Function. Toxicol Sci 2019; 169:543-552. [DOI: 10.1093/toxsci/kfz068] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Affiliation(s)
- Liam Curry
- School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, UK
| | - Hani Almukhtar
- School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, UK
| | - Jala Alahmed
- School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, UK
| | - Richard Roberts
- School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, UK
| | - Paul A Smith
- School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, UK
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Park SW, Shin KC, Park HJ, Yoou SK, Park JY, Kang YS, Sung DJ, Kim JG, Park SH, Kim B, Cho H, Bae YM. Caveolar remodeling is a critical mechanotransduction mechanism of the stretch-induced L-type Ca 2+ channel activation in vascular myocytes. Pflugers Arch 2017; 469:829-842. [PMID: 28303387 DOI: 10.1007/s00424-017-1957-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Revised: 01/26/2017] [Accepted: 02/13/2017] [Indexed: 12/11/2022]
Abstract
Activation of L-type voltage-dependent Ca2+ channels (VDCCL) by membrane stretch contributes to many biological responses such as myogenic contraction of arteries. However, mechanism for the stretch-induced VDCCL activation is unclear. In this study, we examined the hypothesis that caveolar remodeling and its related signaling cascade contribute to the stretch-induced activation of VDCCL in rat mesenteric arterial smooth muscle cells. The VDCCL currents were recorded with nystatin-perforated or with conventional whole-cell patch-clamp technique. Hypotonic (~230 mOsm) swelling-induced membrane stretch reversibly increased the VDCCL currents. Electron microscope and confocal imaging analysis revealed that both hypotonic swelling and cholesterol depletion by methyl-β-cychlodextrin (MβCD) similarly disrupted the caveolae structure and translocated caveolin-1 (Cav-1) from membrane to cytosolic space. Accordingly, MβCD also increased VDCCL currents. Moreover, subsequent hypotonic swelling after MβCD treatment failed to increase the VDCCL currents further. Western blotting experiments revealed that hypotonic swelling phosphorylated Cav-1 and JNK. Inhibitors of tyrosine kinases (genistein) and JNK (SP00125) prevented the swelling-induced facilitation of VDCCL currents. Knockdown of Cav-1 by small interfering RNA blocked both the VDCCL current facilitation by stretch and the related phosphorylation of JNK. Taken together, the results suggest that membrane stretch is transduced to the facilitation of VDCCL currents via caveolar structure-dependent tyrosine phosphorylation of Cav-1 and subsequent activation of JNK in rat mesenteric arterial myocytes.
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Affiliation(s)
- Sang Woong Park
- Department of Emergency Medical Services, Eulji University, Seongnam, Gyeonggi-do, 461-713, South Korea
| | - Kyung Chul Shin
- Department of Physiology, KU Open Innovation Center, Research Institute of Medical Science, Konkuk University School of Medicine, Chungju, Chungbuk, 380-701, South Korea
| | - Hyun Ji Park
- Department of Physiology, KU Open Innovation Center, Research Institute of Medical Science, Konkuk University School of Medicine, Chungju, Chungbuk, 380-701, South Korea
| | - Soon-Kyu Yoou
- Department of Emergency Medical Services, Eulji University, Seongnam, Gyeonggi-do, 461-713, South Korea
| | - Jin-Yeon Park
- Colleage of Veterinary Medicine, Department of Biomedical Science & Technology (DBST), Konkuk University, Seoul, 143-701, South Korea
| | - Young-Sun Kang
- Colleage of Veterinary Medicine, Department of Biomedical Science & Technology (DBST), Konkuk University, Seoul, 143-701, South Korea
| | - Dong Jun Sung
- Division of Sport Science, College of Science and Technology, Konkuk University, Chungju, Chungbuk, 380-701, South Korea
| | - Jae Gon Kim
- Department of Physiology, KU Open Innovation Center, Research Institute of Medical Science, Konkuk University School of Medicine, Chungju, Chungbuk, 380-701, South Korea
| | - Seung Hwa Park
- Department of Anatomy, Research Institute of Medical Science, Konkuk University School of Medicine, Chungju, Chungbuk, 380-701, South Korea
| | - BoKyung Kim
- Department of Physiology, KU Open Innovation Center, Research Institute of Medical Science, Konkuk University School of Medicine, Chungju, Chungbuk, 380-701, South Korea
| | - Hana Cho
- Department of Physiology and Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, South Korea
| | - Young Min Bae
- Department of Physiology, KU Open Innovation Center, Research Institute of Medical Science, Konkuk University School of Medicine, Chungju, Chungbuk, 380-701, South Korea.
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Measuring T-Type Calcium Channel Currents in Isolated Vascular Smooth Muscle Cells. Methods Mol Biol 2017. [PMID: 28116717 DOI: 10.1007/978-1-4939-6625-7_15] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Patch clamp electrophysiology is a powerful tool that has been important in isolating and characterizing the ion channels that govern cellular excitability under physiological and pathophysiological conditions. The ability to enzymatically dissociate blood vessels and acutely isolate vascular smooth muscle cells has enabled the application of patch clamp electrophysiology to the identification of diverse voltage dependent ion channels that ultimately control vasoconstriction and vasodilation. Since intraluminal pressure results in depolarization of vascular smooth muscle, the channels that control the voltage dependent influx of extracellular calcium are of particular interest. This chapter describes methods for isolating smooth muscle cells from resistance vessels, and for recording, isolating, and characterizing voltage dependent calcium channel currents, using patch clamp electrophysiological and pharmacological protocols.
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Role of T-type channels in vasomotor function: team player or chameleon? Pflugers Arch 2014; 466:767-79. [PMID: 24482062 DOI: 10.1007/s00424-013-1430-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2013] [Accepted: 12/19/2013] [Indexed: 01/28/2023]
Abstract
Low-voltage-activated T-type calcium channels play an important role in regulating cellular excitability and are implicated in conditions, such as epilepsy and neuropathic pain. T-type channels, especially Cav3.1 and Cav3.2, are also expressed in the vasculature, although patch clamp studies of isolated vascular smooth muscle cells have in general failed to demonstrate these low-voltage-activated calcium currents. By contrast, the channels which are blocked by T-type channel antagonists are high-voltage activated but distinguishable from their L-type counterparts by their T-type biophysical properties and small negative shifts in activation and inactivation voltages. These changes in T-channel properties may result from vascular-specific expression of splice variants of Cav3 genes, particularly in exon 25/26 of the III-IV linker region. Recent physiological studies suggest that T-type channels make a small contribution to vascular tone at low intraluminal pressures, although the relevance of this contribution is unclear. By contrast, these channels play a larger role in vascular tone of small arterioles, which would be expected to function at lower intra-vascular pressures. Upregulation of T-type channel function following decrease in nitric oxide bioavailability and increase in oxidative stress, which occurs during cardiovascular disease, suggests that a more important role could be played by these channels in pathophysiological situations. The ability of T-type channels to be rapidly recruited to the plasma membrane, coupled with their subtype-specific localisation in signalling microdomains where they could modulate the function of calcium-dependent ion channels and pathways, provides a mechanism for rapid up- and downregulation of vasoconstriction. Future investigation into the molecules which govern these changes may illuminate novel targets for the treatment of conditions such as therapy-resistant hypertension and vasospasm.
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Kuo IYT, Wölfle SE, Hill CE. T-type calcium channels and vascular function: the new kid on the block? J Physiol 2010; 589:783-95. [PMID: 21173074 DOI: 10.1113/jphysiol.2010.199497] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
While L-type voltage-dependent calcium channels have long been considered the predominant source of calcium for myogenic constriction, recent studies of both cerebral and systemic circulations have provided evidence for the prominent expression of other members of the voltage-dependent calcium channel family, in particular the low voltage activated T-type channels. Although physiological studies have not supported the involvement of a classical low voltage activated, T-type channel in vascular function, evidence is accumulating that points to the involvement of a non-L-type, high voltage activated channel with sensitivity to T-type channel antagonists. We propose that this may arise due to expression of a T-type channel splice variant with unique biophysical characteristics resulting in a more depolarised profile. Expression of these channels in smooth muscle cells would broaden the voltage range over which sustained calcium influx occurs, while expression of T-type channels in endothelial cells could provide a feedback mechanism to prevent excessive vasoconstriction. Perturbation of this balance during pathophysiological conditions by upregulation of channel expression and endothelial dysfunction could contribute to vasospastic conditions and therapy-refractory hypertension.
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Affiliation(s)
- Ivana Y-T Kuo
- Department of Neuroscience, John Curtin School of Medical Research, GPO Box 334, Canberra, ACT, Australia 0200
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Kang Y, Zhang Y, Liang T, Leung YM, Ng B, Xie H, Chang N, Chan J, Shyng SL, Tsushima RG, Gaisano HY. ATP modulates interaction of syntaxin-1A with sulfonylurea receptor 1 to regulate pancreatic beta-cell KATP channels. J Biol Chem 2010; 286:5876-83. [PMID: 21173146 DOI: 10.1074/jbc.m109.089607] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ATP-sensitive potassium (K(ATP)) channels are regulated by a variety of cytosolic factors (adenine nucleotides, Mg(2+), phospholipids, and pH). We previously reported that K(ATP) channels are also regulated by endogenous membrane-bound SNARE protein syntaxin-1A (Syn-1A), which binds both nucleotide-binding folds of sulfonylurea receptor (SUR)1 and 2A, causing inhibition of K(ATP) channel activity in pancreatic islet β-cells and cardiac myocytes, respectively. In this study, we show that ATP dose-dependently inhibits Syn-1A binding to SUR1 at physiological concentrations, with the addition of Mg(2+) causing a decrease in the ATP-induced inhibitory effect. This ATP disruption of Syn-1A binding to SUR1 was confirmed by FRET analysis in living HEK293 cells. Electrophysiological studies in pancreatic β-cells demonstrated that reduced ATP concentrations increased K(ATP) channel sensitivity to Syn-1A inhibition. Depletion of endogenous Syn-1A in insulinoma cells by botulinum neurotoxin C1 proteolysis followed by rescue with exogenous Syn-1A showed that Syn-1A modulates K(ATP) channel sensitivity to ATP. Thus, our data indicate that although both ATP and Syn-1A independently inhibit β-cell K(ATP) channel gating, they could also influence the sensitivity of K(ATP) channels to each other. These findings provide new insight into an alternate mechanism by which ATP regulates pancreatic β-cell K(ATP) channel activity, not only by its direct actions on Kir6.2 pore subunit, but also via ATP modulation of Syn-1A binding to SUR1.
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Affiliation(s)
- Youhou Kang
- Department of Medicine, University of Toronto and University Health Network, Toronto, Ontario M5S 1A8, Canada
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Kuo IY, Ellis A, Seymour VAL, Sandow SL, Hill CE. Dihydropyridine-insensitive calcium currents contribute to function of small cerebral arteries. J Cereb Blood Flow Metab 2010; 30:1226-39. [PMID: 20125181 PMCID: PMC2949209 DOI: 10.1038/jcbfm.2010.11] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Although dihydropyridines are widely used for the treatment of vasospasm, their effectiveness is questionable, suggesting that other voltage-dependent calcium channels (VDCCs) contribute to control of cerebrovascular tone. This study therefore investigated the role of dihydropyridine-insensitive VDCCs in cerebrovascular function. Using quantitative PCR and immunohistochemistry, we found mRNA and protein for L-type (Ca(V)1.2) and T-type (Ca(V)3.1 and Ca(V)3.2) channels in adult rat basilar and middle cerebral arteries and their branches. Immunoelectron microscopy revealed both L- and T-type channels in smooth muscle cell (SMC) membranes. Using patch clamp electrophysiology, we found that a high-voltage-activated calcium current, showing T-type channel kinetics and insensitivity to nifedipine and nimodipine, comprised approximately 20% of current in SMCs of the main arteries and approximately 45% of current in SMCs from branches. Both components were abolished by the T-type antagonists mibefradil, NNC 55-0396, and efonidipine. Although nifedipine completely blocked vasoconstriction in pressurized basilar arteries, a nifedipine-insensitive constriction was found in branches and this increased in magnitude as vessel size decreased. We conclude that a heterogeneous population of VDCCs contributes to cerebrovascular function, with dihydropyridine-insensitive channels having a larger role in smaller vessels. Sensitivity of these currents to nonselective T-type channel antagonists suggests that these drugs may provide a more effective treatment for therapy-refractory cerebrovascular constriction.
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Affiliation(s)
- Ivana Y Kuo
- John Curtin School of Medical Research, ANU College of Medicine, Biology and Environment, The Australian National University, Canberra, Australian Capital Territory, Australia
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9
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Touyz RM. Transient receptor potential melastatin 6 and 7 channels, magnesium transport, and vascular biology: implications in hypertension. Am J Physiol Heart Circ Physiol 2008; 294:H1103-18. [PMID: 18192217 DOI: 10.1152/ajpheart.00903.2007] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Magnesium, an essential intracellular cation, is critically involved in many biochemical reactions involved in the regulation of vascular tone and integrity. Decreased magnesium concentration has been implicated in altered vascular reactivity, endothelial dysfunction, vascular inflammation, and structural remodeling, processes important in vascular changes and target organ damage associated with hypertension. Until recently, very little was known about mechanisms regulating cellular magnesium homeostasis, and processes controlling transmembrane magnesium transport had been demonstrated only at the functional level. Two cation channels of the transient receptor potential melastatin (TRPM) cation channel family have now been identified as magnesium transporters, TRPM6 and TRPM7. These unique proteins, termed chanzymes because they possess a channel and a kinase domain, are differentially expressed, with TRPM6 being found primarily in epithelial cells and TRPM7 occurring ubiquitously. Vascular TRPM7 is modulated by vasoactive agents, pressure, stretch, and osmotic changes and may be a novel mechanotransducer. In addition to its magnesium transporter function, TRPM7 has been implicated as a signaling kinase involved in vascular smooth muscle cell growth, apoptosis, adhesion, contraction, cytoskeletal organization, and migration, important processes involved in vascular remodeling associated with hypertension and other vascular diseases. Emerging evidence suggests that vascular TRPM7 function may be altered in hypertension. This review discusses the importance of magnesium in vascular biology and implications in hypertension and highlights the transport systems, particularly TRPM6 and TRPM7, which may play a role in the control of vascular magnesium homeostasis. Since the recent identification and characterization of Mg2+-selective transporters, there has been enormous interest in the field. However, there is still a paucity of information, and much research is needed to clarify the exact mechanisms of magnesium regulation in the cardiovascular system and the implications of aberrant transmembrane magnesium transport in the pathogenesis of hypertension and other vascular diseases.
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Affiliation(s)
- Rhian M Touyz
- Kidney Research Center, Ottawa Heallth Research Institute, University of Ottawa, Ottawa, Ontario, Canada K1H 8M5.
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Park SW, Byun D, Bae YM, Choi BH, Park SH, Kim B, Cho SI. Effects of fluid flow on voltage-dependent calcium channels in rat vascular myocytes: fluid flow as a shear stress and a source of artifacts during patch-clamp studies. Biochem Biophys Res Commun 2007; 358:1021-7. [PMID: 17524365 DOI: 10.1016/j.bbrc.2007.05.024] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2007] [Accepted: 05/02/2007] [Indexed: 11/26/2022]
Abstract
We examined the effects of fluid flow on L-type voltage-dependent Ca(2+) channel (VDCC(L)) currents in rat vascular myocytes using the nystatin perforated patch-clamp technique. The effect of fluid flow on the liquid (bathing solution)-metal (Ag/AgCl ground electrode) junction potential was also studied. With a fluid flow of 0-10 ml/min, changes in the junction potential of up to 5 mV were observed in proportion to the flow rate. Accordingly, fluid flow shifted the current-voltage (I-V) relationship of the recorded VDCC(L) currents in a positive direction. In addition to these shifts, fluid flow also increased the peak VDCC(L) current, suggesting some modulatory role for fluid flow in VDCC(L) currents. The use of a 3-M KCl agar-bridge between the ground electrode and bathing solution abnegated the potential shifts, and fluid flow increased the VDCC(L) currents in a voltage-independent manner. These results suggest that the bathing fluid flow can be both a source of erroneous voltage shift between liquid and metal junctions in the patch-clamp configuration and an important shear stress for the cells. The facilitation of VDCC(L) currents by fluid flow in vascular myocytes may contribute to the myogenic contraction of blood vessels. The mechanism by which fluid flow causes the voltage shift is vigorously discussed.
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Affiliation(s)
- Sang Woong Park
- Artificial Muscle Research Center, Konkuk University, Choongju, Republic of Korea
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11
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Sontia B, Touyz RM. Role of magnesium in hypertension. Arch Biochem Biophys 2006; 458:33-9. [PMID: 16762312 DOI: 10.1016/j.abb.2006.05.005] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2006] [Accepted: 05/03/2006] [Indexed: 12/15/2022]
Abstract
Magnesium affects blood pressure by modulating vascular tone and reactivity. It acts as a calcium channel antagonist, it stimulates production of vasodilator prostacyclins and nitric oxide and it alters vascular responses to vasoactive agonists. Magnesium deficiency has been implicated in the pathogenesis of hypertension with epidemiological and experimental studies demonstrating an inverse correlation between blood pressure and serum magnesium levels. Magnesium also influences glucose and insulin homeostasis, and hypomagnesemia is associated with metabolic syndrome. Although most epidemiological and experimental studies support a role for low magnesium in the pathophysiology of hypertension, data from clinical studies have been less convincing. Furthermore, the therapeutic value of magnesium in the management of hypertension is unclear. The present review addresses the role of magnesium in the regulation of vascular function and blood pressure and discusses the implications of magnesium deficiency in experimental and clinical hypertension, in metabolic syndrome and in pre-eclampsia.
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Affiliation(s)
- Bruno Sontia
- Kidney Research Centre, Ottawa Health Research Institute, University of Ottawa, Ontario, Canada K1H 8M5
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12
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Abstract
1. The influx of Ca2+, Mg2+ and Na+ and the efflux of K+ have central importance for the function and survival of vascular smooth muscle cells, but progress in understanding the influx/efflux pathways has been restricted by a lack of identification of the genes underlying many of the non-voltage-gated cationic channels. 2. The present review highlights evidence suggesting the genes are mammalian homologues of the Transient Receptor Potential (TRP) gene of the fruit-fly Drosophila. The weight of evidence supports roles for TRPC1, TRPP2/1 and TRPC6, but recent studies point also to TRPC3, TRPC4/5, TRPV2, TRPM4 and TRPM7. 3. Activity of these TRP channels is suggested to modulate contraction and sense changes in intracellular Ca2+ storage, G-protein-coupled receptor activation and osmotic stress. Roles in relation to myogenic tone, actions of vasoconstrictors substances, Mg2+ homeostasis and the vascular injury response are suggested. 4. Knowledge that TRP channels are relevant to vascular smooth muscle cells in both their contractile and proliferative phenotypes should pave the way for a better understanding of vascular biology and provide the basis for the discovery of a new set of therapeutic agents targeted to vascular disease.
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Affiliation(s)
- David J Beech
- Membrane Biology Research Group, School of Biomedical Sciences, University of Leeds, Leeds, UK.
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Swärd K, Dreja K, Lindqvist A, Persson E, Hellstrand P. Influence of mitochondrial inhibition on global and local [Ca(2+)](I) in rat tail artery. Circ Res 2002; 90:792-9. [PMID: 11964372 DOI: 10.1161/01.res.0000015214.40360.84] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Inhibition of oxidative metabolism is often found to decrease contractility of systemic vascular smooth muscle, but not to reduce global [Ca(2+)](i). In the present study, we probe the hypothesis that it is associated with an altered pattern of intracellular Ca(2+) oscillations (waves) influencing force development. In the rat tail artery, mitochondrial inhibitors (rotenone, antimycin A, and cyanide) reduced alpha(1)-adrenoceptor-stimulated force by 50% to 80%, but did not reduce global [Ca(2+)](i). Less relaxation (about 30%) was observed after inhibition of myosin phosphatase activity with calyculin A, suggesting that part of the metabolic sensitivity involves the regulation of myosin 20-kDa light chain phosphorylation, although no decrease in phosphorylation was found in freeze-clamped tissue. Confocal imaging revealed that the mitochondrial inhibitors increased the frequency but reduced the amplitude of asynchronous cellular Ca(2+) waves elicited by alpha(1) stimulation. The altered wave pattern, in association with increased basal [Ca(2+)](i), accounted for the unchanged global [Ca(2+)](i). Inhibition of glycolytic ATP production by arsenate caused similar effects on Ca(2+) waves and global [Ca(2+)](i), developing gradually in parallel with decreased contractility. Inhibition of wave activity by the InsP(3) receptor antagonist 2-APB correlated closely with relaxation. Furthermore, abolition of waves with thapsigargin in the presence of verapamil reduced force by about 50%, despite unaltered global [Ca(2+)](i), suggesting that contraction may at least partly depend on Ca(2+) wave activity. This study therefore indicates that mitochondrial inhibition influences Ca(2+) wave activity, possibly due to a close spatial relationship of mitochondria and the sarcoplasmic reticulum and that this contributes to metabolic vascular relaxation.
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Affiliation(s)
- Karl Swärd
- Department of Physiological Sciences, Lund University, Lund, Sweden.
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Sun L, Fan JS, Clark JW, Palade PT. A model of the L-type Ca2+ channel in rat ventricular myocytes: ion selectivity and inactivation mechanisms. J Physiol 2000; 529 Pt 1:139-58. [PMID: 11080258 PMCID: PMC2270174 DOI: 10.1111/j.1469-7793.2000.00139.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. We have developed a mathematical model of the L-type Ca2+ current, which is based on data from whole-cell voltage clamp experiments on rat ventricular myocytes. Ion substitution methods were employed to investigate the ionic selectivity of the channel. Experiments were configured with Na+, Ca2+ or Ba2+ as the majority current carrier. 2. The amplitude of current through the channel is attenuated in the presence of extracellular Ca2+ or Ba2+. Our model accounts for channel selectivity by using a modified Goldman-Hodgkin-Katz (GHK) configuration that employs voltage-dependent channel binding functions for external divalent ions. Stronger binding functions were used for Ca2+ than for Ba2+. 3. Decay of the ionic current during maintained depolarization was characterized by means of voltage- and Ca2+-dependent inactivation pathways embedded in a five-state dynamic channel model. Particularly, Ca2+ first binds to calmodulin and the Ca2+-calmodulin complex is the mediator of Ca2+ inactivation. Ba2+-dependent inactivation was characterized using the ttau same scheme, but with a decreased binding to calmodulin. 4. A reduced amount of steady-state inactivation, as evidenced by a U-shaped curve at higher depolarization levels (>40 mV) in the presence of [Ca2+]o, was observed in double-pulse protocols used to study channel inactivation. To characterize this phenomenon, a mechanism was incorporated into the model whereby Ca2+ or Ba2+ also inhibits the voltage-dependent inactivation pathway. 5. The five-state dynamic channel model was also used to simulate single channel activity. Calculations of the open probability of the channel model are generally consistent with experimental data. A sixth state can be used to simulate modal activity by way of introducing long silent intervals. 6. Our model has been tested extensively using experimental data from a wide variety of voltage clamp protocols and bathing solution manipulations. It provides: (a) biophysically based explanations of putative mechanisms underlying Ca2+- and voltage-dependent channel inactivation, and (b) close fits to voltage clamp data. We conclude that the model can serve as a predictive tool in generating testable hypotheses for further investigation of this complex ion channel.
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Affiliation(s)
- L Sun
- Department of Electrical and Computer Engineering, Rice University, Houston, TX 77005-1892, USA
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15
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Laurant P, Touyz RM. Physiological and pathophysiological role of magnesium in the cardiovascular system: implications in hypertension. J Hypertens 2000; 18:1177-91. [PMID: 10994748 DOI: 10.1097/00004872-200018090-00003] [Citation(s) in RCA: 116] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Attention is growing for a potential role of magnesium in the pathoetiology of cardiovascular disease. Magnesium modulates mechanical, electrical and structural functions of cardiac and vascular cells, and small changes in extracellular magnesium levels and/or intracellular free magnesium concentration may have significant effects on cardiac excitability and on vascular tone, contractility and reactivity. Thus, magnesium may be important in the physiological regulation of blood pressure whereas alterations in cellular magnesium metabolism could contribute to the pathogenesis of blood pressure elevation. Although most epidemiological and experimental studies support a pathological role for magnesium in the etiology and development of hypertension, data from clinical studies have been less convincing. Furthermore, the therapeutic value of magnesium in the management of essential hypertension is unclear. The present review discusses the molecular, biochemical, physiological and pharmacological roles of magnesium in the regulation of vascular function and blood pressure and introduces novel concepts relating to magnesium as a second messenger in intracellular signaling in cardiovascular cells. In addition, alterations in magnesium regulation in experimental and clinical hypertension and the potential antihypertensive therapeutic effects of magnesium are addressed.
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Affiliation(s)
- P Laurant
- Laboratoire Physiologie, Pharmacologie et Nutrition Prèventive Expérimentale, UFR Médecine et Pharmacie, Université de Franche-Comté, Besancon, France
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Nakayama S, Klugbauer N, Kabeya Y, Smith LM, Hofmann F, Kuzuya M. The alpha 1-subunit of smooth muscle Ca(2+) channel preserves multiple open states induced by depolarization. J Physiol 2000; 526 Pt 1:47-56. [PMID: 10878098 PMCID: PMC2270004 DOI: 10.1111/j.1469-7793.2000.00047.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
The cloned alpha 1-subunits of the smooth muscle Ca(2+) channel (alpha (1C-b)) from rabbit lung were expressed in Chinese hamster ovary cells. The effect of large depolarizations was examined using cell-attached patch clamp techniques. After large, long-duration depolarizations (to +80 mV, 4 s), the cloned smooth muscle Ca(2+) channels were still open, and also showed slow channel closure upon repolarization. The sum of unitary channel currents revealed that the tail current seen after large conditioning depolarizations had a slower deactivation time constant compared to that seen when the cell membrane was depolarized briefly with a test step (to +40 mV), suggesting that large depolarizations transform the conformation of the Ca(2+) channels to a second open state. The decay time course of the tail current induced by large conditioning depolarizations was prolonged by reducing the negativity of the repolarization step, and vice versa. Using the slow deactivating characteristic, the current-voltage relationship was directly measured by applying a ramp pulse after a large depolarization. Its slope conductance was approximately 26 pS. Since the patch pipettes contained Ca(2+) agonists, the transition of the Ca(2+) channel conformation to the second, long open state during a large depolarization was distinct from that caused by Ca(2+) agonists, suggesting that the cloned alpha 1-subunits of smooth muscle Ca(2+) channels preserve the characteristic features seen in native smooth muscle Ca(2+) channels. In addition, when skeletal muscle beta-subunits were coexpressed with the alpha 1-subunits, the long channel openings after large, long-duration depolarizations were frequently suppressed. This phenomenon could be explained if the skeletal muscle beta-subunits increased the inactivation rate during the preconditioning depolarization.
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Affiliation(s)
- S Nakayama
- Department of Physiology, School of Medicine, Nagoya University, Nagoya 466, Japan.
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Yang ZW, Gebrewold A, Nowakowski M, Altura BT, Altura BM. Mg(2+)-induced endothelium-dependent relaxation of blood vessels and blood pressure lowering: role of NO. Am J Physiol Regul Integr Comp Physiol 2000; 278:R628-39. [PMID: 10712282 DOI: 10.1152/ajpregu.2000.278.3.r628] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In vitro extracellular Mg(2+) concentration ([Mg(2+)](0)) produces endothelium-dependent and endothelium-independent relaxations in rat aorta in a concentration-dependent manner. These relaxant effects of Mg(2+) on intact rat aortic rings, but not denuded rat aortic rings, were suppressed by either N(G)-monomethyl-L-arginine (L-NMMA), N(omega)-nitro-L-arginine methyl ester (L-NAME), or methylene blue. The inhibitory effects of L-NMMA and L-NAME could be reversed partly by L-arginine. [Mg(2+)](0)-induced dilatation in vivo in rat mesenteric arterioles and venules was almost completely inhibited by N(G)-nitro-L-arginine and L-NMMA. Removal of extracellular Ca(2+) concentration ([Ca(2+)](0)) or buffering intracellular Ca(2+) concentration in endothelial cells, with 10 microM 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM, markedly attenuated the relaxant effects of Mg(2+). Mg(2+) produced nitric oxide (NO) release from the intact aortic rings in a concentration-dependent manner. Removal of [Ca(2+)](0) diminished the increased NO release induced by elevated levels of [Mg(2+)](0). In vivo infusion of increasing doses (1-30 microM/min) of MgSO(4), directly into the femoral veins of anesthetized rats, elicited significant concentration-dependent sustained increases in serum total Mg and concomitant decreases in arterial blood pressure. Before and after employment of various doses of MgSO(4), intravenous administration of either L-NMMA (10 mg/kg) or L-NAME (10 mg/kg) increased (i.e., reversed) the MgSO(4)-lowered blood pressure markedly, and intravenous injection of L-arginine restored partially the increased blood pressure effects of both L-NMMA and L-NAME. Our results suggest that 1) small blood vessels are very dependent on NO release for Mg(2+) dilatations and 2) the endothelium-dependent relaxation induced by extracellular Mg(2+) is mediated by release of endothelium-derived relaxing factor-NO from the endothelium, and requires Ca(2+) and formation of guanosine 3',5'-cyclic monophosphate.
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Affiliation(s)
- Z W Yang
- Department of Physiology, State University of New York, Health Science Center at Brooklyn, Brooklyn, New York 11203, USA
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18
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Abstract
Ca(2+) and H(+) ions can profoundly alter vascular tone. In many physiological and pathological processes, changes in the concentration of both ions occur. Thus, to understand the processes and mechanisms that modify force, it is necessary to understand what changes occur in these ions and, importantly, how they interact with each other. In this minireview, we highlight the quantitatively important mechanisms involved in the contractile responses of vascular tissues to pH change and discuss the cellular and molecular reasons underlying these responses.
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Affiliation(s)
- C Austin
- Department of Medicine, Manchester Royal Infirmary, Manchester, UK.
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19
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Jover T, Altura BT, Altura BM. Effects of protein kinase C inhibitors on ethanol-induced contractions in isolated rat aorta. Alcohol 1999; 18:17-22. [PMID: 10386660 DOI: 10.1016/s0741-8329(98)00062-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The activation of intracellular contractile proteins induces vascular contraction mediated through signal transduction mechanisms. Protein kinase C (PKC) is involved in this signal transduction. The purpose of the present study was designed to investigate the role of PKC on EtOH-, KCl- and phorbol 12, 13-dibutyrate (PDBu)-induced contractions in isolated rat aorta through the use of several different PKC inhibitors. Prior exposure to staurosporine inhibited both EtOH- and KCl-induced contractions in a concentration-dependent manner. The EtOH-induced contractions were completely inhibited by staurosporine (5 x 10(-6) M) but complete inhibition of KCl-induced contractions was not observed. Staurosporine (10(-7) M) also significantly inhibited the contractile response to single doses of both EtOH and PDBu. Bisindolylmaleimide (10(-6) M) effectively inhibited contractile responses to both EtOH- and KCl, added cumulatively, and single doses of PDBu. Chelerythrine (10(-7) M) inhibited maximal EtOH-induced contractions. These results suggest that PKC activation plays an important role in the mechanism(s) involved in the contractile activation of rat aorta smooth muscle by EtOH, KCl and PDBu. However, further work is required to elucidate the precise molecular mechanism.
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Affiliation(s)
- T Jover
- Department of Physiology, State University of New York, Health Science Center at Brookyln, 11203, USA
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20
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Buckler KJ, Vaughan-Jones RD. Effects of mitochondrial uncouplers on intracellular calcium, pH and membrane potential in rat carotid body type I cells. J Physiol 1998; 513 ( Pt 3):819-33. [PMID: 9824720 PMCID: PMC2231310 DOI: 10.1111/j.1469-7793.1998.819ba.x] [Citation(s) in RCA: 142] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. Mitochondrial uncouplers are potent stimulants of the carotid body. We have therefore investigated their effects upon isolated type I cells. Both 2,4-dinitrophenol (DNP) and carbonyl cyanide p-trifluoromethoxyphenyl hydrazone (FCCP) caused an increase in [Ca2+]i which was largely inhibited by removal of extracellular Ca2+ or Na+, or by the addition of 2 mM Ni2+. Methoxyverapamil (D600) also partially inhibited the [Ca2+]i response. 2. In perforated-patch recordings, the rise in [Ca2+]i coincided with membrane depolarization and was greatly reduced by voltage clamping the cell to -70 mV. Uncouplers also inhibited a background K+ current and induced a small inward current. 3. Uncouplers reduced pHi by 0.1 unit. Alkaline media diminished this acidification but had no effect on the [Ca2+]i response. 4. FCCP and DNP also depolarized type I cell mitochondria. The onset of mitochondrial depolarization preceded changes in cell membrane conductance by 3-4 s. 5. We conclude that uncouplers excite the carotid body by inhibiting a background K+ conductance and inducing a small inward current, both of which lead to membrane depolarization and voltage-gated Ca2+ entry. These effects are unlikely to be caused by cell acidification. The inhibition of background K+ current may be related to the uncoupling of oxidative phosphorylation.
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Affiliation(s)
- K J Buckler
- University Laboratory of Physiology, Parks Road, Oxford OX1 3PT, UK.
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21
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Buckler KJ, Vaughan-Jones RD. Effects of mitochondrial uncouplers on intracellular calcium, pH and membrane potential in rat carotid body type I cells. J Physiol 1998. [DOI: 10.1111/j.1469-7793.1998.819ba.x 10.1111/j.1469-7793.1998.819ba.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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22
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Prior HM, Yates MS, Beech DJ. Functions of large conductance Ca2+-activated (BKCa), delayed rectifier (KV) and background K+ channels in the control of membrane potential in rabbit renal arcuate artery. J Physiol 1998; 511 ( Pt 1):159-69. [PMID: 9679171 PMCID: PMC2231112 DOI: 10.1111/j.1469-7793.1998.159bi.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. The types of K+ channel which determine the membrane potential of arcuate artery smooth muscle cells were investigated by patch-clamp recording from isolated cells and lumenal diameter measurements from intact pressurized renal arcuate arteries. 2. Single cells had a mean resting potential of -38 mV and were depolarized by 130 mM K+ but not by the Cl- channel blocker 4,4'-diisothiocyanatostilbene-2, 2'-disulphonic acid (DIDS). 3. Iberiotoxin did not affect the resting potential but inhibited spontaneous transient hyperpolarizations. Iberiotoxin or 1 mM tetraethylammonium (TEA+) constricted intact arteries. 3,4-Diaminopyridine (3,4-DAP)-sensitive delayed rectifier K+ (KV) channel current was elicited by depolarization but 3,4-DAP did not affect the resting potential or induce constriction in the intact artery. 4. A voltage-independent K+ current was inhibited by >= 0.1 mM barium (Ba2+) and unaffected by iberiotoxin, glibenclamide, apamin, 3,4-DAP and ouabain. In six out of ten cells, 1 mM Ba2+ depolarized the resting potential, while in the other cells the potential was resistant to all of the K+ channel blockers and ouabain. Ba2+ (0.1-1 mM) constricted the intact artery, but 10 microM Ba2+, 1 microM glibenclamide or 100 nM apamin had no effect. 5. The data suggest that resting potential is determined by background K+ channels, one type being Ba2+ sensitive and voltage independent, and another type being poorly defined due to its resistance to any inhibitor. Large conductance Ca2+-activated K+ (BKCa) and KV channels do not determine the resting potential but have separate functions to underlie transient Ca2+-induced hyperpolarizations and to protect against depolarization past about -30 mV.
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Affiliation(s)
- H M Prior
- Department of Pharmacology, University of Leeds, Leeds LS2 9JT, UK
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23
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Taggart MJ, Wray S. Hypoxia and smooth muscle function: key regulatory events during metabolic stress. J Physiol 1998; 509 ( Pt 2):315-25. [PMID: 9575282 PMCID: PMC2230985 DOI: 10.1111/j.1469-7793.1998.315bn.x] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/1998] [Accepted: 03/31/1998] [Indexed: 11/28/2022] Open
Abstract
Hypoxia rapidly reduces force in many smooth muscles and we review recent data that shed light on the mechanisms involved. As many regulated cellular processes are integrated to co-ordinate smooth muscle contractility, the processes responsible for decreased force output with altered metabolism are also likely to be many, acting in concert, rather than the actions of one altered parameter. Nevertheless the aim of this study is to elucidate the hierarchical series of events that contribute to reduced smooth muscle force production during altered metabolism. We conclude that in many phasic smooth muscles the decrease in force can be attributed to impaired electro-mechanical coupling whereby the Ca2+ transient is reduced. A direct effect of hypoxia on the Ca2+ channel may be of key importance. In tonic vascular smooth muscles KATP channels may also play a role in the integrated functional responses to hypoxia. There are also many examples of force being reduced, in tonically activated preparations, without a fall in steady-state Ca2+; indeed it usually increases. We examine the roles of altered [ATP], pH, myosin phosphorylation, inorganic phosphate and proteolytic activity on the [Ca2+]-force relationship during hypoxia. We find no defining force-inhibitory role for any one factor acting alone, and suggest that force most probably falls as a result of the combination of myriad factors.
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Affiliation(s)
- M J Taggart
- Physiology Department, University of Liverpool, Crown Street, Liverpool L69 3BX, UK.
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24
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McHugh D, Beech DJ. Protein kinase C requirement of Ca2+ channel stimulation by intracellular ATP in guinea-pig basilar artery smooth muscle cells. J Physiol 1997; 500 ( Pt 2):311-7. [PMID: 9147319 PMCID: PMC1159385 DOI: 10.1113/jphysiol.1997.sp022022] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
1. Smooth muscle cells were isolated from guinea-pig basilar artery and conventional whole-cell recordings of Ca2+ channel activity were made at room temperature within 7 h of the isolation procedure. The purpose of the study was to investigate the mechanism of the stimulatory action of intracellular ATP on Ca2+ channels. 2. High (millimolar) concentrations of ATP were needed to produce stimulation of Ca2+ channels, and neither ADP nor AMP mimicked the action of ATP. 3. The ATP effect was not mimicked by stable ATP derivatives (AMP-PNP or AMP-PCP) and was abolished by incubation of cells in non-specific protein kinase inhibitors (staurosporine or H-7) or specific protein kinase C inhibitors (GF109203x, calphostin C or chelerythrine) but not by tyrosine kinase inhibitors (tyrphostin B42 and genistein). 4. The data suggest that ATP-induced stimulation of L-type Ca2+ channels requires functional activity of a protein kinase C isozyme.
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Affiliation(s)
- D McHugh
- Department of Pharmacology, University of Leeds, UK
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25
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Beech DJ. Actions of neurotransmitters and other messengers on Ca2+ channels and K+ channels in smooth muscle cells. Pharmacol Ther 1997; 73:91-119. [PMID: 9131720 DOI: 10.1016/s0163-7258(97)87271-3] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Ion channels play key roles in determining smooth muscle tone by setting the membrane potential and allowing Ca2+ influx. Perhaps not surprisingly, therefore, they also provide targets for neurotransmitters and other messengers that act on smooth muscle. Application of patch-clamp and molecular biology techniques and the use of selective pharmacology has started to provide a wealth of information on the ion channel systems of smooth muscle cells, revealing complexity and functional significance. Reviewed are the actions of messengers (e.g., noradrenaline, acetylcholine, endothelin, angiotensin II, neuropeptide Y, 5-hydroxytryptamine, histamine, adenosine, calcitonin gene-related peptide, substance P, prostacyclin, nitric oxide and oxygen) on specific types of ion channel in smooth muscle, the L-type calcium channel, and the large conductance Ca(2+)-activated, ATP-sensitive, delayed rectifier and apamin-sensitive K+ channels.
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Affiliation(s)
- D J Beech
- Department of Pharmacology, University of Leeds, England
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