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Pérez-García MT, Colinas O, Miguel-Velado E, Moreno-Domínguez A, López-López JR. Characterization of the Kv channels of mouse carotid body chemoreceptor cells and their role in oxygen sensing. J Physiol 2004; 557:457-71. [PMID: 15034123 PMCID: PMC1665096 DOI: 10.1113/jphysiol.2004.062281] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
As there are wide interspecies variations in the molecular nature of the O(2)-sensitive Kv channels in arterial chemoreceptors, we have characterized the expression of these channels and their hypoxic sensitivity in the mouse carotid body (CB). CB chemoreceptor cells were obtained from a transgenic mouse expressing green fluorescent protein (GFP) under the control of tyrosine hydroxylase (TH) promoter. Immunocytochemical identification of TH in CB cell cultures reveals a good match with GFP-positive cells. Furthermore, these cells show an increase in [Ca(2+)](i) in response to low P(O(2)), demonstrating their ability to engender a physiological response. Whole-cell experiments demonstrated slow-inactivating K(+) currents with activation threshold around -30 mV and a bi-exponential kinetic of deactivation (tau of 6.24 +/- 0.52 and 32.85 +/- 4.14 ms). TEA sensitivity of the currents identified also two different components (IC(50) of 17.8 +/- 2.8 and 940.0 +/- 14.7 microm). Current amplitude decreased reversibly in response to hypoxia, which selectively affected the fast deactivating component. Hypoxic inhibition was also abolished in the presence of low (10-50 microm) concentrations of TEA, suggesting that O(2) interacts with the component of the current most sensitive to TEA. The kinetic and pharmacological profile of the currents suggested the presence of Kv2 and Kv3 channels as their molecular correlates, and we have identified several members of these two subfamilies by single-cell PCR and immunocytochemistry. This report represents the first functional and molecular characterization of Kv channels in mouse CB chemoreceptor cells, and strongly suggests that O(2)-sensitive Kv channels in this preparation belong to the Kv3 subfamily.
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Affiliation(s)
- M Teresa Pérez-García
- Universidad de Valladolid y Consejo Superior de Investigaciones Cientificas (CSIC), Departamento de Bioquímica y Biología Molecular y Fisiología, Facultad de Medicina, Valladolid, Spain.
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52
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Fountain SJ, Cheong A, Flemming R, Mair L, Sivaprasadarao A, Beech DJ. Functional up-regulation of KCNA gene family expression in murine mesenteric resistance artery smooth muscle. J Physiol 2004; 556:29-42. [PMID: 14742730 PMCID: PMC1664901 DOI: 10.1113/jphysiol.2003.058594] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
This study focused on the hypothesis that KCNA genes (which encode K(V)alpha1 voltage-gated K(+) channels) have enhanced functional expression in smooth muscle cells of a primary determinant of peripheral resistance - the small mesenteric artery. Real-time PCR methodology was developed to measure cell type-specific in situ gene expression. Profiles were determined for arterial myocyte expression of RNA species encoding K(V)alpha1 subunits as well as K(V)beta1, K(V)alpha2.1, K(V)gamma9.3, BK(Ca)alpha1 and BK(Ca)beta1. The seven major KCNA genes were expressed and more readily detected in endothelium-denuded mesenteric resistance artery compared with thoracic aorta; quantification revealed dramatic differential expression of one to two orders of magnitude. There was also four times more RNA encoding K(V)alpha2.1 but less or similar amounts encoding K(V)beta1, K(V)gamma9.3, BK(Ca)alpha1 and BK(Cabeta)1. Patch-clamp recordings from freshly isolated smooth muscle cells revealed dominant K(V)alpha1 K(+) current and current density twice as large in mesenteric cells. Therefore, we suggest the increased RNA production of the resistance artery impacts on physiological function, although there is quantitatively less K(+) current than might be expected. The mechanism conferring up-regulated expression of KCNA genes may be common to all the gene family and play a functional role in the physiological control of blood pressure.
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Affiliation(s)
- S J Fountain
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK
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53
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Prentice HM, Milton SL, Scheurle D, Lutz PL. Gene transcription of brain voltage-gated potassium channels is reversibly regulated by oxygen supply. Am J Physiol Regul Integr Comp Physiol 2004; 285:R1317-21. [PMID: 14615400 DOI: 10.1152/ajpregu.00261.2003] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Voltage-dependent potassium channels (Kv channels) are important determinants of brain electrical activity. Hypoxia may be an important modifier, because several voltage-gated K+ channels are reversibly blocked by acute hypoxia and are thought to act as oxygen sensors. Here we show, using the anoxia-tolerant turtle brain (Trachemys scripta) as a model, that brain Kv1 channel transcription is reversibly regulated by oxygen supply. We found that in turtle brains exposed to 4-h anoxia Kv1 transcripts were reduced to 18.5% of normoxic levels. Kv1 channel mRNA levels were restored to normal within 4 h of subsequent reoxygenation. Our results provide clear evidence that brain Kv channel expression is sensitive to oxygen supply and indicate an important mechanism that matches brain activity to oxygen supply.
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Affiliation(s)
- Howard M Prentice
- Department of Biomedical Sciences, Florida Atlantic University, Boca Raton 33431, USA.
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54
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Fujishiro N, Endo Y, Warashina A, Inoue M. Mechanisms for Hypoxia Detection in O2-Sensitive Cells. ACTA ACUST UNITED AC 2004; 54:109-23. [PMID: 15182418 DOI: 10.2170/jjphysiol.54.109] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Since O(2) is the bare necessity for multicellular organisms, they develop multiple protective mechanisms against hypoxia. Mammals will adapt to hypoxia in short and long terms. The short-term responses include enhancement of the respiratory and cardiac functions, adrenaline secretion from adrenal medullary cells, and pulmonary vasoconstriction, whereas the long-term response is the increase in erythropoietin production with the consequent increase in red blood cells. Although much work has been done to elucidate molecular mechanisms for O(2)-sensing for the last ten years, the majority of the mechanisms remain unclear. We will review mechanisms proposed for hypoxia detection in carotid body type I cells, pulmonary artery smooth muscle, adrenal medullary cells, and liver cells, with the special focus on adrenal medullary cells.
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Affiliation(s)
- Naoji Fujishiro
- Department of Cell and System Physiology, University of Occupational and Environmental Health School of Medicine, Kitakyushu, 807-8555 Japan
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55
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Hammarström AKM, Gage PW. Methods to Study Oxygen Sensing Sodium Channels. Methods Enzymol 2004; 381:275-90. [PMID: 15063681 DOI: 10.1016/s0076-6879(04)81019-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
Affiliation(s)
- A K M Hammarström
- Membrane Biology Program, John Curtin School of Medical Research, Australian National University, Canberra, Australia
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56
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Wellman TL, Jenkins J, Penar PL, Tranmer B, Zahr R, Lounsbury KM. Nitric oxide and reactive oxygen species exert opposing effects on the stability of hypoxia-inducible factor-1alpha (HIF-1alpha) in explants of human pial arteries. FASEB J 2003; 18:379-81. [PMID: 14657004 DOI: 10.1096/fj.03-0143fje] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Hypoxia induces angiogenesis, partly through stabilization of hypoxia-inducible factor-1alpha (HIF-1alpha), leading to transcription of pro-angiogenic factors. Here we examined the regulation of HIF-1alpha by hypoxia and nitric oxide (NO) in explants of human cerebrovascular smooth muscle cells. Cells were treated with NO donors under normoxic or hypoxic (2% O2) conditions, followed by analysis of HIF-1alpha protein levels. Treatment with the NO donor sodium nitroprusside reduced levels of HIF-1alpha, whereas NO donors, NOC-18 and S-nitrosoglutathione, increased HIF-1alpha levels. SIN-1, which releases both NO and superoxide (O2*-), reduced HIF-1alpha levels, suggesting that inhibitory NO donors may elicit effects through peroxynitrite (ONOO*-). O2*- generation by xanthine/xanthine oxidase also reduced HIF-1alpha levels, confirming an inhibitory role for reactive oxygen species (ROS). Furthermore, superoxide dismutase increased HIF-1alpha levels, and the NO scavenger carboxy-PTIO reversed HIF-1alpha stabilization by NO donors. Effects on HIF-1alpha levels correlated with vascular endothelial growth factor transcription but did not affect HIF-1alpha transcription, as measured by RT-PCR and luciferase-reporter assays. The results indicate that HIF-1alpha is stabilized by agents that produce NO and reduce ROS but destabilized by agents that increase ROS, including O2*- and ONOO*-. Thus we propose that the effect of NO on HIF-1alpha signaling is critically dependent on the form of NO and the physiological environment of the responding cell.
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Affiliation(s)
- Theresa L Wellman
- Department of Pharmacology, University of Vermont, Given Bldg., 89 Beaumont Ave., Burlington, Vermont 05405, USA
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57
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Conforti L, Takimoto K, Petrovic M, Pongs O, Millhorn D. The pore region of the Kv1.2alpha subunit is an important component of recombinant Kv1.2 channel oxygen sensitivity. Biochem Biophys Res Commun 2003; 306:450-6. [PMID: 12804584 DOI: 10.1016/s0006-291x(03)00989-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Oxygen-sensitive K(+) channels are important elements in the cellular response to hypoxia. Although much progress has been made in identifying their molecular composition, the structural components associated to their O(2)-sensitivity are not yet understood. Recombinant Kv1.2 currents expressed in Xenopus oocytes are inhibited by a decrease in O(2) availability. On the contrary, heterologous Kv2.1 channels are O(2)-insensitive. To elucidate the protein segment responsible for the O(2)-sensitivity of Kv1.2 channels, we analyzed the response to anoxia of Kv1.2/Kv2.1 chimeric channels. Expression of chimeric Kv2.1 channels each containing the S4, the S1-S3 or the S6-COOH segments of Kv1.2 polypeptide resulted in a K(+) current insensitive to anoxia. In contrast, transferring the S5-S6 segment of Kv1.2 into Kv2.1 produced an O(2)-sensitive K(+) current. Finally, mutating a redox-sensitive methionine residue (M380) of Kv1.2 polypeptide did not affect O(2)-sensitivity. Thus, the pore and its surrounding regions of Kv1.2 polypeptide confer its hypoxic inhibition. This response is independent on the redox modulation of methionine residues in this protein segment.
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Affiliation(s)
- Laura Conforti
- Division of Nephrology and Hypertension, Department of Internal Medicine, University of Cincinnati, 231 Albert Sabin Way, Cincinnati, OH 45267-0585, USA.
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58
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Abstract
Sudden cardiac death remains a daunting medical challenge. Rescuers have minutes to defibrillate the heart and prevent ischemic injury to critical organs. Cardiopulmonary resuscitation can extend the window for successful therapy but not for long. Complicating this further is the fact that few new therapies have been proven to protect against the postresuscitation phase of cardiac arrest, when as many as 90% of patients die despite successful defibrillation. Oxidants (both reactive oxygen and nitrogen) likely play critical roles during cardiac arrest, affecting defibrillation success by affecting cardiac gap junctions and after successful defibrillation causing multiorgan damage via direct and programmed cell death. Preconditioning is an intrinsic adaptive response to stress that targets this sequence of events and is highly protective against ischemia/reperfusion injury in the heart, brain, and other critical organs. Thus, how oxidants are affected by preconditioning could provide new insights and therapies for improving both defibrillation success and oxidant-mediated postresuscitation injury of sudden cardiac death.
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Affiliation(s)
- Travis Anderson
- Department of Medicine, The University of Chicago, Illinois 60637, USA
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59
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Littler CM, Morris KG, Fagan KA, McMurtry IF, Messing RO, Dempsey EC. Protein kinase C-epsilon-null mice have decreased hypoxic pulmonary vasoconstriction. Am J Physiol Heart Circ Physiol 2003; 284:H1321-31. [PMID: 12505875 DOI: 10.1152/ajpheart.00795.2002] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
PKC contributes to regulation of pulmonary vascular reactivity in response to hypoxia. The role of individual PKC isozymes is less clear. We used a knockout (null, -/-) mouse to test the hypothesis that PKC-epsilon is important in acute hypoxic pulmonary vasoconstriction (HPV). We asked whether deletion of PKC-epsilon would decrease acute HPV in adult C57BL6xSV129 mice. In isolated, salt solution-perfused lung, reactivity to acute hypoxic challenges (0% and 3% O(2)) was compared with responses to angiotensin II (ANG II) and KCl. PKC-epsilon -/- mice had decreased HPV, whereas responses to ANG II and KCl were preserved. Inhibition of nitric oxide synthase (NOS) with nitro-l-arginine augmented HPV in PKC-epsilon +/+ but not -/- mice. Inhibition of Ca(2+)-gated K(+) channels (K(Ca)) with charybdotoxin and apamin did not enhance HPV in -/- mice relative to wild-type (+/+) controls. In contrast, the voltage-gated K(+) channel (K(V)) antagonist 4-aminopyridine increased the response of -/- mice beyond that of +/+ mice. This suggested that increased K(V) channel expression could contribute to blunted HPV in PKC-epsilon -/- mice. Therefore, expression of the O(2)-sensitive K(V) channel subunit Kv3.1b (100-kDa glycosylated form and 70-kDa core protein) was compared in whole lung and pulmonary artery smooth muscle cell (PASMC) lysates from +/+ and -/- mice. A subtle increase in Kv3.1b was detected in -/- vs. +/+ whole lung lysates. A much greater rise in Kv3.1b expression was found in -/- vs. +/+ PASMC. Thus deletion of PKC-epsilon blunts murine HPV. The decreased response could not be attributed to a general loss in vasoreactivity or derangements in NOS or K(Ca) channel activity. Instead, the absence of PKC-epsilon allows increased expression of K(V) channels (like Kv3.1b) to occur in PASMC, which likely contributes to decreased HPV.
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Affiliation(s)
- Cassana M Littler
- Cardiovascular Pulmonary Research Laboratory, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA
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60
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Vanden Hoek TL, Qin Y, Wojcik K, Li CQ, Shao ZH, Anderson T, Becker LB, Hamann KJ. Reperfusion, not simulated ischemia, initiates intrinsic apoptosis injury in chick cardiomyocytes. Am J Physiol Heart Circ Physiol 2003; 284:H141-50. [PMID: 12388298 PMCID: PMC7359634 DOI: 10.1152/ajpheart.00132.2002] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Although ischemia-reperfusion (I/R) can initiate apoptosis, the timing and contribution of the mitochondrial/cytochrome c apoptosis death pathway to I/R injury is unclear. We studied the timing of cytochrome c release during I/R and whether subsequent caspase activation contributes to reperfusion injury in confluent chick cardiomyocytes. One-hour simulated ischemia followed by 3-h reperfusion resulted in significant cell death, with most cell death evident during the reperfusion phase and demonstrating mitochondrial cytochrome c release within 5 min after reperfusion. By contrast, cells exposed to prolonged ischemia for 4 h had only marginally increased cell death and no detectable cytochrome c release into the cytosol. Caspase activation could not be detected after ischemia only, but it significantly increased after reperfusion. Caspase inhibitors benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone, Ac-Asp-Gln-Thr-Asp-H, or benzyloxycarbonyl-Leu-Glu (Ome)-His-Asp-(Ome)-fluoromethyl ketone given only at reperfusion significantly attenuated cell death and resulted in return of contraction. Antixoxidants decreased cytochrome c release, nuclear condensation, and cell death. These results suggest that reperfusion oxidants initiate cytochrome c release within minutes, and apoptosis within hours, significant enough to increase cell death and contractile dysfunction.
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Affiliation(s)
- Terry L Vanden Hoek
- Sections of Emergency Medicine and Pulmonary/Critical Care, Department of Medicine and Emergency Resuscitation Center, University of Chicago, Illinois 60637, USA
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61
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Kemp PJ, Peers C, Miller P, Lewis A. Oxygen Sensing by Human Recombinant Tandem-P Domain Potassium Channels. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2003; 536:201-8. [PMID: 14635668 DOI: 10.1007/978-1-4419-9280-2_26] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/27/2023]
Affiliation(s)
- Paul J Kemp
- School of Biomedical Sciences, Worsley Medical and Dental Building, University of Leeds, Leeds LS2 9JT, UK
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62
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Hampl V, Bíbová J, Stranák Z, Wu X, Michelakis ED, Hashimoto K, Archer SL. Hypoxic fetoplacental vasoconstriction in humans is mediated by potassium channel inhibition. Am J Physiol Heart Circ Physiol 2002; 283:H2440-9. [PMID: 12388256 DOI: 10.1152/ajpheart.01033.2001] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Fetal to maternal blood flow matching in the placenta, necessary for optimal fetal blood oxygenation, may occur via hypoxic fetoplacental vasoconstriction (HFPV). We hypothesized that HFPV is mediated by K(+) channel inhibition in fetoplacental vascular smooth muscle, as occurs in several other O(2)-sensitive tissues. With the use of an isolated human placental cotyledon perfused at a constant flow rate, we found that hypoxia reversibly increased perfusion pressure by >20%. HFPV was unaffected by cyclooxygenase or nitric oxide synthase inhibition. HFPV and 4-aminopyridine, an inhibitor of voltage-dependent K(+) (K(v)) channels, increased pressure in a nonadditive manner, suggesting they act via a common mechanism. Iberiotoxin, a large conductance Ca(2+)-sensitive K(+) (BK(Ca)) channel inhibitor, had little effect on normoxic pressure. Immunoblotting and RT-PCR showed expression of several putative O(2)-sensitive K(+) channels in peripheral fetoplacental vessels. In patch-clamp experiments with smooth muscle cells isolated from peripheral fetoplacental arteries, hypoxia reversibly inhibited K(v) but not BK(Ca) or ATP-dependent currents. We conclude that human fetoplacental vessels constrict in response to hypoxia. This response is largely mediated by hypoxic inhibition of K(v) channels in the smooth muscle of small fetoplacental arteries.
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Affiliation(s)
- Václav Hampl
- Department of Physiology, Charles University Second Medical School, 15000 Prague 5, Czech Republic.
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63
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Olschewski A, Hong Z, Nelson DP, Weir EK. Graded response of K+ current, membrane potential, and [Ca2+]i to hypoxia in pulmonary arterial smooth muscle. Am J Physiol Lung Cell Mol Physiol 2002; 283:L1143-50. [PMID: 12376369 DOI: 10.1152/ajplung.00104.2002] [Citation(s) in RCA: 43] [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] Open
Abstract
Many studies indicate that hypoxic inhibition of some K+ channels in the membrane of the pulmonary arterial smooth muscle cells (PASMCs) plays a part in initiating hypoxic pulmonary vasoconstriction. The sensitivity of the K+ current (I(k)), resting membrane potential (E(m)), and intracellular Ca2+ concentration ([Ca2+]i) of PASMCs to different levels of hypoxia in these cells has not been explored fully. Reducing PO2 levels gradually inhibited steady-state I(k) of rat resistance PASMCs and depolarized the cell membrane. The block of I(k) by hypoxia was voltage dependent in that low O2 tensions (3 and 0% O2) inhibited I(k) more at 0 and -20 mV than at 50 mV. As expected, the hypoxia-sensitive I(k) was also 4-aminopyridine sensitive. Fura 2-loaded PASMCs showed a graded increase in [Ca2+]i as PO2 levels declined. This increase was reduced markedly by nifedipine and removal of extracellular Ca2+. We conclude that, as in the carotid body type I cells, PC-12 pheochromocytoma cells, and cortical neurons, increasing severity of hypoxia causes a proportional decrease in I(k) and E(m) and an increase of [Ca2+]i.
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64
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Abstract
In response to the increase in oxygen tension at birth, the resistance pulmonary arteries dilate, while the ductus arteriosus constricts. Although modulated by the endothelium, these opposite responses are intrinsic to the vascular smooth muscle. While still controversial, it seems likely that during normoxia the production of reactive oxygen species (ROS) increases and the smooth muscle cell cytoplasm is more oxidized in both pulmonary arteries and ductus, compared to hypoxia. However, the effect of changes in the endogenous redox status or the addition of a redox agent, oxidizing or reducing, is exactly opposite in the two vessels. A reducing agent, dithiothreitol, like hypoxia, in the pulmonary artery will inhibit potassium current, cause depolarization, increase cytosolic calcium and lead to contraction. Responses to dithiothreitol in the ductus are opposite and removal of endogenous H(2)O(2) by intracellular catalase in the ductus increases potassium current. Oxygen sensing in both vessels is probably mediated by redox effects on both calcium influx and calcium release from the sarcoplasmic reticulum (SR).
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Affiliation(s)
- E Kenneth Weir
- Department of Medicine, VA Medical Center, Minneapolis, MN 55417, USA.
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65
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Gonzalez C, Sanz-Alfayate G, Agapito MT, Gomez-Niño A, Rocher A, Obeso A. Significance of ROS in oxygen sensing in cell systems with sensitivity to physiological hypoxia. Respir Physiol Neurobiol 2002; 132:17-41. [PMID: 12126693 DOI: 10.1016/s1569-9048(02)00047-2] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Reactive oxygen species (ROS) are oxygen-containing molecular entities which are more potent and effective oxidizing agents than is molecular oxygen itself. With the exception of phagocytic cells, where ROS play an important physiological role in defense reactions, ROS have classically been considered undesirable byproducts of cell metabolism, existing several cellular mechanisms aimed to dispose them. Recently, however, ROS have been considered important intracellular signaling molecules, which may act as mediators or second messengers in many cell functions. This is the proposed role for ROS in oxygen sensing in systems, such as carotid body chemoreceptor cells, pulmonary artery smooth muscle cells, and erythropoietin-producing cells. These unique cells comprise essential parts of homeostatic loops directed to maintain oxygen levels in multicellular organisms in situations of hypoxia. The present article examines the possible significance of ROS in these three cell systems, and proposes a set of criteria that ROS should satisfy for their consideration as mediators in hypoxic transduction cascades. In none of the three cell types do ROS satisfy these criteria, and thus it appears that alternative mechanisms are responsible for the transduction cascades linking hypoxia to the release of neurotransmitters in chemoreceptor cells, contraction in pulmonary artery smooth muscle cells and erythropoietin secretion in erythropoietin producing cells.
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Affiliation(s)
- Constancio Gonzalez
- Departamento de Bioquímica y Biologia Molecular y Fisiología, Facultad de Medicina, Instituto de Biología y Genética Molecular, Universidad de Valladolid y CSIC, 47005 Valladolid, Spain.
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66
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Hogg DS, Davies ARL, McMurray G, Kozlowski RZ. K(V)2.1 channels mediate hypoxic inhibition of I(KV) in native pulmonary arterial smooth muscle cells of the rat. Cardiovasc Res 2002; 55:349-60. [PMID: 12123774 DOI: 10.1016/s0008-6363(02)00411-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
OBJECTIVE To determine whether, in native pulmonary arterial smooth muscle cells (PASMC), K(V)2.1 delayed-rectifying K(+) channels are central to the process of hypoxic pulmonary vasoconstriction. METHODS In this study, we tested for the presence of K(V)2.1 channel transcripts in rat small pulmonary arteries using RT-PCR, and for the protein itself using immunolocalisation. The contribution of K(V)2.1 channels to whole-cell K(V) currents (I(KV)) and their role in hypoxic inhibition of I(KV) in native PASMC was investigated utilising patch-clamp recordings. RESULTS K(V)2.1 mRNA expression and AbK(V)2.1 (anti-K(V)2.1 antibody) protein immunoreactivity were both present in small pulmonary arteries. Dialysis of PASMC with AbK(V)2.1 significantly attenuated I(KV) by 67% at +50 mV. Hypoxia ( approximately 20-30 mmHg) inhibited I(KV) by approximately 70% at +50 mV. Ablation of currents associated with K(V)2.1 using AbK(V)2.1 caused a marked reduction in the amplitude of I(KV). Hypoxia in the presence of the antibody did not affect the magnitude of I(KV). CONCLUSIONS These results indicate that K(V)2.1 channel subunits exist within small pulmonary arteries and conduct a significant part of I(KV) within native PASMC. Furthermore, application of AbK(V)2.1 abolishes hypoxic inhibition of I(KV) in native PASMC suggesting that K(V)2.1 channels play a pivotal role in mediating hypoxic pulmonary vasoconstriction.
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Affiliation(s)
- Dayle S Hogg
- Department of Pharmacology, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
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67
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Dubuis E, Gautier M, Melin A, Rebocho M, Girardin C, Bonnet P, Vandier C. Chronic carbon monoxide enhanced IbTx-sensitive currents in rat resistance pulmonary artery smooth muscle cells. Am J Physiol Lung Cell Mol Physiol 2002; 283:L120-9. [PMID: 12060568 DOI: 10.1152/ajplung.00004.2002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Exogenous carbon monoxide (CO) can induce pulmonary vasodilation by acting directly on pulmonary artery (PA) smooth muscle cells. We investigated the contribution of K+ channels to the regulation of resistance PA resting membrane potential on control (PAC) rats and rats exposed to CO for 3 wk at 530 parts/million, labeled as PACO rats. Whole cell patch-clamp experiments revealed that the resting membrane potential of PACO cells was more negative than that of PAC cells. This was associated with a decrease of membrane resistance in PACO cells. Additional analysis showed that outward current density in PACO cells was higher (50% at +60 mV) than in PAC cells. This was linked to an increase of iberiotoxin (IbTx)-sensitive current. Chronic CO hyperpolarized membrane of pressurized PA from -46.9 +/- 1.2 to -56.4 +/- 2.6 mV. Additionally, IbTx significantly depolarized membrane of smooth muscle cells from PACO arteries but not from PAC arteries. The present study provides initial evidence of an increase of Ca2+-activated K+ current in smooth muscle cells from PA of rats exposed to chronic CO.
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Affiliation(s)
- Eric Dubuis
- Laboratoire de Physiopathologie de la Paroi Artérielle, Faculté de Médecine, 37032 Tours, France
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68
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Abstract
K(+) channels play critical roles in a wide variety of physiological processes, including the regulation of heart rate, muscle contraction, neurotransmitter release, neuronal excitability, insulin secretion, epithelial electrolyte transport, cell volume regulation, and cell proliferation. As such, K(+) channels have been recognized as potential therapeutic drug targets for many years. Unfortunately, progress toward identifying selective K(+) channel modulators has been severely hampered by the need to use native currents and primary cells in the drug-screening process. Today, however, more than 80 K(+) channel and K(+) channel-related genes have been identified, and an understanding of the molecular composition of many important native K(+) currents has begun to emerge. The identification of these molecular K(+) channel drug targets should lead to the discovery of novel drug candidates. A summary of progress is presented.
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Affiliation(s)
- Alan Wickenden
- Icagen Inc., Suite 460, 4222 Emperor Boulevard, Durham, NC 27703, USA.
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Long W, Zhang L, Longo LD. Fetal and adult cerebral artery K(ATP) and K(Ca) channel responses to long-term hypoxia. J Appl Physiol (1985) 2002; 92:1692-701. [PMID: 11896039 DOI: 10.1152/japplphysiol.01110.2001] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
High-altitude long-term hypoxia (LTH) alters cerebral vascular contractile and relaxation responses in both fetus and adult. We tested the hypotheses that LTH-mediated vascular responses were secondary to altered K+ channel function and that in the fetus these responses differ from those of the adult. In middle cerebral arteries (MCA) from both nonpregnant adult and fetal (approximately 140 days gestation) sheep, which were either acclimatized to high altitude (3,820 m) or sea-level controls, we measured norepinephrine (NE)-induced contractions and intracellular Ca2+ concentration ([Ca2+]i) simultaneously, in the presence or absence of different K+ channel openers or blockers. In adult MCA, LTH was associated with approximately 20% decrease in NE-induced tension and [Ca2+]i, with a significant increase in Ca2+ sensitivity. In contrast, in fetal MCA, LTH failed to affect significantly NE-induced contraction or [Ca2+]i but significantly decreased the ATP-sensitive K+ (K(ATP)) channel and Ca2+-activated K+ (K(Ca)) channel-mediated relaxation. The significant effect of K(ATP) and K(Ca) channel activators on the relaxation responses and the fact that K+ channels play a key role in myogenic tone support the hypotheses that K+ channels play an important role in hypoxia-mediated responses. These results also support the hypothesis of significant developmental differences with maturation from fetus to adult.
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Affiliation(s)
- Wen Long
- Center for Perinatal Biology, Department of Physiology, Loma Linda University, School of Medicine, Loma Linda, California 92350, USA.
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70
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Smirnov SV, Beck R, Tammaro P, Ishii T, Aaronson PI. Electrophysiologically distinct smooth muscle cell subtypes in rat conduit and resistance pulmonary arteries. J Physiol 2002; 538:867-78. [PMID: 11826170 PMCID: PMC2290084 DOI: 10.1113/jphysiol.2001.013003] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2001] [Accepted: 10/29/2001] [Indexed: 11/08/2022] Open
Abstract
Pulmonary arteries (PAs), particularly those of the rat, demonstrate a prominent voltage-gated K+ (Kv) current (I(Kv)), which plays an important role in the regulation of the resting potential. No detailed characterization of electrophysiological and pharmacological properties of I(Kv), particularly in resistance PA myocytes (PAMs), has been performed. The aim of the present study was therefore to compare I(Kv) in rat conduit and resistance PAMs using the standard patch clamp technique. We found that 67% of conduit PAMs demonstrated a large, rapidly activating I(Kv) which was potently blocked by 4-aminopyridine (4-AP; IC50, 232 microM), but was almost insensitive to TEA (18% block at 20 mM). Thirty-three percent of cells exhibited a smaller, more slowly activating I(Kv) which was TEA sensitive (IC50, 2.6 mM) but relatively insensitive to 4-AP (37% block at 20 mM). These currents (termed I(Kv1) and I(Kv2), respectively) inactivated over different ranges of potential (V(0.5) = -20.2 vs. -39.1 mV, respectively). All resistance PAMs demonstrated a large, rapidly activating and TEA-insensitive K+ current resembling I(Kv1) (termed I(KvR)), but differing significantly from it with respect to 4-AP sensitivity (IC50, 352 microM), activation rate, and inactivation potential range (V(0.5), -27.4 mV). Thus, cells from conduit PAMs fall into two populations with respect to functional I(Kv) expression, while resistance arteries uniformly demonstrate a third type of I(Kv). Comparison of the properties of the native I(Kv) with those of cloned Kv channel currents suggest that I(Kv1) and I(KvR) are likely to be mediated by Kv1.5-containing homo/heteromultimers, while I(Kv2) involves a Kv2.1 alpha-subunit.
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Affiliation(s)
- Sergey V Smirnov
- Department of Pharmacy and Pharmacology, University of Bath, Claverton Down, Bath BA2 7AY, London SE1 1UL, UK.
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71
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Peers C, Kemp PJ. Acute oxygen sensing: diverse but convergent mechanisms in airway and arterial chemoreceptors. Respir Res 2002; 2:145-9. [PMID: 11686878 PMCID: PMC2002075 DOI: 10.1186/rr51] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2001] [Revised: 02/28/2001] [Accepted: 03/01/2001] [Indexed: 11/16/2022] Open
Abstract
Airway neuroepithelial bodies sense changes in inspired O2, whereas arterial O2 levels are monitored primarily by the carotid body. Both respond to hypoxia by initiating corrective cardiorespiratory reflexes, thereby optimising gas exchange in the face of a potentially deleterious O2 supply. One unifying theme underpinning chemotransduction in these tissues is K+ channel inhibition. However, the transduction components, from O2 sensor to K+ channel, display considerable tissue specificity yet result in analogous end points. Here we highlight how emerging data are contributing to a more complete understanding of O2 chemosensing at the molecular level.
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Affiliation(s)
- C Peers
- Academic Unit of Cardiovascular Medicine, University of Leeds, Leeds, UK.
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72
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Coppock EA, Tamkun MM. Differential expression of K(V) channel alpha- and beta-subunits in the bovine pulmonary arterial circulation. Am J Physiol Lung Cell Mol Physiol 2001; 281:L1350-60. [PMID: 11704530 DOI: 10.1152/ajplung.2001.281.6.l1350] [Citation(s) in RCA: 45] [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] Open
Abstract
Resistance pulmonary arteries constrict in response to hypoxia, whereas conduit pulmonary arteries typically do not respond or dilate slightly. One proposed mechanism for this differential response is the variable expression of pulmonary arterial smooth muscle cell voltage-gated K(+) (K(V)) channel subunits (Kv1.2, Kv2.1, Kv1.5, and Kv3.1b) shown to be O(2) sensitive in heterologous expression systems. In this study, immunoblotting and immunohistochemistry were used to examine the expression of K(V) channel alpha- and beta-subunits in the bovine pulmonary arterial circulation to determine whether differential K(V) channel subunit distribution is responsible for the distinct sensitivities of pulmonary arteries to hypoxia. Surprisingly, there was little difference in the expression levels of Kv1.2, Kv1.5, and Kv2.1 between conduit and resistance pulmonary arteries. In contrast, expression of the Kv3.1b alpha-subunit and Kv beta.1, Kv beta 1.2, and Kv beta 1.3 accessory subunits dramatically increased along the pulmonary arterial tree. The differential expression of all the beta-subunits but of only one of the putative O(2)-sensitive alpha-subunits suggests that the alpha-subunits alone are not the O(2) sensors but further implicates the auxiliary beta-subunits in pulmonary arterial O(2) sensing.
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Affiliation(s)
- E A Coppock
- Department of Physiology, Colorado State University, Fort Collins, Colorado 80523, USA
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73
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74
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Porwol T, Ehleben W, Brand V, Acker H. Tissue oxygen sensor function of NADPH oxidase isoforms, an unusual cytochrome aa3 and reactive oxygen species. RESPIRATION PHYSIOLOGY 2001; 128:331-48. [PMID: 11718762 DOI: 10.1016/s0034-5687(01)00310-3] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
NADPH oxidase isoforms with different gp91phox subunits as well as an unusual cytochrome aa3 with a heme a/a3 relationship of 9:91 are discussed as putative oxygen sensor proteins influencing gene expression and ion channel conductivity. Reactive oxygen species (ROS) are important second messengers of the oxygen sensing signal cascade determining the stability of transcription factors or the gating of ion channels. The formation of ROS by a perinuclear Fenton reaction is imaged by 1 and 2 photon confocal microscopy revealing mitochondrial and non-mitochondrial generation.
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Affiliation(s)
- T Porwol
- Max-Planck-Institut für Molekulare Physiologie, Otto-Hahn Str. 11, D-44227, Dortmund, Germany
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75
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Archer SL, London B, Hampl V, Wu X, Nsair A, Puttagunta L, Hashimoto K, Waite RE, Michelakis ED. Impairment of hypoxic pulmonary vasoconstriction in mice lacking the voltage-gated potassium channel Kv1.5. FASEB J 2001; 15:1801-3. [PMID: 11481235 DOI: 10.1096/fj.00-0649fje] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- S L Archer
- Vascular Biology Group, Department of Medicine, Division of Cardiology, University of Alberta, Alberta, Canada.
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76
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Clanton TL, Klawitter PF. Invited review: Adaptive responses of skeletal muscle to intermittent hypoxia: the known and the unknown. J Appl Physiol (1985) 2001; 90:2476-87. [PMID: 11356816 DOI: 10.1152/jappl.2001.90.6.2476] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Intermittent hypoxia (IH) describes conditions of repeated, transient reductions in O2 that may trigger unique adaptations. Rest periods during IH may avoid potentially detrimental effects of long-term O2 deprivation. For skeletal muscle, IH can occur in conditions of obstructive sleep apnea, transient altitude exposures (with or without exercise), intermittent claudication, cardiopulmonary resuscitation, neonatal blood flow obstruction, and diving responses of marine animals. Although it is likely that adaptations in these conditions vary, some patterns emerge. Low levels of hypoxia shift metabolic enzyme activity toward greater aerobic poise; extreme hypoxia shifts metabolism toward greater anaerobic potential. Some conditions of IH may also inhibit lactate release during exercise. Many related cellular phenomena could be involved in the response, including activation of specific O2 sensors, reactive oxygen and nitrogen species, preconditioning, hypoxia-induced transcription factors, regulation of ion channels, and influences of paracrine/hormonal stimuli. The net effect of a variety of adaptive programs to IH may be to preserve contractile function and cell integrity in hypoxia or anoxia, a response that does not always translate into improvements in exercise performance.
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Affiliation(s)
- T L Clanton
- Department of Internal Medicine (Pulmonary and Critical Care Division), Dorothy Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio 43210, USA.
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77
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Reeve HL, Michelakis E, Nelson DP, Weir EK, Archer SL. Alterations in a redox oxygen sensing mechanism in chronic hypoxia. J Appl Physiol (1985) 2001; 90:2249-56. [PMID: 11356790 DOI: 10.1152/jappl.2001.90.6.2249] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The mechanism of acute hypoxic pulmonary vasoconstriction (HPV) may involve the inhibition of several voltage-gated K+ channels in pulmonary artery smooth muscle cells. Changes in PO2 can either be sensed directly by the channel(s) or be transmitted to the channel via a redox-based effector mechanism. In control lungs, hypoxia and rotenone acutely decrease production of activated oxygen species, inhibit K+ channels, and cause constriction. Two-day and 3-wk chronic hypoxia (CH) resulted in a decrease in basal activated oxygen species levels, an increase in reduced glutathione, and loss of HPV and rotenone-induced constriction. In contrast, 4-aminopyridine- and KCl-mediated constrictions were preserved. After 3-wk CH, pulmonary arterial smooth muscle cell membrane potential was depolarized, K+ channel density was reduced, and acute hypoxic inhibition of whole cell K+ current was lost. In addition, Kv1.5 and Kv2.1 channel protein was decreased. These data suggest that chronic reduction of the cytosol occurs before changes in K+ channel expression. HPV may be attenuated in CH because of an impaired redox sensor.
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Affiliation(s)
- H L Reeve
- Department of Medicine, University of Minnesota, Minneapolis 55455, USA
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78
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Coppock EA, Martens JR, Tamkun MM. Molecular basis of hypoxia-induced pulmonary vasoconstriction: role of voltage-gated K+ channels. Am J Physiol Lung Cell Mol Physiol 2001; 281:L1-12. [PMID: 11404238 DOI: 10.1152/ajplung.2001.281.1.l1] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The hypoxia-induced membrane depolarization and subsequent constriction of small resistance pulmonary arteries occurs, in part, via inhibition of vascular smooth muscle cell voltage-gated K+ (KV) channels open at the resting membrane potential. Pulmonary arterial smooth muscle cell KV channel expression, antibody-based dissection of the pulmonary arterial smooth muscle cell K+ current, and the O2 sensitivity of cloned KV channels expressed in heterologous expression systems have all been examined to identify the molecular components of the pulmonary arterial O2-sensitive KV current. Likely components include Kv2.1/Kv9.3 and Kv1.2/Kv1.5 heteromeric channels and the Kv3.1b alpha-subunit. Although the mechanism of KV channel inhibition by hypoxia is unknown, it appears that KV alpha-subunits do not sense O2 directly. Rather, they are most likely inhibited through interaction with an unidentified O2 sensor and/or beta-subunit. This review summarizes the role of KV channels in hypoxic pulmonary vasoconstriction, the recent progress toward the identification of KV channel subunits involved in this response, and the possible mechanisms of KV channel regulation by hypoxia.
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Affiliation(s)
- E A Coppock
- Department of Physiology, Colorado State University, Fort Collins, Colorado 80523, USA
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79
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Abstract
Physiological adaptation to acute hypoxia involves oxygen-sensing by a variety of specialized cells including carotid body type I cells, pulmonary neuroepithelial body cells, pulmonary artery myocytes and foetal adrenomedullary chromaffin cells. Hypoxia induces depolarization by closing a specific set of potassium channels and triggers cellular responses. Molecular biology strategies have recently allowed the identification of the K+ channel subunits expressed in these specialized cells. Several voltage-gated K+ channel subunits comprising six transmembrane segments and a single pore domain (Kv1.2, Kv1.5, Kv2.1, Kv3.1, Kv3.3, Kv4.2 and Kv9.3) are reversibly blocked by hypoxia when expressed in heterologous expression systems. Additionally, the background K+ channel subunit TASK-1, which comprises four transmembrane segments and two pore domains, is also involved in both oxygen- and acid-sensing in peripheral chemoreceptors. Progress is currently being made to identify the oxygen sensors. Regulatory beta subunits may play an important role in the modulation of Kv channel subunits by oxygen.
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Affiliation(s)
- A J Patel
- Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France
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80
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Abstract
O2 sensing is a fundamental biological process necessary for adaptation of living organisms to variable habitats and physiological situations. Cellular responses to hypoxia can be acute or chronic. Acute responses rely mainly on O2-regulated ion channels, which mediate adaptive changes in cell excitability, contractility, and secretory activity. Chronic responses depend on the modulation of hypoxia-inducible transcription factors, which determine the expression of numerous genes encoding enzymes, transporters and growth factors. O2-regulated ion channels and transcription factors are part of a widely operating signaling system that helps provide sufficient O2 to the tissues and protect the cells against damage due to O2 deficiency. Despite recent advances in the molecular characterization of O2-regulated ion channels and hypoxia-inducible factors, several unanswered questions remain regarding the nature of the O2 sensor molecules and the mechanisms of interaction between the sensors and the effectors. Current models of O2 sensing are based on either a heme protein capable of reversibly binding O2 or the production of oxygen reactive species by NAD(P)H oxidases and mitochondria. Complete molecular characterization of the hypoxia signaling pathways will help elucidate the differential sensitivity to hypoxia of the various cell types and the gradation of the cellular responses to variable levels of PO2. A deeper understanding of the cellular mechanisms of O2 sensing will facilitate the development of new pharmacological tools effective in the treatment of diseases such as stroke or myocardial ischemia caused by localized deficits of O2.
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Affiliation(s)
- J Lopez-Barneo
- Departamento de Fisiología, Facultad de Medicina y Hospital Universitario Virgen del Rocío, Universidad de Sevilla, Sevilla, E-41009, Spain.
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81
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Abstract
BACKGROUND Oxygen is a potent stimulus for pulmonary vasodilation. Potassium channels have been implicated as both sensors and effectors for oxygen-induced changes in pulmonary vascular tone. We have examined the effect of potassium channel blockers on oxygen-induced vasodilation in isolated pulmonary arterioles from fetal rats at term. MATERIALS AND METHODS Third generation pulmonary arterioles were isolated from fetal rats on Day 22 of gestation, cannulated, pressurized at constant distending pressures, and preconstricted by suffusion with a salt solution bubbled with a "hypoxic gas" mixture (pO(2) <or=50 mm Hg). Oxygen-induced vasodilation was measured as percentage reversal of the "hypoxic" vasoconstriction after 30 min of suffusion with "normoxic" solution (pO(2) 90-145 mm Hg). Responses were recorded in the absence of blockers (controls) or in the presence of a voltage-gated K(+) channel (K(v)) blocker, 4-aminopyridine; an ATP-sensitive K(+) channel (K(ATP)) blocker, glibenclamide; a Ca(2+)-activated K(+) channel (K(Ca)) blocker, charybdotoxin; or a nonspecific K(+) channel blocker, tetraethylammonium. RESULTS In control arterioles, normoxic suffusion for 30 min reversed hypoxic preconstriction by 83 +/- 19%. 4-aminopyridine significantly attenuated (44 +/- 9%), and glibenclamide and charybdotoxin had no effect (80 +/- 16 and 79 +/- 20%) on the magnitude of normoxic vasodilation. CONCLUSIONS Our results are consistent with a contribution of K(v) channels, but not K(ATP) or K(Ca) channels, to oxygen-induced vasodilation in third generation pulmonary arterioles from term fetal rats.
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Affiliation(s)
- J R Gosche
- Department of Surgery, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
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82
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Platoshyn O, Yu Y, Golovina VA, McDaniel SS, Krick S, Li L, Wang JY, Rubin LJ, Yuan JX. Chronic hypoxia decreases K(V) channel expression and function in pulmonary artery myocytes. Am J Physiol Lung Cell Mol Physiol 2001; 280:L801-12. [PMID: 11238022 DOI: 10.1152/ajplung.2001.280.4.l801] [Citation(s) in RCA: 124] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Activity of voltage-gated K+ (KV) channels regulates membrane potential (E(m)) and cytosolic free Ca2+ concentration ([Ca2+](cyt)). A rise in ([Ca2+](cyt))in pulmonary artery (PA) smooth muscle cells (SMCs) triggers pulmonary vasoconstriction and stimulates PASMC proliferation. Chronic hypoxia (PO(2) 30-35 mmHg for 60-72 h) decreased mRNA expression of KV channel alpha-subunits (Kv1.1, Kv1.5, Kv2.1, Kv4.3, and Kv9.3) in PASMCs but not in mesenteric artery (MA) SMCs. Consistently, chronic hypoxia attenuated protein expression of Kv1.1, Kv1.5, and Kv2.1; reduced KV current [I(KV)]; caused E(m) depolarization; and increased ([Ca2+](cyt)) in PASMCs but negligibly affected KV channel expression, increased I(KV), and induced hyperpolarization in MASMCs. These results demonstrate that chronic hypoxia selectively downregulates KV channel expression, reduces I(KV), and induces E(m) depolarization in PASMCs. The subsequent rise in ([Ca2+](cyt)) plays a critical role in the development of pulmonary vasoconstriction and medial hypertrophy. The divergent effects of hypoxia on KV channel alpha-subunit mRNA expression in PASMCs and MASMCs may result from different mechanisms involved in the regulation of KV channel gene expression.
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Affiliation(s)
- O Platoshyn
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, UCSD Medical Center, 200 W. Arbor Dr., San Diego, CA 92103-8382, USA
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83
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Sweeney M, Yuan JX. Hypoxic pulmonary vasoconstriction: role of voltage-gated potassium channels. Respir Res 2000; 1:40-8. [PMID: 11667964 PMCID: PMC59541 DOI: 10.1186/rr11] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2000] [Revised: 06/15/2000] [Accepted: 06/15/2000] [Indexed: 12/25/2022] Open
Abstract
Activity of voltage-gated potassium (Kv) channels controls membrane potential, which subsequently regulates cytoplasmic free calcium concentration ([Ca2+]cyt) in pulmonary artery smooth muscle cells (PASMCs). Acute hypoxia inhibits Kv channel function in PASMCs, inducing membrane depolarization and a rise in [Ca2+ ]cyt that triggers vasoconstriction. Prolonged hypoxia inhibits expression of Kv channels and reduces Kv channel currents in PASMCs. The consequent membrane depolarization raises [Ca2+]cyt, thus stimulating PASMC proliferation. The present review discusses recent evidence for the involvement of Kv channels in initiation of hypoxic pulmonary vasoconstriction and in chronic hypoxia-induced pulmonary hypertension.
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Affiliation(s)
- M Sweeney
- Department of Medicine, University of California, San Diego, California, USA.
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