1
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Saha PS, Knecht TM, Arrick DM, Watt MJ, Scholl JL, Mayhan WG. Prenatal exposure to alcohol impairs responses of cerebral arterioles to activation of potassium channels: Role of oxidative stress. ALCOHOL, CLINICAL & EXPERIMENTAL RESEARCH 2023; 47:87-94. [PMID: 36446735 PMCID: PMC9974881 DOI: 10.1111/acer.14980] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Revised: 10/24/2022] [Accepted: 11/17/2022] [Indexed: 11/23/2022]
Abstract
BACKGROUND Potassium channels play an important role in the basal tone and dilation of cerebral resistance arterioles in response to many stimuli. However, the effect of prenatal alcohol exposure (PAE) on specific potassium channel function remains unknown. The first goal of this study was to determine the influence of PAE on the reactivity of cerebral arterioles to activation of ATP-sensitive potassium (KATP ) and BK channels. Our second goal was to determine whether oxidative stress contributed to potassium channel dysfunction of cerebral arterioles following PAE. METHODS We fed Sprague-Dawley dams a liquid diet with or without alcohol (3% EtOH) for the duration of their pregnancy (21 to 23 days). We examined in vivo responses of cerebral arterioles in control and PAE male and female offspring (14 to 16 weeks after birth) to activators of potassium channels (Iloprost [BK channels] and pinacidil [KATP channels]), before and following inhibition of oxidative stress with apocynin. RESULTS We found that PAE impaired dilation of cerebral arterioles in response to activation of potassium channels with iloprost and pinacidil, and this impairment was similar in male and female rats. In addition, treatment with apocynin reversed the impaired vasodilation to iloprost and pinacidil in PAE rats to levels observed in control rats. This effect of apocynin also was similar in male and female rats. CONCLUSIONS PAE induces dysfunction in the ability of specific potassium channels to dilate cerebral arterioles which appears to be mediated by an increase in oxidative stress. We suggest that these alterations in potassium channel function may contribute to the pathogenesis of cerebral vascular abnormalities and/or behavioral/cognitive deficits observed in fetal alcohol spectrum disorders.
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Affiliation(s)
- Partha S. Saha
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069
| | - Tiffany M. Knecht
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069
| | - Denise M. Arrick
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069
| | - Michael J. Watt
- Department of Anatomy, University of Otago, Dunedin, New Zealand
| | - Jamie L. Scholl
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069
| | - William G. Mayhan
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069
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2
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Sytha SP, Self TS, Heaps CL. K + channels in the coronary microvasculature of the ischemic heart. CURRENT TOPICS IN MEMBRANES 2022; 90:141-166. [PMID: 36368873 PMCID: PMC10494550 DOI: 10.1016/bs.ctm.2022.09.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Ischemic heart disease is the leading cause of death and a major public health and economic burden worldwide with expectations of predicted growth in the foreseeable future. It is now recognized clinically that flow-limiting stenosis of the large coronary conduit arteries as well as microvascular dysfunction in the absence of severe stenosis can each contribute to the etiology of ischemic heart disease. The primary site of coronary vascular resistance, and control of subsequent coronary blood flow, is found in the coronary microvasculature, where small changes in radius can have profound impacts on myocardial perfusion. Basal active tone and responses to vasodilators and vasoconstrictors are paramount in the regulation of coronary blood flow and adaptations in signaling associated with ion channels are a major factor in determining alterations in vascular resistance and thereby myocardial blood flow. K+ channels are of particular importance as contributors to all aspects of the regulation of arteriole resistance and control of perfusion into the myocardium because these channels dictate membrane potential, the resultant activity of voltage-gated calcium channels, and thereby, the contractile state of smooth muscle. Evidence also suggests that K+ channels play a significant role in adaptations with cardiovascular disease states. In this review, we highlight our research examining the role of K+ channels in ischemic heart disease and adaptations with exercise training as treatment, as well as how our findings have contributed to this area of study.
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Affiliation(s)
- Sharanee P Sytha
- Department of Physiology and Pharmacology, School of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, United States
| | - Trevor S Self
- Department of Physiology and Pharmacology, School of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, United States
| | - Cristine L Heaps
- Department of Physiology and Pharmacology, School of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, United States; Michael E. DeBakey Institute for Comparative Cardiovascular Science and Biomedical Devices, School of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, United States.
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3
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Reid C, Romero M, Chang SB, Osman N, Puglisi JL, Wilson CG, Blood AB, Zhang L, Wilson SM. Long-Term Hypoxia Negatively Influences Ca2+ Signaling in Basilar Arterial Myocytes of Fetal and Adult Sheep. Front Physiol 2022; 12:760176. [PMID: 35115953 PMCID: PMC8804533 DOI: 10.3389/fphys.2021.760176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2021] [Accepted: 10/25/2021] [Indexed: 11/21/2022] Open
Abstract
Cerebral arterial vasoreactivity is vital to the regulation of cerebral blood flow. Depolarization of arterial myocytes elicits whole-cell Ca2+ oscillations as well as subcellular Ca2+ sparks due to activation of ryanodine receptors on the sarcoplasmic reticulum. Previous evidence illustrates that contraction of cerebral arteries from sheep and underlying Ca2+ signaling pathways are modified by age and that long-term hypoxia (LTH) causes aberrations in Ca2+ signaling pathways and downstream effectors impacting vasoregulation. We hypothesize that age and LTH affect the influence of membrane depolarization on whole-cell intracellular Ca2+ oscillations and sub-cellular Ca2+ spark activity in cerebral arteries. To test this hypothesis, we examined Ca2+ oscillatory and spark activities using confocal fluorescence imaging techniques of Fluo-4 loaded basilar arterial myocytes of low- and high-altitude term fetal (∼145 days of gestation) and adult sheep, where high-altitude pregnant and non-pregnant sheep were placed at 3,801 m for >100 days. Ca2+ oscillations and sparks were recorded using an in situ preparation evaluated in the absence or presence of 30 mM K+ (30K) to depolarize myocytes. Myocytes from adult animals tended to have a lower basal rate of whole-cell Ca2+ oscillatory activity and 30K increased the activity within cells. LTH decreased the ability of myocytes to respond to depolarization independent of age. These observations illustrate that both altitude and age play a role in affecting whole-cell and localized Ca2+ signaling, which are important to arterial vasoreactivity and cerebral blood flow.
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Affiliation(s)
- Casey Reid
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA, United States
| | - Monica Romero
- Advanced Imaging and Microscopy Core, Loma Linda University School of Medicine, Loma Linda, CA, United States
| | - Stephanie B. Chang
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA, United States
| | - Noah Osman
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA, United States
| | - Jose L. Puglisi
- Department of Biostatistics, School of Medicine, California Northstate University, Elk Grove, CA, United States
| | - Christopher G. Wilson
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA, United States
| | - Arlin B. Blood
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA, United States
| | - Lubo Zhang
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA, United States
| | - Sean M. Wilson
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA, United States
- Advanced Imaging and Microscopy Core, Loma Linda University School of Medicine, Loma Linda, CA, United States
- *Correspondence: Sean M. Wilson,
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4
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Sancho M, Kyle BD. The Large-Conductance, Calcium-Activated Potassium Channel: A Big Key Regulator of Cell Physiology. Front Physiol 2021; 12:750615. [PMID: 34744788 PMCID: PMC8567177 DOI: 10.3389/fphys.2021.750615] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Accepted: 09/29/2021] [Indexed: 12/01/2022] Open
Abstract
Large-conductance Ca2+-activated K+ channels facilitate the efflux of K+ ions from a variety of cells and tissues following channel activation. It is now recognized that BK channels undergo a wide range of pre- and post-translational modifications that can dramatically alter their properties and function. This has downstream consequences in affecting cell and tissue excitability, and therefore, function. While finding the “silver bullet” in terms of clinical therapy has remained elusive, ongoing research is providing an impressive range of viable candidate proteins and mechanisms that associate with and modulate BK channel activity, respectively. Here, we provide the hallmarks of BK channel structure and function generally, and discuss important milestones in the efforts to further elucidate the diverse properties of BK channels in its many forms.
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Affiliation(s)
- Maria Sancho
- Department of Pharmacology, University of Vermont, Burlington, VT, United States
| | - Barry D Kyle
- Department of Pathology and Laboratory Medicine, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada
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5
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Abstract
The cerebral microcirculation undergoes dynamic changes in parallel with the development of neurons, glia, and their energy metabolism throughout gestation and postnatally. Cerebral blood flow (CBF), oxygen consumption, and glucose consumption are as low as 20% of adult levels in humans born prematurely but eventually exceed adult levels at ages 3 to 11 years, which coincide with the period of continued brain growth, synapse formation, synapse pruning, and myelination. Neurovascular coupling to sensory activation is present but attenuated at birth. By 2 postnatal months, the increase in CBF often is disproportionately smaller than the increase in oxygen consumption, in contrast to the relative hyperemia seen in adults. Vascular smooth muscle myogenic tone increases in parallel with developmental increases in arterial pressure. CBF autoregulatory response to increased arterial pressure is intact at birth but has a more limited range with arterial hypotension. Hypoxia-induced vasodilation in preterm fetal sheep with low oxygen consumption does not sustain cerebral oxygen transport, but the response becomes better developed for sustaining oxygen transport by term. Nitric oxide tonically inhibits vasomotor tone, and glutamate receptor activation can evoke its release in lambs and piglets. In piglets, astrocyte-derived carbon monoxide plays a central role in vasodilation evoked by glutamate, ADP, and seizures, and prostanoids play a large role in endothelial-dependent and hypercapnic vasodilation. Overall, homeostatic mechanisms of CBF regulation in response to arterial pressure, neuronal activity, carbon dioxide, and oxygenation are present at birth but continue to develop postnatally as neurovascular signaling pathways are dynamically altered and integrated. © 2021 American Physiological Society. Compr Physiol 11:1-62, 2021.
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6
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Mukherjee S, Sikdar SK. Intracellular activation of full-length human TREK-1 channel by hypoxia, high lactate, and low pH denotes polymodal integration by ischemic factors. Pflugers Arch 2020; 473:167-183. [PMID: 33025137 DOI: 10.1007/s00424-020-02471-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 09/18/2020] [Accepted: 09/30/2020] [Indexed: 10/23/2022]
Abstract
TREK-1, a two-pore domain potassium channel, responds to ischemic levels of intracellular lactate and acidic pH to provide neuroprotection. There are two splice variants of hTREK1: the shorter splice variant having a shorter N-terminus compared with the full-length hTREK1 with similar C-terminus sequence that is widely expressed in the brain. The shorter variant was reported to be irresponsive to hypoxia-a condition attributed to ischemia, which has put the neuroprotective role of hTREK-1 channel into question. Since interaction between N- and C-terminus of different ion channels shapes their gating, we re-examined the sensitivity of the full-length as well as the shorter hTREK-1 channel to intracellular hypoxia along with lactate. Single-channel data obtained from the excised inside-out patches of the full-length channel expressed in HEK293 cells indicated an increase in activity as opposed to a decrease in activity in the shorter isoform. However, both the isoforms showed an increase in activity under combined hypoxia, 20mM lactate, and low pH 6 condition, albeit with subtle differences in their individual actions, confirming the neuroprotective role played by hTREK-1 irrespective of the differences in the N-terminus among the splice variants. Furthermore, E321A mutant that disrupts the interaction of the C-terminus with the membrane showed a decrease in activity with hypoxia indicating the importance of the C-terminus in the hypoxic response of the full-length hTREK-1. We propose an increase in activity of both the splice variants of hTREK-1 in combined hypoxia, high lactate, and low pH conditions typically associated with ischemia provides neuroprotection.
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Affiliation(s)
- Sourajit Mukherjee
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka, 560012, India
| | - Sujit Kumar Sikdar
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka, 560012, India.
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7
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Hydrogen Protons Modulate Perivascular Axo–axonal Interactions in the Middle Cerebral Artery of Rats. J Cardiovasc Pharmacol 2020; 76:112-121. [DOI: 10.1097/fjc.0000000000000838] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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8
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Rosenberry R, Nelson MD. Reactive hyperemia: a review of methods, mechanisms, and considerations. Am J Physiol Regul Integr Comp Physiol 2020; 318:R605-R618. [PMID: 32022580 DOI: 10.1152/ajpregu.00339.2019] [Citation(s) in RCA: 111] [Impact Index Per Article: 27.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Reactive hyperemia is a well-established technique for noninvasive assessment of peripheral microvascular function and a predictor of all-cause and cardiovascular morbidity and mortality. In its simplest form, reactive hyperemia represents the magnitude of limb reperfusion following a brief period of ischemia induced by arterial occlusion. Over the past two decades, investigators have employed a variety of methods, including brachial artery velocity by Doppler ultrasound, tissue reperfusion by near-infrared spectroscopy, limb distension by venous occlusion plethysmography, and peripheral artery tonometry, to measure reactive hyperemia. Regardless of the technique used to measure reactive hyperemia, blunted reactive hyperemia is believed to reflect impaired microvascular function. With the advent of several technological advancements, together with an increased interest in the microcirculation, reactive hyperemia is becoming more common as a research tool and is widely used across multiple disciplines. With this in mind, we sought to review the various methodologies commonly used to assess reactive hyperemia and current mechanistic pathways believed to contribute to reactive hyperemia and reflect on several methodological considerations.
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Affiliation(s)
- Ryan Rosenberry
- Department of Kinesiology, University of Texas at Arlington, Arlington, Texas
| | - Michael D Nelson
- Department of Kinesiology, University of Texas at Arlington, Arlington, Texas.,Department of Bioengineering, University of Texas at Arlington, Arlington, Texas
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9
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Racine ML, Crecelius AR, Luckasen GJ, Larson DG, Dinenno FA. Inhibition of Na + /K + -ATPase and K IR channels abolishes hypoxic hyperaemia in resting but not contracting skeletal muscle of humans. J Physiol 2018; 596:3371-3389. [PMID: 29603743 DOI: 10.1113/jp275913] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2018] [Accepted: 03/27/2018] [Indexed: 12/16/2022] Open
Abstract
KEY POINTS Increasing blood flow (hyperaemia) to exercising muscle helps match oxygen delivery and metabolic demand. During exercise in hypoxia, there is a compensatory increase in muscle hyperaemia that maintains oxygen delivery and tissue oxygen consumption. Nitric oxide (NO) and prostaglandins (PGs) contribute to around half of the augmented hyperaemia during hypoxic exercise, although the contributors to the remaining response are unknown. In the present study, inhibiting NO, PGs, Na+ /K+ -ATPase and inwardly rectifying potassium (KIR ) channels did not blunt augmented hyperaemia during hypoxic exercise beyond previous observations with NO/PG block alone. Furthermore, although inhibition of only Na+ /K+ -ATPase and KIR channels abolished hyperaemia during hypoxia at rest, it had no effect on augmented hyperaemia during hypoxic exercise. This is the first study in humans to demonstrate that Na+ /K+ -ATPase and KIR channel activation is required for augmented muscle hyperaemia during hypoxia at rest but not during hypoxic exercise, thus providing new insight into vascular control. ABSTRACT Exercise hyperaemia in hypoxia is augmented relative to the same exercise intensity in normoxia. During moderate-intensity handgrip exercise, endothelium-derived nitric oxide (NO) and vasodilating prostaglandins (PGs) contribute to ∼50% of the augmented forearm blood flow (FBF) response to hypoxic exercise (HypEx), although the mechanism(s) underlying the remaining response are unclear. We hypothesized that combined inhibition of NO, PGs, Na+ /K+ -ATPase and inwardly rectifying potassium (KIR ) channels would abolish the augmented hyperaemic response in HypEx. In healthy young adults, FBF responses were measured (Doppler ultrasound) and forearm vascular conductance was calculated during 5 min of rhythmic handgrip exercise at 20% maximum voluntary contraction under regional sympathoadrenal inhibition in normoxia and isocapnic HypEx (O2 saturation ∼80%). Compared to control, combined inhibition of NO, PGs, Na+ /K+ -ATPase and KIR channels (l-NMMA + ketorolac + ouabain + BaCl2; Protocol 1; n = 10) blunted the compensatory increase in FBF during HypEx by ∼50% (29 ± 6 mL min-1 vs. 62 ± 8 mL min-1 , respectively, P < 0.05). By contrast, ouabain + BaCl2 alone (Protocol 2; n = 10) did not affect this augmented hyperaemic response (50 ± 11 mL min-1 vs. 60 ± 13 mL min-1 , respectively, P > 0.05). However, the blocked condition in both protocols abolished the hyperaemic response to hypoxia at rest (P < 0.05). We conclude that activation of Na+ /K+ -ATPase and KIR channels is involved in the hyperaemic response to hypoxia at rest, although it does not contribute to the augmented exercise hyperaemia during hypoxia in humans.
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Affiliation(s)
- Matthew L Racine
- Human Cardiovascular Physiology Laboratory, Department of Health and Exercise Science, Colorado State University, Fort Collins, CO, USA
| | - Anne R Crecelius
- Human Cardiovascular Physiology Laboratory, Department of Health and Exercise Science, Colorado State University, Fort Collins, CO, USA
| | - Gary J Luckasen
- Cardiovascular Research Center, Colorado State University, Fort Collins, CO, USA.,Medical Center of the Rockies Foundation, University of Colorado Health System, Loveland, CO, USA
| | - Dennis G Larson
- Medical Center of the Rockies Foundation, University of Colorado Health System, Loveland, CO, USA
| | - Frank A Dinenno
- Human Cardiovascular Physiology Laboratory, Department of Health and Exercise Science, Colorado State University, Fort Collins, CO, USA.,Cardiovascular Research Center, Colorado State University, Fort Collins, CO, USA
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10
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Harder DR, Rarick KR, Gebremedhin D, Cohen SS. Regulation of Cerebral Blood Flow: Response to Cytochrome P450 Lipid Metabolites. Compr Physiol 2018; 8:801-821. [PMID: 29687906 DOI: 10.1002/cphy.c170025] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
There have been numerous reviews related to the cerebral circulation. Most of these reviews are similar in many ways. In the present review, we thought it important to provide an overview of function with specific attention to details of cerebral arterial control related to brain homeostasis, maintenance of neuronal energy demands, and a unique perspective related to the role of astrocytes. A coming review in this series will discuss cerebral vascular development and unique properties of the neonatal circulation and developing brain, thus, many aspects of development are missing here. Similarly, a review of the response of the brain and cerebral circulation to heat stress has recently appeared in this series (8). By trying to make this review unique, some obvious topics were not discussed in lieu of others, which are from recent and provocative research such as endothelium-derived hyperpolarizing factor, circadian regulation of proteins effecting cerebral blood flow, and unique properties of the neurovascular unit. © 2018 American Physiological Society. Compr Physiol 8:801-821, 2018.
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Affiliation(s)
- David R Harder
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.,Clement J. Zablocki VA Medical Center, Milwaukee, Wisconsin, USA
| | - Kevin R Rarick
- Department of Pediatrics, Division of Critical Care, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Debebe Gebremedhin
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Susan S Cohen
- Department of Pediatrics, Division of Neonatology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
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11
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Gebremedhin D, Zhang DX, Weihrauch D, Uche NN, Harder DR. Detection of TRPV4 channel current-like activity in Fawn Hooded hypertensive (FHH) rat cerebral arterial muscle cells. PLoS One 2017; 12:e0176796. [PMID: 28472069 PMCID: PMC5417564 DOI: 10.1371/journal.pone.0176796] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Accepted: 04/17/2017] [Indexed: 11/18/2022] Open
Abstract
The transient receptor potential vallinoid type 4 (TRPV4) is a calcium entry channel known to modulate vascular function by mediating endothelium–dependent vasodilation. The present study investigated if isolated cerebral arterial myocytes of the Fawn Hooded hypertensive (FHH) rat, known to display exaggerated KCa channel current activity and impaired myogenic tone, express TRPV4 channels at the transcript and protein level and exhibit TRPV4-like single-channel cationic current activity. Reverse transcription polymerase chain reaction (RT-PCR), Western blot, and immunostaining analysis detected the expression of mRNA transcript and translated protein of TRPV4 channel in FHH rat cerebral arterial myocytes. Patch clamp recording of single-channel current activity identified the presence of a single-channel cationic current with unitary conductance of ~85 pS and ~96 pS at hyperpolarizing and depolarizing potentials, respectively, that was inhibited by the TRPV4 channel antagonist RN 1734 or HC 067074 and activated by the potent TRPV4 channel agonist GSK1016790A. Application of negative pressure via the interior of the patch pipette increased the NPo of the TRPV4-like single-channel cationic current recorded in cell-attached patches at a patch potential of 60 mV that was inhibited by prior application of the TRPV4 channel antagonist RN 1734 or HC 067047. Treatment with the TRPV4 channel agonist GSK1016790A caused concentration-dependent increase in the NPo of KCa single-channel current recorded in cell-attached patches of cerebral arterial myocytes at a patch potential of 40 mV, which was not influenced by pretreatment with the voltage-gated L-type Ca2+ channel blocker nifedipine or the T-type Ca2+ channel blocker Ni2+. These findings demonstrate that FHH rat cerebral arterial myocytes express mRNA transcript and translated protein for TRPV4 channel and display TRPV4-like single-channel cationic current activity that was stretch-sensitive and activation of which increased the open state probability of KCa single-channel current in these arterial myocytes.
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Affiliation(s)
- Debebe Gebremedhin
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
- Cardiovascular Research Center, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
- * E-mail:
| | - David X. Zhang
- Cardiovascular Research Center, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
- Department of Medicine and, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
| | - Dorothee Weihrauch
- Department of Anesthesiology Medical College of Wisconsin, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
| | - Nnamdi N. Uche
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
| | - David R. Harder
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
- Cardiovascular Research Center, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
- Clement Zablocki VA Medical Center, Milwaukee, Wisconsin, United States of America
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12
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Hashad AM, Mazumdar N, Romero M, Nygren A, Bigdely-Shamloo K, Harraz OF, Puglisi JL, Vigmond EJ, Wilson SM, Welsh DG. Interplay among distinct Ca 2+ conductances drives Ca 2+ sparks/spontaneous transient outward currents in rat cerebral arteries. J Physiol 2016; 595:1111-1126. [PMID: 27805790 DOI: 10.1113/jp273329] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Accepted: 10/30/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Distinct Ca2+ channels work in a coordinated manner to grade Ca2+ spark/spontaneous transient outward currents (STOCs) in rat cerebral arteries. The relative contribution of each Ca2+ channel to Ca2+ spark/STOC production depends upon their biophysical properties and the resting membrane potential of smooth muscle. Na+ /Ca2+ exchanger, but not TRP channels, can also facilitate STOC production. ABSTRACT Ca2+ sparks are generated in a voltage-dependent manner to initiate spontaneous transient outward currents (STOCs), events that moderate arterial constriction. In this study, we defined the mechanisms by which membrane depolarization increases Ca2+ sparks and subsequent STOC production. Using perforated patch clamp electrophysiology and rat cerebral arterial myocytes, we monitored STOCs in the presence and absence of agents that modulate Ca2+ entry. Beginning with CaV 3.2 channel inhibition, Ni2+ was shown to decrease STOC frequency in cells held at hyperpolarized (-40 mV) but not depolarized (-20 mV) voltages. In contrast, nifedipine, a CaV 1.2 inhibitor, markedly suppressed STOC frequency at -20 mV but not -40 mV. These findings aligned with the voltage-dependent profiles of L- and T-type Ca2+ channels. Furthermore, computational and experimental observations illustrated that Ca2+ spark production is intimately tied to the activity of both conductances. Intriguingly, this study observed residual STOC production at depolarized voltages that was independent of CaV 1.2 and CaV 3.2. This residual component was insensitive to TRPV4 channel modulation and was abolished by Na+ /Ca2+ exchanger blockade. In summary, our work highlights that the voltage-dependent triggering of Ca2+ sparks/STOCs is not tied to a single conductance but rather reflects an interplay among multiple Ca2+ permeable pores with distinct electrophysiological properties. This integrated orchestration enables smooth muscle to grade Ca2+ spark/STOC production and thus precisely tune negative electrical feedback.
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Affiliation(s)
- Ahmed M Hashad
- Department of Physiology and Pharmacology, Hotchkiss Brain and Libin Cardiovascular Institute, University of Calgary, Alberta, Canada
| | - Neil Mazumdar
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Monica Romero
- Department of Basic Sciences, Division of Pharmacology, Loma Linda University, CA, USA
| | - Anders Nygren
- Department of Electrical and Computer Engineering, University of Calgary, Calgary, Alberta, Canada
| | - Kamran Bigdely-Shamloo
- Department of Physiology and Pharmacology, Hotchkiss Brain and Libin Cardiovascular Institute, University of Calgary, Alberta, Canada.,Department of Electrical and Computer Engineering, University of Calgary, Calgary, Alberta, Canada
| | - Osama F Harraz
- Department of Pharmacology, University of Vermont, Burlington, VT, USA
| | - Jose L Puglisi
- California Northstate University College of Medicine, CA, USA
| | - Edward J Vigmond
- Department of Electrical and Computer Engineering, University of Calgary, Calgary, Alberta, Canada.,LIRYC Institute and Lab IMB, University of Bordeaux, Bordeaux, France
| | - Sean M Wilson
- Department of Basic Sciences, Division of Pharmacology, Loma Linda University, CA, USA
| | - Donald G Welsh
- Department of Physiology and Pharmacology, Hotchkiss Brain and Libin Cardiovascular Institute, University of Calgary, Alberta, Canada.,Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
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13
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Jackson WF. Arteriolar oxygen reactivity: where is the sensor and what is the mechanism of action? J Physiol 2016; 594:5055-77. [PMID: 27324312 PMCID: PMC5023707 DOI: 10.1113/jp270192] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2015] [Accepted: 06/13/2016] [Indexed: 01/02/2023] Open
Abstract
Arterioles in the peripheral microcirculation are exquisitely sensitive to changes in PO2 in their environment: increases in PO2 cause vasoconstriction while decreases in PO2 result in vasodilatation. However, the cell type that senses O2 (the O2 sensor) and the signalling pathway that couples changes in PO2 to changes in arteriolar tone (the mechanism of action) remain unclear. Many (but not all) ex vivo studies of isolated cannulated resistance arteries and large, first-order arterioles support the hypothesis that these vessels are intrinsically sensitive to PO2 with the smooth muscle, endothelial cells, or red blood cells serving as the O2 sensor. However, in situ studies testing these hypotheses in downstream arterioles have failed to find evidence of intrinsic O2 sensitivity, and instead have supported the idea that extravascular cells sense O2 . Similarly, ex vivo studies of isolated, cannulated resistance arteries and large first-order arterioles support the hypotheses that O2 -dependent inhibition of production of vasodilator cyclooxygenase products or O2 -dependent destruction of nitric oxide mediates O2 reactivity of these upstream vessels. In contrast, most in vivo studies of downstream arterioles have disproved these hypotheses and instead have provided evidence supporting the idea that O2 -dependent production of vasoconstrictors mediates arteriolar O2 reactivity, with significant regional heterogeneity in the specific vasoconstrictor involved. Oxygen-induced vasoconstriction may serve as a protective mechanism to reduce the oxidative burden to which a tissue is exposed, a process that is superimposed on top of the local mechanisms which regulate tissue blood flow to meet a tissue's metabolic demand.
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Affiliation(s)
- William F Jackson
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI, 48824, USA.
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14
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Hermann A, Sitdikova GF, Weiger TM. Oxidative Stress and Maxi Calcium-Activated Potassium (BK) Channels. Biomolecules 2015; 5:1870-911. [PMID: 26287261 PMCID: PMC4598779 DOI: 10.3390/biom5031870] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Revised: 07/17/2015] [Accepted: 07/20/2015] [Indexed: 01/13/2023] Open
Abstract
All cells contain ion channels in their outer (plasma) and inner (organelle) membranes. Ion channels, similar to other proteins, are targets of oxidative impact, which modulates ion fluxes across membranes. Subsequently, these ion currents affect electrical excitability, such as action potential discharge (in neurons, muscle, and receptor cells), alteration of the membrane resting potential, synaptic transmission, hormone secretion, muscle contraction or coordination of the cell cycle. In this chapter we summarize effects of oxidative stress and redox mechanisms on some ion channels, in particular on maxi calcium-activated potassium (BK) channels which play an outstanding role in a plethora of physiological and pathophysiological functions in almost all cells and tissues. We first elaborate on some general features of ion channel structure and function and then summarize effects of oxidative alterations of ion channels and their functional consequences.
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Affiliation(s)
- Anton Hermann
- Department of Cell Biology, Division of Cellular and Molecular Neurobiology, University of Salzburg, Salzburg 5020, Austria.
| | - Guzel F Sitdikova
- Department of Physiology of Man and Animals, Kazan Federal University, Kazan 420008, Russia.
| | - Thomas M Weiger
- Department of Cell Biology, Division of Cellular and Molecular Neurobiology, University of Salzburg, Salzburg 5020, Austria.
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15
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Liu X, Gebremedhin D, Harder DR, Koehler RC. Contribution of epoxyeicosatrienoic acids to the cerebral blood flow response to hypoxemia. J Appl Physiol (1985) 2015; 119:1202-9. [PMID: 25792716 DOI: 10.1152/japplphysiol.01043.2014] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Accepted: 03/17/2015] [Indexed: 02/01/2023] Open
Abstract
Adenosine A2A receptors and ATP-activated K(+) (KATP) channels contribute to part of the cerebral vasodilatory response to systemic hypoxia, but other mediators are likely involved. Epoxyeicosatrienoic acids (EETs) are cerebral vasodilators and are released from astrocytes exposed to hypoxia. Moreover, stimulation of metabotropic glutamate receptors (mGluR) produces vasodilation by an EET-dependent mechanism. Here, we tested the hypothesis that EET signaling and mGluR activation contribute to hypoxic vasodilation. Laser-Doppler flow was measured over cerebral cortex of anesthetized rats subjected to stepwise reductions in arterial oxygen saturation to 50-70%. Hypoxic reactivity was calculated as the slope of the change in laser-Doppler flow vs. the reciprocal of arterial oxygen content. Hypoxic reactivity significantly decreased from 9.2 ± 1.9 (±95% confidence interval) in controls with vehicle treatment to 2.6 ± 1.4 with the EET antagonist 14,15-epoxyeicosa-5(Z)-enoic acid, to 3.0 ± 1.5 with the EET synthesis inhibitor MS-PPOH, to 1.9 ± 2.3 with the combined mGluR subtype 1 and 5 antagonists 2-methyl-6-(phenylethynyl)pyridine and LY367385, to 5.6 ± 1.2 with the KATP channel inhibitor glibenclamide, and to 5.8 ± 2.3 with the A2A receptor antagonist SCH58261. However, reactivity was not significantly altered by the A2B receptor antagonist MRS1754 (6.7 ± 1.8; P = 0.28 Dunnett's test) or by the 20-hydroxyeicosatetraenoic acid synthesis inhibitor HET0016 (7.5 ± 2.3; P = 0.6). These data indicate that, in addition to the known contributions of A2A receptors and KATP channels to the increase in cerebral blood flow during hypoxia, EETs and mGluRs make a major contribution, possibly by mGluR stimulation and hypoxia-induced release of EETs. In contrast, A2B receptors do not make a major contribution, and 20-hydroxyeicosatetraenoic acid does not significantly limit hypoxic vasodilation.
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Affiliation(s)
- Xiaoguang Liu
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University, Baltimore, Maryland
| | - Debebe Gebremedhin
- Department of Physiology and the Cardiovascular Research Center, Medical College of Wisconsin, Milwaukee, Wisconsin; and
| | - David R Harder
- Department of Physiology and the Cardiovascular Research Center, Medical College of Wisconsin, Milwaukee, Wisconsin; and Clement J. Zablocki Veterans Affairs Medical Center, Milwaukee, Wisconsin
| | - Raymond C Koehler
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University, Baltimore, Maryland;
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16
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Tao X, Lin MT, Thorington GU, Wilson SM, Longo LD, Hessinger DA. Long-term hypoxia increases calcium affinity of BK channels in ovine fetal and adult cerebral artery smooth muscle. Am J Physiol Heart Circ Physiol 2015; 308:H707-22. [PMID: 25599571 DOI: 10.1152/ajpheart.00564.2014] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Accepted: 01/14/2015] [Indexed: 01/31/2023]
Abstract
Acclimatization to high-altitude, long-term hypoxia (LTH) reportedly alters cerebral artery contraction-relaxation responses associated with changes in K(+) channel activity. We hypothesized that to maintain oxygenation during LTH, basilar arteries (BA) in the ovine adult and near-term fetus would show increased large-conductance Ca(2+) activated potassium (BK) channel activity. We measured BK channel activity, expression, and cell surface distribution by use of patch-clamp electrophysiology, flow cytometry, and confocal microscopy, respectively, in myocytes from normoxic control and LTH adult and near-term fetus BA. Electrophysiological data showed that BK channels in LTH myocytes exhibited 1) lowered Ca(2+) set points, 2) left-shifted activation voltages, and 3) longer dwell times. BK channels in LTH myocytes also appeared to be more dephosphorylated. These differences collectively make LTH BK channels more sensitive to activation. Studies using flow cytometry showed that the LTH fetus exhibited increased BK β1 subunit surface expression. In addition, in both fetal groups confocal microscopy revealed increased BK channel clustering and colocalization to myocyte lipid rafts. We conclude that increased BK channel activity in LTH BA occurred in association with increased channel affinity for Ca(2+) and left-shifted voltage activation. Increased cerebrovascular BK channel activity may be a mechanism by which LTH adult and near-term fetal sheep can acclimatize to long-term high altitude hypoxia. Our findings suggest that increasing BK channel activity in cerebral myocytes may be a therapeutic target to ameliorate the adverse effects of high altitude in adults or of intrauterine hypoxia in the fetus.
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Affiliation(s)
- Xiaoxiao Tao
- Division of Pharmacology, School of Medicine, Loma Linda University, Loma Linda, California
| | - Mike T Lin
- Division of Physiology, School of Medicine, Loma Linda University, Loma Linda, California; Department of Physiology and Cell Biology, University of South Alabama, Mobile, Alabama
| | - Glyne U Thorington
- Division of Physiology, School of Medicine, Loma Linda University, Loma Linda, California
| | - Sean M Wilson
- Division of Pharmacology, School of Medicine, Loma Linda University, Loma Linda, California; Center for Perinatal Biology, School of Medicine, Loma Linda University, Loma Linda, California; and
| | - Lawrence D Longo
- Division of Physiology, School of Medicine, Loma Linda University, Loma Linda, California; Center for Perinatal Biology, School of Medicine, Loma Linda University, Loma Linda, California; and
| | - David A Hessinger
- Division of Pharmacology, School of Medicine, Loma Linda University, Loma Linda, California; Division of Physiology, School of Medicine, Loma Linda University, Loma Linda, California;
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17
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Hedegaard ER, Nielsen BD, Kun A, Hughes AD, Krøigaard C, Mogensen S, Matchkov VV, Fröbert O, Simonsen U. KV 7 channels are involved in hypoxia-induced vasodilatation of porcine coronary arteries. Br J Pharmacol 2014; 171:69-82. [PMID: 24111896 DOI: 10.1111/bph.12424] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2013] [Revised: 07/08/2013] [Accepted: 09/04/2013] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND AND PURPOSE Hypoxia causes vasodilatation of coronary arteries, but the underlying mechanisms are poorly understood. We hypothesized that hypoxia reduces intracellular Ca(2+) concentration ([Ca(2+)](i)) by opening of K channels and release of H₂S. EXPERIMENTAL APPROACH Porcine coronary arteries without endothelium were mounted for measurement of isometric tension and [Ca(2+)](i), and the expression of voltage-gated K channels K(V)7 channels (encoded by KCNQ genes) and large-conductance calcium-activated K channels (K(Ca)1.1) was examined. Voltage clamp assessed the role of K(V)7 channels in hypoxia. KEY RESULTS Gradual reduction of oxygen concentration from 95 to 1% dilated the precontracted coronary arteries and this was associated with reduced [Ca(2+)](i) in PGF(2α) (10 μM)-contracted arteries whereas no fall in [Ca(2+)](i) was observed in 30 mM K-contracted arteries. Blockers of ATP-sensitive voltage-gated potassium channels and K(Ca)1.1 inhibited hypoxia-induced dilatation in PGF2α -contracted arteries; this inhibition was more marked in the presence of the K(v)7 channel blockers, XE991 and linopirdine, while a K(V)7.1 blocker, failed to change hypoxic vasodilatation. XE991 also inhibited H₂S- and adenosine-induced vasodilatation. PCR revealed the expression of K(V)7.1, K(V)7.4, K(V)7.5 and K(Ca)1.1 channels, and K(Ca)1.1, K(V)7.4 and K(V)7.5 were also identified by immunoblotting. Voltage clamp studies showed the XE991-sensitive current was more marked in hypoxic conditions. CONCLUSION The K(V)7.4 and K(V)7.5 channels, which we identified in the coronary arteries, appear to have a major role in hypoxia-induced vasodilatation. The voltage clamp results further support the involvement of K(V)7 channels in this vasodilatation. Activation of these K(V)7 channels may be induced by H₂S and adenosine.
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Affiliation(s)
- E R Hedegaard
- Department of Biomedicine, Pulmonary and Cardiovascular Pharmacology, University of Aarhus, Aarhus, Denmark
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18
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Hu XQ, Zhang L. Function and regulation of large conductance Ca(2+)-activated K+ channel in vascular smooth muscle cells. Drug Discov Today 2012; 17:974-87. [PMID: 22521666 PMCID: PMC3414640 DOI: 10.1016/j.drudis.2012.04.002] [Citation(s) in RCA: 77] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Revised: 03/06/2012] [Accepted: 04/05/2012] [Indexed: 12/23/2022]
Abstract
Large conductance Ca(2+)-activated K(+) (BK(Ca)) channels are abundantly expressed in vascular smooth muscle cells. Activation of BK(Ca) channels leads to hyperpolarization of cell membrane, which in turn counteracts vasoconstriction. Therefore, BK(Ca) channels have an important role in regulation of vascular tone and blood pressure. The activity of BK(Ca) channels is subject to modulation by various factors. Furthermore, the function of BK(Ca) channels are altered in both physiological and pathophysiological conditions, such as pregnancy, hypertension and diabetes, which has dramatic impacts on vascular tone and hemodynamics. Consequently, compounds and genetic manipulation that alter activity and expression of the channel might be of therapeutic interest.
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Affiliation(s)
- Xiang-Qun Hu
- Center for Perinatal Biology, Division of Pharmacology, Department of Basic Sciences, Loma Linda University School of Medicine, Loma Linda, CA 92350, USA.
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19
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Zhang R, Sun H, Liao C, Yang H, Zhao B, Tian J, Dong S, Zhang Z, Jiao J. Chronic hypoxia in cultured human podocytes inhibits BKCa channels by upregulating its β4-subunit. Biochem Biophys Res Commun 2012; 420:505-10. [DOI: 10.1016/j.bbrc.2012.03.021] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2012] [Accepted: 03/07/2012] [Indexed: 01/30/2023]
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20
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Adebiyi A, McNally EM, Jaggar JH. Vasodilation induced by oxygen/glucose deprivation is attenuated in cerebral arteries of SUR2 null mice. Am J Physiol Heart Circ Physiol 2011; 301:H1360-8. [PMID: 21784985 DOI: 10.1152/ajpheart.00406.2011] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Physiological functions of arterial smooth muscle cell ATP-sensitive K(+) (K(ATP)) channels, which are composed of inwardly rectifying K(+) channel 6.1 and sulfonylurea receptor (SUR)-2 subunits, during metabolic inhibition are unresolved. In the present study, we used a genetic model to investigate the physiological functions of SUR2-containing K(ATP) channels in mediating vasodilation to hypoxia, oxygen and glucose deprivation (OGD) or metabolic inhibition, and functional recovery following these insults. Data indicate that SUR2B is the only SUR isoform expressed in murine cerebral artery smooth muscle cells. Pressurized SUR2 wild-type (SUR2(wt)) and SUR2 null (SUR2(nl)) mouse cerebral arteries developed similar levels of myogenic tone and dilated similarly to hypoxia (<10 mmHg Po(2)). In contrast, vasodilation induced by pinacidil, a K(ATP) channel opener, was ∼71% smaller in SUR2(nl) arteries. Human cerebral arteries also expressed SUR2B, developed myogenic tone, and dilated in response to hypoxia and pinacidil. OGD, oligomycin B (a mitochondrial ATP synthase blocker), and CCCP (a mitochondrial uncoupler) all induced vasodilations that were ∼39-61% smaller in SUR2(nl) than in SUR2(wt) arteries. The restoration of oxygen and glucose following OGD or removal of oligomycin B and CCCP resulted in partial recovery of tone in both SUR2(wt) and SUR2(nl) cerebral arteries. However, SUR(nl) arteries regained ∼60-82% more tone than did SUR2(wt) arteries. These data indicate that SUR2-containing K(ATP) channels are functional molecular targets for OGD, but not hypoxic, vasodilation in cerebral arteries. In addition, OGD activation of SUR2-containing K(ATP) channels may contribute to postischemic loss of myogenic tone.
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Affiliation(s)
- Adebowale Adebiyi
- Department of Physiology, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA
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21
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Shimoda LA, Polak J. Hypoxia. 4. Hypoxia and ion channel function. Am J Physiol Cell Physiol 2011; 300:C951-67. [PMID: 21178108 PMCID: PMC3093942 DOI: 10.1152/ajpcell.00512.2010] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2010] [Accepted: 12/16/2010] [Indexed: 12/19/2022]
Abstract
The ability to sense and respond to oxygen deprivation is required for survival; thus, understanding the mechanisms by which changes in oxygen are linked to cell viability and function is of great importance. Ion channels play a critical role in regulating cell function in a wide variety of biological processes, including neuronal transmission, control of ventilation, cardiac contractility, and control of vasomotor tone. Since the 1988 discovery of oxygen-sensitive potassium channels in chemoreceptors, the effect of hypoxia on an assortment of ion channels has been studied in an array of cell types. In this review, we describe the effects of both acute and sustained hypoxia (continuous and intermittent) on mammalian ion channels in several tissues, the mode of action, and their contribution to diverse cellular processes.
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Affiliation(s)
- Larissa A Shimoda
- Div. of Pulmonary and Critical Care Medicine, Johns Hopkins University, 5501 Hopkins Bayview Circle, Baltimore, MD 21224, USA.
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22
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Aggarwal NT, Pfister SL, Gauthier KM, Chawengsub Y, Baker JE, Campbell WB. Chronic hypoxia enhances 15-lipoxygenase-mediated vasorelaxation in rabbit arteries. Am J Physiol Heart Circ Physiol 2008; 296:H678-88. [PMID: 19112096 DOI: 10.1152/ajpheart.00777.2008] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
15-Lipoxygenase (15-LO-1) metabolizes arachidonic acid (AA) to 11,12,15-trihydroxyeicosatrienoic acids (THETAs) and 15-hydroxy-11,12-epoxyeicosatrienoic acids (HEETA) that dilate rabbit arteries. Increased endothelial 15-LO-1 expression enhances arterial relaxations to agonists. We tested the effect of hypoxia on 15-LO-1 expression, THETA and HEETA synthesis, and relaxations in rabbit arteries. The incubation of rabbit aortic endothelial cells and isolated aortas in 0.7% O(2) increased 15-LO-1 expression. Rabbits were housed in a hypoxic atmosphere of 12% O(2) for 5 days. 15-LO-1 expression increased in the endothelium of the arteries of rabbits in 12% O(2) compared with room air. THETA and HEETA synthesis was also enhanced in aortas and mesenteric arteries. AA hyperpolarized the smooth muscle cells in indomethacin- and phenylephrine-treated mesenteric arteries of hypoxic rabbits from -29.4 +/- 1 to -50.1 +/- 3 mV. The hyperpolarization to AA was less in arteries of normoxic rabbits (from -26.0 +/- 2 to -37 +/- 2 mV). This AA-induced hyperpolarization was inhibited by the 15-LO inhibitor BW-755C. Nitric oxide and prostaglandin-independent maximum relaxations to acetylcholine (79.7 +/- 2%) and AA (38.3 +/- 4%) were enhanced in mesenteric arteries from hypoxic rabbits compared with the normoxic rabbits (49.7 +/- 6% and 19.9 +/- 2%, respectively). These relaxations were inhibited by BW-755C and nordihydroguaiaretic acid. Therefore, hypoxia increased the relaxations to agonists in the rabbit mesenteric arteries by enhancing endothelial 15-LO-1 expression and synthesis of the hyperpolarizing factors THETA and HEETA.
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Affiliation(s)
- Nitin T Aggarwal
- Dept. of Pharmacology and Toxicology, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226, USA
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23
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Sutendra G, Michelakis ED. Chapter 5 A Mitochondria-AOS-Kv Channel Axis in Health and Disease; New Insights and Therapeutic Targets for Vascular Disease and Cancer. CURRENT TOPICS IN MEMBRANES 2008. [DOI: 10.1016/s1063-5823(08)00205-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Sun H, Zhao H, Sharpe GM, Arrick DM, Mayhan WG. Influence of chronic alcohol consumption on inward rectifier potassium channels in cerebral arterioles. Microvasc Res 2007; 75:367-72. [PMID: 18191159 DOI: 10.1016/j.mvr.2007.11.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2007] [Revised: 10/23/2007] [Accepted: 11/26/2007] [Indexed: 11/17/2022]
Abstract
Inward rectifier potassium (K(IR)) channels appear to play an important role in the regulation of cerebral blood flow. Our goal was to examine the influence of chronic alcohol exposure on K(IR) channels in cerebral arterioles. Sprague-Dawley rats were fed liquid diets with or without alcohol for 8-12 weeks. Using intravital microscope, we measured diameter of pial arterioles in response to an inhibitor, BaCl(2), and an activator, KCl, of K(IR) channels in the absence and presence of a scavenger of reactive oxygen species, tempol, or an inhibitor of NAD(P)H oxidase, apocynin. Application of BaCl(2) (30 and 100 microM) produced dose-related vasoconstriction in non-alcohol-fed, but not in alcohol-fed rats. In addition, application of KCl (3, 10, and 30 mM) produced dose-related dilation in non-alcohol-fed and alcohol-fed rats, but the magnitude of vasodilatation was less in alcohol-fed rats. In contrast, nitroglycerin-induced vasodilation was similar in non-alcohol-fed and alcohol-fed rats. Superfusion of cranial window with tempol (0.1 mM) or apocynin (1 mM) did not alter baseline diameter and nitroglycerin-induced dilation of pial arterioles in non-alcohol-fed and alcohol-fed rats but significantly improved impaired KCl-induced dilation in alcohol-fed rats. Our findings suggest that chronic alcohol consumption impairs the role of K(IR) channels in basal tone and KCl-induced dilation of cerebral arterioles. In addition, impaired KCl-induced dilation of cerebral arterioles during alcohol consumption may be related to enhanced release of oxygen-derived free radicals via NAD(P)H oxidase.
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Affiliation(s)
- Hong Sun
- Department of Cellular and Integrative Physiology 985850, University of Nebraska Medical Center, Omaha, NE 68198-5850, USA.
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25
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Gebremedhin D, Yamaura K, Harder DR. Role of 20-HETE in the hypoxia-induced activation of Ca2+-activated K+ channel currents in rat cerebral arterial muscle cells. Am J Physiol Heart Circ Physiol 2007; 294:H107-20. [PMID: 17906097 DOI: 10.1152/ajpheart.01416.2006] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The mechanism of sensing hypoxia and hypoxia-induced activation of cerebral arterial Ca(2+)-activated K(+) (K(Ca)) channel currents and vasodilation is not known. We investigated the roles of the cytochrome P-450 4A (CYP 4A) omega-hydroxylase metabolite of arachidonic acid, 20-hydroxyeicosatetraenoic acid (20-HETE), and generation of superoxide in the hypoxia-evoked activation of the K(Ca) channel current in rat cerebral arterial muscle cells (CAMCs) and cerebral vasodilation. Patch-clamp analysis of K(+) channel current identified a voltage- and Ca(2+)-dependent 238 +/- 21-pS unitary K(+) currents that are inhibitable by tetraethylammonium (TEA, 1 mM) or iberiotoxin (100 nM). Hypoxia (<2% O(2)) reversibly enhanced the open-state probability (NP(o)) of the 238-pS unitary K(Ca) current in cell-attached patches. This effect of hypoxia was not observed on unitary K(Ca) currents recorded from either excised inside-out or outside-out membrane patches. Inhibition of CYP 4A omega-hydroxylase activity increased the NP(o) of K(Ca) single-channel current. Hypoxia reduced the basal endogenous level of 20-HETE by 47 +/- 3% as well as catalytic formation of 20-HETE in cerebral arterial muscle homogenates as determined by liquid chromatography-mass spectrometry analysis. The concentration of authentic 20-HETE was reduced when incubated with the superoxide donor KO(2). Exogenous 20-HETE (100 nM) attenuated the hypoxia-induced activation of the K(Ca) current in CAMCs. Hypoxia did not augment the increase in NP(o) of K(Ca) channel current induced by suicide inhibition of endogenous CYP 4A omega-hydroxylase activity with 17-octadecynoic acid. In pressure (80 mmHg)-constricted cerebral arterial segments, hypoxia induced dilation that was partly attenuated by 20-HETE or by the K(Ca) channel blocker TEA. Exposure to hypoxia caused the generation of intracellular superoxide as evidenced by intense staining of arterial muscle with the fluorescent probe hydroethidine, by quantitation using fluorescent HPLC analysis, and by attenuation of the hypoxia-induced activation of the K(Ca) channel current by superoxide dismutation. These results suggest that the exposure of CAMCs to hypoxia results in the generation of superoxide and reduction in endogenous level of 20-HETE that may account for the hypoxia-induced activation of arterial K(Ca) channel currents and cerebral vasodilation.
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MESH Headings
- Animals
- Antioxidants/pharmacology
- Calcium/metabolism
- Cell Hypoxia
- Cerebral Arteries/metabolism
- Chromatography, High Pressure Liquid
- Cyclic N-Oxides/pharmacology
- Cytochrome P-450 CYP4A/antagonists & inhibitors
- Cytochrome P-450 CYP4A/metabolism
- Enzyme Inhibitors/pharmacology
- Fatty Acids, Unsaturated/pharmacology
- Hydroxyeicosatetraenoic Acids/metabolism
- Hydroxylation
- In Vitro Techniques
- Ion Channel Gating
- Male
- Mass Spectrometry
- Membrane Potentials
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/enzymology
- Muscle, Smooth, Vascular/metabolism
- Myocytes, Smooth Muscle/drug effects
- Myocytes, Smooth Muscle/enzymology
- Myocytes, Smooth Muscle/metabolism
- Patch-Clamp Techniques
- Peptides/pharmacology
- Potassium/metabolism
- Potassium Channel Blockers/pharmacology
- Potassium Channels, Calcium-Activated/antagonists & inhibitors
- Potassium Channels, Calcium-Activated/metabolism
- Rats
- Rats, Sprague-Dawley
- Signal Transduction/drug effects
- Spectrometry, Fluorescence
- Spin Labels
- Superoxides/metabolism
- Tetraethylammonium/pharmacology
- Vasodilation/drug effects
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Affiliation(s)
- Debebe Gebremedhin
- Cardiovascular Research Center, Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226, USA
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26
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Ko EA, Burg ED, Platoshyn O, Msefya J, Firth AL, Yuan JXJ. Functional characterization of voltage-gated K+ channels in mouse pulmonary artery smooth muscle cells. Am J Physiol Cell Physiol 2007; 293:C928-37. [PMID: 17581857 DOI: 10.1152/ajpcell.00101.2007] [Citation(s) in RCA: 17] [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]
Abstract
Mice are useful animal models to study pathogenic mechanisms involved in pulmonary vascular disease. Altered expression and function of voltage-gated K(+) (K(V)) channels in pulmonary artery smooth muscle cells (PASMCs) have been implicated in the development of pulmonary arterial hypertension. K(V) currents (I(K(V))) in mouse PASMCs have not been comprehensively characterized. The main focus of this study was to determine the biophysical and pharmacological properties of I(K(V)) in freshly dissociated mouse PASMCs with the patch-clamp technique. Three distinct whole cell I(K(V)) were identified based on the kinetics of activation and inactivation: rapidly activating and noninactivating currents (in 58% of the cells tested), rapidly activating and slowly inactivating currents (23%), and slowly activating and noninactivating currents (17%). Of the cells that demonstrated the rapidly activating noninactivating current, 69% showed I(K(V)) inhibition with 4-aminopyridine (4-AP), while 31% were unaffected. Whole cell I(K(V)) were very sensitive to tetraethylammonium (TEA), as 1 mM TEA decreased the current amplitude by 32% while it took 10 mM 4-AP to decrease I(K(V)) by a similar amount (37%). Contribution of Ca(2+)-activated K(+) (K(Ca)) channels to whole cell I(K(V)) was minimal, as neither pharmacological inhibition with charybdotoxin or iberiotoxin nor perfusion with Ca(2+)-free solution had an effect on the whole cell I(K(V)). Steady-state activation and inactivation curves revealed a window K(+) current between -40 and -10 mV with a peak at -31.5 mV. Single-channel recordings revealed large-, intermediate-, and small-amplitude currents, with an averaged slope conductance of 119.4 +/- 2.7, 79.8 +/- 2.8, 46.0 +/- 2.2, and 23.6 +/- 0.6 pS, respectively. These studies provide detailed electrophysiological and pharmacological profiles of the native K(V) currents in mouse PASMCs.
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Affiliation(s)
- Eun A Ko
- Div. of Pulmonary and Critical Care Medicine, Dept. of Medicine, Univ. of California, San Diego, 9500 Gilman Dr., MC 0725, La Jolla, CA 92093-0725, USA
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Zhao G, Adebiyi A, Xi Q, Jaggar JH. Hypoxia reduces KCa channel activity by inducing Ca2+ spark uncoupling in cerebral artery smooth muscle cells. Am J Physiol Cell Physiol 2007; 292:C2122-8. [PMID: 17314264 PMCID: PMC2241735 DOI: 10.1152/ajpcell.00629.2006] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Arterial smooth muscle cell large-conductance Ca(2+)-activated potassium (K(Ca)) channels have been implicated in modulating hypoxic dilation of systemic arteries, although this is controversial. K(Ca) channel activity in arterial smooth muscle cells is controlled by localized intracellular Ca(2+) transients, termed Ca(2+) sparks, but hypoxic regulation of Ca(2+) sparks and K(Ca) channel activation by Ca(2+) sparks has not been investigated. We report here that in voltage-clamped (-40 mV) cerebral artery smooth muscle cells, a reduction in dissolved O(2) partial pressure from 150 to 15 mmHg reversibly decreased Ca(2+) spark-induced transient K(Ca) current frequency and amplitude to 61% and 76% of control, respectively. In contrast, hypoxia did not alter Ca(2+) spark frequency, amplitude, global intracellular Ca(2+) concentration, or sarcoplasmic reticulum Ca(2+) load. Hypoxia reduced transient K(Ca) current frequency by decreasing the percentage of Ca(2+) sparks that activated a transient K(Ca) current from 89% to 63%. Hypoxia reduced transient K(Ca) current amplitude by attenuating the amplitude relationship between Ca(2+) sparks that remained coupled and the evoked transient K(Ca) currents. Consistent with these data, in inside-out patches at -40 mV hypoxia reduced K(Ca) channel apparent Ca(2+) sensitivity and increased the K(d) for Ca(2+) from approximately 17 to 32 microM, but did not alter single-channel amplitude. In summary, data indicate that hypoxia reduces K(Ca) channel apparent Ca(2+) sensitivity via a mechanism that is independent of cytosolic signaling messengers, and this leads to uncoupling of K(Ca) channels from Ca(2+) sparks. Transient K(Ca) current inhibition due to uncoupling would oppose hypoxic cerebrovascular dilation.
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Affiliation(s)
- Guiling Zhao
- Dept. of Physiology, University of Tennessee Health Science Center, Memphis, TN 38163, USA
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Shimoda LA, Luke T, Sylvester JT, Shih HW, Jain A, Swenson ER. Inhibition of hypoxia-induced calcium responses in pulmonary arterial smooth muscle by acetazolamide is independent of carbonic anhydrase inhibition. Am J Physiol Lung Cell Mol Physiol 2007; 292:L1002-12. [PMID: 17209136 DOI: 10.1152/ajplung.00161.2006] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hypoxic pulmonary vasoconstriction (HPV) occurs with ascent to high altitude and can contribute to development of high altitude pulmonary edema (HAPE). Vascular smooth muscle contains carbonic anhydrase (CA), and acetazolamide (AZ), a CA inhibitor, blunts HPV and might be useful in the prevention of HAPE. The mechanism by which AZ impairs HPV is uncertain. Originally developed as a diuretic, AZ also has direct effects on systemic vascular smooth muscle, including modulation of pH and membrane potential; however, the effect of AZ on pulmonary arterial smooth muscle cells (PASMCs) is unknown. Since HPV requires Ca2+ influx into PASMCs and can be modulated by pH, we hypothesized that AZ alters hypoxia-induced changes in PASMC intracellular pH (pH(i)) or Ca2+ concentration ([Ca2+](i)). Using fluorescent microscopy, we tested the effect of AZ as well as two other potent CA inhibitors, benzolamide and ethoxzolamide, which exhibit low and high membrane permeability, respectively, on hypoxia-induced responses in PASMCs. Hypoxia caused a significant increase in [Ca2+](i) but no change in pH(i). All three CA inhibitors slightly decreased basal pH(i), but only AZ caused a concentration-dependent decrease in the [Ca2+](i) response to hypoxia. AZ had no effect on the KCl-induced increase in [Ca2+](i) or membrane potential. N-methyl-AZ, a synthesized compound lacking the unsubstituted sulfonamide group required for CA inhibition, had no effect on pH(i) but inhibited hypoxia-induced Ca2+ responses. These results suggest that AZ attenuates HPV by selectively inhibiting hypoxia-induced Ca2+ responses via a mechanism independent of CA inhibition, changes in pH(i), or membrane potential.
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Affiliation(s)
- Larissa A Shimoda
- Division of Pulmonary and Critical Care Medicine, Johns Hopkins University, Baltimore, MD 21224, USA.
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Yamaura K, Gebremedhin D, Zhang C, Narayanan J, Hoefert K, Jacobs ER, Koehler RC, Harder DR. Contribution of epoxyeicosatrienoic acids to the hypoxia-induced activation of Ca2+-activated K+ channel current in cultured rat hippocampal astrocytes. Neuroscience 2006; 143:703-16. [PMID: 17027168 DOI: 10.1016/j.neuroscience.2006.08.021] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2004] [Revised: 07/21/2006] [Accepted: 08/09/2006] [Indexed: 11/28/2022]
Abstract
Brief hypoxia differentially regulates the activities of Ca(2+)-activated K(+) channels (K(Ca)) in a variety of cell types. We investigated the effects of hypoxia (<2% O(2)) on K(Ca) channel currents and on the activities of cytochrome P450 2C11 epoxygenase (CYP epoxygenase) in cultured rat hippocampal astrocytes. Exposure of astrocytes to hypoxia enhanced macroscopic outward K(Ca) current, increased the open state probability (NPo) of 71 pS and 161 pS single-channel K(Ca) currents in cell-attached patches, but failed to increase the NPo of both the 71 pS and 161 pS K(Ca) channel currents recorded from excised inside-out patches. The hypoxia-induced enhancement of macroscopic K(Ca) current was attenuated by pretreatment with tetraethylammonium (TEA, 1 mM) or during recording using low-Ca(2+) external bath solution. Exposure of astrocytes to hypoxia was associated with generation of superoxide as detected by staining of cells with the intracellular superoxide detection probe hydroethidine (HE), attenuation of the hypoxia-induced activation of unitary K(Ca) channel currents by superoxide dismutation with tempol, and as quantitated by high-pressure liquid chromatography/fluorescence assay using HE as a probe. In cultured astrocytes in which endogenous CYP epoxygenase activity has been inhibited with either miconazole or N-methylsulfonyl-6-(2-propargyloxyphenyl) hexanamide (MSPPOH) hypoxia failed to increase the NPo of both the 71 pS and 161 pS K(Ca) currents and generation of superoxide. Hypoxia increased the level of P450 epoxygenase protein and production of epoxyeicosatrienoic acids (EETs) from cultured astrocytes, as determined by immunohistochemical staining and LC/MS analysis, respectively. Exogenous 11,12-EET increased the NPo of both the 71 pS and 161 pS K(Ca) single-channel currents only in cell-attached but not in excised inside-out patches of cultured astrocytes. These findings indicate that hypoxia enhances the activities of two types of unitary K(Ca) currents in astrocytes by a mechanism that appears to involve CYP epoxygenase-dependent generation of superoxide and increased production or release of EETs.
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Affiliation(s)
- K Yamaura
- Department of Physiology, Medical College of Wisconsin and Clement Zablocki VA Medical Center, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
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Morrell ED, Tsai BM, Crisostomo PR, Wang M, Markel TA, Lillemoe KD, Meldrum DR. Therapeutic concepts for hypoxic pulmonary vasoconstriction involving ion regulation and the smooth muscle contractile apparatus. J Mol Cell Cardiol 2006; 40:751-60. [PMID: 16697004 DOI: 10.1016/j.yjmcc.2006.03.431] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/25/2006] [Revised: 03/13/2006] [Accepted: 03/27/2006] [Indexed: 11/25/2022]
Abstract
Hypoxic pulmonary vasoconstriction (HPV) and pulmonary hypertension present a common and formidable clinical problem for practicing intensivists, thoracic, transplant, and trauma surgeons. The Redox Theory for the mechanisms of HPV has provided researchers with a new understanding of the etiology behind HPV that has opened the door to many new avenues of therapy for the disease. Potassium channels have been proposed to be the main mediator contributing to HPV, and treatment concepts that attempt to manipulate the function and number of those channels have been explored. Additionally, attempts to transfer genes that express the formation of specific potassium channels directly into pulmonary hypertensive lungs have proven to be very promising. Finally, rho kinase (ROK) has been discovered to play a very central role in the formation of hypoxia-induced pulmonary hypertension, and the advent of very specific ROK inhibitors has shown positive clinical results. The purposes of this review are to: (1) briefly discuss some of the basic mechanisms that undergird HPV, including the Redox Theory for the mechanisms of HPV; (2) address current research involving treatments concepts related to ion channels; (3) report on research involving gene therapy to combat pulmonary hypertension; and (4) examine potential therapeutic avenues associated with inhibition of rho kinase.
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Affiliation(s)
- Eric D Morrell
- Sections of General and Cardiothoracic Surgery, Department of Surgery, Indiana University Medical Center, Indianapolis, IN 46202, USA
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Abstract
There are several levels of O2 deprivation with different possibilities of adaptation and compensation. All of them appear to be highly conservative in phylogenesis and are active early in ontogenetic development. The coordinated structural and functional responses to systemic and/or local hypoxia form the basis for individual adaptation to environmental requirements and pathological threat.
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Affiliation(s)
- Reinhard Bauer
- Institute for Pathophysiology and Pathobiochemistry, Universitätsklinikum, Friedrich Schiller University, D-07740 Jena, Germany.
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32
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Huang CW, Huang CC, Huang MH, Wu SN, Hsieh YJ. Sodium cyanate-induced opening of calcium-activated potassium currents in hippocampal neuron-derived H19-7 cells. Neurosci Lett 2005; 377:110-4. [PMID: 15740847 DOI: 10.1016/j.neulet.2004.11.081] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2004] [Revised: 11/23/2004] [Accepted: 11/23/2004] [Indexed: 11/18/2022]
Abstract
We investigated the chemical toxic agent sodium cyanate (NaOCN) on the large conductance calcium-activated potassium channels (BK(Ca)) on hippocampal neuron-derived H19-7 cells. The whole-cell and cell-attach configuration of patch-clamp technique were applied to investigate the BK(Ca) currents in H19-7 cells in the presence of NaOCN (0.3 mM). NaOCN activated BK(Ca) channels on H19-7 cells. The single-channel conductance of BK(Ca) channels was 138+/-7pS. The presence of NaOCN (0.3 mM) caused an obvious increase in open probability of BK(Ca) channels. NaOCN did not exert effect on the slope of the activation curve and stimulated the activity of BK(Ca) channels in a voltage-dependent fashion in H19-7 cells. The presence of paxilline or EGTA significantly reduced the BK(Ca) amplitude, in comparison with the presence of NaOCN. These findings suggest that during NaOCN exposure, the activation of BK(Ca) channels in neurons could be one of the ionic mechanisms underlying the decreased neuronal excitability and neurological disorders.
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Affiliation(s)
- Chin-Wei Huang
- Department of Neurology, National Cheng-Kung University Medical Center, No. 1, University Road, Tainan, Taiwan
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33
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Hool LC. Acute hypoxia differentially regulates K+ channels. Implications with respect to cardiac arrhythmia. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2005; 34:369-76. [PMID: 15726346 DOI: 10.1007/s00249-005-0462-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2004] [Revised: 01/03/2005] [Accepted: 01/14/2005] [Indexed: 11/26/2022]
Abstract
The first ion channels demonstrated to be sensitive to changes in oxygen tension were K(+) channels in glomus cells of the carotid body. Since then a number of hypoxia-sensitive ion channels have been identified. However, not all K(+) channels respond to hypoxia alike. This has raised some debate about how cells detect changes in oxygen tension. Because ion channels respond rapidly to hypoxia it has been proposed that the channel is itself an oxygen sensor. However, channel function can also be modified by thiol reducing and oxidizing agents, implicating reactive oxygen species as signals in hypoxic events. Cardiac ion channels can also be modified by hypoxia and redox agents. The rapid and slow components of the delayed rectifier K(+) channel are differentially regulated by hypoxia and beta-adrenergic receptor stimulation. Mutations in the genes that encode the subunits for the channel are associated with Long QT syndrome and sudden cardiac death. The implications with respect to effects of hypoxia on the channel and triggering of cardiac arrhythmia will be discussed.
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Affiliation(s)
- Livia C Hool
- School of Biomedical and Chemical Sciences Australia and The Western Australian Institute of Medical Research, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
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López-Barneo J, del Toro R, Levitsky KL, Chiara MD, Ortega-Sáenz P. Regulation of oxygen sensing by ion channels. J Appl Physiol (1985) 2004; 96:1187-95; discussion 1170-2. [PMID: 14766769 DOI: 10.1152/japplphysiol.00929.2003] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
O(2) sensing is of critical importance for cell survival and adaptation of living organisms to changing environments or physiological conditions. O(2)-sensitive ion channels are major effectors of the cellular responses to hypoxia. These channels are preferentially found in excitable neurosecretory cells (glomus cells of the carotid body, cells in the neuroepithelial bodies of the lung, and neonatal adrenal chromaffin cells), which mediate fast cardiorespiratory adjustments to hypoxia. O(2)-sensitive channels are also expressed in the pulmonary and systemic arterial smooth muscle cells where they participate in the vasomotor responses to low O(2) tension (particularly in hypoxic pulmonary vasoconstriction). The mechanisms underlying O(2) sensing and how the O(2) sensors interact with the ion channels remain unknown. Recent advances in the field give different support to the various current hypotheses. Besides the participation of ion channels in acute O(2) sensing, they also contribute to the gene program developed under chronic hypoxia. Gene expression of T-type calcium channels is upregulated by hypoxia through the same hypoxia-inducible factor-dependent signaling pathway utilized by the classical O(2)-regulated genes. Alteration of acute or chronic O(2) sensing by ion channels could participate in the pathophysiology of human diseases, such as sudden infant death syndrome or primary pulmonary hypertension.
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Affiliation(s)
- José López-Barneo
- Laboratorio de Investigaciones Biomédicas, Departamento de Fisiología, Hospital Universitario Virgen del Rocío, Universidad de Sevilla, Seville, Spain.
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Lombard JH, Frisbee JC, Roman RJ, Falck JR. Evaluation of Cytochrome P450-4A ω-Hydroxylase and 20-Hydroxyeicosatetraenoic Acid as an O2 Sensing Mechanism in the Microcirculation. Methods Enzymol 2004; 381:140-65. [PMID: 15063671 DOI: 10.1016/s0076-6879(04)81009-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
Affiliation(s)
- Julian H Lombard
- Department of Physiology, Medical College of Wisconsin, Milwaukee 53226-1408, USA
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36
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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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Earley S, Pastuszyn A, Walker BR. Cytochrome p-450 epoxygenase products contribute to attenuated vasoconstriction after chronic hypoxia. Am J Physiol Heart Circ Physiol 2003; 285:H127-36. [PMID: 12623785 DOI: 10.1152/ajpheart.01052.2002] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The systemic vasculature exhibits attenuated vasoconstriction following chronic hypoxia (CH) that is associated with endothelium-dependent vascular smooth muscle (VSM) cell hyperpolarization. We hypothesized that increased production of arachidonic acid metabolites such as the cyclooxygenase product prostacyclin or cytochrome p-450 (CYP) epoxygenase-derived epoxyeicosatrienoic acids (EETs) contributes to VSM cell hyperpolarization following CH. VSM cell resting membrane potential (Em) was measured in superior mesenteric artery strips isolated from rats with control barometric pressure (Pb, congruent with 630 Torr) and CH (Pb, 380 Torr for 48 h). VSM cell Em was normalized between groups following administration of the CYP inhibitors 17-octadecynoic acid and SKF-525A. VSM cell hyperpolarization after CH was not altered by cyclooxygenase inhibition, whereas the selective CYP2C9 inhibitor sulfaphenazole normalized VSM cell Em between groups. Iberiotoxin also normalized VSM cell Em, which suggests that large-conductance, Ca2+-activated K+ (BKCa) channel activity is increased after CH. Sulfaphenazole administration restored phenylephrine-induced and myogenic vasoconstriction and Ca2+ responses of mesenteric resistance arteries isolated from CH rats to control levels. Western blot experiments demonstrated that CYP2C9 protein levels were greater in mesenteric arteries from CH rats. In addition, 11,12-EET levels were elevated in endothelial cells from CH rats compared with controls. We conclude that enhanced CYP2C9 expression and 11,12-EET production following CH contributes to BKCa channel-dependent VSM cell hyperpolarization and attenuated vasoreactivity.
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MESH Headings
- 8,11,14-Eicosatrienoic Acid/analogs & derivatives
- 8,11,14-Eicosatrienoic Acid/metabolism
- Animals
- Aryl Hydrocarbon Hydroxylases/antagonists & inhibitors
- Aryl Hydrocarbon Hydroxylases/metabolism
- Blotting, Western
- Calcium Channel Blockers/pharmacology
- Cell Membrane/drug effects
- Cell Membrane/physiology
- Chronic Disease
- Cyclooxygenase Inhibitors/pharmacology
- Cytochrome P-450 CYP2C9
- Cytochrome P-450 CYP2J2
- Cytochrome P-450 Enzyme Inhibitors
- Cytochrome P-450 Enzyme System/metabolism
- Enzyme Inhibitors/pharmacology
- Fatty Acids, Unsaturated/pharmacology
- Hypoxia/physiopathology
- In Vitro Techniques
- Male
- Membrane Potentials/physiology
- Mesenteric Arteries/physiology
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/physiology
- Oxygenases/antagonists & inhibitors
- Oxygenases/metabolism
- Potassium Channels, Calcium-Activated/drug effects
- Potassium Channels, Calcium-Activated/metabolism
- Proadifen/pharmacology
- Prostaglandin-Endoperoxide Synthases/metabolism
- Rats
- Rats, Sprague-Dawley
- Vasoconstriction/physiology
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Affiliation(s)
- Scott Earley
- Department of Cell Biology and Physiology, University of New Mexico, Albuquerque, NM 87131-0001, USA.
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COHEN KENNETHD, JACKSON WILLIAMF. Hypoxia inhibits contraction but not calcium channel currents or changes in intracellular calcium in arteriolar muscle cells. Microcirculation 2003; 10:133-41. [PMID: 12700582 PMCID: PMC1382023 DOI: 10.1038/sj.mn.7800178] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2002] [Accepted: 09/13/2002] [Indexed: 11/08/2022]
Abstract
OBJECTIVE We tested the hypothesis that hypoxia inhibits currents through L-type Ca(2+) channels and inhibits norepinephrine-induced rises in intracellular Ca(2+) in cremasteric arteriolar muscle cells, thus accounting for the inhibitory effect of hypoxia on norepinephrine-induced contraction of these cells. METHODS Single smooth muscle cells were enzymatically isolated from second-order and third-order arterioles from hamster cremaster muscles. The effects of hypoxia (partial pressure of oxygen: 10-15 mm Hg) were examined on Ba(2+) (10 mM) currents through L-type Ca(2+) channels by use of the perforated patch clamp technique. Also, the effect of hypoxia on norepinephrine-induced calcium changes was studied using Fura 2 microfluorimetry. RESULTS Hypoxia inhibited the norepinephrine-induced (10 microM) contraction of single arteriolar muscle cells by 32.9 +/- 5.6% (mean +/- SE, n = 4). However, hypoxia had no significant effect on whole-cell currents through L-type Ca(2+) channels: the peak current densities measured at +20 mV were -3.83 +/- 0.40 pA/pF before hypoxia and -3.97 +/- 0.36 pA/pF during hypoxia (n = 15; p > 0.05). In addition, hypoxia did not inhibit Ca(2+) transients in arteriolar muscle cells elicited by 10 microM norepinephrine. Instead, hypoxia increased basal Ca(2+) (13.8 +/- 3.2%) and augmented peak Ca(2+) levels (29.4 +/- 7.3%) and steady-state Ca(2+) levels (15.2 +/- 5.4%) elicited by 10 microM norepinephrine (n = 21; p < 0.05). CONCLUSIONS These data indicate that hypoxia inhibits norepinephrine-induced contraction of single cremasteric arteriolar muscle cells by a mechanism that involves neither L-type Ca(2+) channels nor norepinephrine-induced Ca(2+) mobilization. Instead, our findings suggest that hypoxia must inhibit norepinephrine-induced contraction by affecting a component of the signaling pathway that lies downstream from the increases in Ca(2+) produced by this neurotransmitter.
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Affiliation(s)
| | - WILLIAM F. JACKSON
- For reprints of this article, contact William F. Jackson, Department of Biological Sciences, 1903 W Michigan Ave, 3441 Wood Hall, Western Michigan University, Kalamazoo, MI 49008-5410, USA; e-mail:
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Tirapelli CR, Mingatto FE, De Godoy MAF, Ferreira R, De Oliviera AM. Vitamin K1 attenuates hypoxia-induced relaxation of rat carotid artery. Pharmacol Res 2002; 46:483-90. [PMID: 12457620 DOI: 10.1016/s104366180200227x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Vascular responses to hypoxia are heterogeneous and involve the release of vasodilators substances such as nitric oxide (NO) and prostacyclin (PGI(2)). In vitro studies have shown that Vitamin K(1) modulates the release of arachidonic acid (AA) in vascular cells, and thus inhibits the capacity of blood vessels to synthesise vasodilator AA metabolites. The aim of our work was to investigate the effects of Vitamin K(1) on the hypoxia-induced vasorelaxation. Hypoxia was induced by changing the gas from 95% O(2)/5% CO(2) to a mixture containing 95% N(2)/5% CO(2). Rat carotid arteries were pre-contracted with phenylephrine (Phe, 10(-8)mol/l) and when the contraction reached a plateau, the bath was bubbled with 95% N(2)/5% CO(2) for 15 min. In intact rings, there was a total relaxation after 15 min of exposure to hypoxia. Removal of the endothelium strongly reduced hypoxia-induced relaxation. In intact rings, indomethacin and L-NAME reduced the hypoxic relaxation after 5 min of exposure but not after 10 or 15 min. Exposure of endothelium-intact rings to Vitamin K(1) (5 x 10(-6) and 5 x 10(-5)mol/l), L-NAME+indomethacin as well as the combination of L-NAME+indomethacin+Vitamin K(1) reduced the hypoxic relaxation after 5 and 10 min of exposure but not after 15 min. At 5 x 10(-7)mol/l Vitamin K(1) did not attenuate hypoxia-induced relaxation. It was also found that Vitamin K(1) (5 x 10(-6) and 5 x 10(-5)mol/l) inhibited ACh-induced relaxation in normoxic conditions. These results show that the effect of Vitamin K(1) on attenuating hypoxia-induced vasorelaxation is concentration-dependent and probably related to its action on endothelial cells.
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Affiliation(s)
- Carlos R Tirapelli
- Department of Pharmacology, Faculty of Medicine, University of São Paulo, Ribeirão Preto, SP, Brazil
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40
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Liu Y, Harder DR, Lombard JH. Interaction of myogenic mechanisms and hypoxic dilation in rat middle cerebral arteries. Am J Physiol Heart Circ Physiol 2002; 283:H2276-81. [PMID: 12388266 DOI: 10.1152/ajpheart.00635.2002] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The goal of this study was to determine how myogenic responses and vascular responses to reduced Po(2) interact to determine vascular smooth muscle (VSM) transmembrane potential and active tone in isolated middle cerebral arteries from Sprague-Dawley rats. Stepwise elevation of transmural pressure led to depolarization of the VSM cells and myogenic constriction, and reduction of the O(2) concentration of the perfusion and superfusion reservoirs from 21% O(2) to 0% O(2) caused vasodilation and VSM hyperpolarization. Myogenic constriction and VSM depolarization in response to transmural pressure elevation still occurred at reduced Po(2). Arterial dilation in response to reduced Po(2) was not impaired by pressure elevation but was significantly reduced at the lowest transmural pressure (60 mmHg). However, the magnitude of VSM hyperpolarization was unaffected by transmural pressure elevation. This study demonstrates that myogenic activation in response to transmural pressure elevation does not override hypoxic relaxation of middle cerebral arteries and that myogenic responses and hypoxic relaxation can independently regulate vessel diameter despite substantial changes in the other variable.
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Affiliation(s)
- Yanping Liu
- Department of Physiology, Medical College of Wisconsin, Milwaukee 53226, USA
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Frisbee JC, Maier KG, Falck JR, Roman RJ, Lombard JH. Integration of hypoxic dilation signaling pathways for skeletal muscle resistance arteries. Am J Physiol Regul Integr Comp Physiol 2002; 283:R309-19. [PMID: 12121842 DOI: 10.1152/ajpregu.00741.2001] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mediator contributions to hypoxic dilation of rat gracilis muscle resistance arteries were determined by measuring dilation, vascular smooth muscle hyperpolarization, and metabolite production after incremental hypoxia. Nitric oxide (NO) synthase inhibition abolished responses to mild hypoxia, whereas COX inhibition impaired responses to more severe hypoxia by 77%. Blocking 20-hydroxyeicosatetraenoic acid (20-HETE) impaired responses to moderate hypoxia. With only NO systems intact, responses were maintained with mild hypoxia (88% normal) mediated via K(Ca) channels. When only COX pathways were intact, responses to moderate-severe hypoxia were largely retained (79% of normal) mediated via K(ATP) channels. Vessel responses to moderate hypoxia were retained with only 20-HETE systems intact mediated via K(Ca) channels. NO production increased 5.6-fold with mild hypoxia; greater hypoxia was without further effect. With increased hypoxia, 20-HETE levels fell to 40% of control values. 6-keto-PGF(1alpha) levels were not altered with mild hypoxia, but increased 4.6-fold with severe hypoxia. These results suggest vascular reactivity to progressive hypoxia represents an integration of NO production (mild hypoxia), PGI(2) production (severe hypoxia), and reduced 20-HETE levels (moderate hypoxia).
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Affiliation(s)
- Jefferson C Frisbee
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA.
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Thorne GD, Conforti L, Paul RJ. Hypoxic vasorelaxation inhibition by organ culture correlates with loss of Kv channels but not Ca(2+) channels. Am J Physiol Heart Circ Physiol 2002; 283:H247-53. [PMID: 12063297 DOI: 10.1152/ajpheart.00569.2001] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We (Thorne GD, Shimizu S, and Paul RJ. Am J Physiol Cell Physiol 281: C24-C32, 2001) have recently shown that organ culture for 24 h specifically inhibits relaxation to acute hypoxia (95% N(2)-5% CO(2)) in the porcine coronary artery. Here we show similar results in the porcine carotid artery and the rat and mouse aorta. In the coronary artery, part of the inability to relax to hypoxia after organ culture is associated with a concomitant loss in ability to reduce intracellular Ca(2+) concentration ([Ca(2+)](i)) during hypoxia (Thorne GD, Shimizu S, and Paul RJ. Am J Physiol Cell Physiol 281: C24-C32, 2001). To elucidate the mechanisms responsible for the loss of relaxation to hypoxia, we investigated changes in K(+) and Ca(2+) channel activity and gene expression that play key roles in [Ca(2+)](i) regulation in vascular smooth muscle (VSM). Reduced mRNA expression of O(2)-sensitive K(+) channels (Kv1.5 and Kv2.1) was shown by reverse transcriptase-polymerase chain reaction in the rat aorta. In contrast, no change in other expressed voltage-gated K(+) channels (Kv1.2 and Kv1.3) or Ca(2+) channel subtypes was found. Modified K(+) channel expression is supported by functional evidence indicating a reduced response to general K(+) channel activation, by pinacidil, and to specific voltage-dependent K(+) (Kv) channel blockade by 4-aminopyridine. In conclusion, organ culture decreases expression of specific Kv channels. These changes are consistent with altered mechanisms of VSM contractility that may be involved in Ca(2+)-dependent pathways of hypoxia-induced vasodilation.
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Affiliation(s)
- George D Thorne
- Department of Molecular and Cellular Physiology, University of Cincinnati, College of Medicine, Cincinnati, Ohio 45267-0576, USA
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Michelakis ED, Hampl V, Nsair A, Wu X, Harry G, Haromy A, Gurtu R, Archer SL. Diversity in mitochondrial function explains differences in vascular oxygen sensing. Circ Res 2002; 90:1307-15. [PMID: 12089069 DOI: 10.1161/01.res.0000024689.07590.c2] [Citation(s) in RCA: 228] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Renal arteries (RAs) dilate in response to hypoxia, whereas the pulmonary arteries (PAs) constrict. In the PA, O2 tension is detected by an unidentified redox sensor, which controls K+ channel function and thus smooth muscle cell (SMC) membrane potential and cytosolic calcium. Mitochondria are important regulators of cellular redox status and are candidate vascular O2 sensors. Mitochondria-derived activated oxygen species (AOS), like H2O2, can diffuse to the cytoplasm and cause vasodilatation by activating sarcolemmal K+ channels. We hypothesize that mitochondrial diversity between vascular beds explains the opposing responses to hypoxia in PAs versus RAs. The effects of hypoxia and proximal electron transport chain (pETC) inhibitors (rotenone and antimycin A) were compared in rat isolated arteries, vascular SMCs, and perfused organs. Hypoxia and pETC inhibitors decrease production of AOS and outward K+ current and constrict PAs while increasing AOS production and outward K+ current and dilating RAs. At baseline, lung mitochondria have lower respiratory rates and higher rates of AOS and H2O2 production. Similarly, production of AOS and H2O2 is greater in PA versus RA rings. SMC mitochondrial membrane potential is more depolarized in PAs versus RAs. These differences relate in part to the lower expression of proximal ETC components and greater expression of mitochondrial manganese superoxide dismutase in PAs versus RAs. Differential regulation of a tonically produced, mitochondria-derived, vasodilating factor, possibly H2O2, can explain the opposing effects of hypoxia on the PAs versus RAs. We conclude that the PA and RA have different mitochondria.
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Affiliation(s)
- Evangelos D Michelakis
- Department of Medicine (Cardiology) and the Vascular Biology Group, University of Alberta, Edmonton, Alberta, Canada.
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Frisbee JC, Lombard JH. Parenchymal tissue cytochrome P450 4A enzymes contribute to oxygen-induced alterations in skeletal muscle arteriolar tone. Microvasc Res 2002; 63:340-3. [PMID: 11969311 DOI: 10.1006/mvre.2002.2409] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Jefferson C Frisbee
- Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee 53226, USA.
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Frisbee JC, Krishna UM, Falck JR, Lombard JH. Role of prostanoids and 20-HETE in mediating oxygen-induced constriction of skeletal muscle resistance arteries. Microvasc Res 2001; 62:271-83. [PMID: 11678630 DOI: 10.1006/mvre.2001.2341] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study determined the contribution of cytochrome P450 (CP450) 4A enzyme metabolites of arachidonic acid in mediating the constriction of isolated rat skeletal muscle resistance arteries in response to elevated PO2. Gracilis arteries (GA) were viewed via television microscopy and constrictor responses to elevated PO2 were measured with a video micrometer. Endothelium removal and treatment of GA with 17-octadecynoic acid (17-ODYA; suicide substrate inhibitor of CP450 4A enzymes) impaired oxygen-induced constriction of the vessels; treatment of endothelium-denuded GA with 17-ODYA eliminated responses to elevated PO2. NOS inhibition and inhibition of EET production had no effect on oxygen-induced constriction of the vessels, although cyclooxygenase inhibition with indomethacin impaired GA responses to elevated PO2. Treatment of GA with dibromododecenyl methylsulfimide (DDMS; inhibitor of 20-hydroxyeicosatetraenoic acid (20-HETE) production) or 6(Z),15(Z)-20-HEDE (antagonist for 20-HETE receptors) mimicked the effects of 17-ODYA on GA responses to elevated PO2. Treatment of vessels with iberiotoxin or glibenclamide reduced the constriction of the vessels in response to elevated PO2 while treatment with both K+ channel blockers eliminated oxygen-induced constriction of the vessels. Following treatment of GA with indomethacin and 20-HETE, the vessels failed to respond to elevated PO2. These results suggest that oxygen-induced constriction of skeletal muscle resistance arteries represents the combined effects of reduced prostanoid release from the vascular endothelium and enhanced 20-HETE production in vascular smooth muscle cells.
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Affiliation(s)
- J C Frisbee
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA
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Abstract
Large-conductance, Ca(2+)-activated K(+) (BK(Ca)) channels in smooth muscle cells are unique because they integrate changes in both intracellular Ca(2+) and membrane potential. Protein kinases such as cAMP-dependent protein kinase, cGMP-dependent protein kinase and protein kinase C can affect tissue function by 'tuning' the apparent Ca(2+)- and/or voltage-sensitivity of the BK(Ca) channel to physiological changes in both Ca(2+) concentrations and membrane potential. However, despite the central importance of kinase-mediated modulation of BK(Ca) channels in different smooth muscle tissues, many key issues, including the sites and mechanisms of actions of protein kinases, remain unresolved. In this article, the role of protein kinases in the regulation of BK(Ca) channels is discussed.
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Affiliation(s)
- R Schubert
- Institute of Physiology, University of Rostock, PSF 100888, D-18055, Rostock, Germany.
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Cheong A, Dedman AM, Beech DJ. Expression and function of native potassium channel [K(V)alpha1] subunits in terminal arterioles of rabbit. J Physiol 2001; 534:691-700. [PMID: 11483700 PMCID: PMC2278752 DOI: 10.1111/j.1469-7793.2001.00691.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. In this study we investigated the expression and function of the K(V)alpha1 subfamily of voltage-gated K(+) channels in terminal arterioles from rabbit cerebral circulation. 2. K(+) current was measured from smooth muscle cells within intact freshly isolated arteriolar fragments. Current activated on depolarisation positive of about -45 mV and a large fraction of this current was blocked by 3,4-diaminopyridine (3,4-DAP) or 4-aminopyridine (4-AP), inhibitors of K(V) channels. Expression of cRNA encoding K(V)1.6 in Xenopus oocytes also generated a 4-AP-sensitive K(+) current with a threshold for activation near -45 mV. 3. Immunofluorescence labelling revealed K(V)1.2 to be specifically localised to endothelial cells, and K(V)1.5 and K(V)1.6 to plasma membranes of smooth muscle cells. 4. K(V) channel current in arteriolar fragments was blocked by correolide (which is specific for the K(V)alpha1 family of K(V) channels) but was resistant to recombinant agitoxin-2 (rAgTX2; which inhibits K(V)1.6 but not K(V)1.5). Heterologously expressed K(V)2.1 was resistant to correolide, and K(V)1.6 was blocked by rAgTX2. 5. Arterioles that were mildly preconstricted and depolarised by 0.1-0.3 nM endothelin-1 constricted further in response to 3,4-DAP, 4-AP or correolide, but not to rAgTX2. 6. We suggest that K(V)alpha1 channels are expressed in smooth muscle cells of terminal arterioles, underlie a major part of the voltage-dependent K(+) current, and have a physiological function to oppose vasoconstriction. K(V)alpha1 complexes without K(V)1.5 appear to be uncommon.
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Affiliation(s)
- A Cheong
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK
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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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FRISBEE JEFFERSONC, ROMAN RICHARDJ, KRISHNA UMURALI, FALCK JOHNR, LOMBARD JULIANH. Altered Mechanisms Underlying Hypoxic Dilation of Skeletal Muscle Resistance Arteries of Hypertensive versus Normotensive Dahl Rats. Microcirculation 2001. [DOI: 10.1111/j.1549-8719.2001.tb00162.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Kunert MP, Roman RJ, Alonso-Galicia M, Falck JR, Lombard JH. Cytochrome P-450 omega-hydroxylase: a potential O(2) sensor in rat arterioles and skeletal muscle cells. Am J Physiol Heart Circ Physiol 2001; 280:H1840-5. [PMID: 11247799 DOI: 10.1152/ajpheart.2001.280.4.h1840] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The purposes of this study were to 1) further evaluate the possible role that vasoconstrictor metabolites of cytochrome P-450 (CYP) omega-hydroxylase plays in O(2)-induced constriction of arterioles in the rat skeletal muscle microcirculation, 2) determine whether omega-hydroxylases are expressed in rat cremaster muscle, and 3) determine whether the enzyme is located in the parenchyma or the arterioles. O(2)-induced constriction of third-order arterioles in the in situ cremaster muscle of Sprague-Dawley rats was significantly inhibited by the CYP inhibitors N-methyl-sulfonyl-12,12-dibromododec-11-enamide (DDMS; 50 microM) and 17-octadecynoic acid (ODYA; 10 microM). Immunoblot analysis with antibody raised against CYP4A protein indicated the presence of immunoreactive proteins in the cremaster muscle and in isolated arterioles and muscle fibers from this tissue. However, the molecular mass of the immunoreactive proteins was 85 kDa instead of the expected 50--52 kDa for CYP4A omega-hydroxylase isolated from rat liver or kidney. Treatment of the cremaster muscle with deglycosidases shifted the bands to the expected range which indicates that these proteins are likely glycosylated in skeletal muscle. Immunohistochemistry revealed intense staining of both muscle fibers and microvessels in the cremaster muscle. The results of this study indicate that O(2) sensing in the skeletal muscle microcirculation may be mediated by CYP4A omega-hydroxylases in both arterioles and parenchymal cells.
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Affiliation(s)
- M P Kunert
- Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA
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