scholarly journals Hypoxia reduces KCa channel activity by inducing Ca2+ spark uncoupling in cerebral artery smooth muscle cells

2007 ◽  
Vol 292 (6) ◽  
pp. C2122-C2128 ◽  
Author(s):  
Guiling Zhao ◽  
Adebowale Adebiyi ◽  
Qi Xi ◽  
Jonathan H. Jaggar
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Cerebral Artery ◽  
Single Channel ◽  
Muscle Cells ◽  
Channel Activity ◽  
Arterial Smooth Muscle ◽  
Current Frequency ◽  
Intracellular Ca ◽  
Systemic Arteries

Arterial smooth muscle cell large-conductance Ca2+-activated potassium (KCa) channels have been implicated in modulating hypoxic dilation of systemic arteries, although this is controversial. KCa channel activity in arterial smooth muscle cells is controlled by localized intracellular Ca2+ transients, termed Ca2+ sparks, but hypoxic regulation of Ca2+ sparks and KCa channel activation by Ca2+ sparks has not been investigated. We report here that in voltage-clamped (−40 mV) cerebral artery smooth muscle cells, a reduction in dissolved O2 partial pressure from 150 to 15 mmHg reversibly decreased Ca2+ spark-induced transient KCa current frequency and amplitude to 61% and 76% of control, respectively. In contrast, hypoxia did not alter Ca2+ spark frequency, amplitude, global intracellular Ca2+ concentration, or sarcoplasmic reticulum Ca2+ load. Hypoxia reduced transient KCa current frequency by decreasing the percentage of Ca2+ sparks that activated a transient KCa current from 89% to 63%. Hypoxia reduced transient KCa current amplitude by attenuating the amplitude relationship between Ca2+ sparks that remained coupled and the evoked transient KCa currents. Consistent with these data, in inside-out patches at −40 mV hypoxia reduced KCa channel apparent Ca2+ sensitivity and increased the Kd for Ca2+ from ∼17 to 32 μM, but did not alter single-channel amplitude. In summary, data indicate that hypoxia reduces KCa channel apparent Ca2+ sensitivity via a mechanism that is independent of cytosolic signaling messengers, and this leads to uncoupling of KCa channels from Ca2+ sparks. Transient KCa current inhibition due to uncoupling would oppose hypoxic cerebrovascular dilation.

Ketamine blocks Ca2+-activated K+ channels in rabbit cerebral arterial smooth muscle cells

2003 ◽  
Vol 285 (3) ◽  
pp. H1347-H1355 ◽  
Author(s):  
Jin Han ◽  
Nari Kim ◽  
Hyun Joo ◽  
Euiyong Kim
Keyword(s):  
Smooth Muscle ◽  
Patch Clamp ◽  
Smooth Muscle Cells ◽  
Cerebral Arteries ◽  
Muscle Cells ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Arterial Smooth Muscle ◽  
Clamp Technique ◽  
Arterial Smooth Muscle Cells

Although ketamine and Ca2+-activated K+ (KCa) channels have been implicated in the contractile activity regulation of cerebral arteries, no studies have addressed the specific interactions between ketamine and the KCa channels in cerebral arteries. The purpose of this study was to examine the direct effects of ketamine on KCa channel activities using the patch-clamp technique in single-cell preparations of rabbit middle cerebral arterial smooth muscle. We tested the hypothesis that ketamine modulates the KCa channel activity of the cerebral arterial smooth muscle cells of the rabbit. Vascular myocytes were isolated from rabbit middle cerebral arteries using enzymatic dissociation. Single KCa channel activities of smooth muscle cells from rabbit cerebral arteries were recorded using the patch-clamp technique. In the inside-out patches, ketamine in the micromolar range inhibited channel activity with a half-maximal inhibition of the ketamine conentration value of 83.8 ± 12.9 μM. The Hill coefficient was 1.2 ± 0.3. The slope conductance of the current-voltage relationship was 320.1 ± 2.0 pS between 0 and +60 mV in the presence of ketamine and symmetrical 145 mM K+. Ketamine had little effect on either the voltage-dependency or open- and closed-time histograms of KCa channel. The present study clearly demonstrates that ketamine inhibits KCa channel activities in rabbit middle cerebral arterial smooth muscle cells. This inhibition of KCa channels may represent a mechanism for ketamine-induced cerebral vasoconstriction.

Intravascular pressure regulates local and global Ca2+ signaling in cerebral artery smooth muscle cells

2001 ◽  
Vol 281 (2) ◽  
pp. C439-C448 ◽  
Author(s):  
Jonathan H. Jaggar
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Laser Scanning ◽  
Muscle Cells ◽  
Membrane Depolarization ◽  
Wave Frequency ◽  
Current Frequency ◽  
Frequency Wave ◽  
Intracellular Ca ◽  
Intravascular Pressure

The regulation of intracellular Ca2+ signals in smooth muscle cells and arterial diameter by intravascular pressure was investigated in rat cerebral arteries (∼150 μm) using a laser scanning confocal microscope and the fluorescent Ca2+ indicator fluo 3. Elevation of pressure from 10 to 60 mmHg increased Ca2+spark frequency 2.6-fold, Ca2+ wave frequency 1.9-fold, and global intracellular Ca2+ concentration ([Ca2+]i) 1.4-fold in smooth muscle cells, and constricted arteries. Ryanodine (10 μM), an inhibitor of ryanodine-sensitive Ca2+ release channels, or thapsigargin (100 nM), an inhibitor of the sarcoplasmic reticulum Ca2+-ATPase, abolished sparks and waves, elevated global [Ca2+]i, and constricted pressurized (60 mmHg) arteries. Diltiazem (25 μM), a voltage-dependent Ca2+ channel (VDCC) blocker, significantly reduced sparks, waves, and global [Ca2+]i, and dilated pressurized (60 mmHg) arteries. Steady membrane depolarization elevated Ca2+ signaling similar to pressure and increased transient Ca2+-sensitive K+ channel current frequency e-fold for ∼7 mV, and these effects were prevented by VDCC blockers. Data are consistent with the hypothesis that pressure induces a steady membrane depolarization that activates VDCCs, leading to an elevation of spark frequency, wave frequency, and global [Ca2+]i. In addition, pressure induces contraction via an elevation of global [Ca2+]i, whereas the net effect of sparks and waves, which do not significantly contribute to global [Ca2+]i in arteries pressurized to between 10 and 60 mmHg, is to oppose contraction.

Mobilization of intracellular Ca2+ by endothelin-1 in rat intrapulmonary arterial smooth muscle cells

2000 ◽  
Vol 278 (1) ◽  
pp. L157-L164 ◽  
Author(s):  
Larissa A. Shimoda ◽  
J. T. Sylvester ◽  
James S. K. Sham
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Arterial Smooth Muscle ◽  
Voltage Gated ◽  
Endothelin 1 ◽  
Intracellular Release ◽  
Intracellular Ca ◽  
Pulmonary Arterial ◽  
Arterial Smooth Muscle Cells

Endothelin-1 (ET-1) increases intracellular Ca2+ concentration ([Ca2+]i) in pulmonary arterial smooth muscle cells (PASMCs); however, the mechanisms for Ca2+ mobilization are not clear. We determined the contributions of extracellular influx and intracellular release to the ET-1-induced Ca2+ response using Indo 1 fluorescence and electrophysiological techniques. Application of ET-1 (10−10 to 10−8 M) to transiently (24–48 h) cultured rat PASMCs caused concentration-dependent increases in [Ca2+]i. At 10−8 M, ET-1 caused a large, transient increase in [Ca2+]i (>1 μM) followed by a sustained elevation in [Ca2+]i(<200 nM). The ET-1-induced increase in [Ca2+]i was attenuated (<80%) by extracellular Ca2+ removal; by verapamil, a voltage-gated Ca2+-channel antagonist; and by ryanodine, an inhibitor of Ca2+ release from caffeine-sensitive stores. Depleting intracellular stores with thapsigargin abolished the peak in [Ca2+]i, but the sustained phase was unaffected. Simultaneously measuring membrane potential and [Ca2+]i indicated that depolarization preceded the rise in [Ca2+]i. These results suggest that ET-1 initiates depolarization in PASMCs, leading to Ca2+influx through voltage-gated Ca2+ channels and Ca2+ release from ryanodine- and inositol 1,4,5-trisphosphate-sensitive stores.

Phosphatidylinositol 3,5-bisphosphate increases intracellular free Ca2+ in arterial smooth muscle cells and elicits vasocontraction

2011 ◽  
Vol 300 (6) ◽  
pp. H2016-H2026 ◽  
Author(s):  
Neerupma Silswal ◽  
Nikhil K. Parelkar ◽  
Michael J. Wacker ◽  
Marco Brotto ◽  
Jon Andresen
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Ryanodine Receptors ◽  
Muscle Cells ◽  
Arterial Smooth Muscle ◽  
Aortic Smooth Muscle Cells ◽  
Aortic Smooth Muscle ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Arterial Smooth Muscle Cells

Phosphoinositide (3,5)-bisphosphate [PI(3,5)P2] is a newly identified phosphoinositide that modulates intracellular Ca2+ by activating ryanodine receptors (RyRs). Since the contractile state of arterial smooth muscle depends on the concentration of intracellular Ca2+, we hypothesized that by mobilizing sarcoplasmic reticulum (SR) Ca2+ stores PI(3,5)P2 would increase intracellular Ca2+ in arterial smooth muscle cells and cause vasocontraction. Using immunohistochemistry, we found that PI(3,5)P2 was present in the mouse aorta and that exogenously applied PI(3,5)P2 readily entered aortic smooth muscle cells. In isolated aortic smooth muscle cells, exogenous PI(3,5)P2 elevated intracellular Ca2+, and it also contracted aortic rings. Both the rise in intracellular Ca2+ and the contraction caused by PI(3,5)P2 were prevented by antagonizing RyRs, while the majority of the PI(3,5)P2 response was intact after blockade of inositol (1,4,5)-trisphosphate receptors. Depletion of SR Ca2+ stores with thapsigargin or caffeine and/or ryanodine blunted the Ca2+ response and greatly attenuated the contraction elicited by PI(3,5)P2. The removal of extracellular Ca2+ or addition of verapamil to inhibit voltage-dependent Ca2+ channels reduced but did not eliminate the Ca2+ or contractile responses to PI(3,5)P2. We also found that PI(3,5)P2 depolarized aortic smooth muscle cells and that LaCl3 inhibited those aspects of the PI(3,5)P2 response attributable to extracellular Ca2+. Thus, full and sustained aortic contractions to PI(3,5)P2 required the release of SR Ca2+, probably via the activation of RyR, and also extracellular Ca2+ entry via voltage-dependent Ca2+ channels.

scholarly journals Type 1 inositol 1,4,5-trisphosphate receptors mediate UTP-induced cation currents, Ca2+ signals, and vasoconstriction in cerebral arteries

2008 ◽  
Vol 295 (5) ◽  
pp. C1376-C1384 ◽  
Author(s):  
Guiling Zhao ◽  
Adebowale Adebiyi ◽  
Eva Blaskova ◽  
Qi Xi ◽  
Jonathan H. Jaggar
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Cerebral Artery ◽  
Purinergic Receptor ◽  
Cerebral Arteries ◽  
Muscle Cells ◽  
Physiological Functions ◽  
Inositol 1,4,5 Trisphosphate ◽  
Intracellular Ca

Inositol 1,4,5-trisphosphate receptors (IP3Rs) regulate diverse physiological functions, including contraction and proliferation. There are three IP3R isoforms, but their functional significance in arterial smooth muscle cells is unclear. Here, we investigated relative expression and physiological functions of IP3R isoforms in cerebral artery smooth muscle cells. We show that 2-aminoethoxydiphenyl borate and xestospongin C, membrane-permeant IP3R blockers, reduced Ca2+ wave activation and global intracellular Ca2+ ([Ca2+]i) elevation stimulated by UTP, a phospholipase C-coupled purinergic receptor agonist. Quantitative PCR, Western blotting, and immunofluorescence indicated that all three IP3R isoforms were expressed in acutely isolated cerebral artery smooth muscle cells, with IP3R1 being the most abundant isoform at 82% of total IP3R message. IP3R1 knockdown with short hairpin RNA (shRNA) did not alter baseline Ca2+ wave frequency and global [Ca2+]i but abolished UTP-induced Ca2+ wave activation and reduced the UTP-induced global [Ca2+]i elevation by ∼61%. Antibodies targeting IP3R1 and IP3R1 knockdown reduced UTP-induced nonselective cation current ( Icat) activation. IP3R1 knockdown also reduced UTP-induced vasoconstriction in pressurized arteries with both intact and depleted sarcoplasmic reticulum (SR) Ca2+ by ∼45%. These data indicate that IP3R1 is the predominant IP3R isoform expressed in rat cerebral artery smooth muscle cells. IP3R1 stimulation contributes to UTP-induced Icat activation, Ca2+ wave generation, global [Ca2+]i elevation, and vasoconstriction. In addition, IP3R1 activation constricts cerebral arteries in the absence of SR Ca2+ release by stimulating plasma membrane Icat.

Potassium currents in cultured human pulmonary arterial smooth muscle cells

1996 ◽  
Vol 80 (4) ◽  
pp. 1187-1196 ◽  
Author(s):  
W. Peng ◽  
S. V. Karwande ◽  
J. R. Hoidal ◽  
I. S. Farrukh
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Single Channel ◽  
Muscle Cells ◽  
Arterial Smooth Muscle ◽  
Whole Cell ◽  
Low Concentrations ◽  
Pulmonary Arterial ◽  
Arterial Smooth Muscle Cells ◽  
Pulmonary Arterial Smooth Muscle

In this study, using whole cell and single-channel configurations of the patch-clamp technique, we characterized K+ currents (IK) in cultured human pulmonary arterial smooth muscle cells. The net whole cell outward membrane current (IKo) was activated at potentials positive to -60 mV. One component of IKo, IK(dr), was inhibited by 4-aminopyridine (4-AP) and high concentrations of tetraethylammonium (TEA) but was Ca2+ and charybdotoxin (CTX) insensitive. The other component of IKo, IK(Ca), was voltage and Ca2+ dependent and was inhibited by CTX and low concentrations of TEA. Activation of IKo in single-channel recordings was voltage dependent and demonstrated a high-conductance channel (245 +/- 2 pS) that was Ca2+ and CTX sensitive [IK(Ca)] and a low-conductance channel (109 +/- 2 pS) that was inhibited by 4-AP [IK(dr)] but was insensitive to low concentrations of TEA or to an increase in intracellular [Ca2+]. In isolated pulmonary arterial rings, TEA and 4-AP caused an additive increase in arterial tension. To our knowledge these data provide the first characterization of the IK in human pulmonary arterial smooth muscle cells and indicate that IK(Ca) and IK(dr) play an important role in maintaining pulmonary vascular tone. The data confirm previous observations in pulmonary smooth muscle cells of animal models.

scholarly journals Genetic ablation of caveolin-1 modifies Ca2+ spark coupling in murine arterial smooth muscle cells

2006 ◽  
Vol 290 (6) ◽  
pp. H2309-H2319 ◽  
Author(s):  
Xiaoyang Cheng ◽  
Jonathan H. Jaggar
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Cerebral Artery ◽  
Muscle Cells ◽  
Channel Blockers ◽  
Current Frequency ◽  
Genetic Ablation ◽  
Caveolin 1 ◽  
Channel Density ◽  
Voltage Dependent

L-type, voltage-dependent calcium (Ca2+) channels, ryanodine-sensitive Ca2+ release (RyR) channels, and large-conductance Ca2+-activated potassium (KCa) channels comprise a functional unit that regulates smooth muscle contractility. Here, we investigated whether genetic ablation of caveolin-1 (cav-1), a caveolae protein, alters Ca2+ spark to KCa channel coupling and Ca2+ spark regulation by voltage-dependent Ca2+ channels in murine cerebral artery smooth muscle cells. Caveolae were abundant in the sarcolemma of control (cav-1+/+) cells but were not observed in cav-1-deficient (cav-1−/−) cells. Ca2+ spark and transient KCa current frequency were approximately twofold higher in cav-1−/− than in cav-1+/+ cells. Although voltage-dependent Ca2+ current density was similar in cav-1+/+ and cav-1−/− cells, diltiazem and Cd2+, voltage-dependent Ca2+ channel blockers, reduced transient KCa current frequency to ∼55% of control in cav-1+/+ cells but did not alter transient KCa current frequency in cav-1−/− cells. Furthermore, although KCa channel density was elevated in cav-1−/− cells, transient KCa current amplitude was similar to that in cav-1+/+ cells. Higher Ca2+ spark frequency in cav-1−/− cells was not due to elevated intracellular Ca2+ concentration, sarcoplasmic reticulum Ca2+ load, or nitric oxide synthase activity. Similarly, Ca2+ spark amplitude and spread, the percentage of Ca2+ sparks that activated a transient KCa current, the amplitude relationship between sparks and transient KCa currents, and KCa channel conductance and apparent Ca2+ sensitivity were similar in cav-1+/+ and cav-1−/− cells. In summary, cav-1 ablation elevates Ca2+ spark and transient KCa current frequency, attenuates the coupling relationship between voltage-dependent Ca2+ channels and RyR channels that generate Ca2+ sparks, and elevates KCa channel density but does not alter transient KCa current activation by Ca2+ sparks. These findings indicate that cav-1 is required for physiological Ca2+ spark and transient KCa current regulation in cerebral artery smooth muscle cells.

Fatty acid modifies Ca 2+ -dependent potassium channel activity in smooth muscle cells from the human aorta

1989 ◽  
Vol 237 (1288) ◽  
pp. 259-266 ◽  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Single Channel ◽  
Membrane Surface ◽  
Muscle Cells ◽  
Human Aorta ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Membrane Fluidization ◽  
Potassium Channel Activity

By using the patch–clamp technique the effect of 2-decenoic acid (DA) on Ca 2+ -activated potassium (K + ) channels in the membrane of smooth muscle cells from the human aorta was studied. In the presence of 0.5 μM Ca 2+ and 2 mM Mg 2+ on the cytoplasmic side of the membrane, a more than tenfold elevation in the probability of the channels being open ( p o ) was observed under the effect of DA. With divalent cation concentrations of less than 1 nM DA caused a more than twofold elevation in p o . In the DA-treated membranes Mg 2+ ions, which normally fail to activate the channels, brought about a nearly threefold increase in the channel activity when applied to the inner membrane surface. Channel sensitivity to the activating effect of cytoplasmic Ca 2+ ions did not increase with the application of DA. Single-channel conductance was unchanged by DA exposure. We suggest that DA alters the Ca 2+ -binding mechanism of the channel, increasing its sensitivity to Mg 2+ ions, presumably owing to membrane fluidization.

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