Vasa recta pericytes express a strong inward rectifier K+ conductance

2006 ◽  
Vol 290 (6) ◽  
pp. R1601-R1607 ◽  
Author(s):  
Chunhua Cao ◽  
Jae Hwan Goo ◽  
Whaseon Lee-Kwon ◽  
Thomas L. Pallone
Keyword(s):  
Smooth Muscle ◽  
Binding Constants ◽  
Inward Rectifier ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Inward Rectifier Potassium Channels ◽  
Whole Cell Patch Clamp ◽  
Vasa Recta ◽  
Voltage Dependent ◽  
Inward Currents

Strong inward rectifier potassium channels are expressed by some vascular smooth muscle cells and facilitate K+-induced hyperpolarization. Using whole cell patch clamp of isolated descending vasa recta (DVR), we tested whether strong inward rectifier K+ currents are present in smooth muscle and pericytes. Increasing extracellular K+ from 5 to 50 and 140 mmol/l induced inward rectifying currents. Those currents were Ba2+ sensitive and reversed at the K+ equilibrium potential imposed by the electrode and extracellular buffers. Ba2+ binding constants in symmetrical K+ varied between 0.24 and 24 μmol/l at −150 and −20 mV, respectively. Ba2+ blockade was time and voltage dependent. Extracellular Cs+ also blocked the inward currents with binding constants between 268 and 4,938 μmol/l at −150 and −50 mV, respectively. Ba2+ (30 μmol/l) and ouabain (1 mmol/l) depolarized pericytes by an average of 11 and 24 mV, respectively. Elevation of extracellular K+ from 5 to 10 mmol/l hyperpolarized pericytes by 6 mV. That hyperpolarization was reversed by Ba2+ (30 μmol/l). We conclude that strong inward rectifier K+ channels and Na+-K+-ATPase contribute to resting potential and that KIR channels can mediate K+-induced hyperpolarization of DVR pericytes.

Potassium Channel-mediated Hyperpolarization of Mesenteric Vascular Smooth Muscle by Isoflurane 

1999 ◽  
Vol 90 (3) ◽  
pp. 779-788 ◽  
Author(s):  
Naohiro Kokita ◽  
Thomas A. Stekiel ◽  
Mitsuaki Yamazaki ◽  
Zeljko J. Bosnjak ◽  
John P. Kampine ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Potassium Channels ◽  
Vascular Smooth Muscle ◽  
Potassium Channel ◽  
Potassium Conductance ◽  
Inward Rectifier ◽  
Sprague Dawley ◽  
Resistance Arteries ◽  
Inward Rectifier Potassium Channels ◽  
Voltage Dependent

Background A primary source of calcium (Ca2+) necessary for excitation contraction in vascular smooth muscle (VSM) is influx via voltage-dependent Ca2+ channels. Thus, force generation in VSM is coupled closely to resting transmembrane potential, which itself is primarily a function of potassium conductance. Previously, the authors reported that volatile anesthetics hyperpolarize VSM of small mesenteric resistance arteries and capacitance veins. The current study was designed to determine whether isoflurane-mediated hyperpolarization is the result of specific effects on one or more of four types of potassium channels known to exist in VSM. Methods Transmembrane potentials (Em) were recorded from in situ mesenteric capacitance and resistance vessels in Sprague-Dawley rats weighing 250-300 g. In separate experiments, selective inhibitors of each of four types of potassium channels known to exist in VSM were administered in the superfusate of the vessel preparations to assess their effects on isoflurane-mediated hyperpolarization. Results Resting VSM Em ranged from -38 to -43 mV after local sympathetic denervation. Isoflurane produced a significant hyperpolarization (2.7-4.3 mV), whereas each potassium channel inhibitor significantly depolarized (2.8-8.5 mV) the VSM. Both 100 nM iberiotoxin (inhibitor of high conductance calcium-activated potassium channels) and 1 microM glybenclamide (inhibitor of adenosine triphosphatase-sensitive potassium channels) significantly inhibited VSM hyperpolarization induced by 1 MAC (minimum alveolar concentration) levels of inhaled isoflurane (0.1-0.9 mV Em change, which was not significant). In contrast, isoflurane hyperpolarized the VSM significantly despite the presence of 3 mM 4 aminopyridine (inhibitor of voltage-dependent potassium channels) or 10 microM barium chloride (an inhibitor of inward rectifier potassium channels) (3.7-8.2 mV change in VSM Em). Conclusions These results suggest that isoflurane-mediated hyperpolarization (and associated relaxation) of VSM can be attributed in part to an enhanced (or maintained) opening of calcium-activated and adenosine triphosphate-sensitive potassium channels but not voltage-dependent or inward rectifier potassium channels.

Screening Technologies for Inward Rectifier Potassium Channels: Discovery of New Blockers and Activators

2020 ◽  
Vol 25 (5) ◽  
pp. 420-433 ◽  
Author(s):  
Kenneth B. Walsh
Keyword(s):  
Membrane Potential ◽  
G Protein ◽  
Critical Role ◽  
Inward Rectifier ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Inward Rectification ◽  
Resting Membrane Potential ◽  
Kir Channels ◽  
Inward Rectifier Potassium Channels

K+ channels play a critical role in maintaining the normal electrical activity of excitable cells by setting the cell resting membrane potential and by determining the shape and duration of the action potential. In nonexcitable cells, K+ channels establish electrochemical gradients necessary for maintaining salt and volume homeostasis of body fluids. Inward rectifier K+ (Kir) channels typically conduct larger inward currents than outward currents, resulting in an inwardly rectifying current versus voltage relationship. This property of inward rectification results from the voltage-dependent block of the channels by intracellular polyvalent cations and makes these channels uniquely designed for maintaining the resting potential near the K+ equilibrium potential (EK). The Kir family of channels consist of seven subfamilies of channels (Kir1.x through Kir7.x) that include the classic inward rectifier (Kir2.x) channel, the G-protein-gated inward rectifier K+ (GIRK) (Kir3.x), and the adenosine triphosphate (ATP)-sensitive (KATP) (Kir 6.x) channels as well as the renal Kir1.1 (ROMK), Kir4.1, and Kir7.1 channels. These channels not only function to regulate electrical/electrolyte transport activity, but also serve as effector molecules for G-protein-coupled receptors (GPCRs) and as molecular sensors for cell metabolism. Of significance, Kir channels represent promising pharmacological targets for treating a number of clinical conditions, including cardiac arrhythmias, anxiety, chronic pain, and hypertension. This review provides a brief background on the structure, function, and pharmacology of Kir channels and then focuses on describing and evaluating current high-throughput screening (HTS) technologies, such as membrane potential-sensitive fluorescent dye assays, ion flux measurements, and automated patch clamp systems used for Kir channel drug discovery.

Inward rectifier K+ currents in smooth muscle cells from rat resistance-sized cerebral arteries

1993 ◽  
Vol 265 (5) ◽  
pp. C1363-C1370 ◽  
Author(s):  
J. M. Quayle ◽  
J. G. McCarron ◽  
J. E. Brayden ◽  
M. T. Nelson
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Cerebral Arteries ◽  
Muscle Cells ◽  
Inward Rectifier ◽  
Equilibrium Potential ◽  
Membrane Hyperpolarization ◽  
Whole Cell ◽  
Inward Currents ◽  
K Currents

Inward rectifier K+ channels have been implicated in the control of membrane potential and external K(+)-induced dilations of small cerebral arteries. In the present study, whole cell K+ currents through the inward rectifier K+ channel were measured in single smooth muscle cells isolated from the posterior cerebral artery of Wistar-Kyoto rats. The whole cell K+ current-voltage relationship showed inward rectification. Inward currents were recorded negative to the K+ equilibrium potential, whereas outward currents were small. When extracellular K+ was elevated, the zero current potential shifted to the new K+ equilibrium potential, and the conductance of the inward current increased. Inward currents were reduced by external barium or cesium. Inhibition by barium and cesium increased with membrane hyperpolarization. The half-inhibition constant for barium was 2.2 microM at -60 mV, increasing e-fold for a 23-mV depolarization. We provide the first direct measurements of inward rectifier K+ currents in single smooth muscle cells and show that external barium ions are effective blockers of these currents.

Descending vasa recta endothelia express inward rectifier potassium channels

2007 ◽  
Vol 293 (4) ◽  
pp. F1248-F1255 ◽  
Author(s):  
Chunhua Cao ◽  
Whaseon Lee-Kwon ◽  
Kristie Payne ◽  
Aurélie Edwards ◽  
Thomas L. Pallone
Keyword(s):  
Endothelial Cells ◽  
Membrane Potential ◽  
Potassium Channels ◽  
Inward Rectifier ◽  
Equilibrium Potential ◽  
Dependent Manner ◽  
Membrane Hyperpolarization ◽  
Inward Rectifier Potassium Channels ◽  
Vasa Recta ◽  
Inwardly Rectifying

Descending vasa recta (DVR) are capillary-sized microvessels that supply blood flow to the renal medulla. They are composed of contractile pericytes and endothelial cells. In this study, we used the whole cell patch-clamp method to determine whether inward rectifier potassium channels (KIR) exist in the endothelia, affect membrane potential, and modulate intracellular Ca2+ concentration ([Ca2+]cyt). The endothelium was accessed for electrophysiology by removing abluminal pericytes from collagenase-digested vessels. KIR currents were recorded using symmetrical 140 mM K+ solutions that served to maximize currents and eliminate cell-to-cell coupling by closing gap junctions. Large, inwardly rectifying currents were observed at membrane potentials below the equilibrium potential for K+. Ba2+ potently inhibited those currents in a voltage-dependent manner, with affinity k = 0.18, 0.33, 0.60, and 1.20 μM at −160, −120, −80, and −40 mV, respectively. Cs+ also blocked those currents with k = 20, 48, 253, and 1,856 μM at −160, −120, −80, and −40 mV, respectively. In the presence of 1 mM ouabain, increasing extracellular K+ concentration from 5 to 10 mM hyperpolarized endothelial membrane potential by 15 mV and raised endothelial [Ca2+]cyt. Both the K+-induced membrane hyperpolarization and the [Ca2+]cyt elevation were reversed by Ba2+. Immunochemical staining verified that both pericytes and endothelial cells of DVR express KIR2.1, KIR2.2, and KIR2.3 subunits. We conclude that strong, inwardly rectifying KIR2.x isoforms are expressed in DVR and mediate K+-induced hyperpolarization of the endothelium.

Beta-adrenergic actions on membrane electrical properties of dissociated smooth muscle cells

1988 ◽  
Vol 254 (3) ◽  
pp. C423-C431 ◽  
Author(s):  
H. Yamaguchi ◽  
T. W. Honeyman ◽  
F. S. Fay
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Electrical Properties ◽  
Smooth Muscle Cells ◽  
Input Resistance ◽  
Muscle Cells ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Dependent Manner ◽  
Beta Adrenergic

Studies were carried out to determine the effects of the beta-adrenergic agent, isoproterenol (ISO), on membrane electrical properties in single smooth muscle cells enzymatically dispersed from toad stomach. In cells bathed in buffer of physiological composition, the average resting potential was -56.4 +/- 1.4 mV (mean +/- SE, n = 35). The dominant effect of exposure to ISO was hyperpolarization. The hyperpolarization was apparent in all cells studied and averaged 11.6 +/- 1.2 mV (n = 27). In the majority of the cells, hyperpolarization was accompanied by a decreased input resistance (Rin). Often the change in resistance appeared to lag behind the change in membrane potential. The lack of coincident changes in membrane potential and resistance may reflect a superposition of the outward rectification properties of the membrane on beta-adrenergic-induced increases in ionic conductance. In about half of the cells, an initial small depolarization (3.1 +/- 0.3 mV, n = 14) was accompanied by a small but distinct increase in Rin (12 +/- 2.5%). When membrane potential was made more negative than the estimated equilibrium potential for K+ (EK) by injection of current, ISO also produced biphasic effects, an initial hyperpolarization which reversed to a sustained depolarization to a value (-90 mV) near the estimated EK. The hyperpolarization by ISO could be diminished in a time-dependent manner by previous exposure to ouabain. The inhibition by ouabain, however, appeared to be a fortuitous result of glycoside-induced positive shifts in EK. These observations indicate that the dominant electrophysiological effect of beta-adrenergic stimuli is to hyperpolarize the cell membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Membrane currents in canine bronchial artery and their regulation by excitatory agonists

2002 ◽  
Vol 282 (6) ◽  
pp. L1358-L1365 ◽  
Author(s):  
Q. J. Li ◽  
L. J. Janssen
Keyword(s):  
Smooth Muscle ◽  
Bronchial Artery ◽  
Similar Degree ◽  
Ion Currents ◽  
Significant Suppression ◽  
Bronchial Smooth Muscle ◽  
Voltage Dependent ◽  
Inward Currents ◽  
Bronchial Smooth Muscle Cells ◽  
Airway Physiology

The bronchial vasculature plays an important role in airway physiology and pathophysiology. We investigated the ion currents in canine bronchial smooth muscle cells using patch-clamp techniques. Sustained outward K+current evoked by step depolarizations was significantly inhibited by tetraethylamonium (1 and 10 mM) or by charybdotoxin (10−6M) but was not significantly affected by 4-aminopyridine (1 or 5 mM), suggesting that it was primarily a Ca2+-activated K+current. Consistent with this, the K+current was markedly increased by raising external Ca2+to 4 mM but was decreased by nifedipine (10−6M) or by removing external Ca2+. When K+currents were blocked (by Cs+in the pipette), step depolarizations evoked transient inward currents with characteristics of L-type Ca2+current as follows: 1) activation that was voltage dependent (threshold and maximal at −50 and −10 mV, respectively); 2) inactivation that was time dependent and voltage dependent (voltage causing 50% maximal inactivation of −26 ± 22 mV); and 3) blockade by nifedipine (10−6M). The thromboxane mimetic U-46619 (10−6M) caused a marked augmentation of outward K+current (as did 10 mM caffeine) lasting only 10–20 s; this was followed by significant suppression of the K+current lasting several minutes. Phenylephrine (10−4M) also suppressed the K+current to a similar degree but did not cause the initial transient augmentation. None of these three agonists elicited inward current of any kind. We conclude that bronchial arterial smooth muscle expresses Ca2+-dependent K+channels and voltage-dependent Ca2+channels and that its excitation does not involve activation of Cl−channels.

Effects of sevoflurane on inward rectifier K+ current in guinea pig ventricular cardiomyocytes

1997 ◽  
Vol 273 (1) ◽  
pp. H324-H332 ◽  
Author(s):  
A. Stadnicka ◽  
Z. J. Bosnjak ◽  
J. P. Kampine ◽  
W. M. Kwok
Keyword(s):  
Steady State ◽  
Guinea Pig ◽  
Outward Current ◽  
Inward Rectifier ◽  
Equilibrium Potential ◽  
Ventricular Cardiomyocytes ◽  
Steady State Current ◽  
Voltage Dependent ◽  
Current Activation ◽  
Extracellular Side

The effects of sevoflurane on the inward rectifier potassium current (IKIR) were examined in guinea pig ventricular cardiomyocytes using the whole cell patch-clamp methodology. Sevoflurane had a unique dual effect on the steady-state current amplitude, producing a reversible, concentration- and voltage-dependent block of the inward current at potentials negative to the potassium equilibrium potential (EK) but enhancing the outward current positive to EK. Accordingly, the steady-state conductance negative to EK was reduced by sevoflurane, but conductance positive to EK was increased. The chord conductance-voltage relationship showed depolarizing shifts at 0.7, 1.3, and 1.6 mM sevoflurane. When the myocytes were dialyzed with 10 mM Mg2+, but not with 1.0 mM Mg2+, sevoflurane further slowed current activation kinetics. With 10 mM intracellular Mg2+, the outward current enhancement by sevoflurane and the associated shifts in half-activation potential were abolished. Polyamines abolished all effects of sevoflurane on IKIR. With the use of the Woodhull model for voltage-dependent block, we determined the sevoflurane interaction site with the inward rectifier potassium channel to be at an electrical distance of 0.2 from the extracellular side.

scholarly journals Calcium Channels and Nifedipine Inhibition of Serotonin-Induced [3H]Thymidine Incorporation in Cultured Cerebral Smooth Muscle Cells

1992 ◽  
Vol 12 (1) ◽  
pp. 139-146 ◽  
Author(s):  
Thomas A. Kent ◽  
Allahyar Jazayeri ◽  
J. Marc Simard
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Thymidine Incorporation ◽  
Membrane Surface ◽  
Muscle Cells ◽  
Thymidine Uptake ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
Alternate Mechanism

Cultures of smooth muscle cells were prepared from the basilar artery of adult guinea pigs. Passaged cultures (10–30 passages) that expressed serotonin receptors were studied using [3H]thymidine incorporation. When tested in quiescent medium, serotonin potently stimulated [3H]thymidine incorporation (EC50 of 31 n M) by as much as 400% at 24 h. The number of cells was not significantly increased at 24 or 48 h. At concentrations of 10−8–10−5 M 5-HT, [3H]thymidine uptake was reduced 40–50% by the dihydropyridine Ca2+ channel blocker, nifedipine (1 μ M). To demonstrate a possible mechanism for the sensitivity to nifedipine, Ca2+ currents were measured using the whole cell patch clamp technique. The cells expressed dihydropyridine-sensitive L-type Ca2+ channels, but not other subtypes of Ca2+ channels, as indicated by the kinetic and voltage-dependent characteristics of the current and by the stimulatory effect of Bay K 8644. The magnitude of the Ca2+ currents was related exponentially to the membrane surface area, measured as cell capacitance. These data support the association of dihydropyridine-sensitive Ca2+ channels with mitogenesis in vascular smooth muscle, and suggest an alternate mechanism of action for the beneficial effect of dihydropyridines in prophylaxis of cerebral vasospasm.

Inward rectifier K+ currents in smooth muscle cells from rat coronary arteries: block by Mg2+, Ca2+, and Ba2+

1996 ◽  
Vol 271 (2) ◽  
pp. H696-H705 ◽  
Author(s):  
B. E. Robertson ◽  
A. D. Bonev ◽  
M. T. Nelson
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Coronary Artery ◽  
Smooth Muscle Cells ◽  
Coronary Arteries ◽  
Inward Rectifier ◽  
Inward Rectification ◽  
K Channels ◽  
Inward Currents ◽  
K Currents

Inward rectifier K+ channels have been implicated in the control of membrane potential and external K(+)-induced dilations of small coronary arteries. To identify and characterize inward rectifier K+ currents in coronary artery smooth muscle, whole cell K+ currents in smooth muscle cells enzymatically isolated from rat coronary (septal) arteries (diameters, 100-150 microns) were measured in the conventional and perforated configurations of the patch-clamp technique. Ba(2+)-sensitive, whole cell K+ current-voltage relationships exhibited inward rectification. Blockers of Ca(2+)-activated K+ channels (1 mM tetraethylammonium ion), ATP-sensitive K+ channels (10 microM glibenclamide), and voltage-dependent K+ channels (1 mM 4-aminopyridine) in smooth muscle did not affect inward rectifier K+ currents. The nonselective K+ channel inhibitor phencyclidine (100 microM) reduced inward rectifier K+ currents by approximately 50%. External Ba2+ reduced inward currents, with membrane potential hyperpolarization increasing inhibition. The half-inhibition constant for Ba2+ was 2.1 microM at -60 mV, decreasing e-fold for a 25-mV hyperpolarization. External Cs+ also blocked inward rectifier K+ currents, with the half-inhibition constant for Cs+ of 2.9 mM at -60 mV. External Ca2+ and Mg2+ reduced inward rectifier K+ currents. At -60 mV, Ca2+ and Mg2+ (1 mM) reduced inward currents by 33 and 21%, respectively. Inward rectification was not affected by dialysis of the cell's interior with a nominally Ca(2+)- and Mg(2+)-free solution. These findings indicate that inward rectifier K+ channels exist in coronary artery smooth muscle and that Ba2+ may be a useful probe for the functional role of inward rectifier K+ channels in coronary arteries.

scholarly journals Functional characterization of voltage-dependent Ca2+ channels in mouse pulmonary arterial smooth muscle cells: divergent effect of ROS

2013 ◽  
Vol 304 (11) ◽  
pp. C1042-C1052 ◽  
Author(s):  
Eun A. Ko ◽  
Jun Wan ◽  
Aya Yamamura ◽  
Adriana M. Zimnicka ◽  
Hisao Yamamura ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Vascular Function ◽  
Electromechanical Coupling ◽  
Functional Characterization ◽  
Muscle Cells ◽  
Pulmonary Vascular Disease ◽  
High K ◽  
Voltage Dependent ◽  
Inward Currents

Electromechanical coupling via membrane depolarization-mediated activation of voltage-dependent Ca2+ channels (VDCC) is an important mechanism in regulating pulmonary vascular tone, while mouse is an animal model often used to study pathogenic mechanisms of pulmonary vascular disease. The function of VDCC in mouse pulmonary artery (PA) smooth muscle cells (PASMC), however, has not been characterized, and their functional role in reactive oxygen species (ROS)-mediated regulation of vascular function remains unclear. In this study, we characterized the electrophysiological and pharmacological properties of VDCC in PASMC and the divergent effects of ROS produced by xanthine oxidase (XO) and hypoxanthine (HX) on VDCC in PA and mesenteric artery (MA). Our data show that removal of extracellular Ca2+ or application of nifedipine, a dihydropyridine VDCC blocker, both significantly inhibited 80 mM K+-mediated PA contraction. In freshly dissociated PASMC, the maximum inward Ca2+ currents were −2.6 ± 0.2 pA/pF at +10 mV (with a holding potential of −70 mV). Window currents were between −40 and +10 mV with a peak at −15.4 mV. Nifedipine inhibited currents with an IC50 of 0.023 μM, and 1 μM Bay K8644, a dihydropyridine VDCC agonist, increased the inward currents by 61%. XO/HX attenuated 60 mM K+-mediated increase in cytosolic free Ca2+ concentration ([Ca2+]cyt) due to Ca2+ influx through VDCC in PASMC. Exposure to XO/HX caused relaxation in PA preconstricted by 80 mM K+ but not in aorta and MA. In contrast, H2O2 inhibited high K+-mediated increase in [Ca2+]cyt and caused relaxation in both PA and MA. Indeed, RT-PCR and Western blot analysis revealed significantly lower expression of CaV1.3 in MA compared with PA. Thus our study characterized the properties of VDCC and demonstrates that ROS differentially regulate vascular contraction by regulating VDCC in PA and systemic arteries.

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