Potassium current in circular smooth muscle of human jejunum activated by fenamates

1993 ◽  
Vol 265 (5) ◽  
pp. G873-G879 ◽  
Author(s):  
G. Farrugia ◽  
J. L. Rae ◽  
M. G. Sarr ◽  
J. H. Szurszewski
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Outward Current ◽  
Major Determinant ◽  
Flufenamic Acid ◽  
Blood Levels ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Circular Smooth Muscle ◽  
Normal Human

Thirty-eight cells, freshly isolated from circular smooth muscle of normal human jejunum obtained from nine patients undergoing weight-reduction surgery for morbid obesity, were patch clamped using a perforated patch-clamp technique. A highly potassium-selective voltage-dependent outward current was present in all cells. The current was carried by a 220-pS channel that activated near -75 mV and reached unit open probability at about +10 mV. Blockade of the current by quinidine (50 microM) and tetraethylammonium (25 mM) was accompanied by membrane depolarization to 0 to -3 mV, suggesting that this current was the major determinant of the membrane potential. Flufenamic and mefenamic acid at concentrations comparable with blood levels reached when these drugs are used in clinical therapy as nonsteroidal anti-inflammatory agents, activated the potassium outward current and hyperpolarized the membrane potential. The shift in the membrane potential for 250 microM flufenamic acid was -36 +/- 24 (SD) mV. Activation was rapid (seconds) and reversible. It was concluded that normal human jejunal circular smooth muscle cells have a highly potassium-selective outward current, which is the major determinant of the membrane potential and which is activated by fenamates.

Nitric oxide mediates outward potassium currents in opossum esophageal circular smooth muscle

1996 ◽  
Vol 270 (6) ◽  
pp. G932-G938 ◽  
Author(s):  
J. Jury ◽  
K. R. Boev ◽  
E. E. Daniel
Keyword(s):  
Nitric Oxide ◽  
Smooth Muscle ◽  
Circular Muscle ◽  
Outward Current ◽  
Equilibrium Potential ◽  
Patch Clamp Technique ◽  
Pipette Solution ◽  
Whole Cell ◽  
Circular Smooth Muscle ◽  
Outward Currents

Single smooth muscle cells from the opossum body circular muscle were isolated and whole cell currents were characterized by the whole cell patch-clamp technique. When the cells were held at -50 mV and depolarized to 70 mV in 20-mV increments, initial small inactivating inward currents were evoked (-30 to 30 mV) followed by larger sustained outward currents. Depolarization from a holding potential of -90 mV evoked an initial fast inactivating outward current sensitive to 4-aminopyridine but not to high levels of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). The outward currents reversed near K+ equilibrium potential and were abolished when KCl was replaced by CsCl in the pipette solution. The sustained outward current was inhibited by quinine and cesium. High EGTA in the pipette solution reduced but did not abolish the sustained outward currents, suggesting that both Ca(2+)-dependent and -independent currents were evoked. The nitric oxide (NO)-releasing agents Sin-1 and sodium nitroprusside increased outward K+ currents. High levels of EGTA in the pipette solution abolished the increase in outward current induced by Sin-1. The presence of cyclopiazonic acid, an inhibitor of the sarcoplasmic reticulum (SR) Ca2+ pump, blocked the effects of NO-releasing agents. We conclude that NO release activates K+ outward currents in opossum esophagus circular muscle, which may depend on Ca2+ release from the SR stores.

scholarly journals Small-conductance Ca2+-dependent K+ channels activated by ATP in murine colonic smooth muscle

1997 ◽  
Vol 273 (6) ◽  
pp. C2010-C2021 ◽  
Author(s):  
S. D. Koh ◽  
G. M. Dick ◽  
K. M. Sanders
Keyword(s):  
Smooth Muscle ◽  
Pyridoxal Phosphate ◽  
Single Channel ◽  
Outward Current ◽  
Disulfonic Acid ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Outward Currents ◽  
Murine Colon ◽  
Small Conductance

The patch-clamp technique was used to determine the ionic conductances activated by ATP in murine colonic smooth muscle cells. Extracellular ATP, UTP, and 2-methylthioadenosine 5′-triphosphate (2-MeS-ATP) increased outward currents in cells with amphotericin B-perforated patches. ATP (0.5–1 mM) did not affect whole cell currents of cells dialyzed with solutions containing ethylene glycol-bis(β-aminoethyl ether)- N, N, N′, N′-tetraacetic acid. Apamin (3 × 10−7M) reduced the outward current activated by ATP by 32 ± 5%. Single channel recordings from cell-attached patches showed that ATP, UTP, and 2-MeS-ATP increased the open probability of small-conductance, Ca2+-dependent K+ channels with a slope conductance of 5.3 ± 0.02 pS. Caffeine (500 μM) enhanced the open probability of the small-conductance K+ channels, and ATP had no effect after caffeine. Pyridoxal phosphate 6-azophenyl-2′,4′-disulfonic acid tetrasodium (PPADS, 10−4 M), a nonselective P2 receptor antagonist, prevented the increase in open probability caused by ATP and 2-MeS-ATP. PPADS had no effect on the response to caffeine. ATP-induced hyperpolarization in the murine colon may be mediated by P2y-induced release of Ca2+ from intracellular stores and activation of the 5.3-pS Ca2+-activated K+ channels.

Regional differences in cholinergic regulation of potassium current in feline esophageal circular smooth muscle

2005 ◽  
Vol 288 (6) ◽  
pp. G1233-G1240 ◽  
Author(s):  
Ahmad Muinuddin ◽  
Khurram Naqvi ◽  
Laura Sheu ◽  
Herbert Y. Gaisano ◽  
Nicholas E. Diamant
Keyword(s):  
Smooth Muscle ◽  
Receptor Antagonist ◽  
Regional Differences ◽  
Outward Current ◽  
Receptor Expression ◽  
Membrane Excitability ◽  
Patch Clamp Technique ◽  
Current Increase ◽  
Esophageal Body ◽  
Circular Smooth Muscle

Potassium channels are important contributors to membrane excitability in smooth muscles. There are regional differences in resting membrane potential and K+-channel density along the length of the feline circular smooth muscle esophagus. The aim of this study was to assess responses of K+-channel currents to cholinergic (ACh) stimulation along the length of the feline circular smooth muscle esophageal body. Perforated patch-clamp technique assessed K+-channel responses to ACh stimulation in isolated smooth muscle cells from the circular muscle layer of the esophageal body at 2 (distal)- and 4-cm (proximal) sites above the lower esophageal sphincter. Western immunoblots assessed ion channel and receptor expression. ACh stimulation produced a transient increase in outward current followed by inhibition of spontaneous transient outward currents. These ACh-induced currents were abolished by blockers of large-conductance Ca2+-dependent K+ channels (BKCa). Distal cells demonstrated a greater peak current density in outward current than cells from the proximal region and a longer-lasting outward current increase. These responses were abolished by atropine and the specific M3 receptor antagonist 4-DAMP but not the M1 receptor antagonist pirenzipine or the M2 receptor antagonist methoctramine. BKCa expression along the smooth muscle esophagus was similar, but M3 receptor expression was greater in the distal region. Therefore, ACh can differentially activate a potassium channel (BKCa) current along the smooth muscle esophagus. This activation probably occurs through release of intracellular calcium via an M3 pathway and has the potential to modulate the timing and amplitude of peristaltic contraction along the esophagus.

Whole cell current and membrane potential regulation by a human smooth muscle mechanosensitive calcium channel

2000 ◽  
Vol 279 (6) ◽  
pp. G1155-G1161 ◽  
Author(s):  
Adrian N. Holm ◽  
Adam Rich ◽  
Michael G. Sarr ◽  
Gianrico Farrugia
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Smooth Muscle Cells ◽  
Outward Current ◽  
Muscle Cells ◽  
Membrane Hyperpolarization ◽  
Whole Cell ◽  
Circular Smooth Muscle ◽  
Channel Current ◽  
Cell Current

Mechanotransduction is required for a wide variety of biological functions. The aim of this study was to determine the effect of activation of a mechanosensitive Ca2+ channel, present in human jejunal circular smooth muscle cells, on whole cell currents and on membrane potential. Currents were recorded using patch-clamp techniques, and perfusion of the bath (10 ml/min, 30 s) was used to mechanoactivate the L-type Ca2+ channel. Perfusion resulted in activation of L-type Ca2+ channels and an increase in outward current from 664 ± 57 to 773 ± 72 pA at +60 mV. Membrane potential hyperpolarized from −42 ± 4 to −50 ± 5 mV. In the presence of nifedipine (10 μM), there was no increase in outward current or change in membrane potential with perfusion. In the presence of charybdotoxin or iberiotoxin, perfusion of the bath did not increase outward current or change membrane potential. A model is proposed in which mechanoactivation of an L-type Ca2+ channel current in human jejunal circular smooth muscle cells results in increased Ca2+ entry and cell contraction. Ca2+ entry activates large-conductance Ca2+-activated K+channels, resulting in membrane hyperpolarization and relaxation.

Effect of purinergic blockers on outward current in isolated smooth muscle cells of the sheep bladder

1996 ◽  
Vol 270 (3) ◽  
pp. C969-C973 ◽  
Author(s):  
K. D. Cotton ◽  
M. A. Hollywood ◽  
K. D. Thornbury ◽  
N. G. McHale
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Outward Current ◽  
Muscle Cells ◽  
Maximal Response ◽  
Physiological Salt Solution ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Cibacron Blue

Freshly dispersed cells from sheep urinary bladder were voltage clamped using the whole cell and inside-out patch-clamp technique. Cibacron and Basilen blue increased outward current in a dose-dependent manner with a half-maximal response at 10(-5)M. Suramin, in concentrations to 10(-3)M, had no such effect. The Cibacron blue response was abolished in Ca2+ -free physiological salt solution, suggesting that it was acting on a Ca2+ -dependent current. Similarly, the Cibacron blue-sensitive current was significantly attenuated by charybdotoxin. Cibacron blue did not modulate inward current nor were its effects modified by caffeine or heparin, suggesting that its effect on outward current was not secondary to an increase in intracellular Ca2+. Application of 10(-4)M Cibacron blue to the inside membrane of excised patches caused a rapid increase in open probability of a large conductance (300 pS) K+ channel. These results suggest that Cibacron blue is a potent activator of a Ca2+ -dependent outward current in bladder smooth muscle cells in addition to its action as a purinergic blocker.

scholarly journals Large-conductance voltage- and Ca2+-activated K+ channel regulation by protein kinase C in guinea pig urinary bladder smooth muscle

2014 ◽  
Vol 306 (5) ◽  
pp. C460-C470 ◽  
Author(s):  
Kiril L. Hristov ◽  
Amy C. Smith ◽  
Shankar P. Parajuli ◽  
John Malysz ◽  
Georgi V. Petkov
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Guinea Pig ◽  
Bk Channels ◽  
Bk Channel ◽  
K Channel ◽  
Channel Activity ◽  
Open Probability ◽  
Channel Regulation ◽  
Pkc Activation

Large-conductance voltage- and Ca2+-activated K+ (BK) channels are critical regulators of detrusor smooth muscle (DSM) excitability and contractility. PKC modulates the contraction of DSM and BK channel activity in non-DSM cells; however, the cellular mechanism regulating the PKC-BK channel interaction in DSM remains unknown. We provide a novel mechanistic insight into BK channel regulation by PKC in DSM. We used patch-clamp electrophysiology, live-cell Ca2+ imaging, and functional studies of DSM contractility to elucidate BK channel regulation by PKC at cellular and tissue levels. Voltage-clamp experiments showed that pharmacological activation of PKC with PMA inhibited the spontaneous transient BK currents in native freshly isolated guinea pig DSM cells. Current-clamp recordings revealed that PMA significantly depolarized DSM membrane potential and inhibited the spontaneous transient hyperpolarizations in DSM cells. The PMA inhibitory effects on DSM membrane potential were completely abolished by the selective BK channel inhibitor paxilline. Activation of PKC with PMA did not affect the amplitude of the voltage-step-induced whole cell steady-state BK current or the single BK channel open probability (recorded in cell-attached mode) upon inhibition of all major Ca2+ sources for BK channel activation with thapsigargin, ryanodine, and nifedipine. PKC activation with PMA elevated intracellular Ca2+ levels in DSM cells and increased spontaneous phasic and nerve-evoked contractions of DSM isolated strips. Our results support the concept that PKC activation leads to a reduction of BK channel activity in DSM via a Ca2+-dependent mechanism, thus increasing DSM contractility.

Role of HERG-like K+ currents in opossum esophageal circular smooth muscle

1999 ◽  
Vol 277 (6) ◽  
pp. C1284-C1290 ◽  
Author(s):  
Hamid I. Akbarali ◽  
Hemant Thatte ◽  
Xue Dao He ◽  
Wayne R. Giles ◽  
Raj K. Goyal
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Smooth Muscle Cells ◽  
Single Cells ◽  
Circular Muscle ◽  
Muscle Cells ◽  
Resting Membrane Potential ◽  
Channel Blockers ◽  
Circular Smooth Muscle ◽  
Inward Currents

An inwardly rectifying K+ conductance closely resembling the human ether-a-go-go-related gene (HERG) current was identified in single smooth muscle cells of opossum esophageal circular muscle. When cells were voltage clamped at 0 mV, in isotonic K+ solution (140 mM), step hyperpolarizations to −120 mV in 10-mV increments resulted in large inward currents that activated rapidly and then declined slowly (inactivated) during the test pulse in a time- and voltage- dependent fashion. The HERG K+ channel blockers E-4031 (1 μM), cisapride (1 μM), and La3+ (100 μM) strongly inhibited these currents as did millimolar concentrations of Ba2+. Immunoflourescence staining with anti-HERG antibody in single cells resulted in punctate staining at the sarcolemma. At membrane potentials near the resting membrane potential (−50 to −70 mV), this K+ conductance did not inactivate completely. In conventional microelectrode recordings, both E-4031 and cisapride depolarized tissue strips by 10 mV and also induced phasic contractions. In combination, these results provide direct experimental evidence for expression of HERG-like K+ currents in gastrointestinal smooth muscle cells and suggest that HERG plays an important role in modulating the resting membrane potential.

Effect of cromakalim and lemakalim on slow waves and membrane currents in colonic smooth muscle

1991 ◽  
Vol 260 (2) ◽  
pp. C375-C382 ◽  
Author(s):  
J. M. Post ◽  
R. J. Stevens ◽  
K. M. Sanders ◽  
J. R. Hume
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Slow Wave ◽  
Outward Current ◽  
Wave Activity ◽  
Slow Waves ◽  
Slow Wave Activity ◽  
Ca Current ◽  
K Current ◽  
Stimulation Of

The effects of cromakalim (BRL 34915) and its optical isomer lemakalim (BRL 38227) were investigated in intact tissue and freshly dispersed circular muscle cells from canine proximal colon. Cromakalim and lemakalim hyperpolarized resting membrane potential, shortened the duration of slow waves by abolishing the plateau phase, and decreased the frequency of slow waves. Glyburide, a K channel blocker, prevented the effect of cromakalim on slow-wave activity. The mechanisms of these alterations in slow-wave activity were studied in isolated myocytes under voltage-clamp conditions. Cromakalim and lemakalim increased the magnitude of a time-independent outward K current, but cromakalim also reduced the peak outward K current. Glyburide inhibited lemakalim stimulation of the time-independent background current. Nisoldipine also reduced the peak outward current, and in the presence of nisoldipine, cromakalim did not affect the peak outward component of current. This suggested that cromakalim may block a Ca-dependent component of the outward current. Lemakalim did not affect the peak outward current. We tested whether the effects of cromakalim on outward current might be indirect due to an effect on inward Ca current. Cromakalim, but not lemakalim, was found to inhibit L-type Ca channels; however, glyburide did not alter cromakalim inhibition of inward Ca current. We conclude that the effects of cromakalim and lemakalim on membrane potential and slow waves in colonic smooth muscle appear to result primarily from stimulation of a time-independent background K conductance. The effects of these compounds on channel activity may explain the inhibitory effect of these compounds on contractile activity.

scholarly journals Effect of Auxin (IAA) on the Fast Vacuolar (FV) Channels in Red Beet (Beta vulgaris L.) Taproot Vacuoles

2020 ◽  
Vol 21 (14) ◽  
pp. 4876
Author(s):  
Zbigniew Burdach ◽  
Agnieszka Siemieniuk ◽  
Waldemar Karcz
Keyword(s):  
Single Channel ◽  
Outward Current ◽  
K Channel ◽  
Single Channels ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Inward Current ◽  
Bath Solution ◽  
Outward Currents ◽  
Inward Currents

In contrast to the well-studied effect of auxin on the plasma membrane K+ channel activity, little is known about the role of this hormone in regulating the vacuolar K+ channels. Here, the patch-clamp technique was used to investigate the effect of auxin (IAA) on the fast-activating vacuolar (FV) channels. It was found that the macroscopic currents displayed instantaneous currents, which at the positive potentials were about three-fold greater compared to the one at the negative potentials. When auxin was added to the bath solution at a final concentration of 1 µM, it increased the outward currents by about 60%, but did not change the inward currents. The imposition of a ten-fold vacuole-to-cytosol KCl gradient stimulated the efflux of K+ from the vacuole into the cytosol and reduced the K+ current in the opposite direction. The addition of IAA to the bath solution with the 10/100 KCl gradient decreased the outward current and increased the inward current. Luminal auxin reduced both the outward and inward current by approximately 25% compared to the control. The single channel recordings demonstrated that cytosolic auxin changed the open probability of the FV channels at the positive voltages to a moderate extent, while it significantly increased the amplitudes of the single channel outward currents and the number of open channels. At the positive voltages, auxin did not change the unitary conductance of the single channels. We suggest that auxin regulates the activity of the fast-activating vacuolar (FV) channels, thereby causing changes of the K+ fluxes across the vacuolar membrane. This mechanism might serve to tightly adjust the volume of the vacuole during plant cell expansion.

Effect of acute experimental colitis on rabbit colonic smooth muscle

1986 ◽  
Vol 251 (4) ◽  
pp. G538-G545 ◽  
Author(s):  
J. D. Cohen ◽  
H. W. Kao ◽  
S. T. Tan ◽  
J. Lechago ◽  
W. J. Snape
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Current Pulse ◽  
Mechanical Response ◽  
Contractile Activity ◽  
Experimental Colitis ◽  
Isometric Tension ◽  
Mucosal Inflammation ◽  
Resting Membrane Potential ◽  
Circular Smooth Muscle

The membrane potential and contractile activity of colonic circular smooth muscle from New Zealand White rabbits were studied after the production of acute experimental colitis. Colitis was induced in the distal colon by rectal infusion of formaldehyde solution, followed by an intravenous bolus of soluble immune complexes. Despite active mucosal inflammation, there are only occasional inflammatory cells in the muscularis. Electrophysiological studies on tissue from control rabbits and rabbits with colitis were performed using double sucrose gap and intracellular microelectrode techniques. The resting membrane potential was lower (-44 +/- 3 mV) in muscle from rabbits with colitis compared with control animals (-54 +/- 2 mV) (P less than 0.02). Amplitude of the electrotonic potential after a hyperpolarizing current pulse was decreased (P less than 0.05) and the time constant was shortened (P less than 0.01) in muscle from animals with colitis compared with normal animals. Amplitude (13.1 +/- 2.3 mV) and maximum rate of rise (0.24 +/- 0.06 V/s) of the spike potential, initiated by a depolarizing current pulse, were decreased in muscle from animals with colitis compared with muscle from healthy animals (P less than 0.001). Isometric tension generation after electrical and chemical depolarization of the membrane or bethanechol administration was decreased (P less than 0.001) in muscle from colitic animals. These studies suggest 1) membrane resistance and membrane potential are decreased in muscle strips from animals with colitis; and 2) there is a disturbance in the electrical and mechanical response of these tissues after stimulation.

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