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.

Nitric oxide suppresses a Ca2+-stimulated Cl− current in smooth muscle cells of opossum esophagus

1998 ◽  
Vol 274 (5) ◽  
pp. G886-G890 ◽  
Author(s):  
Yong Zhang ◽  
Fivos Vogalis ◽  
Raj K. Goyal
Keyword(s):  
Nitric Oxide ◽  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Smooth Muscles ◽  
Reversal Potential ◽  
Circular Muscle ◽  
Muscle Cells ◽  
Patch Clamp Technique ◽  
No Donor ◽  
Pipette Solution

Nitric oxide (NO) hyperpolarizes visceral smooth muscles. Using the patch-clamp technique, we investigated the possibility that NO-mediated hyperpolarization in the circular muscle of opossum esophagus results from the suppression of a Ca2+-stimulated Cl− current. Smooth muscle cells were dissociated from the circular layer and bathed in high-K+Ca2+-EGTA-buffered solution. Macroscopic ramp currents were recorded from cell-attached patches. Contaminating K+-channel currents were blocked with tetrapentylammonium chloride (200 μM) added to all solutions. Raising bath Ca2+concentration above 150 nM in the presence of A-23187 (10 μM) activated a leak current ( I L-Ca) with an EC50 of 1.2 μM at −100 mV. The reversal potential ( E rev) of I L-Ca (−8.5 ± 1.8 mV, n = 8) was significantly different ( P < 0.05) from E rev of the background current (+4.2 ± 1.2 mV, n = 8). Equimolar substitution of 135 mM Cl− in the pipette solution with gluconate significantly shifted E rev of I L-Ca to +16.6 ± 3.4 mV ( n = 4) ( P < 0.05 compared with background), whereas replacement of total Na+with Tris+ suppressed I L-Ca but did not affect E rev(−15 ± 3 mV, n = 3; P > 0.05). I L-Ca was inhibited by DIDS (500 μM). Diethylenetriamine-NO adduct (200 μM), a NO• donor, and 8-bromo-cGMP (200 μM) suppressed I L-Ca by 59 ± 15% ( n = 5) and 62 ± 21% ( n = 4) at −100 mV, respectively. We conclude that in opossum esophageal smooth muscle NO-mediated hyperpolarization may be produced by suppression of a Ca2+-stimulated Cl−-permeable conductance via formation of cGMP.

Nitric oxide modulates a calcium-activated potassium current in muscle cells from opossum esophagus

1995 ◽  
Vol 269 (4) ◽  
pp. G606-G612 ◽  
Author(s):  
J. A. Murray ◽  
E. F. Shibata ◽  
T. L. Buresh ◽  
H. Picken ◽  
B. W. O'Meara ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Smooth Muscle ◽  
Protein Kinase ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Protein Kinase G ◽  
Patch Clamp Technique ◽  
Whole Cell ◽  
Circular Smooth Muscle ◽  
K Current

Nitric oxide mediates nerve-induced hyperpolarization of circular smooth muscle of the esophagus. Two mechanisms are proposed to explain this hyperpolarization: an increase in K+ current or a decrease in Cl- current. These studies test the hypothesis that nitric oxide increases a K+ current in esophageal smooth muscle. Three outward K+ currents are present in circular smooth muscle cells from the opossum esophagus. One current is a Ca(2+)-activated K+ current (IKCa2+). This current is inhibited by charybdotoxin. Whole cell currents were recorded from isolated opossum esophageal smooth muscle cells using the whole cell patch-clamp technique. These studies showed that IKCa2+ is activated at potentials more positive than -30 mV. Bath application of S-nitroso-L-cysteine increased IKCa2+ by 50% above control levels throughout the entire activation range of potentials. The enhanced current was reversible on washout. Either charybdotoxin, an inhibitor of IKCa2+, or (R)-p-8-(4-chloropenylthio)-guanosine 3',5'-cyclic monophosphorothioate, an inhibitor of protein kinase G, antagonized the increase in outward current induced by S-nitroso-L-cysteine. These data suggest that nitric oxide activates IKCa2+ via the guanosine 3',5'-cyclic monophosphate-protein kinase G signal transduction pathway.

Caffeine- and carbachol-induced Cl- and cation currents in single opossum esophageal circular muscle cells

1996 ◽  
Vol 271 (5) ◽  
pp. C1725-C1734 ◽  
Author(s):  
Q. Wang ◽  
H. I. Akbarali ◽  
N. Hatakeyama ◽  
R. K. Goyal
Keyword(s):  
Smooth Muscle ◽  
Single Cells ◽  
Circular Muscle ◽  
Outward Current ◽  
Muscle Cells ◽  
Membrane Currents ◽  
Muscle Membrane ◽  
Pipette Solution ◽  
Inward Current ◽  
Outward Currents

Cl- and cation currents may play important roles in esophageal smooth muscle membrane potential changes and contraction. We studied Ca2+ release-activated cell-shortening and membrane currents in single cells freshly dispersed from the circular muscle of the opossum esophagus using the standard patch-clamp whole cell recording method. Caffeine (10-20 microM) and carbachol (10-100 microM) shortened the single smooth muscle cells by releasing intracellular Ca2+. At a holding potential of 0 mV, spontaneous transient outward currents STOCs, representing spontaneous Ca(2+)-activated K+ currents) were recorded. Caffeine, carbachol, or ionomycin evoked large outward currents (up to 1,650 pA) and subsequently abolished STOCs. At a holding potential of -50 mV in K(+)-containing solutions, an outward current in response to the agonists was observed; in some cells, the outward current followed an inward current. In K(+)-free solutions, the agonists induced only an inward current whose reversal potential was shifted by alteration of the anion gradient but not by that of the cation. With a low-Cl- pipette solution (Cl- substituted by glucuronate or glutamate), the inward currents were dependent mainly on the external cation gradient. This cation channel was permeable to Ba2+. Inclusion of 10 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid in the pipette solution abolished all these currents. These data suggest that in the opossum esophageal circular muscle 1) Ca2+ released from the intracellular stores by caffeine and carbachol is sufficient to induce single smooth muscle cell contraction and 2) the caffeine-, carbachol-, and ionomycin-induced membrane currents consist of Ca(2+)-activated K+, Cl-, and cation conductances.

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.

Transient potassium currents in avian sensory neurons

1990 ◽  
Vol 63 (4) ◽  
pp. 725-737 ◽  
Author(s):  
S. K. Florio ◽  
C. D. Westbrook ◽  
M. R. Vasko ◽  
R. J. Bauer ◽  
J. L. Kenyon
Keyword(s):  
Single Channel ◽  
Outward Current ◽  
Potassium Currents ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Single Channels ◽  
Patch Clamp Technique ◽  
Small Component ◽  
Whole Cell ◽  
Outward Currents

1. We used the patch-clamp technique to study voltage-activated transient potassium currents in freshly dispersed and cultured chick dorsal root ganglion (DRG) cells. Whole-cell and cell-attached patch currents were recorded under conditions appropriate for recording potassium currents. 2. In whole-cell experiments, 100-ms depolarizations from normal resting potentials (-50 to -70 mV) elicited sustained outward currents that inactivated over a time scale of seconds. We attribute this behavior to a component of delayed rectifier current. After conditioning hyperpolarizations to potentials negative to -80 mV, depolarizations elicited transient outward current components that inactivated with time constants in the range of 8-26 ms. We attribute this behavior to a transient outward current component. 3. Conditioning hyperpolarizations increased the rate of activation of the net outward current implying that the removal of inactivation of the transient outward current allows it to contribute to early outward current during depolarizations from negative potentials. 4. Transient current was more prominent on the day the cells were dispersed and decreased with time in culture. 5. In cell-attached patches, single channels mediating outward currents were observed that were inactive at resting potentials but were active transiently during depolarizations to potentials positive to -30 mV. The probability of channels being open increased rapidly (peaking within approximately 6 ms) and then declined with a time constant in the range of 13-30 ms. With sodium as the main extracellular cation, single-channel conductances ranged from 18 to 32 pS. With potassium as the main extracellular cation, the single-channel conductance was approximately 43 pS, and the channel current reversed near 0 mV, as expected for a potassium current. 6. We conclude that the transient potassium channels mediate the component of transient outward current seen in the whole-cell experiments. This current is a relatively small component of the net current during depolarizations from normal resting potentials, but it can contribute significant outward current early in depolarizations from hyperpolarized potentials.

Apical maxi K channels in intercalated cells of CCT

1991 ◽  
Vol 261 (4) ◽  
pp. F696-F705 ◽  
Author(s):  
J. Pacha ◽  
G. Frindt ◽  
H. Sackin ◽  
L. G. Palmer
Keyword(s):  
Cell Volume Regulation ◽  
Outward Current ◽  
Intercalated Cells ◽  
Patch Clamp Technique ◽  
Pipette Solution ◽  
Whole Cell ◽  
K Channels ◽  
Clamp Technique ◽  
Collecting Tubules ◽  
High Conductance

High-conductance (maxi) K channels in the apical membrane of rat and rabbit cortical collecting tubules (CCT) were studied using the patch-clamp technique. Principal cells (PC) and intercalated cells (IC) were distinguished with Hoffman modulation optics in split-open tubules. IC were further identified by staining tubules with the fluorescent mitochondrial dye, rhodamine 123. Maxi-K channels were distinguished by their high conductance (greater than 80 pS) and voltage-dependent kinetics. In CCT of rats on a low-Na diet, maxi K channels were observed in 11% of the cell-attached patches on PC and 79% of patches on IC. In rats on a normal diet, the channels were seen in 23 and 79% of patches on PC and IC, respectively. In the rabbit CCT, maxi K channels were observed in 12% (4 of 32) of the patches on PC and 82% (122 of 148) of the patches on IC. The greater abundance of channels in IC was confirmed in rat CCT using the whole-cell clamp technique. Current through the maxi K channels (IK) was measured as the tetraethylammonium (TEA)-sensitive (2.5 mM) outward current in cells equilibrated with 115 mM K and 10(-5) M Ca2+ in the pipette solution. When the cell was clamped to an internal potential of +40 mV, the average IK per cell was -4 +/- 5 pA in PC and 290 +/- 90 pA in IC. Lowering cytoplasmic Ca2+ from 10(-5) M to 10(-7) M reduced IK to 32 +/- 21 pA. Neither single Na channels nor amiloride-sensitive whole-cell currents were seen in IC. Finally, maxi K channels could be activated by pipette suction (10-40 cm H2O) in either cell-attached or inside-out patches on IC from rabbit CCT. This mechanosensitivity was observed even after chelation of free Ca2+ with ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) in the pipette or the bath solutions, implying that stretch activation of these channels was not mediated by increased Ca2+ entry into the cell. The IC maxi K channel may play a role in cell volume regulation or in K secretion during elevation of luminal hydrostatic pressure.

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 nitric oxide on calcium-activated potassium channels in colonic smooth muscle of rabbits

1998 ◽  
Vol 274 (5) ◽  
pp. G848-G856 ◽  
Author(s):  
Gang Lu ◽  
Bruno Mazet ◽  
Michael G. Sarr ◽  
Joseph H. Szurszewski
Keyword(s):  
Nitric Oxide ◽  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Nerve Fibers ◽  
Nadph Diaphorase ◽  
Whole Cell ◽  
Circular Smooth Muscle ◽  
Rabbit Colon ◽  
Inside Out

Nitric oxide (NO) hyperpolarizes intestinal smooth muscle cells. This study was designed to determine the mechanism whereby NO activates KCa channels of circular smooth muscle of the rabbit colon. Transmural biopsies of the rabbit colon were stained for NADPH-diaphorase. Freshly dispersed circular smooth muscle cells were studied in the whole cell configuration, as well as in on-cell and excised inside-out patch recording configurations, while KCa current and the activity of KCa channels, respectively, were monitored. NADPH-diaphorase-positive nerve fibers were found in both muscle layers. NO (1%) increased whole cell net outward current by 79% and hyperpolarized resting membrane voltage from −59 to −73 mV ( n = 8 cells, P < 0.01). In the on-cell patch recording configuration, NO (0.5% or 1%) in the bath increased NP o of KCa channels; charybdotoxin (125 nM) in the pipette solution blocked this effect. In the excised inside-out patch recording configuration, NO (1%) had no effect on NP o of KCa channels. In the on-cell patch recording configuration, methylene blue (1 μM) or cystamine (5 mM) in the bath solution decreased the effect of NO (1%) on NP o of KCa channels. NP o was increased by 8-bromo-cGMP (8-BrcGMP; 1 mM), a cGMP analog, and zaprinast (100 μM), an inhibitor of cGMP phosphodiesterase. These data suggest that NO increased whole cell outward K+current by activating KCa channels through a cGMP pathway.

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.

Sign in / Sign up

Export Citation Format

Share Document