Potassium channel diversity within the muscular components of the feline lower esophageal sphincter

2004 ◽  
Vol 82 (11) ◽  
pp. 1006-1017 ◽  
Author(s):  
Anne Marie F Salapatek ◽  
Junzhi Ji ◽  
Ahmad Muinuddin ◽  
Nicholas E Diamant
Keyword(s):  
Lower Esophageal Sphincter ◽  
Circular Muscle ◽  
Outward Current ◽  
Resting Membrane Potential ◽  
Delayed Rectifier ◽  
Electrophysiological Properties ◽  
Voltage Dependent ◽  
Esophageal Smooth Muscle Cells ◽  
Esophageal Sphincter ◽  
Resting Tone

We hypothesized that regional differences in electrophysiological properties exist within the musculature of the feline lower esophageal sphincter (LES) and that they may potentially contribute to functional asymmetry within the LES. Freshly isolated esophageal smooth muscle cells (SMCs) from the circular muscle and sling regions within the LES were studied under a patch clamp. The resting membrane potential (RMP) of the circular SMCs was significantly more depolarized than was the RMP of the sling SMCs, resulting from a higher Na+and Cl–permeability in circular muscle than in sling muscle. Large conductance Ca2+-activated K+(BKCa) set the RMP at both levels, since specific BKCainhibitors caused depolarization; however, BKCadensity was greatest in the circular region. A significant portion of the outward current was due to non-BKCa, especially in sling muscle, and likely delayed rectifier K+channels (KDR). There was a large reduction in outward current with 4-aminopyridine (4-AP) in sling muscle, while BKCablockers had a limited effect on the voltage-activated outward current in sling muscle. Differences in BKCa:KDRchannel ratios were also manifest by a leftward shift in the voltage-dependent activation curve in circular cells compared to sling cells. The electrophysiological differences seen between the circular and sling muscles provide a basis for their different contributions to LES activities such as resting tone and neurotransmitter responsiveness, and in turn could impart asymmetric drug responses and provide specific therapeutic targets.Key words: esophagus, esophageal motility, gastroesophageal reflux, KCa, KDR, LES tone.

Guanylate cyclase inhibitors: effect on tone, relaxation, and cGMP content of lower esophageal sphincter

1992 ◽  
Vol 263 (1) ◽  
pp. G97-G101 ◽  
Author(s):  
J. A. Murray ◽  
C. Du ◽  
A. Ledlow ◽  
P. L. Manternach ◽  
J. L. Conklin
Keyword(s):  
Membrane Potential ◽  
Lower Esophageal Sphincter ◽  
Guanylate Cyclase ◽  
Circular Muscle ◽  
Resting Membrane Potential ◽  
Base Line ◽  
Sphincter Muscle ◽  
Dependent Manner ◽  
Esophageal Sphincter ◽  
Resting Tone

Relaxation of the lower esophageal sphincter (LES) results from activation of its intrinsic innervation. This relaxation is associated temporally with an increase in the guanosine 3',5'-cyclic monophosphate (cGMP) content of the muscle. This study tests the hypothesis that variations in the production of cGMP mediate resting LES tone and nerve-induced relaxation. We examined the effects of guanylate cyclase inhibitors, such as cystamine and methylene blue (MB), on the resting tone, resting membrane potential, electrical field stimulation (EFS)-induced relaxation, and cGMP content of circular smooth muscle from the LES of the opossum. Strips of sphincter muscle were placed in a tissue bath and stretched to 125% resting length. Both cystamine and MB increased the resting tone of LES muscle in a concentration-dependent manner (EC50 = 1.1 +/- 0.2, n = 12, and 1.6 +/- 0.4 mM, n = 10, respectively). The increase in tone by cystamine was not blocked by tetrodotoxin, atropine, or propranolol. Cystamine (1 mM) did not alter the resting membrane potential of circular muscle cells of the LES. The removal of extracellular Ca2+ by the addition of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA, 4 mM) and nifedipine (1 microM) shortened the duration but not the amplitude of the response to cystamine. Pretreatment with caffeine (5 mM) in the presence of EGTA and nifedipine to deplete intracellular Ca2+ stores blocked the increase in tone by cystamine. Cystamine (1 mM) failed to inhibit LES relaxation induced by EFS. Carbachol, at a concentration that induced a similar increase in base-line tone, attenuated the nerve-mediated relaxation. Cystamine did not alter basal cGMP levels, but inhibited the rise in cGMP induced by EFS. The data indicate that cystamine increases LES tone but does not inhibit EFS-induced relaxation, even though it inhibits EFS-induced increases in cGMP content. The increase in tone is dependent on the presence of intracellular Ca2+ stores.

Feline lower esophageal sphincter sling and circular muscles have different functional inhibitory neuronal responses

2006 ◽  
Vol 290 (1) ◽  
pp. G23-G29 ◽  
Author(s):  
Marie-Claude L'Heureux ◽  
Ahmad Muinuddin ◽  
Herbert Y. Gaisano ◽  
Nicholas E. Diamant
Keyword(s):  
Lower Esophageal Sphincter ◽  
Circular Muscle ◽  
Electrical Field Stimulation ◽  
Cholinergic Receptor ◽  
Cholinergic Innervation ◽  
Inhibitory Influence ◽  
Cholinergic Stimulation ◽  
Esophageal Sphincter ◽  
Low Tone ◽  
Resting Tone

The lower esophageal sphincter (LES) has a circular muscle component exhibiting spontaneous tone that is relaxed by nitric oxide (NO) and a low-tone sling muscle that contracts vigorously to cholinergic stimulation but with little or no evidence of NO responsiveness. This study dissected the responses of the sling muscle to nitrergic innervation in relationship to its cholinergic innervation and circular muscle responses. Motor responses were induced by electrical field stimulation (EFS; 1–30 Hz) of muscle strips from sling and circular regions of the feline LES in the presence of cholinergic receptor inhibition (atropine) or NO synthase inhibition [ NG-nitro-l-arginine (l-NNA) ± atropine]. This study showed the following. First, sling muscle developed less intrinsic resting tone compared with circular muscle. Second, with EFS, sling muscle contracted (most at ≤10 Hz), whereas circular muscle relaxed >50% by 5 Hz. Third, on neural blockade with atropine or l-NNA ± atropine, 1) sling muscle, although predominantly influenced by excitatory cholinergic stimulation, had a small neural NO-mediated inhibition, with no significant non-NO-mediated inhibition and 2) circular muscle, although little affected by cholinergic influence, underwent relaxation predominantly by neural release of NO and some non-NO inhibitory influence (at higher EFS frequency). Fourth, the sling, precontracted with bethanecol, could relax with NO and some non-NO inhibition. Finally, the tension range of both muscles is similar. In conclusion, sling muscle has limited NO-mediated inhibition to potentially augment or replace sling relaxation effected by switching off its cholinergic excitation. Differences within the LES sling and circular muscles could provide new directions for therapy of LES disorders.

Opposing roles of K+and Cl−channels in maintenance of opossum lower esophageal sphincter tone

2000 ◽  
Vol 279 (6) ◽  
pp. G1226-G1234 ◽  
Author(s):  
Yong Zhang ◽  
David V. Miller ◽  
William G. Paterson
Keyword(s):  
Lower Esophageal Sphincter ◽  
Circular Muscle ◽  
Isometric Tension ◽  
Niflumic Acid ◽  
Resting Membrane Potential ◽  
Channel Blockers ◽  
Microelectrode Recordings ◽  
Basal Tone ◽  
Esophageal Sphincter

The ionic basis underlying the maintenance of myogenic tone of lower esophageal sphincter circular muscle (LES) was investigated in opossum with the use of standard isometric tension and conventional intracellular microelectrode recordings in vitro. In tension recording studies, nifedipine (1 μM) reduced basal tone to 27.7 ± 3.8% of control. The K+channel blockers tetraethylammonium (TEA, 2 mM), charybdotoxin (100 nM), and 4-aminopyridine (4-AP, 2 mM) enhanced resting tone, whereas apamin and glibenclamide were without affect. Cl−channel blockers DIDS (500 μM) and 5-nitro-2-(3-phenylpropylamino)-benzoic acid (500 μM), as well as niflumic acid (0.1–300 μM), decreased basal tone, but tamoxifen was without effect. Intracellular microelectrode recordings revealed ongoing, spontaneous, spike-like action potentials (APs). Nifedipine abolished APs and depolarized resting membrane potential (RMP). Both TEA and 4-AP significantly depolarized RMP and augmented APs, whereas niflumic acid dose-dependently hyperpolarized RMP and abolished APs. These data suggest that, in the opossum, basal tone is associated with continuous APs and that K+and Ca2+-activated Cl−channels have important opposing roles in the genesis of LES tone.

A maturational shift in pulmonary K+ channels, from Ca2+ sensitive to voltage dependent

1998 ◽  
Vol 275 (6) ◽  
pp. L1019-L1025 ◽  
Author(s):  
Helen L. Reeve ◽  
E. Kenneth Weir ◽  
Stephen L. Archer ◽  
David N. Cornfield
Keyword(s):  
Pulmonary Circulation ◽  
Acute Hypoxia ◽  
Outward Current ◽  
Resting Membrane Potential ◽  
Transient Outward Current ◽  
Abrupt Decrease ◽  
Whole Cell ◽  
Electrophysiological Properties ◽  
Voltage Dependent ◽  
Intracellular Ca

The mechanism responsible for the abrupt decrease in resistance of the pulmonary circulation at birth may include changes in the activity of O2-sensitive K+ channels. We characterized the electrophysiological properties of fetal and adult ovine pulmonary arterial (PA) smooth muscle cells (SMCs) using conventional and amphotericin B-perforated patch-clamp techniques. Whole cell K+ currents of fetal PASMCs in hypoxia were small and characteristic of spontaneously transient outward currents. The average resting membrane potential (RMP) was −36 ± 3 mV and could be depolarized by charybdotoxin (100 nM) or tetraethylammonium chloride (5 mM; both blockers of Ca2+-dependent K+ channels) but not by 4-aminopyridine (4-AP; 1 mM; blocker of voltage-gated K+ channels) or glibenclamide (10 μM; blocker of ATP-dependent K+channels). In hypoxia, chelation of intracellular Ca2+ by 5 mM 1,2-bis(2-aminophenoxy)ethane- N, N, N′, N′-tetraacetic acid further reduced the amplitude of the whole cell K+ current and prevented spontaneously transient outward current activity. Under these conditions, the remaining current was partially inhibited by 1 mM 4-AP. K+ currents of fetal PASMCs maintained in normoxia were not significantly reduced by acute hypoxia. In normoxic adult PASMCs, whole cell K+ currents were large and RMP was −49 ± 3 mV. These 4-AP-sensitive K+ currents were partially inhibited by exposure to acute hypoxia. We conclude that the K+ channel regulating RMP in the ovine pulmonary circulation changes after birth from a Ca2+-dependent K+ channel to a voltage-dependent K+ channel. The maturational-dependent differences in the mechanism of the response to acute hypoxia may be due to this difference in K+ channels.

scholarly journals Ionic currents in intimal cultured synoviocytes from the rabbit

2010 ◽  
Vol 299 (5) ◽  
pp. C1180-C1194 ◽  
Author(s):  
R. J. Large ◽  
M. A. Hollywood ◽  
G. P. Sergeant ◽  
K. D. Thornbury ◽  
S. Bourke ◽  
...  
Keyword(s):  
Ion Channels ◽  
Intracellular Calcium ◽  
Outward Current ◽  
Input Resistance ◽  
Ionic Currents ◽  
Resting Membrane Potential ◽  
Delayed Rectifier ◽  
Pipette Solution ◽  
Voltage Dependent ◽  
Fibroblast Like Synoviocytes

Hyaluronan, a joint lubricant and regulator of synovial fluid content, is secreted by fibroblast-like synoviocytes lining the joint cavity, and secretion is greatly stimulated by Ca2+-dependent protein kinase C. This study aimed to define synoviocyte membrane currents and channels that may influence synoviocyte Ca2+ dynamics. Resting membrane potential ranged from −30 mV to −66 mV (mean −45 ± 8.60 mV, n = 40). Input resistance ranged from 0.54 GΩ to 2.6 GΩ (mean 1.28 ± 0.57 GΩ; ν = 33). Cell capacitance averaged 97.97 ± 5.93 pF. Voltage clamp using Cs+ pipette solution yielded a transient inward current that disappeared in Ca2+-free solutions and was blocked by 1 μM nifedipine, indicating an L-type calcium current. The current was increased fourfold by the calcium channel activator FPL 64176 (300 nM). Using K+ pipette solution, depolarizing steps positive to −40 mV evoked an outward current that showed kinetics and voltage dependence of activation and inactivation typical of the delayed rectifier potassium current. This was blocked by the nonspecific delayed rectifier blocker 4-aminopyridine. The synoviocytes expressed mRNA for four Kv1 subtypes (Kv1.1, Kv1.4, Kv1.5, and Kv1.6). Correolide (1 μM), margatoxin (100 nM), and α-dendrotoxin block these Kv1 subtypes, and all of these drugs significantly reduced synoviocyte outward current. The current was blocked most effectively by 50 nM κ-dendrotoxin, which is specific for channels containing a Kv1.1 subunit, indicating that Kv1.1 is critical, either as a homomultimeric channel or as a component of a heteromultimeric Kv1 channel. When 50 nM κ-dendrotoxin was added to current-clamped synoviocytes, the cells depolarized by >20 mV and this was accompanied by an increase in intracellular calcium concentration. Similarly, depolarization of the cells with high external potassium solution caused an increase in intracellular calcium, and this effect was greatly reduced by 1 μM nifedipine. In conclusion, fibroblast-like synoviocytes cultured from the inner synovium of the rabbit exhibit voltage-dependent inward and outward currents, including Ca2+ currents. They thus express ion channels regulating membrane Ca2+ permeability and electrochemical gradient. Since Ca2+-dependent kinases are major regulators of synovial hyaluronan secretion, the synoviocyte ion channels are likely to be important in the regulation of hyaluronan secretion.

Differential signal transduction pathways in cat lower esophageal sphincter tone and response to ACh

1994 ◽  
Vol 266 (5) ◽  
pp. G767-G774 ◽  
Author(s):  
P. Biancani ◽  
K. M. Harnett ◽  
U. D. Sohn ◽  
B. Y. Rhim ◽  
J. Behar ◽  
...  
Keyword(s):  
Phospholipase C ◽  
Lower Esophageal Sphincter ◽  
Calcium Release ◽  
Circular Muscle ◽  
Dependent Manner ◽  
Differential Signal ◽  
Esophageal Sphincter ◽  
Resting Tone ◽  
Dependent Pathway

Lower esophageal sphincter (LES) basal tone and contraction in response to maximally effective doses (Emax) of acetylcholine (ACh) may be mediated by different intracellular transduction pathways. In the basal state resting tone, inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] formation and levels of diacylglycerol (DAG) (C. Hillemeier, K. N. Bitar, and P. Biancani, unpublished data) are higher in LES circular muscle than in esophageal muscle, which does not maintain tone. In vitro resting tone and spontaneously elevated formation of Ins(1,4,5)P3 in LES circular muscle strips decrease in a dose-dependent manner in response to the phospholipase C antagonist 1-[6-([(17-beta)-3-methoxyestra-1,3, 5(10)-trien-17-yl]amino)hexyl]-1H-pyrrole-2,5-dione (U-73122). Basal Ins(1,4,5)P3 formation, however, is submaximal, since it can be increased by cholinergic stimulation. These data suggest that LES tone is associated with partial activation of phospholipase C. We therefore tested submaximal doses of Ins(1,4,5)P3 and DAG in permeabilized LES muscle cells and found that they act synergistically; their interaction depends on calcium release and is mediated through a protein kinase C (PKC)-dependent pathway. In contrast, we have previously shown that contraction induced by Emax of ACh is mediated through calmodulin-dependent mechanisms (14). To investigate these differences, we tested high and low doses of ACh. Contraction induced by high doses of ACh was inhibited by calmodulin but not by PKC antagonists, as previously reported, but low ACh doses were preferentially inhibited by PKC antagonists. Similarly, low Ins(1,4,5)P3 concentrations activated a PKC-dependent pathway, whereas contraction induced by Emax of Ins(1,4,5)P3 was calmodulin dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization and functional consequences of delayed rectifier current transient in ventricular repolarization

2000 ◽  
Vol 278 (3) ◽  
pp. H806-H817 ◽  
Author(s):  
Gary A. Gintant
Keyword(s):  
Action Potential ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Inward Rectifier ◽  
Ventricular Repolarization ◽  
Delayed Rectifier ◽  
Voltage Range ◽  
Delayed Rectifier Current ◽  
Recovery From Inactivation ◽  
Voltage Dependent

Although inactivation of the rapidly activating delayed rectifier current ( I Kr) limits outward current on depolarization, the role of I Kr (and recovery from inactivation) during repolarization is uncertain. To characterize I Krduring ventricular repolarization (and compare with the inward rectifier current, I K1), voltage-clamp waveforms simulating the action potential were applied to canine ventricular, atrial, and Purkinje myocytes. In ventricular myocytes, I Kr was minimal at plateau potentials but transiently increased during repolarizing ramps. The I Kr transient was unaffected by repolarization rate and maximal after 150-ms depolarizations (+25 mV). Action potential clamps revealed the I Kr transient terminating the plateau. Although peak I Kr transient density was relatively uniform among myocytes, potentials characterizing the peak transients were widely dispersed. In contrast, peak inward rectifier current ( I K1) density during repolarization was dispersed, whereas potentials characterizing I K1 defined a narrower (more negative) voltage range. In summary, rapidly activating I Kr provides a delayed voltage-dependent (and functionally time-independent) outward transient during ventricular repolarization, consistent with rapid recovery from inactivation. The heterogeneous voltage dependence of I Kr provides a novel means for modulating the contribution of this current during repolarization.

Identification of longitudinal muscle activity in opossum lower esophageal sphincter

1991 ◽  
Vol 261 (6) ◽  
pp. G974-G980 ◽  
Author(s):  
S. S. Harrington ◽  
W. J. Dodds ◽  
R. K. Mittal
Keyword(s):  
Muscle Contraction ◽  
Lower Esophageal Sphincter ◽  
Strain Gauge ◽  
Longitudinal Muscle ◽  
Pressure Fluctuations ◽  
Circular Muscle ◽  
Pharmacological Agents ◽  
Esophageal Sphincter ◽  
High Pressure Zone ◽  
Contraction And Relaxation

The aim of this study was to characterize lower esophageal sphincter (LES) longitudinal muscle contraction during changes in LES pressure in opossums. LES pressure was used as a marker of LES circular muscle contraction. Longitudinal muscle contraction was measured by strain gauge transducers. For precise placement of the strain gauge on the LES, the high-pressure zone was identified using a manometric-laser illumination technique. Measurements were made during 1) spontaneous LES pressure fluctuations, 2) LES pressure changes induced by pharmacological agents, and 3) LES relaxation induced by vagal nerve stimulation. These studies show that 1) spontaneous LES pressure fluctuations correlated with spontaneous changes in LES longitudinal muscle contraction; 2) pharmacologically induced contraction and relaxation of LES pressure correlated with contraction and relaxation of LES longitudinal muscle, respectively; 3) a close temporal relationship existed between changes in LES longitudinal muscle contraction and LES pressure that occurred spontaneously or were induced pharmacologically; and 4) vagal stimulation caused LES longitudinal muscle contraction and LES pressure relaxation. We propose that LES longitudinal muscle may play a role in the modulation of intraluminal LES pressure.

Modulation of the delayed rectifier, IK, by cadmium in cat ventricular myocytes

1992 ◽  
Vol 262 (1) ◽  
pp. C75-C83 ◽  
Author(s):  
C. H. Follmer ◽  
N. J. Lodge ◽  
C. A. Cullinan ◽  
T. J. Colatsky
Keyword(s):  
Voltage Clamp ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Membrane Potentials ◽  
Delayed Rectifier ◽  
Voltage Range ◽  
Control Value ◽  
Current Voltage ◽  
Voltage Dependent ◽  
Slope Factor

The effects of cadmium on the delayed outward potassium current (IK) were investigated in isolated cat ventricular myocytes using the single suction pipette voltage-clamp technique. IK activation was examined using peak tail currents elicited after 750-ms voltage-clamp steps to selected membrane potentials from a holding potential of -40 mV. In the presence of Cd2+ (0.2 mM), peak tail currents increased from a control value of 85 +/- 12 to 125 +/- 18 pA (n = 4). Activation curves constructed from the average peak tail-current measurements in all experiments showed that Cd2+ shifted the voltage dependence of activation to more positive potentials by 16.4 +/- 2.0 mV and increased the slope factor of the activation curve from 6.1 +/- 0.2 to 6.9 +/- 0.2 mV. In the absence of Cd2+, increases in holding potential from -30 to -70 mV had no effect on the magnitude of the peak tail currents, suggesting that the Cd(2+)-induced increase was not the result of a voltage-dependent increase in the number of available K+ channels at the holding potential. Slow voltage ramps from -70 to +70 mV revealed that Cd2+ increased the outward current at membrane potentials positive to +20 mV and shifted the voltage range in which IK inwardly rectified to more positive potentials. The fully activated current-voltage relationship was also shifted to more positive potentials by Cd2+. Cd2+ did not alter channel selectivity for K+.(ABSTRACT TRUNCATED AT 250 WORDS)

Complexity of the outward K+ current of the rat megakaryocyte

1997 ◽  
Vol 272 (5) ◽  
pp. C1525-C1531 ◽  
Author(s):  
E. Romero ◽  
R. Sullivan
Keyword(s):  
K Channel ◽  
Delayed Rectifier ◽  
Channel Blockers ◽  
Excitable Cells ◽  
Electrophysiological Properties ◽  
Relative Contribution ◽  
Delayed Rectifier Current ◽  
Dependent Inactivation ◽  
Voltage Dependent ◽  
K Current

Megakaryocytes isolated from rat bone marrow express a voltage-dependent, outward K+ current with complex kinetics of activation and inactivation. We found that this current could be separated into at least two components based on differential responses to K+ channel blockers. One component, which exhibited features of the "transient" or "A-type" K+ current of excitable cells, was more strongly blocked by 4-aminopyridine (4-AP) than by tetrabutylammonium (TBA). This current, which we designated as "4-AP-sensitive" current, activated rapidly at potentials more positive than -40 mV and subsequently underwent rapid voltage-dependent inactivation. A separate current that activated slowly was blocked much more effectively by TBA than by 4-AP. This "TBA-sensitive" component, which resembled a typical delayed rectifier current, was much more resistant to voltage-dependent inactivation. The relative contribution of each of these components varied from cell to cell. The effect of charybdotoxin was similar to that of 4-AP. Our data indicate that the voltage-dependent K+ current of resting megakaryocytes is more complex than heretofore believed and support the emerging concept that megakaryocytes possess intricate electrophysiological properties.

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