Ionic basis for spontaneous depolarizations in isolated smooth muscle cells of canine colon

1992 ◽  
Vol 263 (3) ◽  
pp. C691-C699 ◽  
Author(s):  
J. M. Post ◽  
J. R. Hume
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Cell Voltage ◽  
Muscle Cells ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Channel Blockers ◽  
Inward Current ◽  
Circular Smooth Muscle ◽  
Ionic Basis

The type of cell that serves as the pacemaker in the colon is presently unknown. This study evaluated the ionic basis of spontaneous depolarizations in circular smooth muscle cells isolated from canine colon using whole cell voltage and current clamp techniques. Increasing temperature increased the probability of observing spontaneous depolarizations, depolarized the resting membrane potential (RMP), and increased Ca2+ and K+ currents. Spontaneous depolarizations occurred as rhythmic events, in bursts, or as isolated events. Varying the holding potential from -100 to -40 mV inhibited a component of inward current thought to be necessary for spontaneous depolarizations. The Ca2+ channel blockers, nickel and nisoldipine, inhibited spontaneous depolarizations. Nickel caused a hyperpolarization, whereas nisoldipine did not affect RMP. Ouabain depolarized the RMP and inhibited spontaneous depolarizations. The K+ channel blocker, tetraethylammonium, depolarized the RMP and lengthened the duration of spontaneous depolarizations. The key finding is that single colon circular smooth muscle cells are capable of generating spontaneous depolarizations similar to those described for slow waves in intact tissues and that a temperature- and nickel-sensitive inward current is essential for spontaneous activity.

Ca2+ currents in human colonic smooth muscle cells

1995 ◽  
Vol 269 (3) ◽  
pp. G378-G385 ◽  
Author(s):  
Z. Xiong ◽  
N. Sperelakis ◽  
A. Noffsinger ◽  
C. Fenoglio-Preiser
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Cell Voltage ◽  
Muscle Cells ◽  
Human Colon ◽  
Physiological Salt Solution ◽  
Channel Blockers ◽  
Threshold Potential ◽  
Tissue Samples ◽  
Inward Current

Voltage-gated Ca2+ currents were investigated in single smooth muscle cells freshly isolated from the circular layer of the human colon (ascending and descending portions) using the whole cell voltage-clamp technique. Tissue samples were obtained at the time of therapeutic surgery. In physiological salt solution (containing 2 mM Ca2+), an inward current was observed when the cell membrane was depolarized in the presence of tetrodotoxin. This current disappeared when Ca2+ was removed from the bath solution and was inhibited when Ca2+ channel blockers were applied, indicating that the inward current was a Ca2+ current (ICa). Changing the holding potential (HP) from -100 mV to more positive potentials (e.g., -60 and -40 mV) markedly decreased the amplitude of ICa. The voltage dependence of steady-state activation and inactivation was represented by Boltzmann distributions; there was a substantial amount of overlap (window current) between -60 and -10 mV. A fast-inactivating ICa component followed by a slow-inactivating ICa component was observed in some cells from both ascending and descending colons. The fast ICa component was observed only when cells were held at -80 or -100 mV, and had a more negative threshold potential (-70 to -60 mV). This component was sensitive to low concentrations of Ni2+ (30 microM) but was resistant to nifedipine (10-20 microM). In contrast, the slow (sustained) ICa component was observed at all HPs (-40 to -100 mV) and had a more positive threshold potential (about -40 mV). This component was insensitive to low concentration of Ni2+ but was sensitive to nifedipine and BAY K 8644.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Motilin and OHM-11526 activate a calcium current in human and canine jejunal circular smooth muscle

1997 ◽  
Vol 273 (2) ◽  
pp. G404-G412 ◽  
Author(s):  
G. Farrugia ◽  
M. J. Macielag ◽  
T. L. Peeters ◽  
M. G. Sarr ◽  
A. Galdes ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Smooth Muscle Contraction ◽  
Phase Iii ◽  
Inward Current ◽  
Circular Smooth Muscle ◽  
Whole Cell Patch Clamp ◽  
Potent Agonist ◽  
G Protein Coupled

Motilin is a potent agonist for gastrointestinal smooth muscle contraction and has been proposed to regulate the onset of phase III of the migrating motor complex in dogs and humans. The effects of motilin and OHM-11526, a motilin antagonist in rabbit smooth muscle strips, were examined in isolated canine and human jejunal circular smooth muscle cells using whole cell patch-clamp techniques with Ba2+ as the charge carrier. Effects of both drugs on inward current through L-type Ca2+ channels (ICaL) in both canine and human cells were first observed at 10(-3) M. At 10(-6) M, motilin increased ICaL in canine and human jejunal circular smooth muscle cells by 43 +/- 20 and 45 +/- 11%, respectively, and OHM-11526 increased ICaL by 54 +/- 8 and 54 +/- 14%, respectively. The increase in inward current was blocked by nifedipine and by guanosine 5'-O-(2-thiodiphosphate) but not by pertussis toxin. Washout of both drugs resulted in a further increase in ICaL. These data suggest that both motilin and OHM-11526 activate and ICaL in human and canine jejunal circular smooth muscle cells through a G protein-coupled mechanism.

Ionic basis for spontaneous depolarizations in isolated circular smooth muscle cells of the canine colon

1992 ◽  
Vol 103 (4) ◽  
pp. 1393
Author(s):  
Joseph M. Post ◽  
Joseph R. Hume
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Circular Smooth Muscle ◽  
Ionic Basis

scholarly journals Muscarinic activation of transient inward current and contraction in canine colon circular smooth muscle cells

2001 ◽  
Vol 79 (1) ◽  
pp. 34-42
Author(s):  
A Molleman ◽  
L WC Liu ◽  
J D Huizinga
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Muscarinic Receptor ◽  
Outward Current ◽  
Cyclopiazonic Acid ◽  
Muscle Cells ◽  
Transient Outward Current ◽  
Inward Current ◽  
Circular Smooth Muscle ◽  
Transient Inward Current

Muscarinic receptor mediated membrane currents and contractions were studied in isolated canine colon circular smooth muscle cells. Carbachol (10–5M) evoked a slow transient inward current that was superimposed by a transient outward current at holding potentials greater than –50 mV. Carbachol contracted the cells by 70 ± 2%. The effects of carbachol were blocked by atropine (10–6M), tetraethyl ammonium (20 mM), and BAPTA-AM (25 mM applied for 20 min). The inward current and contraction were not sensitive to diltiazem (10–5M), nitrendipine (3 × 10–7M), niflumic acid (10–5M), or N-phenylanthranilic acid (10–4M), but were gradually inhibited after repetitive stimulations in Ca2+free solution. Ni2+(2 mM) inhibited the inward current by 67 ± 4%. The inward current reversed at +15 mV. The outward component could be selectively inhibited by iberiotoxin (20 nM) or by intracellular Cs+. Repeated stimulation in the presence of cyclopiazonic acid (CPA, 3 µM) inhibited the carbachol-induced outward current and partially inhibited contraction. CPA did not inhibit the inward current. In conclusion, muscarinic receptor stimulation evoked a CPA-sensitive calcium release that caused contraction and a CPA-insensitive transient inward current was activated that is primarily carried by Ca2+ions and is sensitive to Ni2+.Key words: calcium, carbachol, smooth muscle, cyclopiazonic acid, sarcoplasmic reticulum.

Neurotransmission in lower esophageal sphincter ofW/Wvmutant mice

2010 ◽  
Vol 298 (1) ◽  
pp. G14-G24 ◽  
Author(s):  
Y. Zhang ◽  
S. A. Carmichael ◽  
X. Y. Wang ◽  
J. D. Huizinga ◽  
W. G. Paterson
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Lower Esophageal Sphincter ◽  
Significant Proportion ◽  
Muscle Cells ◽  
Mutant Mice ◽  
Resting Membrane Potential ◽  
Wild Type ◽  
Circular Smooth Muscle ◽  
Esophageal Sphincter

To address the controversy surrounding the role of interstitial cells of Cajal (ICC) in nitrergic neurotransmission to gastrointestinal smooth muscle, circular smooth muscle from the lower esophageal sphincter (LES) of W/Wvwild-type and mutant (ICC-deficient) mice were studied by using intracellular and tension recordings in vitro. Resting membrane potential was more negative, and the spontaneous unitary potentials diminished in mutant mice. In wild-type mice, nerve stimulation induced a biphasic inhibitory junction potential (IJP) consisting of a fast initial IJP followed by a long-lasting slow IJP (LSIJP). The IJP was markedly impaired in a significant proportion of mutant mice, whereas in others it was normal. Pharmacological studies in the mice with markedly impaired IJPs revealed that cholinergic and purinergic components of the nerve-mediated responses appeared intact. In wild-type mice, caffeine hyperpolarized smooth muscle cells, inhibited the initial fast IJP, and completely abolished the LSIJP. In mutant mice, caffeine depolarized smooth muscle cells and abolished the impaired LSIJP but did not affect the initial fast IJP. Immunohistochemical staining for c-Kit confirmed deficiency of ICC in mutant mice with a normal nitrergic IJP. Rings of LES circular smooth muscle from W/Wvmutant mice generated significantly less spontaneous tone than controls. When tone was restored with carbachol, normal nitrergic LES relaxation was recorded. These data suggest that 1) there is significant variability in the generation of nitrergic neurotransmission in the LES of W/Wvmutant mice, whereas purinergic and cholinergic neurotransmission are intact; 2) the altered nitrergic responses appear to be associated with abnormal Ca2+-dependent signaling initiated by spontaneous Ca2+release from sarcoplasmic reticulum in smooth muscle cells; and 3) c-Kit-positive ICC are not essential for nitrergic neurotransmission in mouse LES smooth muscle.

Effect of chronic hypoxia on K+ channels: regulation in human pulmonary vascular smooth muscle cells

1997 ◽  
Vol 272 (4) ◽  
pp. C1271-C1278 ◽  
Author(s):  
W. Peng ◽  
J. R. Hoidal ◽  
S. V. Karwande ◽  
I. S. Farrukh
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Chronic Hypoxia ◽  
Muscle Cells ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Delayed Rectifier ◽  
Voltage Dependent ◽  
Dependent Protein ◽  
Pulmonary Arterial

We investigated the effects of chronic hypoxia on the major outward K+ currents in early cultured human main pulmonary arterial smooth muscle cells (HPSMC). Unitary currents were measured from inside-out, outside-out, and cell-attached patches of HPSMC. Chronic hypoxia depolarized resting membrane potential (Em) and reduced the activity of a charybdotoxin (CTX)- and iberiotoxin-sensitive, Ca2+-dependent K+ channel (KCa). The 4-aminopyridine-sensitive and CTX-insensitive channel or the delayed rectifier K+ channel was unaffected by chronic hypoxia. Chronic hypoxia caused a +33- to +53-mV right shift in voltage-dependent activation of K(Ca) and a decrease in K(Ca) activity at all cytosolic Ca2+ concentrations ([Ca2+]i) in the range of 0.1-10 microM. Thus the hypoxia-induced decrease in K(Ca) activity was most likely due to a decrease in K(Ca) sensitivity to Em and [Ca2+]i. Chronic hypoxia reduced the ability of nitric oxide (NO.) and guanosine 3',5'-cyclic monophosphate (cGMP) to activate K(Ca). The cGMP-dependent protein kinase-induced activation of K(Ca) was also significantly inhibited by chronic hypoxia. In addition, inhibiting channel dephosphorylation with calyculin A caused significantly less increase in K(Ca) activity in membrane patches excised from chronically hypoxic HPSMC compared with normoxic controls. This suggests that the mechanism by which hypoxia modulates NO.-induced K(Ca) activation is by decreasing the NO./cGMP-mediated phosphorylation of the channel.

Vasopressin modulates K(+)-channel activities of cultured smooth muscle cells from porcine coronary artery

1992 ◽  
Vol 263 (2) ◽  
pp. H491-H496 ◽  
Author(s):  
T. Wakatsuki ◽  
Y. Nakaya ◽  
I. Inoue
Keyword(s):  
Smooth Muscle ◽  
Coronary Artery ◽  
Smooth Muscle Cells ◽  
Katp Channel ◽  
Muscle Cells ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Dependent Manner ◽  
Porcine Coronary Artery ◽  
Cultured Smooth Muscle Cells

The ATP-sensitive K+ channel (KATP channel) and the Ca(2+)-activated K+ channel (KCa channel) were active in cell-attached and excised inside-out patch configurations in cultured smooth muscle cells of the porcine coronary artery. Vasopressin activated the KCa channel (240 pS) when it was applied in the bath in the cell-attached patch mode presumably because of an increase in intracellular Ca2+, but it had no direct effect on the KCa channel. However, vasopressin directly blocked the KATP channel from outside the cell membranes in a concentration-dependent manner in both outside-out and cell-attached patch configurations; the K(+)-channel opener, nicorandil, reversed this effect. The KATP channel (30 pS) was highly active in the intact cell-attached patch configuration when the pipette contained a physiological concentration of Ca2+, suggesting that this channel may control the resting membrane potential. (The block might produce depolarization of the cells and might result in the contraction of smooth muscle cells.) These observations suggest that the KATP channel may play a role, at least in part, in controlling the contraction of smooth muscle cells of the coronary artery and that the control of vascular tone by vasopressin may be related to its ability to block the KATP channel.

scholarly journals The effects of K+ channel blockers in the all-or-none response to acetylcholine of isolated smooth muscle cells.

1991 ◽  
Vol 55 ◽  
pp. 323
Author(s):  
Mitsuo Mita ◽  
Masaatsu K. Uchida ◽  
Takao Hashimoto
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
K Channel ◽  
Channel Blockers ◽  
Isolated Smooth Muscle Cells

NUMERICAL SIMULATION OF THE ROLE OF CO-TRANSMISSION BY ACETYLCHOLINE AND SEROTONIN ON MOTILITY OF THE GUT

2006 ◽  
Vol 06 (04) ◽  
pp. 399-428
Author(s):  
R. MIFTAHOF
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Transit Time ◽  
Receptor Agonist ◽  
Muscle Cells ◽  
Receptor Antagonists ◽  
One Dimensional ◽  
Circular Smooth Muscle ◽  
Spatio Temporal ◽  
Stimulation Of

Electrophysiological mechanisms of co-transmission by serotonin (5-HT) and acetylcholine (ACh), co-expression of their receptor types, i.e., 5-HT type 3 and 4, nicotinic cholinerginc (nACh) and muscarinic cholinergic (μACh), and effects of selective and non-selective 5-HT3 and 5-HT4 receptor agonists/antagonists, on electromechanical activity of the gut were studied numerically. Two series of numerical experiments were performed. First, the dynamics of the generation and propagation of electrical signals interconnected with the primary sensory (AH) neurons, motor (S) neurons and smooth muscle cells were studied in a one-dimensional model. Simulations showed that stimulation of the 5-HT3 receptors reduced the threshold of activation of the mechanoreceptors by 17.6%. Conjoint excitation of the 5-HT3 and 5-HT4 receptors by endogenous serotonin converted the regular firing pattern of electrical discharges of the AH and S neurons to a beating mode. Activation confined to 5-HT3 receptors, located on the somas of the adjacent AH and S type neurons, could not sustain normal signal transduction between them. It required ACh as a co-transmitter and co-activation of the nACh receptors. Application of selective 5-HT3 receptor antagonists inhibited dose-dependently the production of action potentials at the level of mechanoreceptors and the soma of the primary sensory neuron and increased the threshold activation of the mechanoreceptors. Normal mechanical contractile activity depended on co-stimulation of the 5-HT4 and μACh receptors on the membrane of smooth muscle cells. In the second series of simulations, which involved a spatio-temporal model of the functional unit, effects of co-transmission by ACh and 5-HT on the electromechanical response in a segment of the gut were analyzed. Results indicated that propagation of the wave of excitation between the AH and S neurons within the myenteric nervous plexus in the presence of 5-HT3 receptor antagonists was supported by co-release of ACh. Co-stimulation of 5-HT3, nACh and μACh receptors impaired propulsive activity of the gut. The bolus showed uncoordinated movements. In an ACh-free environment Lotronex (GlaxoSmithKline), a 5-HT3 receptor antagonist, significantly increased the transit time of the pellet along the gut. In the presence of ACh, Lotronex produced intensive tonic-type contractions in the longitudinal and circular smooth muscle layers and eliminated propulsive activity. The 5HT4 receptor agonist, Zelnorm (Novartis), preserved the reciprocal electromechanical relationships between the longitudinal and circular smooth muscle layers. The drug changed the normal propulsive pattern of activity to an expulsive (non-mixing) type. Treatment of the gut with selective 5HT4 receptor antagonists increased the transit time by disrupting the migrating myoelectrical complex. Cisapride (Janssen), a mixed 5HT3 and 5HT4 receptor agonist, increased excitability of the AH and S neurons and the frequency of slow waves. Longitudinal and circular smooth muscle syncytia responded with the generation of long-lasting tonic contractions, resulting in a "squeezing" type of pellet movement. Comparison of the theoretical results obtained on one-dimensional and spatio-temporal models to in vivo and in vitro experimental data indicated satisfactory qualitative, and where available, quantitative agreement.

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