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)

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.

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.

Effects of nitrates and calcium channel blockers on Ca2+-ATPase in the microsomal fraction of porcine coronary artery smooth muscle cells

Cell Calcium ◽  
1987 ◽  
Vol 8 (5) ◽  
pp. 397-410 ◽  
Author(s):  
E. Koh ◽  
S. Morimoto ◽  
K. Fukuo ◽  
T. Shiraishi ◽  
T. Hironaka ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Coronary Artery ◽  
Smooth Muscle Cells ◽  
Calcium Channel ◽  
Calcium Channel Blockers ◽  
Microsomal Fraction ◽  
Muscle Cells ◽  
Channel Blockers ◽  
Porcine Coronary Artery

scholarly journals Characteristics of caffeine-induced inward current and spontaneous transient inward currents in tracheal smooth muscle cells of the guinea-pig.

1994 ◽  
Vol 64 ◽  
pp. 133
Author(s):  
Satoshi Henmi ◽  
Katsuhiko Muraki ◽  
Yuji Imaizumi ◽  
Minoru Watanabe
Keyword(s):  
Smooth Muscle ◽  
Guinea Pig ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Tracheal Smooth Muscle ◽  
Inward Current ◽  
Inward Currents

scholarly journals Inward current response to carbachol in intestinal smooth muscle cells of the rat.

1993 ◽  
Vol 61 ◽  
pp. 311
Author(s):  
Shigeo Ito ◽  
Toshio Ohta ◽  
Yoshikazu Nakazato
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Intestinal Smooth Muscle ◽  
Current Response ◽  
Inward Current

Differential effects of Ca2+ channel blockers on Ca2+ transients and cell cycle progression in vascular smooth muscle cells

1998 ◽  
Vol 344 (2-3) ◽  
pp. 323-331 ◽  
Author(s):  
Abu Ahmed ◽  
Sei Kobayashi ◽  
Tomomi Shikasho ◽  
Junji Nishimura ◽  
Hideo Kanaide
Keyword(s):  
Cell Cycle ◽  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Vascular Smooth Muscle Cells ◽  
Cell Cycle Progression ◽  
Muscle Cells ◽  
Channel Blockers ◽  
Cycle Progression ◽  
Differential Effects

Fast Na+ channels in smooth muscle from pregnant rat uterus

1992 ◽  
Vol 70 (4) ◽  
pp. 491-500 ◽  
Author(s):  
Nicholas Sperelakis ◽  
Yoshihito Inoue ◽  
Yusuke Ohya
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Current Density ◽  
Sodium Current ◽  
Muscle Cells ◽  
Slow Inward Current ◽  
Rat Uterus ◽  
Pregnant Rat ◽  
Inward Current ◽  
Channel Current

Smooth muscle cells normally do not possess fast Na+ channels, but inward current is carried through two types of Ca2+ channels: slow (L type) Ca2+ channels and fast (T type) Ca2+ channels. Whole-cell voltage clamp was done on single smooth muscle cells isolated from the longitudinal layer of the 18-day pregnant rat uterus. Depolarizing pulses, applied from a holding potential of −90 mV, evoked two types of inward current, fast and slow. The fast inward current decayed within 30 ms, depended on [Na]o, and was inhibited by tetrodotoxin (TTX) (K0.5 = 27 nM). The slow inward current decayed slowly, was dependent on [Ca]o (or Ba2+), and was inhibited by nifedipine. These results suggest that the fast inward current is a fast Na+ channel current and that the slow inward current is a Ca2+ slow channel current. A fast-inactivating Ca2+ channel current was not evident. We conclude that the ion channels that generate inward currents in pregnant rat uterine cells are TTX-sensitive fast Na+ channels and dihydropyridine-sensitive slow Ca2+ channels. The number of fast Na+ channels increased during gestation. The averaged current density increased from 0 on day 5, to 0.19 on day 9, to 0.56 on day 14, to 0.90 on day 18, and to 0.86 pA/pF on day 21. This almost linear increase occurs because of an increase in the fraction of cells that possess fast Na+ channels. The Ca2+ channel current density was also higher during the latter half of gestation. These results indicate that the fast Na+ channels and Ca2+ slow channels in myometrium become more numerous as term approaches, and we suggest that the fast Na+ current may be involved in spread of excitation. Isoproterenol (β-agonist) did not affect either ICa(s) or INa(f), whereas Mg2+ (K0.5 = 12 mM) and nifedipine (K0.5 = 3.3 nM) depressed ICa(s). Oxytocin had no effect on INa(f) and actually depressed ICa(s) to a small extent. Therefore, the tocolytic action of β-agonists cannot be explained by an inhibition of ICa(s), whereas that of Mg2+ can be so explained. The stimulating action of oxytocin on uterine contractions cannot be explained by a stimulation of ICa(s).Key words: sodium current, fast sodium current, calcium currents, myometrial smooth muscle cells, pregnant uterine muscle.

Dual regulation of L-type Ca2+ channels by serotonin 2 receptor stimulation in vascular smooth muscle cells

1995 ◽  
Vol 268 (2) ◽  
pp. H544-H549 ◽  
Author(s):  
Y. Hirakawa ◽  
T. Kuga ◽  
S. Kobayashi ◽  
H. Kanaide ◽  
A. Takeshita
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Cell Voltage ◽  
Muscle Cells ◽  
Receptor Stimulation ◽  
Aortic Smooth Muscle ◽  
A 23187 ◽  
Inositol 1,4,5 Trisphosphate ◽  
Voltage Dependent ◽  
Ca2 Channels

The purpose of the present study was to investigate regulation of voltage-dependent Ca2+ channels by serotonin in rat aortic smooth muscle cells in primary culture. L- and T-type Ca2+ currents (ICa) were recorded using the whole cell voltage-clamp method. Without pretreatment, in 25 of 30 cells examined, 10 microM serotonin decreased L-type ICa to various extents (-14 to -72%). However, in the remaining five cells, serotonin increased L-type ICa 21 +/- 4%. Thus, in 30 cells, serotonin decreased L-type ICa an average of 22 +/- 5%. In the presence of intracellular heparin (100 micrograms/ml), a blocker of inositol 1,4,5-trisphosphate binding to its receptor, serotonin increased L-type ICa in all cells 29 +/- 3% (n = 6). When stored Ca2+ was depleted by pretreatment either with 20 microM ryanodine and 20 mM caffeine or with 100 nM A-23187, serotonin also increased L-type ICa in all cells 30 +/- 5 (n = 4) or 37 +/- 5% (n = 12), respectively. In the presence of heparin, the serotonin-induced increase of L-type ICa was prevented by 100 nM staurosporine (2 +/- 3%; n = 6, P < 0.01). The serotonin-induced decrease of L-type ICa was significantly augmented by 100 nM staurosporine (-43 +/- 10%; n = 5). Phorbol 12,13-dibutylate (PDBu; 1 microM) increased L-type ICa 29 +/- 3% (n = 6), and serotonin did not further increase L-type ICa after its potentiation by PDBu.(ABSTRACT TRUNCATED AT 250 WORDS)

Gestational change in Na+ and Ca2+ channel current densities in rat myometrial smooth muscle cells

1991 ◽  
Vol 260 (3) ◽  
pp. C658-C663 ◽  
Author(s):  
Y. Inoue ◽  
N. Sperelakis
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Reversal Potential ◽  
Cell Voltage ◽  
Muscle Cells ◽  
Linear Increase ◽  
Na Channels ◽  
Pregnant Rat ◽  
Spread Of Excitation ◽  
Current Densities

The change of Na+ and Ca2+ channel currents during gestation was investigated using the whole cell voltage-clamp method on single smooth muscle cells freshly isolated from the longitudinal layer of pregnant rat uterus. The current-voltage relationships for both the Na+ and Ca2+ currents did not change during gestation. The threshold voltage, the voltage at the peak inward current, and the reversal potential (extrapolated) were virtually identical. The averaged current densities of Ca2+ channel were almost unchanged between days 9 and 21; this value at day 5 was somewhat lower. In contrast, the averaged current density of fast Na+ channels increased markedly in the myometrium during gestation: from 0 at day 5 to 0.19 +/- 0.16 at day 9, to 0.56 +/- 0.13 at day 14, to 0.90 +/- 0.13 at day 18, and to 0.86 +/- 0.14 pA/pF at day 21. This almost linear increase in the averaged density of fast Na+ channels during gestation occurs because of an increase in the fraction of cells which possessed fast Na+ channels. These results suggest that the role of fast Na+ channels in myometrial activity becomes more and more important as term approaches. We suggest that the fast Na+ current may be involved in spread of excitation.

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