Calcium current in embryonic Xenopus muscle cells in culture

1989 ◽  
Vol 67 (10) ◽  
pp. 1259-1264 ◽  
Author(s):  
F. Moody-Corbett ◽  
R. Gilbert ◽  
H. Akbarali ◽  
J. Hall
Keyword(s):  
Skeletal Muscle ◽  
Calcium Current ◽  
Extracellular Recording ◽  
Outward Current ◽  
Muscle Cells ◽  
Slow Inward Current ◽  
Muscle Membrane ◽  
Inward Current ◽  
Muscle Calcium ◽  
Sodium And Potassium

We have investigated the appearance of calcium current in Xenopus muscle cells in 1- to 6-day-old cultures. Whole cell currents were recorded using a patch-clamp amplifier with sodium and potassium replaced with tetraethylammonium and cesium, respectively, and BaCl2 used in place of CaCl2. When the muscle membrane was depolarized above −30 mV, a slow inward current was activated, the current reached a peak amplitude near 0 mV, and an outward current became apparent above + 10 mV. This slow current was enhanced by adding barium or Bay K 8644 to the extracellular recording solution and was blocked by the addition of cobalt, cadmium, or the dihydropyridines nifedipine or (+)PN 200-110. Taken together these results indicate the presence of an inward calcium current mediated through L-type channels. Thirty-one percent of the cells examined on the first day in culture showed no discernible slow inward current; however, as the age of the culture increased, all cells showed slow inward current and there was an increase in the amplitude of the current. A small proportion of the muscle cells (5 out of 34) also showed a fast activating and inactivating inward current. This current, which activated at more hyperpolarized potentials (−40 mV) was only present when 5 mM ATP was included in the internal recording solution. It also appeared to be mediated through a calcium channel but not a dihydropyridine, sensitive channel.Key words: embryonic skeletal muscle, calcium current.

scholarly journals Calcium currents in a fast-twitch skeletal muscle of the rat.

1983 ◽  
Vol 82 (4) ◽  
pp. 449-468 ◽  
Author(s):  
P L Donaldson ◽  
K G Beam
Keyword(s):  
Skeletal Muscle ◽  
Leakage Current ◽  
Calcium Current ◽  
Outward Current ◽  
Extracellular Calcium ◽  
Calcium Currents ◽  
Slow Inward Current ◽  
Delayed Rectifier ◽  
Inward Current ◽  
Time To Peak

Slow ionic currents were measured in the rat omohyoid muscle with the three-microelectrode voltage-clamp technique. Sodium and delayed rectifier potassium currents were blocked pharmacologically. Under these conditions, depolarizing test pulses elicited an early outward current, followed by a transient slow inward current, followed in turn by a late outward current. The early outward current appeared to be a residual delayed rectifier current. The slow inward current was identified as a calcium current on the basis that (a) its magnitude depended on extracellular calcium concentration, (b) it was blocked by the addition of the divalent cations cadmium or nickel, and reduced in magnitude by the addition of manganese or cobalt, and (c) barium was able to replace calcium as an inward current carrier. The threshold potential for inward calcium current was around -20 mV in 10mM extracellular calcium and about -35 mV in 2 mM calcium. Currents were net inward over part of their time course for potentials up to at least +30 mV. At temperatures of 20-26 degrees C, the peak inward current (at approximately 0 mV) was 139 +/- 14 microA/cm2 (mean +/- SD), increasing to 226 +/- 28 microA/cm2 at temperatures of 27-37 degrees C. The late outward current exhibited considerable fiber-to-fiber variability. In some fibers it was primarily a time-independent, nonlinear leakage current. In other fibers it was primarily a time-independent, nonlinear leakage current. In other fibers it appeared to be the sum of both leak and a slowly activated outward current. The rate of activation of inward calcium current was strongly temperature dependent. For example, in a representative fiber, the time-to-peak inward current for a +10-mV test pulse decreased from approximately 250 ms at 20 degrees C to 100 ms at 30 degrees C. At 37 degrees C, the time-to-peak current was typically approximately 25 ms. The earliest phase of activation was difficult to quantify because the ionic current was partially obscured by nonlinear charge movement. Nonetheless, at physiological temperatures, the rate of calcium channel activation in rat skeletal muscle is about five times faster than activation of calcium channels in frog muscle. This pathway may be an important source of calcium entry in mammalian muscle.

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.

A lethal mutation in mice eliminates the slow calcium current in skeletal muscle cells

Nature ◽  
1986 ◽  
Vol 320 (6058) ◽  
pp. 168-170 ◽  
Author(s):  
Kurt G. Beam ◽  
C. Michael Knudson ◽  
Jeanne A. Powell
Keyword(s):  
Skeletal Muscle ◽  
Calcium Current ◽  
Muscle Cells ◽  
Lethal Mutation ◽  
Skeletal Muscle Cells

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.

Slow inward current may produce many results attributed to IX1 in cardiac Purkinje fibers

1985 ◽  
Vol 249 (1) ◽  
pp. H122-H132
Author(s):  
J. M. Jaeger ◽  
W. R. Gibbons
Keyword(s):  
Action Potential ◽  
Outward Current ◽  
Purkinje Fiber ◽  
Slow Inward Current ◽  
Channel Blockers ◽  
Inward Current ◽  
Purkinje Fibers ◽  
Cardiac Purkinje Fibers ◽  
Current Voltage ◽  
Current Voltage Relation

We have tried to answer two fundamental questions concerning the outward current IX1 of cardiac Purkinje fibers. 1) Is it possible that current changes identified as arising from IX1 in voltage-clamp experiments are actually manifestations of changes in the slow inward current (Isi); and 2) is IX1 in fact required to produce the electrical phenomena attributed to it? Isi behavior and the role of IX1 were explored using computer simulation. The Isi model produced current changes during depolarizations and hyperpolarizations from depolarized resting potentials like those attributed to IX1. It also produced a component of "tail currents" that behaved like IX1. If these current changes were analyzed, assuming that an outward current is responsible, the resulting kinetics and current voltage relation would be very similar to the kinetics and current voltage relation reported for IX1. Using the McAllister, Noble, and Tsien formulation of the Purkinje fiber action potential, we found that IX1 is not essential for repolarization of the reconstructed action potential nor is it needed to reproduce interval duration effects and the effects of applied current in that model. Data suggesting that calcium channel blockers reduce IX1 and that catecholamines increase IX1 may be explained as arising from changes in Isi. Thus many manifestations of IX1 can be explained as arising from unanticipated behavior of Isi, and IX1 does not necessarily play a key role in generating Purkinje fiber electrical activity.

FMRFamide effects on membrane properties of heart cells isolated from the leech, Hirudo medicinalis

1992 ◽  
Vol 67 (2) ◽  
pp. 280-291 ◽  
Author(s):  
K. J. Thompson ◽  
R. L. Calabrese
Keyword(s):  
Isolated Heart ◽  
Muscle Cells ◽  
Membrane Properties ◽  
Slow Inward Current ◽  
Heart Cells ◽  
Linear Component ◽  
Inward Current ◽  
Isolated Heart Cells ◽  
Voltage Dependent ◽  
K Currents

1. The effects of the cardioactive peptide FMRFamide were tested on enzymatically dissociated muscle cells isolated from hearts of the leech. These cells were normally quiescent, with resting potentials near -60 mV. 2. Superfusion of FMRFamide induced a strong depolarization in isolated heart cells (e.g., greater than 40 mV with 10(-6) M FMRFamide). The depolarization was maintained in the continued presence of peptide and persisted long after its removal. Less frequently, FMRFamide superfusion elicited an episodic polarization rhythm. 3. The response of isolated heart cells to bath-applied FMRFamide showed a 1- to 2-min latency. The latency decreased with repeated applications of FMRFamide. 4. The FMRFamide response was diminished by Na+ replacement but persisted with Ca2+ channel blockade. 5. In voltage-clamped heart cells (-60 mv), superfusion of FMRFamide elicited a slow inward current with a transient and a sustained component. 6. Current-voltage (I-V) curves during FMRFamide superfusion in normal leech saline showed that FMRFamide also enhanced voltage-dependent outward currents activated at depolarized levels. 7. Under conditions in which K+ currents were substantially blocked, the FMRFamide-dependent I-V curve was net inward from -90 to +50 mV. A voltage-dependent component was blocked by Co2+ and a linear component by Na+ replacement. 8. We conclude that FMRFamide elicits a persistent inward current with a Na+ component and in addition modulates both voltage-dependent Ca2+ and K+ currents that may contribute to the normal myogenic activity of leech heart muscle cells.

Inositol trisphosphate and activators of protein kinase C modulate membrane currents in tail motor neurons of Aplysia

1989 ◽  
Vol 61 (2) ◽  
pp. 302-310 ◽  
Author(s):  
M. Sawada ◽  
L. J. Cleary ◽  
J. H. Byrne
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Motor Neurons ◽  
Outward Current ◽  
Membrane Currents ◽  
Slow Inward Current ◽  
Apparent Increase ◽  
Inward Current ◽  
Kinase C ◽  
Hydrolysis Of

1. We have investigated how activation of the inositol lipid second messenger pathway may contribute to modulation of membrane currents in tail motor neurons of Aplysia. Specifically, we examined the effects of injected inositol 1,4,5-trisphosphate (IP3) and analogues of diacylglycerol (DAG), both of which are products of the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2). 2. Injection of IP3 produced an outward current associated with an apparent increase in membrane conductance. Ion substitution experiments, the sensitivity of the response to low concentrations of TEA and its attenuation by intracellular injections of EGTA suggest that the current produced by injection of IP3 is a calcium-activated K+ current (IK,Ca). 3. The response to IP3 was mimicked by intracellular injection of Ca2+. Injection of Ca2+ produced an outward current that was associated with an apparent increase in input conductance of the membrane. The same manipulations that affected the response to IP3 (see above) also affected the response to injections of Ca2+. 4. Injections of activators of protein kinase C (PKC) produced a relatively slow inward current. The inward current has not been fully analyzed, but it does not appear to be due to the actions of any single conventional ion channel. 5. Activators of PKC attenuated responses to subsequent injections of IP3 indicating that one component of PIP2 hydrolysis can attenuate the other. 6. The results suggest that hydrolysis of inositol phospholipids is a mechanism for regulation of membrane properties in tail motor neurons of Aplysia.

Calcium and potassium currents in canine gastric smooth muscle cells

1992 ◽  
Vol 262 (5) ◽  
pp. G859-G867 ◽  
Author(s):  
S. M. Sims
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Outward Current ◽  
Muscle Cells ◽  
Current Evidence ◽  
Equilibrium Potential ◽  
Inward Current ◽  
K Current ◽  
Gastric Corpus ◽  
Ca2 Channels

Membrane ionic currents were recorded in single smooth muscle cells dissociated from circular muscle of dog stomach (corpus region). When studied under voltage clamp with K+ in the patch electrode, depolarization to potentials more positive than -40 mV, from a holding potential of -70 or -80 mV, evoked transient inward current followed by outward current. Evidence that the outward current was due to K+ came from analysis of deactivation tail currents, which reversed direction close to the K+ equilibrium potential. In addition, the outward current was reduced by tetraethylammonium (TEA, 1-5 mM) applied to the external surface of cells. The Ca(2+)-channel blocker Cd2+ blocked the inward current and also reduced outward current, suggesting Ca(2+)-activated K+ current contributed to the outward current. The voltage-activated inward current was studied in isolation with Cs+ and TEA in the recording electrode to block K+ current. In standard bathing solution containing 2.5 mM Ca2+, the inward current activated between -50 and -40 mV, with peak inward current at +10 mV. The depolarization-activated inward current was blocked by nifedipine and enhanced by BAY K 8644, providing evidence that it was Ca2+ current. The Ca2+ current showed transient and sustained components, both of which showed similar voltage activation and inactivation ranges. The half-inactivation potential was approximately -37 mV. These results provide evidence that smooth muscle cells from the canine gastric corpus possess K+ and Ca2+ channels. Based on the voltage dependence of activation and inactivation and sensitivity to dihydropyridines, L-type Ca2+ channels predominate in canine gastric corpus smooth muscle.

Sign in / Sign up

Export Citation Format

Share Document