Ca(2+)-induced inhibition of 45Ca2+ influx and Ca2+ current in smooth muscle of the rat vas deferens

1996 ◽  
Vol 270 (5) ◽  
pp. C1468-C1477 ◽  
Author(s):  
M. A. Khoyi ◽  
T. Ishikawa ◽  
K. D. Keef ◽  
D. P. Westfall
Keyword(s):  
Vas Deferens ◽  
Rat Vas Deferens ◽  
Inhibitory Effects ◽  
Isolated Cells ◽  
Inositol 1,4,5 Trisphosphate ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Inward Currents ◽  
K Concentration ◽  
Ca2 Channels

The present study investigates how changes in intracellular Ca2+ concentration modulate the influx of 45Ca2+ in isolated rat vasa deferentia. Raising extracellular K+ concentration ([K+]0) to > or = 32 mM increased 45Ca2+ influx during the 1st min in solutions containing 0.03-1.5 mM extracellular Ca2+ concentration ([Ca2+]0). During the 6th min in [K+]0 > or = 50 mM, 45Ca2+ influx was less than during the 1st min. This decline in 45Ca2+ influx occurred for [Ca2+]0 > or = 0.4 mM. Procaine potentiated K(+)-stimulated 45Ca2+ influx in 1.5 mM [Ca2+]0 and eliminated the decline of 45Ca2+ influx in low [Ca2-]0. Ryanodine and norepinephrine reduced K(+)-stimulated 45Ca2+ influx. 45Ca2+ content changed with time in accordance with the changes observed in 45Ca2+ influx. In isolated cells, voltage-dependent inward currents inactivated more rapidly with 1.5 mM Ca2+ as the charge carrier than with 1.5 mM Ba2+, and the steady-state inactivation relationship was shifted in the hyperpolarizing direction. Inward current was reduced with either caffeine, ryanodine, or norepinephrine. The inhibitory effects of norepinephrine were abolished by depletion of intracellular Ca2+ stores. These results are compatible with the hypothesis that K(+)-stimulated 45Ca2+ influx declines with time due to Ca(2+)-induced inhibition of Ca2- channels. Ca(2+)- and inositol 1,4,5-trisphosphate-induced releases of Ca2+ from the sarcoplasmic reticulum appear to play an important role in this process.

Voltage-dependent sodium and calcium currents of rat myenteric neurons in cell culture

1993 ◽  
Vol 69 (4) ◽  
pp. 1264-1275 ◽  
Author(s):  
J. L. Franklin ◽  
A. L. Willard
Keyword(s):  
Low Voltage ◽  
Calcium Currents ◽  
Adult Rats ◽  
Myenteric Neurons ◽  
Na Currents ◽  
Current Voltage ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Inward Currents ◽  
Ca2 Channels

1. Inward currents of myenteric neurons that had been grown in cell cultures prepared from the small intestines of neonatal or young adult rats were studied with tight seal whole-cell recordings. The kinetic and pharmacological properties of these neurons were analyzed. 2. All neurons had rapidly inactivating, tetrodotoxin (TTX)-sensitive Na+ currents that could be evoked by steps to potentials more positive than -50 mV. Holding potentials more negative than -65 mV were necessary to remove steady-state inactivation. No TTX-insensitive Na+ currents were observed, thus the ability of subsets of myenteric neurons to fire action potentials in TTX must depend upon their density of Ca2+ channels. 3. Ca2+ and Ba2+ currents were studied in neurons perfused internally with CsCl to block K+ currents and bathed with solutions containing TTX and antagonists of K+ channels. Currents were significantly larger when Ba2+ replaced Ca2+ as the charge carrier. Cd2+ and Gd3+ blocked Ca2+ and Ba2+ currents rapidly and reversibly. High-voltage-activated (HVA) Ca2+ and Ba2+ currents were observed in all neurons. Too few neurons possessed detectable low-voltage-activated Ca2+ currents to permit detailed study. 4. HVA Ca2+ and Ba2+ currents evoked from holding potentials more negative than -50 mV could be divided into two kinetically distinguishable components with very different rates of inactivation. A "decaying" component inactivated relatively rapidly with a t1/2 of 25-75 ms. A "sustained" component inactivated quite slowly with a t1/2 of 1-5 s. At more positive holding potentials, only the sustained component was observed. Although the two kinetically distinguishable components had different current-voltage relationships, they had indistinguishable rates of deactivation: a single time constant was sufficient to fit the decay of tail currents. The relative amplitudes of the two components varied considerably among different neurons. 5. Ca2+ and Ba2+ currents could be divided into two pharmacologically distinct components on the basis of sensitivity to omega-conotoxin GVIA (I omega CgTX) and to dihydropyridine antagonists (IDHP). At holding potentials more positive than -70 mV, a combination of omega CgTX and DHPs completely blocked Ca2+ and Ba2+ currents in most neurons. At holding potentials more negative than -50 mV, I omega CgTX and IDHP each contained decaying and sustained components. I omega CgTX activated more slowly than did IDHP. The DHP agonist Bay K8644 increased the amplitude of IDHP and slowed its rate of deactivation. 6. The results suggest that myenteric neurons may have as few as two subtypes of HVA Ca2+ channels; omega CgTX-sensitive ones and DHP-sensitive ones.(ABSTRACT TRUNCATED AT 400 WORDS)

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)

scholarly journals Voltage-dependent inactivation of slow calcium channels in intact twitch muscle fibers of the frog.

1989 ◽  
Vol 94 (5) ◽  
pp. 937-951 ◽  
Author(s):  
G Cota ◽  
E Stefani
Keyword(s):  
Steady State ◽  
Rate Constant ◽  
Voltage Dependence ◽  
Muscle Fibers ◽  
Dependent Manner ◽  
Inactivation Curve ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Intact Muscle ◽  
Ca2 Channels

Inactivation of slow Ca2+ channels was studied in intact twitch skeletal muscle fibers of the frog by using the three-microelectrode voltage-clamp technique. Hypertonic sucrose solutions were used to abolish contraction. The rate constant of decay of the slow Ca2+ current (ICa) remained practically unchanged when the recording solution containing 10 mM Ca2+ was replaced by a Ca2+-buffered solution (126 mM Ca-maleate). The rate constant of decay of ICa monotonically increased with depolarization although the corresponding time integral of ICa followed a bell-shaped function. The replacement of Ca2+ by Ba2+ did not result in a slowing of the rate of decay of the inward current nor did it reduce the degree of steady-state inactivation. The voltage dependence of the steady-state inactivation curve was steeper in the presence of Ba2+. In two-pulse experiments with large conditioning depolarizations ICa inactivation remained unchanged although Ca2+ influx during the prepulse greatly decreased. Dantrolene (12 microM) increased mechanical threshold at all pulse durations tested, the effect being more prominent for short pulses. Dantrolene did not significantly modify ICa decay and the voltage dependence of inactivation. These results indicate that in intact muscle fibers Ca2+ channels inactivate in a voltage-dependent manner through a mechanism that does not require Ca2+ entry into the cell.

Dependence of tonic tension on extracellular calcium in rat extraocular muscle

1987 ◽  
Vol 253 (3) ◽  
pp. C375-C383 ◽  
Author(s):  
D. J. Chiarandini ◽  
J. Jacoby
Keyword(s):  
Extraocular Muscle ◽  
Specific Interactions ◽  
Contraction Coupling ◽  
Resting Tension ◽  
High K ◽  
Voltage Dependent ◽  
K Concentration ◽  
The Right ◽  
Tonic Tension ◽  
Ca2 Channels

Ca2+-free saline containing 3.0 mM Mg2+ virtually abolishes the tonic tension evoked by depolarization with a high K+ concentration of the tonic multiply innervated fibers of rat extraocular muscles. The tonic tension abolished by Ca2+ withdrawal is restored when Ca2+ is substituted by Sr2+ but not by Ni2+. The increase of Mg2+ reduces the tonic tension and displaces the tension-log K+ relationship to the right. Cd2+ significantly reduces the tension amplitude but does not shift the tension-log K+ relationship. The organic blocker of Ca2+ channels, nifedipine (1-10 microM), has no effect on the tonic tension. In contrast, diltiazem (20 microM) reduces the amplitude of the responses without changing the tension-log K+ relationship. Both foreign anions NO3- and SCN- potentiate tonic tension without changing the tension-log K+ relationship. SCN- increases the resting tension of the muscle; this effect depends on Ca2+. In conclusion, the disappearance of tonic tension after Ca2+ withdrawal is not due to depolarization of the fibers or inactivation of the contractile responses. It is suggested that entry of extracellular Ca2+, via a voltage-dependent Ca2+ conductance, or specific interactions of Ca2+ with membrane sites involved in the regulation of excitation-contraction coupling play a role in evoking tension in tonic fibers.

Sign in / Sign up

Export Citation Format

Share Document