American Journal of Physiology-Cell Physiology, 1986
We have studied the effects of Co2+ (5 mM), low-Ca2+ solution [0 added CaCl2, 5 mM ethyleneglycol... more We have studied the effects of Co2+ (5 mM), low-Ca2+ solution [0 added CaCl2, 5 mM ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid, 3 mM MgCl2 Ringer], and verapamil (0.1 mM) on mechanical and electrical properties of rat soleus muscle in vitro at 34 degrees C. Muscle fibers had normal resting potentials in Co2+ and verapamil solutions. Low-Ca2+ solution produces a depolarization of approximately 4 mV. The action potentials are smaller and have a slower time course when exposed to test solutions. Iterative generation of action potentials in the presence of Co2+ and low-Ca2+ solution is not modified. In the presence of Co2+ or low-Ca2+ solution, the mechanical output, twitch and tetanus tensions, and caffeine contracture are reduced significantly. Verapamil produces a decrease in the twitch and tetanic tensions but does not modify the caffeine contracture tension. The effect of verapamil on the twitch becomes more manifest when the muscle is stimulated at 3-5 Hz. W...
Acta physiologica et pharmacologica latinoamericana : organo de la Asociación Latinoamericana de Ciencias Fisiológicas y de la Asociación Latinoamericana de Farmacología, 1987
The effects of verapamil (0.01-0.1 mM) and Ca-free solutions (0 Ca, 3 mM MgCl2, 5 mM EGTA) upon m... more The effects of verapamil (0.01-0.1 mM) and Ca-free solutions (0 Ca, 3 mM MgCl2, 5 mM EGTA) upon mechanical and electrical properties of a fast twitch mammalian skeletal muscle (extensor digitorum longus) have been studied. Ca-free saline reduces twitch and tetanus tension. The response to single pulses was not affected in the presence of verapamil, but as the rate of stimulation increased, peak tensions were lower and a gradual decrease of tension was observed: frequency-dependent effect. Caffeine (30 mM) contracture was significantly reduced by both solutions. The fibers in Ca-free saline were depolarized (6 mV) and +dV/dt, -dV/dt and overshoot of the AP's were reduced. On the other hand, verapamil did not affect Vm. The presence of 0.1 mM verapamil hindered the ability of the fibers to generate AP's at high rates of stimulation. Lower concentration of verapamil (0.01) did not affect the repetitive electrical activity, but tetanic tension was decreased. These findings suppo...
We have studied the effects of changes in the resting membrane potential (Vm) and T-tubules on ca... more We have studied the effects of changes in the resting membrane potential (Vm) and T-tubules on caffeine contracture (25 mM) elicited in rat soleus muscle in vitro at 34 degrees C. In high [K]o (30-140 mM, [K]o X [Cl]o constant) caffeine contractures were reduced by about 40-50% and had a faster time course than in normal Krebs ([K]o = 5 mM). Detubulation of the muscles by an osmotic treatment produces a reduction of about 30% in the caffeine contracture tension. Our results with high K solutions suggest a reduced sensitivity of the myofibrils to calcium released by caffeine. The effects of detubulation on caffeine contracture suggest that caffeine may have a direct effect on sarcolemma in addition to its well known action on the sarcoplasmic reticulum (SR). However, a depletion of the calcium content in the SR of depolarized muscle fibres as well as an anatomical damage produced by the osmotic treatment can not be ruled out as an explanation for the reduced caffeine contracture.
American Journal of Physiology-Cell Physiology, 1986
We have studied the effects of Co2+ (5 mM), low-Ca2+ solution [0 added CaCl2, 5 mM ethyleneglycol... more We have studied the effects of Co2+ (5 mM), low-Ca2+ solution [0 added CaCl2, 5 mM ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid, 3 mM MgCl2 Ringer], and verapamil (0.1 mM) on mechanical and electrical properties of rat soleus muscle in vitro at 34 degrees C. Muscle fibers had normal resting potentials in Co2+ and verapamil solutions. Low-Ca2+ solution produces a depolarization of approximately 4 mV. The action potentials are smaller and have a slower time course when exposed to test solutions. Iterative generation of action potentials in the presence of Co2+ and low-Ca2+ solution is not modified. In the presence of Co2+ or low-Ca2+ solution, the mechanical output, twitch and tetanus tensions, and caffeine contracture are reduced significantly. Verapamil produces a decrease in the twitch and tetanic tensions but does not modify the caffeine contracture tension. The effect of verapamil on the twitch becomes more manifest when the muscle is stimulated at 3-5 Hz. W...
Acta physiologica et pharmacologica latinoamericana : organo de la Asociación Latinoamericana de Ciencias Fisiológicas y de la Asociación Latinoamericana de Farmacología, 1987
The effects of verapamil (0.01-0.1 mM) and Ca-free solutions (0 Ca, 3 mM MgCl2, 5 mM EGTA) upon m... more The effects of verapamil (0.01-0.1 mM) and Ca-free solutions (0 Ca, 3 mM MgCl2, 5 mM EGTA) upon mechanical and electrical properties of a fast twitch mammalian skeletal muscle (extensor digitorum longus) have been studied. Ca-free saline reduces twitch and tetanus tension. The response to single pulses was not affected in the presence of verapamil, but as the rate of stimulation increased, peak tensions were lower and a gradual decrease of tension was observed: frequency-dependent effect. Caffeine (30 mM) contracture was significantly reduced by both solutions. The fibers in Ca-free saline were depolarized (6 mV) and +dV/dt, -dV/dt and overshoot of the AP's were reduced. On the other hand, verapamil did not affect Vm. The presence of 0.1 mM verapamil hindered the ability of the fibers to generate AP's at high rates of stimulation. Lower concentration of verapamil (0.01) did not affect the repetitive electrical activity, but tetanic tension was decreased. These findings suppo...
We have studied the effects of changes in the resting membrane potential (Vm) and T-tubules on ca... more We have studied the effects of changes in the resting membrane potential (Vm) and T-tubules on caffeine contracture (25 mM) elicited in rat soleus muscle in vitro at 34 degrees C. In high [K]o (30-140 mM, [K]o X [Cl]o constant) caffeine contractures were reduced by about 40-50% and had a faster time course than in normal Krebs ([K]o = 5 mM). Detubulation of the muscles by an osmotic treatment produces a reduction of about 30% in the caffeine contracture tension. Our results with high K solutions suggest a reduced sensitivity of the myofibrils to calcium released by caffeine. The effects of detubulation on caffeine contracture suggest that caffeine may have a direct effect on sarcolemma in addition to its well known action on the sarcoplasmic reticulum (SR). However, a depletion of the calcium content in the SR of depolarized muscle fibres as well as an anatomical damage produced by the osmotic treatment can not be ruled out as an explanation for the reduced caffeine contracture.
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