Effects of cyclopiazonic acid on Ca(2+)-activated tension production in skinned skeletal muscle fibres of the ferret.
The effect of cyclopiazonic acid, an inhibitor of sarcoplasmic reticulum Ca(2+)-ATPase, was investigated on force generation by the contractile apparatus in Triton-skinned fibres from extensor digitorum longus and soleus. Concentrations of cyclopiazonic acid lower than 10 microM were without effect on Ca(2+)-activated tension in both types of muscles. In contrast, in soleus, cyclopiazonic acid (20, 50, 100 microM) was found to shift reversibly the relation-tension pCa (-log[Ca2+]) towards lower free Ca2+ and to decrease maximal Ca(2+)-activated tension, in a dose-dependent manner. In extensor digitorum longus, the Ca2+ sensitivity was significantly increased only at a high cyclopiazonic acid concentration (100 microM) and for all the concentrations tested between 5 to 100 microM maximal Ca(2+)-activated tension was unchanged. These results suggest that cyclopiazonic acid has a direct effect on contractile proteins, in a dose-dependent manner. Ca2+ sensitivity and Ca(2+)-activated maximal tension of the contractile apparatus were differentially affected in fast- (extensor digitorum longus) and slow-twitch (soleus) fibres from ferret skeletal muscle.
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Laboratoire de Physiologie Générale, URA CNRS 1340, Ecole Nationale Vétérinaire, Nantes, France.
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D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D005289:Ferrets; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology*; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000166:cytology / Q000187:drug effects*; D009183:Mycotoxins / Q000494:pharmacology*; D009210:Myofibrils / Q000187:drug effects
D007211:Indoles; D009183:Mycotoxins; D000252:Calcium-Transporting ATPases; D002118:Calcium; C000543:cyclopiazonic acid