[The effect of verdazyl radicals on Ca2+ metabolism in preparations of heavy sarcoplasmic reticulum].

Three verdazyl radicals were studied for their effect on calcium accumulation and outflux (passive and Ca- or caffeine-induced) and conformational state of the Ca-ATPase. All three compounds differently affected the ATP-dependent Ca-accumulation. Their effect on the Ca-release from the sarcoplasmic reticulum vesicles could not be explained by their influence on the Ca-accumulation system. The Ca2+ amount liberated by the calcium or caffeine addition was equal in both cases but was modified differently by the used verdazyl compounds. The data obtained suggest that Ca-induced and caffeine-induced calcium release is realized by different mechanisms.