COMPARISON OF EFFECTS OF SKF 525-A AND PROCAINE ON EXCITATION-CONTRACTION COUPLING IN SINGLE CRAYFISH MUSCLE-FIBERS

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Abstract
The effects of .beta.-diethylaminoethyldiphenylpropylacetate hydrochloride (SKF 525-A) on excitation-contraction coupling and Ca-dependent electrogenesis are compared to those of procaine [using isolated flexor muscle fibers from the walking leg of Orconectes virilis]. At pH 7.2, SKF 525-A and procaine occur essentially (> 97%) as a free base and as a cation, respectively. At this pH SKF 525-A elicited tension development, blocked K-induced contractures and the K-induced repriming of caffeine contractions, potentiated caffeine-induced tensions, inhibited the procaine-induced spikes and twitches and, depending on the concentration, either potentiated (25-50 .mu.M) or depressed (> 100 .mu.M) the tensions associated with the graded membrane electrogenesis. At the same pH procaine blocked the contractions elicited by SKF 525-A, high K media, graded electrogenesis and caffeine, and converted the graded membrane responses into all-or-none spikes. Probably, SKF 525-A as a free base inhibits membrane Ca activation more effectively than it depresses K conductance and is synergistic with caffeine in reducing the effectiveness of Ca sequestration by the sarcoplasmic reticulum. Procaine as a cationic molecule may depress K activation more than Ca activation during depolarization and block the release of Ca2+ from the sarcoplasmic reticulum.