Abstract
1. Effects of the catch-relaxing peptide (CARP) on contractile responses were examined in the anterior byssus retractor muscle (ABRM) of Mytilus edulis and in various other molluscan muscles. 2. In the ABRM, phasic contraction in response to repetitive electrical pulses of stimulation was potentiated by low concentrations of CARP and inhibited by high concentrations. The inhibitory effect reached maximum in 2–10 min after applying the peptide. Contractions of the muscle in response to acetylcholine (ACh) and 100 mM K + artificial seawater (ASW) were also potentiated by low concentrations of CARP and inhibited by high concentrations. Contractions in response to FMRFamide and caffeine were simply inhibited by CARP. 3. In the radula protractor and retractor muscles of Rapana thomasiana and Fusinus perplexus, contractions in response to electrical pulse, ACh and glutamate were inhibited by CARP. 4. In the herats of Mytilus edulis, Merelrix lusoria, Tapes japonica and Rapana thomasiana, their activities were inhibited by CARP. The ACh-antagonist benzoquinonium did not affect the inhibitory effect of the peptide. 5. The results of the present study suggest that CARP has modulatory effects on contractions in many molluscan muscles and that its principal modulatory effect is one of inhibition.
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