ACETYLCHOLINE-INDUCED CONTRACTIONS IN A HOLOTHURIAN (ISOSTICHOPUS-BADIONOTUS) SMOOTH-MUSCLE ARE BLOCKED BY THE CALCIUM-ANTAGONISTS, DILTIAZEM AND VERAPAMIL

1. The longitudinal muscle of the body wall (LMBW) of the holothurian, Isostichopus badionotus contracted when treated with acetylcholine (ACh). The threshold concentration for initiating a contraction was 10(-8) M ACh. 2. Inward calcium (Ca2+) current blockers, diltiazem and verapamil, blocked contractions induced by ACh suggesting that Ca2+ channels are involved. Verapamil caused small rhythmic contractions to occur in some muscle preparations. 3. Caffeine initiated contractions only at the high concentration of 10 mM and caused rhythmic contractions in otherwise non-spontaneously beating muscle. The caffeine-contractions were partially blocked by verapamil.