SPONTANEOUS ACTIVITY OF ANNELID VISCERAL MUSCLE AND RELATED CALCIUM MOVEMENTS - EFFECT OF KCL DEPOLARIZATION, CAFFEINE, ACETYLCHOLINE AND ADRENALINE

1. Nereis pharangeal muscle exhibited rhythmic bursts of contractions accompanied by bursts of spike discharges. 2. KCl application induced contractures which were inhibited in calcium-free media as was normal spontaneous activity. 3. Caffeine and acetylcholine stimulated spontaneous activity and induced contractures in the muscle. At 10°C, adrenaline was without effect but it was slightly excitatory at 20°C. 4. Calcium efflux studies revealed a two-component efflux curve, with 89% of activity related to the extracellular compartment and only 11% related to the intracellular compartment. 5. KCl, caffeine and acetylcholine stimulated the slow efflux component but adrenaline inhibited efflux. KCl and acetylcholine stimulated calcium influx into the muscle fibres but caffeine did not. 6. It is concluded that this muscle has little intracellular calcium storage capacity and is dependent upon calcium influx for the maintenance of normal contractility. © 1979.