Pharmacological studies on the invertebrate non-striated muscles—III. The ventral muscles of the polychaete Chaetopterus variopedatus

Abstract

1. The responses of quiet and active preparations of the ventral muscles of the polychaete Chaetopterus variopedatus to drugs are reported. 2. In quiet preparations, on a molar base, butyrylcholine was by far the most potent choline ester assayed, followed by propionylcholine and acetylthiocholine (much less). Mecholyl, pilocarpine and benzoylcholine were ineffective. Acetylcholine was found to be often without effect. 3. Nicotine and crude homogenates of sea urchin pedicellariae were very active on the ventral muscles. 4. The actions of acetylcholine and butyrylcholine were potentiated by anticholinesterases such as physostigmine and prostigmine. 5. The responses to butyrylcholine were significantly depressed by d-tubocurarine. 6. In active preparations, there occurred an increase in sensitivity to acetylcholine; butyrylcholine (more) and propionylcholine (less) elicited sustained contractions in spontaneously active muscles. 7. The response of active muscles to butyrylcholine was significantly depressed by both atropine and d-tubocurarine. 8. GABA abolished a fair spontaneous activity of the muscles and potentiated the subsequent application of acetylcholine; picrotoxin, however, did not restore the abolished activity. 9. Crude homogenates of the ventral muscles showed cholinesterase activity against several choline esters, including mecholyl. 10. The results suggest that the ventral muscles are the effector part of a cholinergic system; but it was not ascertained whether or not the muscle receptors are nicotinic. 11. The nature of the spontaneous activity is discussed. The fact that it was not suppressed by cholinergic blocking drugs and a ganglioplegic agent (hexamethonium) was taken as indicating that this activity is myogenic.