The effects of some transmitter substances on the tube foot muscles of the starfish, Asterias amurensis (Lütken)

Abstract

1. 1. Cholinergic, adrenergic, and some other drugs known as neurotransmitters were tested on the whole (“intact”) isolated tube feet of Asterias amurensis as well as on those dissected to expose the connective tissue layer (“cleaned” tube feet). 2. 2. Acetylcholine (ACh) and γ-aminobutyric acid (GABA) caused contractions of the tube feet, being 1000 times as potent on the “cleaned” tube feet as on “intact” ones. Catecholamines, on the contrary, proved to be more effective on the “intact” tube feet. 3. 3. ACh potency (EC 50 = 1 × 10 −6 M) was greatly increased in the presence of neostigmine or physostigmine. Nicotinomimetics were as a rule 10- to 100-fold as potent as muscarinomimetics. More or less selective suppression of responses to nicotinomimetic or to muscarinomimetic agents by appropriate blocking agents suggests the existence of two kinds of cholinoreceptors in the tube foot muscles. 4. 4. The inability of cholinergic blocking agents to prevent GABA responses, as well as the fact that the muscle desensitized to GABA still responds to ACh, suggests that ACh and GABA interact with different receptors. 5. 5. Glycine and 5-HT were ineffective; l-glutamic acid produced only small contractions and histamine caused relaxations.