Cholinoreceptors of the dentis retractor muscle of the sea urchin Strongylocentrotus intermedius.

Neostigmine increases and cholinergic blocking agents block contractions of Strongylocentrotus intermedius dentis retractor muscle caused by either acetylcholine or indirect stimulation. Both innervated and non-innervated parts of the muscle are sensitive to low acetylcholine concentration suggesting that there are both synaptic and extra-synaptic cholinoreceptors. Nicotinomimetics are more potent than muscarinomimetics. Both d-tubocurarine and atropine are weak blocking agents as compared to pentadecamethylene-bis-trimethylammonium or hexadecamethylene-bis-trimethylammonium, Kd being 1 X 10(-4) to 5 X 10(-5) and 5 X 10(-7) to 4 X 10(-7) M respectively. Disulphide bonds and carboxylic (or phosphate) groups were revealed in dentis retractor muscle cholinoreceptors using drugs modifying receptor structure. Cholinoreceptors of both nicotinic and muscarinic type were revealed in oesophagus longitudinal muscles of Strongylocentrotus intermedius.