EFFECT OF D-TUBOCURARINE AND ATROPINE ON THE RESPONSES OF HELIX NEURONS TO FAST ACETYLCHOLINE APPLICATIONS

It was shown that D-tubocurarine reversibly inhibits membrane currents induced by instant acetylcholine application. The blocking effect of D-tubocurarine was observed for both ouabain-sensitive ACh responses (type A) and ouabain-insensitive responses (type B). The investigation of the effect of D-tubocurarine on dose-response curves for both types of ACh-responses and approximation of data obtained by means of Hill's equation revealed that in A-type neurons tubocurarine caused a shift of dose-response curve to high concentration of agonists. The maximal value of currents induced by application of saturating doses of ACh to A-type neurons was not changed. In B-type neurons the dose-response curve under application of D-tubocurarine was also shifted to higher concentration of agonists, which was accompanied by decrease of current induced by ACh in saturating concentration. The calculated values of apparent constants of dissociation were increased by D-tubocurarine 1,4 times for A-type responce and 2 times for B-type. Atropine inhibited A-type responses and had no effect on B-type responses. The data obtained assumed B-type responses to be nicotinic and A-type to be the mixed ones. The inhibitory effect of atropine on type A ACh-responses was abolished by lowering the temperature to 4-degrees-C, while the effect of D-tubocurarine remained unchanged. Atropine was shown to induce the increase of intracellular level of cGMP (but not cAMP) and to enhance membrane phosphorylation. It was suggested that atropine has an inhibitory effect on ACh-responses type A through stimulation of the cAMP-independent membrane phosphorylation.