Demonstration of different type cholinoreceptors on the membrane of an isolated Planorbarius corneus mollusk membrane

: In experiments on isolated and identified neurones of the pedal ganglion of the gastropod mollusc P. corneus, it was demonstrated that biphasic response to ACh may be obtained both to superfusion and electrophoretic application. Fast (depolarizing) phase may be imitated by a nicotinomimetic drug, suberyldicholine, and blocked by d-tubocurarine. These data indicate that this phase results from activation of nicotinic cholinoreceptors. Slow (hyperpolarizing) phase may be evoked by a muscarinomimetic, dioxolane F-2268, which is taken as an indication of the muscarinic nature of cholinoreceptors responsible for this phase. Experiments on completely isolated neurones directly show that both kinds of cholinoreceptors belong to the same neurone. Biphasic pattern of the response depends on the level of the membrane potential and on the conditions of ACh application. The fast phase is more evident at membrane hyperpolarization, the slow one--at depolarization. The fast phase is more readily obtained by superfusion by high concentrations of ACh or at close position of electrophoretic micropipette to neuronal surface, whereas the slow phase may be easily obtained by superfusion with low concentrations of ACh or when the micropipette is not attached so closely to the cell.