[Reaction of cholinoreceptors from an isolated molluskan neuron with analogs of acetylcholine and tetramethylammonium].

The effect of 13 acetylcholine and tetramethylammonium derivatives on cholinoreceptors of isolated neurone on the pond snail has been investigated by the analysis of membrane current fluctuations at 10 and 20 degrees C. The elementary current was independent from the agonist structure. The channel open time and its Q10 coefficient were found to be maximum for acetylcholine. At low concentrations, acetylcholine derivative with four groups in its methylene chain exhibited the weakest activity. Agonist activity at higher concentrations was evaluated by maximum increase in the membrane current. With respect to this character, the derivative with two ethyl radicals in its cation group was found to be the weakest one. Possible causes of low activities of the agonists studied in comparison with that of acetylcholine are discussed.