Pharmacological study of two kinds of cholinoreceptors on the membrane of identified completely isolated neurones of Planorbarius corneus

Completely isolated identified neurones (LPed-2 and LPed-3) of the left pedal ganglion of Planorbarius corneus were shown to have two kinds of cholinoreceptors (ChR) on their membrane. One kind of ChR is a classical nicotinic receptor which is sensitive to nicotinomimetics and can be blocked by tubocurarine; the depolarization caused by activation of this ChR type is chloride-dependent. The other kind of ChR, which mediates a potassium-dependent hyperpolarization, has some common features with muscarinic (M) ChR of vertebrates, being sensitive to the muscarinomimetics, dioxolane F-2268, methylfurmethide, mecholyl, and arecoline, although insensitive to oxotremorine. The sensitivity of this receptor to muscarine, itself, was not tested. Like the muscarinic ChR of vertebrates, it can be blocked by benzilylcholine mustard, but, in contrast to vertebrate muscarinic receptors, it cannot be blocked by atropine and cannot distinguish between the optical isomers of F-2268. TEA, mytolon, and cooling prevent the hyperpolarization caused by ACh and muscarinomimetics. The two kinds of ChR in P. corneus neurones seem to be similar to those found by Kehoe 24–26 on the medial cells of Aplysia pleural ganglia, both in their pharmacological characteristics and in the ionic permeability changes which they control.