A K+-selective conductance sensitive to cholinergic antagonists obtained by the fusion of axonal membrane vesicles to planar bilayers.

In several preparations, electric parameters of axon and (or) Schwann cell may be affected by cholinergic ligands [1 4]. It has also been demonstrated that axonal membranes contain binding sites for a variety of cholinergic ligands [5 7]. Visualization of these binding sites proved possible by the use of a conjugate of a-bungarotoxin and horseradish peroxidase [8,9]. An important question that arises is whether the cholinergic binding sites of axons are associated with specific receptor channels. Here we address this question in an in vitro membrane system readily accessible to electrical measurements: a hybrid membrane formed by the fusion of axonal vesicles to a planar phospholipid bilayer. Using conditions shown to enhance fusion of native or reconstituted membrane vesicles to planar bilayers [10-12], we demonstrate here tile incorporation of a K+-selective conductance from crustacean axonal membranes and the effect of cholinergic antagonists on this conductance.