Differentiation between intrinsic and extrinsic acetylcholine receptors of the chick biventer cervicis muscle.

Abstract

The intrinsic and extrinsic acetylcholine receptors were studied by analysing the effects of α-bungarotoxin and desipramine on the contractile response elicited by nerve stimulation (single shocks) and that by application of acetylcholine. In the absence of anticholinesterases, α-bungarotoxin as well as desipramine blocked the response to exogenous acetylcholine with a time-course much faster than that of the inhibition of the response to nerve stimulation. After complete blockade of neuromuscular transmission by α-bungarotoxin, washout of the toxin gradually resulted in recovery of the response to acetylcholine, whereas the response to nerve stimulation was not appreciably restored. (+)-Tubocurarine, on the other hand, blocked both types of responses to a parallel extent. (+)-Tubocurarine as well as acetylcholine at high concentration protected both responses from blockade by α-bungarotoxin. In the presence of anticholinesterases, the inhibition by α-bungarotoxin of responses to nerve stimulation and to acetylcholine was parallel. The recovery of acetylcholine-induced responses after washout of the toxin, however, was smaller than in the absence of anticholinesterases.