The identity of 'intrinsic’ and ‘extrinsic’ acetylcholine receptors in the motor end-plate

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Abstract
A possible distinction between "extrinsic" drug receptors and "intrinsic" neuro-receptors at the motor end-plate has been considered, and an experiment described to test the validity of such a differentiation. A dose of d-tubocurarine is applied ionophoretically to a motor end-plate, and its inhibitory effects are examined on (i) a "massive" local discharge of miniature end-plate potentials (involving "intrinsic" release of acetylcholine) and (ii) artificially produced acetylcholine potentials. Under suitable experimental conditions, curare is shown to suppress both types of depolarization with equal speed and efficacy. It is considered, therefore, that there is no basis for differentiating, in accessibility, location or pharmacological behaviour, between "drug-" and "neuro-receptors" of the motor end-plate.