Exposure of receptor sites on rat muscle membranes by a neurally released factor

Isolated phrenic nerve-diaphragm preparations of the rat were stimulated electrically via the nerve. The medium bathing the preparation contained a factor which increased the specific binding (Bmax) of [125I]alpha-bungarotoxin to isolated sarcolemmal membranes. Medium from control preparations, left unstimulated, had no significant effect on the binding. The nerve stumps in the stimulated preparations were relatively depleted of the factor which increased the binding. The possibility that latent acetylcholine receptors are exposed by a factor released from the nerve during impulse activity is suggested.