The distribution of acetylcholine receptors on muscle fibres of regenerating salamander limbs.

Abstract

Muscle fibers developing during limb regeneration were examined for responsiveness to acetylcholine (ACh) applied iontophoretically along the membrane. Fibers which were uninnervated and those with nontransmitting synapses had high over-all sensitivities, with only minor variations along their length. Functionally innervated fibers in which depolarization did not yet elicit action potentials had high over-all sensitivities, even when the synaptic potentials had amplitudes of 40-50 mV. In these the membrane in the vicinity of synapses tended to have sensitivities above the background level. Upon the appearance of action potentials, several weeks after fiber innervation, the responsiveness to ACh began to decline in synapse free regions of the membrane. In mature muscle the sensitivity to ACh was restricted to sites of synaptic contact.