Characteristics of membrane channels induced by acetylcholine at frog muscle-tendon junctions.

The membrane at the tendinous ends of frog muscle fibres has acetylcholine (ACh) receptors that are blocked by alpha-bungarotoxin. The properties of ACh-activated channels in the myotendinous region were investigated by noise analysis. These channels displayed the same characteristics in normal, denervated and reinnervated muscles. The mean lifetime and conductance of ACh-induced channels at the myotendinous junction resembled those of channels at the normal neuromuscular junction. Both channels opened with a lifetime shorter than that of extrajunctional receptors. Channels of short lifetime could be detected at distances of several hundred micrometres from the tendon junction. The similarity of ACh-activated channels at neuromuscular and myotendon junctions was found both in the fast, 'singly' innervated sartorius and cutaneous pectoris muscle and in the intermediate, multiply innervated submaxillaris muscle.