ABSTRACT
The general path by which the activating signals reach skeletal muscles starts in the central nervous system, but we will pick up the transmission of signals at the motor neurons. The open-shut nature of gating in single channels can be seen directly with patch-clamp recording methods. Arrival of the action potential at the presynaptic motor nerve terminals leads to release of acetylcholine (ACh) in previously prepackaged vesicles. Early quantitative experiments with frog neuromuscular junction indicated that the probability of release of ACh vesicles during an action potential increases as the fourth power of in the external medium. Like all channels, the end-plate channel is a glycoprotein, however, more is known of its structure than of any other channel. Since the signal inducing proper localization is nerve-derived, it is possible that isoforms facilitate the process through inducer-specific binding sites. The question of Na+ channel localization is inseparable from the question of lateral mobility of membrane proteins in general.
