Metabolism of acetylcholine receptors in skeletal muscle.

The acetylcholine receptor in skeletal muscle is an integral plasma membrane glycoprotein. Its biosynthesis and incorporation into plasma membrane and its degradation are being studied with the use of biochemical, biophysical, and microscopic techniques. In this report, previously published data are combined with new information to yield a consistent and fairly detailed description ofthe mechanisms involved in receptor metabolism. It is proposed that the biosynthesis, transport, and incorporation of the receptor into plasma membranes involve a mechanism similar, or identical, to that used by the cell for production and secretion of secretory proteins. The receptor is degraded by a random-hit process, which involves internalization, transport to secondary lysosomes, and hydrolysis. Sites of regulation of receptor metabolism are discussed in the context of regulation of the number and distribution of receptors in plasma membranes, particularly with respect to the formation and stability of neuromuscular junctions.