Secretion of acetylcholinesterase: relation to acetylcholine receptor metabolism.

Acetylcholinesterase (AChE) and acetylcholine receptors (AChR) are muscle-specific glycoproteins present (AChR) are muscle-specific glycoproteins present in cultured chick embryo muscle cells. The first is found as both a secreted and a membrane-bound enzyme whereas the ACh receptor is strictly an integral membrane protein. We have studied the transport and externalization of these two proteins in the same cells using several compounds known to affect secretory processes: colchicine, tunicamycin and the ionophores X-537A, Nigericin and Monensin. Under all experimental conditions, any change in the rate of AChE secretion was accompanied by an identical change in the rate of ACh receptor incorporation into the plasma membrane. These studies were designed to test directly the hypothesis that secreted and integral membrane proteins are transported together to the plasma membrane. Our results are consistent with a single transport pathway in muscle cells for the externalization of membrane and secreted proteins.