Cellular Localization of the Molecular Forms of Acetylcholinesterase in Primary Cultures of Rat Sympathetic Neurons and Analysis of the Secreted Enzyme

Abstract

The secretion and cellular localizing of the molecular forms of acetylcholinesterase (AChE) were studied in primary cultures of rat sympathetic neurons. When cultured under conditions favoring a noradrenergic phenotype, these neurons synthesized and secreted large quantities of the tetrameric G4, and the docecameric A12 forms, and minor amounts of the G1 and G2 forms. When these neurons adopted the cholinergic phenotype, i.e., in the presence of muscle-conditioned medium, the development of the cellular A12 form was completely inhibited. These neurons secreted only globular, mainl G4, AChE. Both cellular and secreted A12 AChE in adrenergic cultures aggregated at an ionic strength similar to that of the culture medium, raising the hypothesis that this forms was associated with a polyanionic component of basal lamina. In noradrenergic neurons, 60-80% of the catalytic sites were exposed at the cell surface. In particular, 80% of G4 form, but only 60% of the A12 form, was external, demonstrating for the A12 form a sizeable intracellular pool. The hydrophobic character of the molecular forms was studied in relation to their cellular localization. As in muscle cells, most of the G4 form was membrane-bound. Whereas 76% of the cell surface A12 form was solubilized in the aqueous phase by high salt concentrations, only 50% of the intracellular A12 form was solubilized under these conditions. The rest of intercellular A12 could be solubilized by detergents and was thus eitehr membrane-bound or entrapped in vesicles originating from, e.g., the Golgi apparatus.