Electric Field-Induced Redistribution of ACh Receptors on Cultured Muscle Cells: Electromigration, Diffusion, and Aggregation.

Xenopus myoball cultures were used to examine the lateral migration and clustering of acetylcholine receptors in response to electric fields. In contrast to concanavalin A binding sites, which behave in a manner explained by electromigration and diffusion, acetylcholine receptors form stabile aggregates at the cathode-facing cell pole. Interestingly, receptor aggregation continues there after termination of the field. This post-field receptor aggregation is consistent with the action of a specific diffusion-trap mechanism mediated by adhesion or cohesion events on the cell surface. The simplest hypothesis for the triggering of receptor aggregation is that receptors are accumulated in response to the electric field and, once past a threshold density, autoaggregation is initiated. This model was tested by examining field-induced distributions of receptors following enzymatic treatment to reverse the electromigration of receptors. After neuraminidase treatment, and exposure to electric fields, receptor distributions were consistent with reversed electromigration (towards the anodal cell pole) but continued to show receptor aggregation at the cathodal cell pole. We conclude that the diffusion-trapping of acetylcholine receptors requires the participation of non-receptor molecules. In addition to providing a useful experimental tool in these studies, electric fields may play a role in receptor clustering at the neuromuscular junction.