Specificity of neuronal factors which aggregate acetylcholine receptors on cultured myotubes

Neuronal factors from conditioned medium of neuroblastoma X glioma hybrid cells or isolated from embryonic pig brain aggregate acetylcholine receptors (AChR) on cultured chicken and rat myotubes. A membrane surface protein labelled with a fluorescent monospecific antibody was not aggregated with the same treatment. Antibodies against AChR block the action of the aggregating factors but do not produce large aggregates themselves. These findings indicate that the factors specifically react with the AChR on developing myotubes.