Local induction of acetylcholine receptor aggregates on cultured rat myotubes by a partially purified protein from fetal pig brain.

ABSTRACT

It has been suggested that at the time of innervation, developing neurites release one or more soluble factors that locally induce acetylcholine receptor (AChR) aggregate formation at the synaptic site. To test this hypothesis, we developed a model system that mimics the local, neural induction of AChR aggregation at developing synapses. Partially purified protein derived from fetal pig brain was applied locally to the surface of cultured myotubes via a micropipet. We found that local application of this factor for as little as 30 min induced the formation of AChR aggregates that were restricted to a region within 30 microns around the release site. In addition, the locally applied factor induced a local AChR aggregation response, but did not cause a detectable change in the myotube resting membrane potential at the release site. Our data support a soluble factor hypothesis and suggest that neither cell-cell contact nor local electric fields are necessary for the initial induction of AChR aggregation.