Formation of @entity934 receptor clusters at neuromuscular junction in XXXX cultures.

@entity8008 @entity1238 @entity1867 @entity934
The formation of @entity934 receptor (AChR) clusters at the neuromuscular junction was investigated by observing the sequential changes in AChR cluster distribution on cultured @entity1238 muscle cells. AChRs were labeled with @entity8008 -conjugated alpha-bungarotoxin (TMR-alpha BT). Before innervation AChRs were distributed over the entire surface of muscle cells with occasional spots of high density ( @entity1867 ). When the nerve contacted the muscle cell, the large existing @entity1867 disappeared and small AChR clusters (less than 1 micron in diameter) initially emerged from the background along the area of nerve contact. They grew in size, increased in number, and fused to form larger clusters over a period of 1 or 2 days. Receptor clusters did not migrate as a whole as observed during "cap" formation in B lymphocytes. The rate of recruitment of AChRs at the nerve-muscle junction varied from less than 50 binding sites to 1000 sites/hr for alpha BT. In this study the diffusion-trap mechanism was tested for the nerve-induced receptor accumulation. The diffusion coefficient of diffusely distributed AChRs was measured using the fluorescence photobleaching recovery method and found to be 2.45 X 10(-10) cm2/sec at 22 degrees C. There was no significant difference in these values among the muscle cells cultured without nerve, the non-nerve-contacted muscle cells in nerve-muscle cultures, and the nerve-contacted muscle cells. It was found that the diffusion of receptors in the membrane is not rate-limiting for AChR accumulation.
