Fig. 2.

Protein associations with the AChR in C2 myotubes. Myotubes were incubated with 5 nm neural (4,8) or muscle (0,0) agrin as indicated. Cells were then extracted under mild conditions, using 1% digitonin, and AChRs were precipitated with α-BT-Sepharose. As controls, an excess (10 μm) of free toxin was added (+T), or in some experiments unconjugated Sepharose was used (C). Precipitates were analyzed by immunoblotting using specific antibodies as indicated. The AChR content in each lane was visualized by reprobing stripped blots with an antiserum, mAb 88b, reactive with the AChR γ and δ subunits. For comparison, a fraction (0.2%) of the total cell lysate was analyzed (L). Solid arrowheadsindicate the proteins detected by the antibodies used for immunoblotting; open arrowheads point to the AChR γ and δ subunits.