Fig. 9.

Concatameric pentamers form large numbers of ACh binding sites labeled with [³H]epibatidine. Oocytes were injected with 20 ng of mRNA for β3-α6-β2-α4-β2 or β3-α4-β2-α6-β2 or 90 ng of mRNA for β3-α6-β2-α6-β2 (to compensate for its low surface expression). AChRs were extracted with Triton X-100, immune-isolated using mAb 295 to β2 subunits, then labeled with [³H]epibatidine. β3-α6-β2-α6-β2 resulted in the formation of very large amounts of [³H]epibatidine binding sites, primarily reflecting the large amount of mRNA expressed. As will be shown subsequently, these binding sites are primarily in pentameric AChRs that have not been efficiently transported to the cell surface.