Properties of embryonic and adult muscle acetylcholine receptors transiently expressed in COS cells

Abstract We used transient transfection in COS cells to compare the properties of mouse muscle acetylcholine receptors (AChRs) containing α, β, S, and either γ or e subunits. γ- and e-AChRs had identical association rates for binding 125 I-a-bungarotoxin, and identical curves for inhibition of toxin binding by d-tubocurarine, but e-AChRs had a significantly longer half-time of turnover in the membrane than γ-AChRs. A myasthenic serum specific for the embryonic form of the AChR reduced toxin binding to γ-, but not e-AChRs. The γ-AChRs had channel characteristics of embryonic AChRs, whereas the major class of e-AChR channels had the characteristics of adult AChRs. Two minor channel classes with smaller conductances were also seen with e AChR. Thus, some, but not all, of the differences between AChRs at adult endplates and those in the extrasynaptic membrane can be explained by the difference in subunit composition of γ- and e-AChRs.