PROPERTIES OF EMBRYONIC AND ADULT MUSCLE ACETYLCHOLINE-RECEPTORS TRANSIENTLY EXPRESSED IN COS CELLS

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 ε subunits. γ- and ε-AChRs had identical association rates for binding 125I-a-bungarotoxin, and identical curves for inhibition of toxin binding by d-tubocurarine, but ε-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 ε-AChRs. The γ-AChRs had channel characteristics of embryonic AChRs, whereas the major class of ε-AChR channels had the characteristics of adult AChRs. Two minor channel classes with smaller conductances were also seen with ε 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 ε-AChRs. © 1990.