Two populations of AChR in rat myotubes have different degradation rates and responses to cAMP

Abstract

Acetylcholine receptors (AChRs) of rat muscle cells grown in culture for 4 days were labeled with 125I-α-bungarotoxin and their degradation rate measured. Two AChR populations, a rapidly degrading one (R(r), t(1/2) ˜ 1 day) and a slowly degrading one (R(s),(t 1/2) ˜ 4 days) were identified at a ratio of approximately 9 to 1. The degradation rate of the R(s) was slowed to a t(1/2) of ˜ 10 days by cAMP while that of the R(r) remained unchanged. These data provide further evidence that two AChR-populations with different degradation rates can exist in noninnervated muscle and that they can be further distinguished by their differing response to cAMP. We suggest that the two AChR populations seen in myotubes may be physiologically equivalent to the R(s) and R(r) components seen at the neuromuscular junction of denervated adult muscle and could thus provide a good model for characterizing the R(r) and R(s) AChRs. © 1993 Academic Press, Inc.