||p.107 left column bottom paragraph:"Two populations of AChRs, differing in their degradation rate and in their responses to stabilizing factors, exist in vertebrate muscle. These are the slowly degrading (Rs) and the rapidly degrading (Rr). Rs AChRs are synthesized in adult innervated muscles and inserted at the neuromuscular junction (nmj). As long as the muscle remains innervated, they degrade slowly with a half-life (t1/2) of ~8–10 days (reviewed in primary source). Rr AChRs are the predominant (~90%) receptor population synthesized in denervated and aneural embryonic muscle and normally degrade rapidly with a t1/2 of ~1 day (Levitt et al., 1980 Levitt and Salpeter, 1981 Reiness and Weinberg, 1981 Shyng and Salpeter, 1989, 1990)."