Metabolism of acetylcholine receptors on embryonic amphibian muscle.

The functional properties of acetylcholine receptors are altered during the development of Xenopus myotomal muscle. A similar change also occurs in dissociated cell cultures of embryonic myotomal muscle. Metabolism of acetylcholine receptors was examined in order to ascertain whether the turnover rate changed at a time when the functional changes were detected. Incorporation of newly synthesized receptors occurred at a constant rate over a 24-hr period. The degradation of receptors followed first order kinetics with a half-life of 52 hr. Incorporation and degradation occurred at approximately equal rates such that 1 to 1.5% of the total receptor number was replaced every hour at equilibrium. Addition of neural tube cells to muscle cell culture, which altered the functional properties of channels, had no effect on either the incorporation or the degradation rate. We conclude that the changes in the functional properties of receptors occur independent of changes in the turnover rate of receptors.