REGULATION OF ACETYLCHOLINE RECEPTORS ON MUSCLE

The acetylcholine receptor on skeletal muscle is subject to changes in
functional properties during development. We have shown that this altered
function results from the expression of an acetylcholine receptor channel
type bearing faster gating kinetics. This proposal examines two aspects of
this change in gating. First, what is the role of nerve in causing
increased expression of the fast gated channel type? To this end, we will
test the idea that nerve causes endplate specific changes in gating through
neuronal "imprinting", by denervation of embryonic muscle just prior to the
onset of developmental changes in channel gating. Also, we will directly
evaluate neuronal effects on gating by study of embryonic muscle
co-cultured with neurons or neuron-conditioned medium. Finally, the
hypothesis that endplate specific channel gating exists will be tested by
direct comparison of junctional and non-junctional channel gating on mature
muscle. The second major question addressed by this proposal relates to
the metabolic requirements for changes in channel function. Is the
appearance of the fast gated channel type the result of a newly synthesized
channel type or the result of altered functional properties of the
pre-existing "embryonic" slow gated channel type? For this purpose, we
will take advantage of the fact that the developmental change in receptor
kinetics, observed in vivo, continues to occur on tissue-cultured embryonic
muscle. Both single channel and noise analysis techniques will be used to
quantitate the developmental alterations in channel function in vitro.
These experiments form the basis for understanding the molecular mechanisms
underlying the long term changes in acetylcholine receptor channel function.