In vitro denervation of frog skeletal muscle: expression of several conductance classes of nicotinic receptors.

The question arose as to whether the altered kinetic properties of the nicotinic acetylcholine receptor-ion channel complex (AChR) observed after muscle denervation could be due to post-translational modifications. Single AChR properties of in vitro denervated skeletal muscle were studied using the cell-attached patch-clamp technique. Patch-clamp recordings from junctional regions of fibers daily treated with cycloheximide, a protein synthesis inhibitor, and phenylmethylsulfonyl fluoride, a protease inhibitor, revealed single conductance class of acetylcholine (ACh)-activated currents after acute dissociation and several conductance classes 3-14 days after muscle denervation. alpha-Bungarotoxin blocked all conductance states induced by ACh. Biochemical assays carried out on the same experimental conditions disclosed that chronic treatment of the fibers with cycloheximide inhibited the incorporation of [3H]leucine into precipitable protein. The present findings provided evidence that the altered functional properties of nicotinic receptors after muscle denervation may occur without new transcription.