Development of electrophysiological and biochemical membrane properties during differentiation of embryonic skeletal muscle in culture.

Abstract

Newly fused chick myotubes underwent simultaneous and rapid changes in cell membrane properties during synchronous differentiation in culture. These changes were coordinately regulated and included increases in acetylcholine receptor, acetylcholinesterase, resting potential and the appearance of action potentials in discrete membrane areas upon stimulation. The acetylcholine receptor reached maximal levels, whereas the development of electrical properties was marked by a further increase in resting potential, changes in the characteristics of the elicited action potential and the recruitment of additional membrane areas for action potential generation. Maturation of electrical excitability, marked by the acquisition of the ability to fire repetitively and to conduct action potentials along the membrane, occurred well after resting potential had reached a maximum. During postmaturational development, myotubes exhibited spontaneous electrical and contractile activity and levels of acetylcholine receptor accessible to externally applied 125I-labeled .alpha.-bungarotoxin decreased markedly. Electrophysiological membrane maturation was autonomously regulated with no requirement for neuronal intervention and involved the coordinated biosynthesis of discrete membrane components and their subsequent organization in the myotube membrane.