Turnover of junctional and extrajunctional acetylcholine receptors of the rat diaphragm

Abstract

THE junctional acetylcholine receptors on the motor end-plate mediate the transmission of nerve impulses to skeletal muscle, and their number per endplate is normally kept constant at 1.4–4.7×10⁷ for various vertebrate muscles^1–4. In some conditions, as in rats chronically treated with neostigmine^5,6 or in myasthenia gravis⁶, the number of acetylcholine receptors is markedly decreased; whereas, like denervation, insufficiency of neuromuscular transmission caused by various blocking agents, such as hemicholiniurn-3 and β bungarotoxin, tends to increase the number of receptors both at end-plate and non–end-plate zones (C. C. C., S. T. Chuang and M. C. H., unpublished). We, therefore, examined the turnover of acetylcholine receptors at end-plate and non–end-plate zones (extrajunctional) to shed more light on the pathophysiology of skeletal muscle.