Electrical and chemosensitive properties of normal and dystrophic chicken muscles

Abstract

A comparative study of the resting membrane potential, directly elicited action potential, and acetylcholine (ACh) sensitivity was made on the innervated and chronically denervated posterior latissimus dorsi muscles of normal (line 200) and dystrophic (line 304) chickens. No significant differences were found between the resting membrane potentials and directly elicited action potentials of surface fibers of the innervated normal and dystrophic muscles. Similarly, the ACh sensitivity at the endplate regions of both muscles reached values of 2600–2800 mv/nC. The ACh sensitivity of the normal, innervated muscle was restricted to the area 600 μm from the endplate and, in a few fibers, to a limited area at the myotendinous junction; the innervated dystrophic muscle, however, contained a small number of fibers which had cholinergic receptors scattered over the entire membrane surface. Values of about 300 mv/nC for extrajunctional ACh sensitivity were recorded 3–14 days after denervation of normal and dystrophic muscles; the resting membrane potentials decreased to about −60 mv during this period. At 21 days after denervation, individual values for extrajunctional ACh sensitivity as high as 2200–2800 mv/nC were observed when the resting membrane potential was −60 mv. In contrast to denervated skeletal muscle of rats, neither the shape nor the rate of rise of the directly elicited action potentials of the avian muscle were markedly affected during denervation, and the potentials remained sensitive to tetrodotoxin. We suggest that there is no relationship between the development of extrajunctional ACh sensitivity and the appearance of tetrodotoxin-resistant action potentials in denervated skeletal muscle.