Physiologic and pharmacologic properties of normal and dystrophic muscle in the domestic fowl (Gallus domesticus)

Abstract

This study examined some physiologic and pharmacologic properties of normal and dystrophic chicken muscle. The pathogenesis of muscular dystrophy is unknown, and several competing hypotheses have been proposed. As recent evidence suggests that it may be linked to a muscle membrane defect, these studies are of interest in assessing the functional state of dystrophic muscle membranes. -- The contractile responses to intra-arterial injections of acetylcholine, carbachol, potassium chloride, caffeine and neostigmine were examined in innervated and denervated in vivo extensor digitorum communis (EDC) muscle preparations from normal and dystrophic chickens. In addition, the electrophysiologic properties of this preparation were characterized in normal and dystrophic muscles. The pharmacologic responses to serotonin and noradrenalin were assessed in vitro ischiatic artery preparations of the chicken. -- Sensitivity to acetylcholine was reduced in dystrophic muscle, although this appears to be associated with enhanced hydrolysis of acetylcholine in dystrophic muscle. The development of extrajunctional acetylcholine sensitivity in denervated dystrophic muscle was also reduced when compared to normal muscle. Denervated dystrophic muscle did not exhibit denervation atrophy. In the disease group, the duration of the intracellular action potential was increased. The results also suggested that the dystrophic ischiatic artery was less sensitive to serotonin than was normal muscle. -- This study supports the hypothesis that the functional state of the dystrophic muscle membrane is altered in the muscular dystrophies. The defect may also be present in the vascular smooth muscle of dystrophic chickens. -- Keywords: chicken; muscular dystrophy; smooth muscle; electrophysiology; denervation; pharmacology; contractile physiology.