Phosphorylase activation in stimulated dystrophic mouse muscle

¹ Department of Physiology, College of Medicine, State University of Iowa, Iowa City, Iowa

Phosphorylase a, t(a + b), and a:t x 100 values/g of wet muscle were determined on paired anterior tibial muscles from Bar Harbor strain 129 dystrophic and littermate control mice after tetanizing one member of the pair from 1/2–15 sec with an electrical stimulus. Rapid interruption of chemical events was accomplished by simultaneously quick-freezing resting and stimulated muscles at the last pulse from stimulator. Dystrophic muscle, with approximately one-quarter the phosphorylase t activity exhibited by control muscles, showed a significant decline in enzyme activity with age (60–115 days) which was not paralleled in the control muscle. Short bouts of stimulation (1/2–1 sec) produced greater a:t increases in dystrophic mice; intermediate stimulation (3–8 sec) produced similar a:t increases in both groups; and after 15 sec the control muscles showed greater increases in a:t values. Control muscles activate the enzyme in a progressive manner with lengthening stimulation periods; dystrophic muscles show a fluctuating activation.