Effect Oe Denervation on Contractile Properties and Myosin Light Chain Phosphorylation in Rat Past-Twitch Skeletal Muscles

Changes in the contractile properties and phosphorylation of myosin light chain 2 (LC2) in extensor digitorum longus (EDL) muscles of rats were studied for the 7-day period following denervation. Post-tetanic potentiation (PTP) of isometric twitch tension, a property of fast-twitch muscles, was recorded 10 sec after a 1-sectetanic stimulation (200 Hz) and the extent of LC2 phosphorylation was determined by urea-glycerol-acrylamide gel electrophoresis. The degree of PTP decreased and was almost abolished by 7 days after denervation. On the other hand, the extent of LC2 phosphorylation in the resting state decreased to about half of the control value after 1 day and fell to zero by 7 days. At 10 sec following the tetanic stimulation, the extent of LC2 phosphorylation of control muscles exceeded 50%, and this decreased to 32% after 1 day, and to 14% after 2 days. Virtually no phosphorylation reaction occurred after 3 days. The rates of reduction in PTP and LC2 phosphorylation following tetanic stimulation correlated well during the 7-day period after denervation. These results suggest that the innervation influences PTP in association with the regulation of LC2 phosphorylation, supporting the hypothesis that LC2 phosphorylation plays an important role in producing twitch tension potentiation in fast-twitch skeletal muscles.