Prolonged electromechanical coupling time intervals in skeletal muscle of pigs susceptible to malignant hyperthermia

Electromechanical properties of skeletal muscle were compared between malignant hyperthermia (MH)-susceptible and control pigs. These muscle properties were studied both in vivo and in vitro. The in vivo time interval from nerve stimulation to onset of mechanical tension was longer in muscle of pigs susceptible to MH. Kinetics of formation of the in vivo compound muscle action potential did not differ between pig groups, whereas the time from peak of the muscle action potential to tension onset was longer for MH muscle. In vitro the time from direct stimulation to tension onset was also longer for MH muscle. These results suggest that the mechanism causing longer electromechanical time intervals in MH skeletal muscle is distal to the myoneural junction. Data comparing contraction kinetics between muscle from MH and control pigs indicates that the mechanism contributing to the longer time interval involves the transfer of signal from the transverse tubule to the sarcoplasmic reticulum in the pigs studied.