THE EFFECTS OF MM-CREATINE KINASE-DEFICIENCY ON SUSTAINED FORCE PRODUCTION OF MOUSE FAST SKELETAL-MUSCLE

Twitch force production was normal in muscles of mice which lack MM-cr eatine kinase, but the tetanic force:twitch force ratio was lower than in control muscles (3.60 vs. 4.27; P < 0.05). In a series of repeated tetanic contractions the force in the second contraction was already markedly depressed (20-50%), while subsequently only small changes wer e observed. The effect was greater in exercise that would require a hi gher metabolic peak flux. The depressed force production was not accom panied by a slowing of relaxation, indicating that enough ATP was pres ent to sustain myofibrillar ATPase and Ca2+-ATPase activity.