Muscle Creatine Kinase-deficient Mice

Functional properties of in situ mitochondria and of mitochondrial creatine kinase were studied in saponin-skinned fibers taken from normal and M-creatine kinase-deficient mice. In control animals, apparent Km values of mitochondrial respiration for ADP in cardiac (ventricular) and slow-twitch (soleus) muscles (137 ± 16 μM and 209 ± 10 μM, respectively) were manyfold higher than that in fast-twitch (gastrocnemius) muscle (7.5 ± 0.5 μM). Creatine substantially decreased the Km values only in cardiac and slow-twitch muscles (73 ± 11 μM and 131 ± 21 μM, respectively). As compared to control, in situ mitochondria in transgenic ventricular and slow-twitch muscles showed two times lower Kmvalues for ADP, and the presence of creatine only slightly decreased the Km values. In mutant fast-twitch muscle, a decrease rather than increase in mitochondrial sensitivity to ADP occurred, but creatine still had no effect. Furthermore, in these muscles, relatively low oxidative capacity was considerably elevated. It is suggested that in the mutant mice, impairment of energy transport function in ventricular and slow-twitch muscles is compensated by a facilitation of adenine nucleotide transportation between mitochondria and cellular ATPases; in fast-twitch muscle, mainly energy buffering function is depressed, and that is overcome by an increase in energy-producing potential.