Mitochondrial affinity for ADP is twofold lower in creatine kinase knock-out muscles

Adaptations of the kinetic properties of mitochondria in striated muscle lacking cytosolic (M) and/or mitochondrial (Mi) creatine kinase (CK) isoforms in comparison to wild-type (WT) were investigated in vitro. Intact mitochondria were isolated from heart and gastrocnemius muscle of WT and single- and double CK-knock-out mice strains (cytosolic (M-CK–/–), mitochondrial (Mi-CK–/–) and double knock-out (MiM-CK–/–), respectively). Maximal ADP-stimulated oxygen consumption flux (State3 Vmax; nmol O2·mg mitochondrial protein-1·min-1) and ADP affinity ( ; µm) were determined by respirometry. State 3 Vmax and of M-CK–/– and MiM-CK–/– gastrocnemius mitochondria were twofold higher than those of WT, but were unchanged for Mi-CK–/–. For mutant cardiac mitochondria, only the of mitochondria isolated from the MiM-CK–/– phenotype was different (i.e. twofold higher) than that of WT. The implications of these adaptations for striated muscle function were explored by constructing force-flow relations of skeletal muscle respiration. It was found that the identified shift in affinity towards higher ADP concentrations in MiM-CK–/– muscle genotypes may contribute to linear mitochondrial control of the reduced cytosolic ATP free energy potentials in these phenotypes.