INFLUENCE OF MITOCHONDRIAL CREATINE-KINASE ON THE MITOCHONDRIAL EXTRAMITOCHONDRIAL DISTRIBUTION OF HIGH-ENERGY PHOSPHATES IN MUSCLE-TISSUE - EVIDENCE FOR A LEAK IN THE CREATINE SHUTTLE/

The influence of mitochondrial creatine kinase on subcellular high ene rgy systems has been investigated using isolated rat heart mitochondri a, mitoplasts and intact heart and skeletal muscle tissue. In isolated mitochondria, the creatine kinase is functionally coupled to oxidativ e phosphorylation at active respiratory chain, so that it catalyses th e formation of creatine phosphate against its thermodynamic equilibriu m. Therefore the mass action ratio is shifted from the equilibrium rat io to lower values. At inhibited respiration, it is close to the equil ibrium value, irrespective of the mechanism of the inhibition. The sam e results were obtained for mitoplasts under conditions where the mito chondrial creatine kinase is still associated with the inner membrane. In intact tissue increasing amounts of creatine phosphate are found i n the mitochondrial compartment when respiration and/or muscle work ar e increased. It is suggested that at high rates of oxidative phosphory lation creatine phosphate is accumulated in the intermembrane space du e to the high activity of mitochondrial creatine kinase and the restri cted permeability of reactants into the extramitochondrial space. A ce rtain amount of this creatine phosphate 'leaks' into the mitochondrial matrix. This leak is confirmed in isolated rat heart mitochondria whe re creatine phosphate is taken up when it is generated by the mitochon drial creatine kinase reaction. At inhibited creatine kinase, external creatine phosphate is not taken up. Likewise, mitoplasts only take up creatine phosphate when creatine kinase is still associated with the inner membrane. Both findings indicate that uptake is dependent on the functional active creatine kinase coupled to oxidative phosphorylatio n. Creatine phosphate uptake into mitochondria is inhibited with carbo xyatractyloside. This suggests a possible role of the mitochondrial ad enine nucleotide translocase in creatine phosphate uptake. Taken toget her, our findings are in agreement with the proposal that creatine kin ase operates in the intermembrane space as a functional unit with the adenine nucleotide translocase in the inner membrane for optimal trans fer of energy from the electron transport chain to extramitochondrial ATP-consuming reactions.