RETARDED DIFFUSION OF ADP IN CARDIOMYOCYTES - POSSIBLE ROLE OF MITOCHONDRIAL OUTER-MEMBRANE AND CREATINE-KINASE IN CELLULAR-REGULATION OF OXIDATIVE-PHOSPHORYLATION

Possible reasons for retarded intracellular diffusion of ADP were inve stigated. The isolated skinned cardiac fibers were used to study appar ent kinetic parameters for externally added ADP in control of mitochon drial respiration. Participation of myosin-ATPase in binding of ADP wi thin cells as it was supposed earlier (Saks, V.A., Belikova, Yu.O. and Kuznetsov, A.V. (1991) Biochim. Biophys. Acta 1074, 302-311) was comp letely excluded, since myosin-deprived skinned cardiac fibers ('ghosts ') displayed the same kinetic parameters as intact ones (K(m)app for A DP about 300 muM). Significantly lower apparent K(m) values were obtai ned for fibers with osmotically disrupted outer mitochondrial membrane (25-35 muM), which was close to that observed for isolated heart mito chondria. The data obtained are in favor of limitation of ADP movement via anion-selective low-conductance porine channels in the outer memb rane of mitochondria. It is proposed that the permeability of this mem brane is controlled by some unknown intracellular factor(s). In the pr esence of saturating concentrations of creatine (25 mM) the apparent K (m) for ADP significantly decreases due to coupling of creatine kinase and oxidative phosphorylation reactions in mitochondria. This couplin g is not observed in KCl medium in which mitochondrial creatine kinase is detached from the membrane. It is concluded that in the cells in-v ivo ADP movement between cytoplasm and intramitochondrial space is con trolled by low-conductivity anion channels in the outer membrane. Thus , the mitochondrial creatine kinase reaction coupled to the adenine nu cleotide translocase is an important mechanism in control of oxidative phosphorylation in vivo due to its ability to manifold amplify these very weak ADP signals from cytoplasm.