Role of mitochondrial oxidative phosphorylation in the maintenance of intracellular pH*1

Abstract The oxidative phosphorylation of isolated rabbit heart mitochondria and the accompanying pH changes were simultaneously measured in the same sample. The nearly constant extramitochondrial proton concentration during State 4 respiration decreased considerably under conditions of oxidative phosphorylation. On the other hand, the proton concentration increased when ATP was hydrolysed by the mitochondrial ATPase. The lysis of mitochondria by Triton X-100 equilibrating the pH difference across the inner membrane did not cause significant change in the proton concentration of the sample neither before nor after State 3 respiration. The accumulation of protons during the extramitochondrial hexokinase reaction was reduced by the mitochondrial oxidative phosphorylation. It is suggested that in the normoxic myocardial cell, the protons generated by the extramitochondrial hydrolysis of ATP are utilized during mitochondrial oxidative phosphorylation.