Rapid postnatal developmental changes in the passive proton permeability of the inner membrane in rat liver mitochondria.

Titration of mitochondrial respiration against the membrane potential with the inhibitor malonate has been carried out during the perinatal period in isolated rat liver mitochondria. Neonatal and adult mitochondria exhibited the characteristic "nonohmic" behavior for the proton conductance (CmH+). In contrast, fetal mitochondria exhibited an "anomalous" "ohmic" behavior for CmH+. The calculated passive proton permeability of the membrane undergoes a profound reduction during the first postnatal hour. The results reported demonstrate that the hypothesis [Pollak, J.K. & Sutton, R. (1980) Trends Biochem. Sci. 5, 23-27] of the existence of a "leaky" mitochondria in the fetal rat liver, and of its sudden neonatal change towards a state of higher energy conservation of the proton electrochemical gradient, is correct.