Factors limiting mitochondrial respiration in media of high solute content

Abstract

The state-3 rate of respiration of rat-liver mitochondria was depressed in media containing KCl, sucrose, or mannitol at concentrations in excess of 125 mM. At equivalent concentrations, glucose caused less inhibition than sucrose or mannitol, and no inhibition was observed with glycine. These observations establish that solute inhibition of respiration is not a consequence of the reduced chemical potential of water in the system. The accumulation of succinate by mitochondria was not reduced by high sucrose concentrations. Sonication only partially relieved inhibition by sucrose or mannitol, and not at all that by KCl, and the evidence indicates that solute inhibition is not primarily an inhibition of substrate entry into mitochondria. Sucrose in the assay media inhibited succinate dehydrogenase [succinate: PMS oxidoreductase (EC.1. 3. 91)] and malate dehydrogenase [l-malate: NAD oxidoreductase (EC.1.1.1.37)] activities, but these inhibitions were less than those of succinate-and malate-dependent oxygen uptake by mitochondria. Disruption of the mitochondrial membrane by detergent abolished the inhibition of respiration by sucrose, and the evidence indicates that solute inhibits the functional capacity of the membrane-associated respiratory system.