Effect of Na+ and K+ on Mitochondrial Respiratory Control, Oxygen Uptake, and Adenosine Triphosphatase Activity

Abstract

Abstract Isolated rat liver mitochondria incubated with ethylene-diaminetetraacetate in the absence of added Mg++ show a loss of respiratory control toward ADP in a medium which contains Na+, while in a medium which contains K+, this function is preserved; respiratory control in these conditions is restored by including Mg++ into the mixture. On the other hand, mitochondria incubated in the sodium medium with ADP have adequate respiratory responses to added inorganic phosphate. Mitochondria incubated in the sodium medium in the absence of Mg++ also have a high rate of respiration in the absence of agents which stimulate oxygen uptake. This is accompanied by a loss in the sensitivity to 2,4-dinitrophenol. Rotenone stimulates a latent ATPase activity in mitochondria incubated with Na+ at concentrations which inhibit the oxidation of NADH. The data obtained seem to indicate that the rotenone site is the energy-coupling site and that K+, Mg++, and ADP may protect against the detrimental action of Na+ on this system. Evidence is also presented which suggests that ADP may regulate oligomycin-insensitive respiratory activity.