Active transport of potassium by mitochondria II. Effect of substrates and inhibitors

1. 1. The effect on mitochondrial phosphate metabolism of glutamate and P_i, which energise K⁺ uptake, was compared with that of succinate and P_i, which do not. Glutamate induced a 3-fold increase in the turnover of ATP, as compared with succinate. The effect on phosphoprotein was even greater. 2. 2. K⁺-depleted mitochondria carried out oxidative phosphorylation at normal rates in the presence or absence of external K⁺. 3. 3. 2,4-Dinitrophenol caused K⁺ efflux from freshly prepared mitochondria. There was an equivalent H⁺ influx. This was due to an increase in permeability of the mitochondria to cations. Nupercaine decreased the change in permeability. 4. 4. 2,4-Dinitrophenol failed to induce H⁺ influx in mitochondria previously depleted of K⁺. H⁺ influx could also be decreased by balancing intramitochondrial K⁺ with equivalent concentrations of external K⁺, Na⁺ or NH₄⁺ were less effective than K⁺. 5. 5. Oligomycin and amytal had no effect on mitochondrial permeability to cations. Azide had a lesser effect than 2,4-dinitrophenol. 6. 6. Oligomycin had no effect upon the K⁺ uptake energised by β-hydroxybutyrate, but blocked that energised by ATP.