The relationship between translocation of K+ and respiration has been studied under conditions where large variations of the transmembrane K+ concentration gradient were obtained. It is found that the energy expenditure is a function of the number of ions translocated and not of the transmembrane concentration gradient. The K+/∼ ratio is slightly below 3 when measured on the total oxygen uptake and between 3 and 4 when measured on the Δ oxygen uptake.
The maximal [K+]i/[K+]o ratio maintained by respiring liver mitochondria is about 1,600 corresponding to an equilibrium potential of 192 mV. When the [K+]i/[K+]o ratio exceeds 2,000 times addition of valinomycin under aerobic conditions causes an efflux instead of an uptake of K+.
Mitochondria behave as perfect osmometers in a wide range of osmolarities. It can be calculated that the concentration of osmotically active internal K+ corresponds to 45% of the total osmolarity of the medium.
The effect of succinate on the stoichiometry of proton translocation and on mitochondrial swelling during K4 uptake has been studied. The decrease of the H4 :K4 ratio from 1 to 0.2 is accounted for quantitatively by the intramitochondrial accumulation of succinate.When the accumulation of succinate is inhibited at alkaline pH the H4:K4 ratio increases.
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