Ion Transport in Liver Mitochondria

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.