Ionic fluxes and permeabilities of cell membranes in rat liver

1. Intracellular ion concentrations, measured in rat liver perfused with saline solutions were, at steady state:[K](1) = 113; [Na](1) = 16.4; [Cl](1) = 25.5 m-mole l.(-1) of cells.2. Intracellular Cl concentration was measured when both [Cl](o) and membrane potential were changed. The experimental values were close to the predicted ones by the Nernst equation, indicating a passive distribution of this ion across the cell membrane.3. Fluxes were determined by means of radioactive tracers and had the following values:m(K) = 6.6; m(Na) = 12.4 and m(Cl) = 8 x 10(-12) mole cm(-2) sec(-1).4. When Na was replaced by Li in the perfusing solutions, the Na efflux was decreased by 3.3 x 10(-12) mole cm(-2) sec(-1). This was attributed to a Na-for-Na exchange (exchange-diffusion).5. A mathematical model was applied to the perfused liver. It allowed estimation of the actual fluxes across the membrane. Corrections resulting from the application of the model remain small.6. The permeability coefficients were calculated from the passive fluxes and were:P(K) = 7.6; P(Na) = 4.0; P(Cl) = 12.3 x 10(-8) cm sec(-1), corresponding to relative permeabilities of P(Na)/P(K) = 0.52 and P(Cl)/P(K) = 1.6.7. The membrane potential calculated from the Goldman equation was significantly different from the measured one. This may be accounted for by an electrogenic activity of the Na-K pump. Applying the Mullins & Noda equation, the ratio of active Na flux to active K flux becomes 3/2.