Ionic transport and membrane potential of rat liver cells in normal and low-chloride solutions

1. The ouabain-sensitive component of Na efflux and K influx amount to 58 and 72% respectively. Taking into account also (a) the diffusional passive fluxes of Na (5%) and K (13%), as estimated by Ussing's equation and (b) the ouabain-insensitive Na-Na exchange (28%), 85% (K) and 90% (Na) of the measured total fluxes can be accounted for.2. Na efflux is diminished when K is partially or totally removed from the medium. This effect is reversible, indicating probably activation of the Na pump by external K.3. The coupling ratio of Na and K ouabain-sensitive fluxes is equal to 1.58, suggesting that three Na ions are removed from and two K ions are carried into the cell in one cycle of the pump. Hence, in liver cell membranes, the Na pump must be electrogenic.4. A tenfold decrease in [Cl](o) by substitution with an impermeant anion results in a membrane hyperpolarization and a decrease in [Cl](i). Cl loss from the liver is compensated by an equivalent loss of intracellular K to preserve electroneutrality.5. The measurement of passive fluxes indicates that Cl removal from the perfusing solutions increases P(K) but does not alter P(Na).6. Addition of ouabain brings about a depolarization which is three times greater in low-Cl solutions (21.9 mV) than in normal-Cl solutions (6.8 mV).7. It is concluded that hyperpolarization which develops when Cl ions are removed can be accounted for entirely by (a) the increase in P(K), (b) the increase of the contribution of the electrogenic pump to membrane potential.