Volume‐ and temperature‐dependent permeabilities in isolated rat liver cells.

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Abstract
1. Water, K, Na and Cl contents and fluxes of K and Na were determined in isolated rat hepatocytes incubated at 1 degrees C (90 min) then at 38 degrees C (60 min). At 1 degrees C cells progressively gained Na and Cl, lost K and increased their volume by 17%. 2. Rewarming triggered a net loss of K and gain of Na. They were transitory (about 60 sec) being overcome rapidly by movements in the opposite direction until cells recovered their initial K and Na gradients. 3. Determination of time courses of the K rate constant (kappa' K) and net Na influx (phi Na) in cells incubated in ouabain K‐free media indicated that these paradoxical movements were due to a temporary shunting of the Na pump by sudden increases in K and Na permeabilities. 4. Increases in kappa' K and phi' Na were not sensitive to inhibitors of Ca‐activated K channels such as quinine (10(‐3) M) of apamin (10(‐8) M), suggesting they were not dependent on internal ionized Ca. 5. In control media containing 1.8 mM‐Ca divalent ionophore A23187, though stimulating the Ca pump (Ca efflux), presumably by increasing internal ionized Ca concentration, did not cause substantial and rapid changes in K permeability. This supports the hypothesis that Ca‐sensitive K channels are lacking in rat hepatocytes. 6. A 10% increase in cell volume provoked by a hypo‐osmotic shock triggered increases in both kappa' K and phi' Na with time courses very similar to those brought about by rewarming. 7. It is proposed that transient changes in K and Na permeabilities are the consequence of the cell swelling, induced by cooling. These volume‐dependent permeabilities are blocked at 1 degrees C and revealed by rewarming.