Regulation of ion permeabilities of isolated rat liver cells by external calcium concentration and temperature

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Abstract
Regulation of ion transport through the plasma membrane was studied on single cell suspensions of hepatocytes, obtained after perfusion of rat liver with collagenase/hyaluronidase solution. Steady-state intracellular K and Na contents were shown to be markedly dependent on external Ca concentration and temperature, the sum of both ion concentrations remaining nearly constant. In contrast, steady-state intracellular chloride content was found to be independent of external Ca concentration, but dependent on temperature. Using the constant field relations, the passive permeabilitiesP K andP Cl for potassium and chloride, respectively, were derived from the experimental data. At temperatures at and above 37°C, with increasing external Ca concentration,P K exhibits a sharp decrease at about 10−4 m. In contrast,P Cl at 37°C was found to be independent of Ca concentration within experimental error. Earth alkali ions other than Ca, show marked but different effects onP K if compared at equal concentrations. Preincubation of the cells with cholesterol leads to a broadening of the dependence ofP K on external Ca concentration. The above results, as well as those on the dependence ofP K on external Ca concentration obtained by other authors, could be quantitatively described by a theoretical model of the plasma membrane proposed earlier. This model postulates regulatory binding sites, which cooperatively undergo a cation exchange of divalent cations by K+ ions from the external medium, if the cation composition of the latter is altered.