Accumulation of Potassium in Living Cells—a Non-equilibrium Condition

Abstract

Previous workers 1 , 2 have suggested that the relative excess of potassium observed in divers living cells and tissues might be accounted for by assuming that ionic equilibrium is not attained during the life of such systems but is most nearly approached by the most mobile ions. But no completely satisfactory theory has yet been proposed, nor has any experimental proof been adduced. This paper gives experimental proof that a non-equilibrium state exists, and explains the mechanism of accumulation.

If in its normal state a living cell were in ionic equilibrium with the surrounding medium any increase in the concentration, or, more properly, in the activity of an ion in the surrounding medium should, if it leads to any change, result in an increase in the activity of the same ion within the cell. Conversely, decrease outside should lead to decrease inside. If decrease outside should be found to produce increase inside or vice versa, it appears impossible to account for the observed facts except by assuming the existence of a non-equilibrium state.

Experiments were made on the unicellular coenocytic marine alga Valonia macrophysa Kütz. from which large amounts of intracellular sap may be obtained for analysis. Under normal conditions this sap has a pH of: about 6.2 and potassium and sodium ion concentrations of roughly 0.5 M and 0.1 M, as compared with a pH of 8.2, and potassium and sodium ion concentrations of roughly 0.01 M and 0.5 M, respectively, in sea water. Since both this sap and sea water are dilute aqueous solutions containing little or no organic material, no sensible error will be introduced by considering ion concentrations rather than activities.