The effect of multivalent cations on the membrane potential of the ehrlich ascites tumor cell

The effect of di‐ and trivalent cations on the membrane potential of the Ehrlich ascites tumor cell has been investigated using micro‐electrode techniques. In solutions free of multivalent cations the average membrane potential for 46 cells was 8.3 ± 0.5 mv (SE). However, the potentials were not stable and decayed with a half‐time of about six seconds. Addition of Ca⁺⁺ decreased the rate of decay and concomitantly increased the membrane potential. The magnitude of these effects was a function of the Ca⁺⁺ concentration. At the optimum concentration (2 mM), the half‐time of decay was increased to 12 seconds and the membrane potential was raised to 17.8 ± 1.7 mv (SE). The related alkaline‐earth cations, Sr⁺⁺, Ba⁺⁺ and Mg⁺⁺ had similar effects on both the stability and magnitude of the membrane potential. The effect of La⁺⁺⁺, which was qualitatively similar to that of the divalent cations, was also concentration dependent. However, 100‐fold lower concentrations were adequate to achieve comparable effects. Moreover, membrane potentials were stable for up to ten minutes in La⁺⁺⁺‐containing solutions. Variations in intracellular Cl⁻ content induced by temperature changes were paralleled by changes in membrane potentials. However, the potentials were not those expected for a simple Cl⁻ electrode.