The effects of divalent cations on the ionic permeability of cell membranes in normal and tumour tissues

Abstract

It is shown that the ability of three strains of transplanted rat tumours to maintain cellular potassium contents on incubation in media devoid of calcium salts is due to a tumour calcium requirement which is satisfied by concentrations of at least an order of magnitude less than required by the normal tissues yet studied. The evidence is that potassium loss by the tumours on incubation in the presence of very low free calcium ion concentrations maintained by metal-ion buffers, is due to an increase of plasma membrane permeability, similar to those which are believed to occur in normal tissues where the calcium ion “thresholds” are much higher. The cell membranes of the tumours are thus more resistant to lowering of the calcium ion concentration than the normal tissues. Differences also occur in the extent to which other divalent cations, in particular magnesium, can substitute for calcium.