Effect of magnesium-dependent cell membrane alterations on the transport of K+ in Ehrlich ascites tumour cells.

Mg-deficiency or Mg-loading of tumour cells changes the permeability of the cell membrane. The influence of this change on the K+ transport across the membrane was investigated using 86Rb+ and K+ analog. The time course of the influx and efflux rates were estimated by means of a mathematical approach for a two-compartment system with inconstant pool sizes. The comparison of the two states of the cells demonstrates that in Mg-deficient cells the passive K+ efflux is significantly enhanced (40%). This in turn stimulates the active counter transport mediated by the (Na+-K+)-ATPase, raising the ATP consumption by about 30%. However, the enzyme is not able to maintain the cellular K+ content under these conditions. After a short transient increase due to the initially enhanced influx the passive net efflux prevails. Differences in the electrophoretic mobility of the two states of the cells confirm Mg-dependent changes of the cell membrane structure.