Relationship between intracellular K+ concentrations and K+ fluxes in growing and contact-inhibited cells

The K+ content and the K+ flux were measured in the cell lines ME2 and MF2 isolated from plasmocytoma MOPC 173. Both cell lines were shown to have the seem K+ content and the same K+ steady state flux per unit of surface area. In ME2 cells, no modification of the exchange movement was observed during contact inhibition. However, contact-inhibited cells exhibited an increased resistance to depletion, characterized by a lower K+ net movement. The (Na+ plus K+)-ATPase measured in homogenates is poorly correlated to in vivo cation fluxes both because of the enhancement due, presumably, to the drop of K+ concentration on the cytoplasmic face of the membrane and because of losses during preparation which can be conspicuous, especially in contact-inhibited cells. The K+ net flux is considerable increased when the intracellular K+ level is reduced after preincubation of the cells in a K+ -free medium. Thus, internal K+ seems to regulate the K+ influx.