Adaptation of potassium metabolism and restoration of mitosis during prolonged treatment of mouse lymphoblasts with ouabain.

The effects of ouabain on the growth of murine lymphoblasts in vitro have been studied. Exposure of cells to ouabain (0.1 mM) initially inhibited 86Rb+ uptake rate, reduced the intracellular potassium concentration, and decreased population growth rates. Continued exposure to the same ouabain concentration resulted in an increase of 86Rb+ uptake rate, intracellular potassium content and population growth rates to control values (adaptation). When treated cells were resuspended in medium free of ouabain after 12 to 15 hours of ouabain treatment, 86Rb+ uptake rates and intracellular potassium levels exceeded those of untreated cells. Adaptation was inhibited by cycloheximide (3 mug/ml) and by actinomycin D (0.05 mug/ml). Kinetic analysis of transport suggested that while the total capacity of the Na/, K+ transport system increased, the affinity for both the cation (86Rb+) and ouabain decreased.