Vasopressin rapidly stimulates Na entry and Na-K pump activity in quiescent cultures of mouse 3T3 cells.

Addition of (Arg) vasopressin to quiescent cultures of Swiss 3T3 cells rapidly stimulates an ouabain-sensitive 86Rb uptake. In contrast the hormone has no significant effect on the rate of efflux of this cation from preloaded cells. The stimulation of 86Rb uptake is cycloheximide-insensitive, occurs within minutes of hormone addition and results from an increase in the Vmax of the uptake system. Vasopressin stimulates ion uptake in a concentration-dependent fashion (1--100 ng/ml); oxytocin also stimulated the Na-K pump but at significantly higher concentrations. The stimulation of the Na-K pump by vasopressin is apparently mediated by an increase in Na entry into the cells, since the hormone 1) strikingly shifts the concentration dependence on Na+ of the Na-K pump, 2) increases 22Na uptake, and 3) increases intracellular Na contents when the efflux of this ion is blocked by ouabain. Since vasopressin is a potent mitogen for Swiss 3T3 cells, the results provide further evidence in support of a possible role of monovalent ion fluxes in signalling the initiation of growth stimulation.