Na+/H+ antiport in Swiss 3T3 cells: mitogenic stimulation leads to cytoplasmic alkalinization.

Addition of Na+ to Na+-depleted Swiss 3T3 cells causes a rapid and dramatic increase in intracellular pH, as monitored by uptake of the weak acid 5,5-dimethyloxazolidine-2,4-dione. The effect of Na+ is concentration dependent (half-maximal effect at 38 mM); this cation can be replaced by Li+ but not by K+ or the choline ion. Amiloride prevents the Na+-induced increase in intracellular pH and also blocks the entry of Na+ into 3T3 cells; the half-maximal concentrations of amiloride for inhibiting the two processes are similar (40 microM). Increase in extracellular pH caused an increase in the initial rate of Na+ influx that was of sufficient magnitude to stimulate the activity of the Na+/K+ pump in quiescent 3T3 cells. Taken together, these findings suggest the presence of a functional Na+/H+ antiport in Swiss 3T3 cells. Addition of the potent mitogenic combination platelet-derived growth factor, vasopressin, and insulin to quiescent Swiss 3T3 cells increased the intracellular pH from 7.21 +/- 0.07 to 7.36 +/- 0.09 in 10 independent experiments (P less than 0.001). This combination of growth factors also stimulated Na+ entry and ouabain-sensitive Rb+ uptake. The data support the hypothesis that early changes in ion fluxes play a role in signaling mitogenesis in 3T3 cells.