Control of free cytoplasmic calcium by intracellular pH in rat lymphocytes.

Activation of Na+-H+ exchange in rat thymocytes was found to be followed by an increase in free cytoplasmic Ca2+ concentration [( Ca2+]i). We determined whether the change in [Ca2+]i was secondary to the uptake of Na+, or to the cytoplasmic alkalinization that result from activation of the antiport. Increasing intracellular [Na+] by treating the cells with ouabain or gramicidin failed to affect [Ca2+]i. In contrast, procedures that increased the cytoplasmic pH, such as addition of monensin or NH3, significantly elevated [Ca2+]i. These results suggest an important role of cytoplasmic pH in the control of [Ca2+]i in lymphocytes.