Sodium, PMA and Calcium Play an Important Role on Intracellular pH Modulation in Rat Mast Cells

Abstract

In a series of experiments aimed to understand the signaling pathways that regulate intracellular pH (pHi) in rat mast cells, the effect of different intracellular mechanisms on the activity of the Na⁺/H⁺ exchanger was studied. After promoting an artificial acidification with sodium propionate we determined the variations on pHi rate recovery. pHi was measured with the dye 2,7-bis(carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester. We studied the effect that the inhibition of some cellular exchangers with different drugs induced on pHi. When the Na⁺/H⁺ exchanger was inhibited in the presence of amiloride, the recovery rate constant was twofold smaller than the control value. After the recovery, the final pH was lower than the initial value when the cells were treated either with amiloride or with 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (an anionic antiport inhibitor). No effect was observed when the Na⁺/K⁺-ATPase or the Na⁺/Ca²⁺ exchanger were inhibited. The suppression of intracellular and extracellular calcium did not induced any change in pHi. The addition of thapsigargin, an activator of capacitative calcium influx, or the phorbol esther 12-O-tetradecanoylphorbol-13-acetate (PMA), a protein kinase C (PKC) activator, increased the activity of the antiporter. Both effects were abrogated by inhibition of the Na⁺/K⁺-ATPase with ouabain. The increase in cAMP levels did not affect the effect of PMA on pHi recovery, but it blocked the effect of thapsigargin. Our results indicate that rat mast cells regulate pHi by the combination of some anionic exchanger and the Na⁺/H⁺ antiporter. And also that the modulation of this exchanger is the consequence of the connection between different intracellular mechanisms, Na⁺/K⁺-ATPase-PKC-calcium, among which cAMP seems not to have a direct role.