Sodium, PMA and calcium play an important role on intracellular pH modulation in rat mast cells

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 studie d. After promoting an artificial acidification with sodium propionate we de termined the variations on pi-Ii rate recovery. pHi was measured with the d ye 2,7-bis(carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester. We st udied the effect that the inhibition of some cellular exchangers with diffe rent drugs induced on pi-Ii, 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 ini tial value when the cells were treated either with amiloride or with 4,4'-d iisothiocyanatostilbene-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 activat or of capacitative calcium influx, or the phorbol esther 12-O-tetradecanoyl phorbol-13-acetate (PMA), a protein kinase C (PKC) activator, increased the activity of the antiporter. Both effects were abrogated by inhibition of t he Na+/K+-ATPase with ouabain, The increase in cAMP levels did not affect t he effect of PMA on pi-Ii recovery, but it blocked the effect of thapsigarg in. Our results indicate that rat mast cells regulate pHi by the combinatio n of some anionic exchanger and the Na+/H+ antiporter, And also that the mo dulation of this exchanger is the consequence of the connection between dif ferent intracellular mechanisms, Na+/K+-ATPase-PKC-calcium, among which cAM P seems not to have a direct role.