Functional characterization of the Na(+)-H+ exchanger in rat mast cells: crosstalks between different kinase pathways

In our effort to understand the mechanisms by which rat mast cells regulate intracellular pH (pHi), we studied the effect of drugs acting on different transducting signals on the Na(+)-H+ antiport. We studied the activity of the antiporter in recovering pHi after an acid load with sodium propionate. The drugs used were okadaic acid, which inhibits the phosphatases 1 and 2A, pertussis toxin, which ADP-rybosylates the Gi-protein, cholera toxin, which ADP-rybosylates the Gs-protein, NaF which non-specifically activates G-proteins, and the phorbol esther 12-O-tetradecanoylphorbol 13-acetate (TPA) which specifically activates protein kinase C. The effect of TPA is a two-fold stimulation of the activity of the antiporter. A similar activation was observed with the combination okadaic acid plus cholera toxin. All the drugs alone did not modify the activity of the antiporter, and they all blocked the stimulatory activity of TPA. In a Ca(2+)-free medium, okadaic acid inhibits the activity of the antiporter. All the mechanisms affected by these drugs have some regulatory role on the Na(+)-H+ antiport. Our results indicate the great complexity of the crosstalks between the different signal transducing pathways.