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 reg ulate intracellular pH (pH(i)), we studied the effect of drugs acting on different transducting signals on the Na+-H+ antiport. We studied t he activity of the antiporter in recovering pH(i) after an acid load w ith sodium propionate. The drugs used were okadaic acid, which inhibit s the phosphatases 1 and 2A, pertussis toxin, which ADP-rybosylates th e G(i)-protein, cholera toxin, which ADP-rybosylates the G(s)-protein, NaF which non-specifically activates G-proteins, and the phorbol esth er 12-O-tetradecanoylphorbol 13-acetate (TPA) which specifically activ ates 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 th e stimulatory activity of TPA. In a Ca2+-free medium, okadaic acid inh ibits the activity of the antiporter. Ah the mechanisms affected by th ese drugs have some regulatory role on the Na+-H+ antiport. Our result s indicate the great complexity of the crosstalks between the differen t signal transducing pathways.