MODULATION OF NA H ANTIPORT IN ERYTHROCYTES OF THE TELEOST FISH, OREOCHROMIS-MOSSAMBICUS - EFFECT OF VASOPRESSIN/

The mechanism of modulation of the Na/H antiport was studied in erythr ocytes of the tilapia, Oreochromis mossambicus. Activation of the anti port was determined through measurements of variations of intracellula r pH, using a pi-I-sensitive, intracellular fluorescent probe 2', 7'-b is (carboxyethyl)-5 (6)-carboxyfluorescein (BCECF). Phorbol ester (5 m u M), a stimulator of protein kinase C, activated the antiport resulti ng in an increase of intracellular pH; a maximum of 0.125 +/- 0.027 pH units over basal level (mean +/- SD; n = 4-6) was reached in 20 min. The effect was blocked by protein kinase C inhibitors staurosporine an d H-7, and also by the antiport inhibitor 5-(ethyl-N-isopropyl) amilor ide; this demonstrates that the stimulation of the antiport in tilapia erythrocytes can take place through a protein kinase C-mediated mecha nism. Vasopressin, an important osmoregulator hormone in teleosts, was able to activate the Na/H antiport, in a manner similar to phorbol es ter, but its effect was only partially sensitive to staurosporine inhi bition. Considering that the physiological role of the Na/H exchanger in fish is known to be different from its role in mammalian cells, the se results indicate that other signal transduction mechanisms can be i nvolved in the modulation of intracellular pH by vasopressin.