EFFECTS OF CGRP, FORSKOLIN, PMA, AND IONOMYCIN ON PH(I) DEPENDENCE OF NA-H EXCHANGE IN UMR-106 CELLS

We examined the effects of calcitonin gene-related peptide (CGRP), forskolin, phorbol la-myristate 13-acetate (PMA), and ionomycin on the intracellular pH (pH(i)) dependence of Na-H exchange in UMR-106 cells. In the nominal absence of CO2-HCO3-, each agent increased pH(i), measured with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). From the rate of pH(i) recovery (dpH(i)/dt) from an acid load, and intracellular buffering power, we computed the pH(i) dependence of the total acid-extruding flux (J(Total)). All four agents increased J(Total) From dpH(i)/dt data obtained in the presence of ethylisopropyl amiloride (EIPA, a blocker of Na-H exchange), we determined the EIPA-resistant component of J(Total) (J(EIPA/R)). We estimated the Na-H exchange flux (J(Na.H)) as the difference J(Total) - J(EIPA/R).CGRP, forskolin, and PMA produced similar increases in the slope of the J(Na.H) vs. pH(i)-relationship. The net effect of these agents, as well as ionomycin, was to increase J(Na.H) over a broad pH(i) range. Ionomycin alkaline shifted the J(EIPA/R) vs. pH(i) relationship; the other agents had no effect. Our results indicate that CGRP increased J(Total) by Stimulating Na-H exchange, with little effect on EIPA-resistant processes. A signaling pathway involving only adenosine 3',5'-cyclic monophosphate, only protein kinase C, or only Ca2+ cannot account for the effects of CGRP on both pH(i) and pH(i) dependence of J(Na.H) Thus, CGRP probably affects UMR-106 pH(i) physiology via more than one pathway.