AJP - Cell Physiology, Vol 266, C1083-C1092, Copyright © 1994 by the American Physiological Society

Effects of CGRP, forskolin, PMA, and ionomycin on pH_i dependence of Na-H exchange in UMR-106 cells

¹ Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510

We examined the effects of calcitonin gene-related peptide (CGRP), forskolin, phorbol 12-myristate 13-acetate (PMA), and ionomytin 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.

Submitted on February 19, 1993
Accepted on October 8, 1993