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

Abstract

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 (pHi) dependence of Na-H exchange in UMR-106 cells. In the nominal absence of CO2-HCO3-, each agent increased pHi, measured with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). From the rate of pHi recovery (dpHi/dt) from an acid load, and intracellular buffering power, we computed the pHi dependence of the total acid-extruding flux (JTotal). All four agents increased JTotal. From dpHi/dt data obtained in the presence of ethylisopropyl amiloride (EIPA, a blocker of Na-H exchange), we determined the EIPA-resistant component of JTotal (JEIPA/R). We estimated the Na-H exchange flux (JNa-H as the difference JTotal - JEIPA/R. CGRP, forskolin, and PMA produced similar increases in the slope of the JNa-H vs. pHi-relationship. The net effect of these agents, as well as ionomycin, was to increase JNa-H over a broad pHi range. Ionomycin alkaline shifted the JEIPA/R vs. pHi relationship; the other agents had no effect. Our results indicate that CGRP increased JTotal 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 pHi and pHi dependence of JNa-H. Thus, CGRP probably affects UMR-106 pHi physiology via more than one pathway. acid-base balance; ion transport; ethylisopropyl amiloride; amiloride analogs; osteoblasts; fluorescence; 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein; calcium; adenosine 3',5'-cyclic monophosphate; protein kinase C Submitted on February 19, 1993 Accepted on October 8, 1993