Effects of CGRP, forskolin, PMA, and ionomycin on pHi dependence of Na-H exchange in UMR-106 cells.
We examined the effects of calcitonin gene-related peptide (CGRP), forskolin, phorbol 12-myristate 13-acetate (PMA), and ionomycin 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.
Gupta
A
A
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
Schwiening
C J
CJ
Boron
W F
WF
D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D010006:Osteoblasts / Q000378:metabolism*; D051381:Rats; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D017923:Sodium-Hydrogen Exchangers; D005576:Colforsin; D015759:Ionomycin; D015740:Calcitonin Gene-Related Peptide; D013755:Tetradecanoylphorbol Acetate