Regulation of cytosolic pH of cultured mesangial cells by prostaglandin F2 alpha and thromboxane A2

Abstract

Prostaglandins (PG) and thromboxane A2 (TxA2) have marked vasoactive effects on the renal glomerular microcirculation. Exposure of cultured mesangial cells to PGF2 alpha and TxA2 mimetics results in a rapid elevation of free cytosolic Ca2+ ([Ca2+]i) followed by contraction and cell proliferation. We studied whether other ionic changes mediate these effects of eicosanoids on cells of rat and human origin. Cytoplasmic pH (pHi) was monitored in cells loaded with the fluorescent, intracellularly trapped pH-sensitive probe 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein. PGF2 alpha in rat cells and the TxA2 mimetic U-46619 in human cells induced rapid, dose-dependent cytosolic acidification followed by recovery and net alkalinization mediated by enhanced Na(+)-H+ exchange. The early acidification was also stimulated by ionomycin and Ca2(+)-mobilizing peptides, implicating a Ca2(+)-dependent mechanism. Alkalinization was abolished by removal of extracellular Na+ and by amiloride. Both components of the responses were inhibited by phorbol myristate acetate, which could mimic alkalinization, suggesting a regulatory role of protein kinase C in activation of the Na(+)-H+ exchanger by eicosanoids. Vasoconstrictor arachidonate metabolites may control glomerular cell function by a signaling mechanism centered on concurrent changes of pHi and [Ca2+]i.