Intracellular pH Regulation in Cultured Human Pleural Mesothelial Cells

The human pleural space is lined by a single layer of mesothelial cells, the intracellular pH (pH(i)) of which has never been investigated. In the present study, the intrinsic buffering power of H+ ions (beta(i)) and the pH(i) regulatory systems were investigated in primary cultures of human pleural mesothelial cells (PMCs) with microspectrofluorimetry. We found: (1) that at the resting pH(i), the beta(i) was low and increased as the pH(i) decreased; (2) that the pH(i) recovery was largely inhibited either with Na+-free medium or nominally HCO3 free medium containing ethyl-isopropyl amiloride (EIPA); (3) a 4-4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS)-sensitive, Na+/HCO3-dependent, but Cl(-)-independent acid extrusion mechanism in CO2/HCO3 buffer; and (4) that in the same buffer, a DIDS- sensitive but Na+-independent alkalosis was induced by intracellular Cl- depletion. We therefore conclude that at least three membrane pH(i) regulators are involved in regulating the pH(i) in PMCs, these being the EIPA-sensitive Na+-H+ exchanger; a novel electroneutral, DIDS-sensitive Na+-HCO3 cotransporter; and the DIDS-sensitive Cl(-)-HCO3 exchanger. Furthermore, under physiologic conditions, the Na+-HCO3 cotransporter plays a more important role in extrusion of excess intracellular H+ ions than does the Na+-H+ exchanger.