Na(+)-dependent and -independent Cl-/HCO3- exchangers in cultured rabbit esophageal epithelial cells.

Abstract

The mechanisms by which esophageal epithelial cells regulate intracellular pH (pHi) in a physiological solution are unknown. Basal-type esophageal cells growing in primary culture were loaded with the fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) to study pHi by microfluorimetry. The pHi in HEPES buffer was 7.7 +/- 0.03, a value higher than that in CO2/HCO3- buffer, 7.2 +/- 0.1. Cells in HEPES switched to CO2/HCO3- buffer rapidly acidified to pHi of 7, then alkalinized to a new steady-state pHi. The mechanisms for alkalinization in CO2/HCO3- were dependent on two exchangers, one amiloride-sensitive and the other 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS)-sensitive, the latter dependent on Nao and Cli, and so indicative of an Na(+)-dependent Cl-/HCO3- exchanger. Cells in a CO2/HCO3- buffer rapidly alkalinized to pH 8.2 when switched to HEPES, then acidified to a new steady-state pHi. Acidification in HEPES was largely caused by a DIDS-sensitive, Clo-dependent, non-Nao-requiring mechanism, indicative of a cell-acidifying Na-independent Cl-/HCO3- exchanger. In a physiological buffer, esophageal cells have at least three exchangers for regulation of pHi.