Human esophageal epithelial cells possess an Na+/H+ exchanger for H+ extrusion.

Abstract

The human esophagus is regularly exposed to refluxed gastric acid. Therefore, its epithelial cells require for survival a means of extruding excess H+ from the cytoplasm. Because Na+/H+ exchange activity has been observed in many mammalian cell types, including that of rabbit esophagus, we sought its presence in human esophageal epithelium. Human esophageal epithelial cells derived from endoscopic biopsy specimens or surgical esophagectomy specimens were grown in primary culture and loaded with the fluorescent dye, 2'7'-bis(carboxyethyl)-5(6)-carboxyfluorescein, to monitor intracellular pH (pHi). Resting pHi in bicarbonate-free N'-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid was 7.5 +/- 0.03 (n = 50). Acidification using the NH4Cl prepulse technique lowered pHi by 0.6 +/- 0.02 pH units, with recovery ensuing at an initial rate of 0.09 +/- 0.04 pH units/min. Notably, the rate of recovery was faster the more acidic the pHi, and recovery was abolished by amiloride or replacement with an Na+-free buffer. Acidification by lowering pHo with HCl resulted in a similarly rapid rate of return as with the NH4Cl technique, and resting cells acidified by 0.17 +/- 0.02 pH units/5 min upon exposure to amiloride. Human esophageal cells possess an H+-extruding mechanism consistent with an Na+/H+ exchanger. This mechanism is active in resting cells, adapts to the degree of pHi lowering, and extrudes H+ efficiently whether loaded by intracellular or extracellular means, making it well suited for epithelial defense against acid injury.