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

Abstract

Objective: 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. Methods: 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 (pH i). Results: Resting pH i in bicarbonate-free N′-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid was 7.5 ± 0.03 (n = 50). Acidification using the NH 4Cl prepulse technique lowered pH i 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 pH i, and recovery was abolished by amiloride or replacement with an Na +-free buffer. Acidification by lowering pH o with HCl resulted in a similarly rapid rate of return as with the NH 4Cl technique, and resting cells acidified by 0.17 ± 0.02 pH units/5 min upon exposure to amiloride. Conclusions: 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 pH i lowering, and extrudes H + efficiently whether loaded by intracellular or extracellular means, making it well suited for epithelial defense against acid injury.