HUMAN ESOPHAGEAL EPITHELIAL-CELLS POSSESS AN NA+ H+ EXCHANGER FOR H+ EXTRUSION/

Objective: The human esophagus is regularly exposed to refluxed gastri c acid. Therefore, its epithelial cells require for survival a means o f extruding excess H+ from the cytoplasm, Because Na+/H+ exchange acti vity has been observed in many mammalian cell types, including that of rabbit esophagus, we sought its presence in human esophageal epitheli um. Methods: Human esophageal epithelial cells derived from endoscopic biopsy specimens or surgical esophagectomy specimens were grown in pr imary culture and loaded with the fluorescent dye, 2'7'-bis(carboxyeth yl)-5(6)-carboxyfluorescein, to monitor intracellular pH (pH(i)), Resu lts: Resting pH, in bicarbonate-free N'-2-hydroxyethylpiperazine-N'-2- ethanesulfonic acid was 7.5 +/- 0.03 (n = 50), Acidification using the NH4Cl 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. No tably, the rate of recovery was faster the more acidic the pH(i), and recovery was abolished by amiloride or replacement with an Na+-free bu ffer. Acidification by lowering pH(o) with HCl resulted in a similarly rapid rate of return as with the NH4Cl technique, and resting cells a cidified by 0.17 +/- 0.02 pH units/5 min upon exposure to amiloride, C onclusions: Human esophageal cells possess an H+-extruding mechanism c onsistent with an Na+/H+ exchanger, This mechanism is active in restin g cells, adapts to the degree of pH(i) lowering, and extrudes H+ effic iently whether loaded by intracellular or extracellular means, making it well suited for epithelial defense against acid injury. (C) 1998 by Am. Coll. of Gastroenterology.