ACID BASE TRANSPORTERS IN HUMAN DUODENAL ENTEROCYTES/

Background: Duodenal mucosal bicarbonate secretion serves as a key def ensive factor against mucosal injury. The purpose of the present study was to isolate human proximal duodenal enterocytes and identify their inherent acid/base transporters that participate in duodenal alkaline secretion. Methods: Biopsy specimens were obtained from the duodenal bulb in 18 healthy volunteers. Individual duodenal epithelial cells we re isolated by means of a combination of calcium chelation and collage nase. Intracellular pH (pH(i)) was measured by the pH-sensitive dye BC ECF and dynamic fluorescence ratio imaging. Results: Cytologic and his tologic examination confirmed that isolated cells were of epithelial o rigin. In HCO3--free media, pH(i) recovery after acidification with NH 4Cl was amiloride-sensitive and Na+-dependent, indicating the presence of an Na+/H+ exchanger. pH(i) recovery after acidification was signif icantly enhanced by the presence of HCO3-, showing the presence of an HCO3--dependent recovery mechanism (that is, a base loader/acid extrud er). HCO3--dependent recovery required external Na+ yet was Cl-- and a miloride-insensitive, characteristic of an NaHCO3 cotransporter. In th e presence of HCO3-, a Cl--dependent anion exchanger serving as a base extruder was shown, indicative of a Cl-/HCO3- exchanger. Conclusions: Human duodenal enterocytes contain at least three acid/base transport ers: an Na+/H+ exchanger that serves as to extrude acid, an NaHCO3 cot ransporter that functions as base loader, and a Cl-/HCO3- exchanger th at operates as a base extruder.