CARBONIC-ANHYDRASE ISOENZYME-I, ISOENZYME-II, ISOENZYME-III, AND ISOENZYME-IV ARE PRESENT IN HUMAN ESOPHAGEAL EPITHELIUM

Carbonic anhydrase (CA) isoenzymes have been widely studied in the gas trointestinal tract, where they mediate membrane transport events and pH regulation. However, the esophagus has generally received scant att ention. In an immunohistochemical study confirmed by Western blotting, we have detected four CA isoenzymes (CAI, II, III, and IV) in the epi thelium of human esophagus. Isoenzymes I, III, and sometimes IV (<10%) were present in the cytoplasm of basal cells and II and IV in the cyt oplasm and cell surface membranes, respectively, of suprabasal cells ( prickle cells). The localization of CAIV to the plasma membranes was c onfirmed by electron microscopic immunocytochemistry. CA was effective ly divided at the basal-suprabasal interface between low-activity CAI and III (basal) and high-activity CAII and IV (suprabasal). Carbonic a nhydrase in esophageal epithelial cells may have several functions: el imination of CO2 and metabolites, participation in membrane transport events during active cell growth, and pH regulation as a protective me chanism against acidic gastric reflux.