A histochemical study of carbonic anhydrase in the plasma membranes of human oral epithelial cells

Carbonic anhydrase (EC 4.2.1.1) was detected histochemically from the following regions in patients of various ages (14–84 yr): buccal mucosa, buccal flap, hard palate and tongue. The enzyme was principally located in the cell membranes but was also present in nuclei. There was a gradation in activity from basal (strong) to superficial cells (weak/negative). The carbonic anhydrase inhibitors ethoxyzolamide and acetazolamide abolished activity at 0.001 mM, but were ineffective, even at 1.2 mM, against a reaction associated with the granules of the stratum granulosum. No activity was detected in the absence of bicarbonate from the substrate.