Carbonic Anhydrase in Human Nasal Epithelium: Localization and Effect of the Inhibition by Dichlorphenamide

Abstract

Carbonic anhydrase has not hitherto been reported in nasal mucosa. In the first part of this study, five specimens of human nasal mucosa from the inferior turbinate were obtained from five healthy subjects and tested for this enzyme with a histochemical reaction. Carbonic anhydrase was identified in the columnar ciliated respiratory epithelium, but was absent in the adjacent stratified squamous epithelium. The effect of the inhibition of this enzyme on the pH values and Na, K, and Cl activity in nasal secretion was subsequently investigated. Fifteen patients, affected by endocranial hypertension and to whom dichlorphenamide—an inhibitor of carbonic anhydrase—was administered, were studied. The pH value, determined with a surface electrode before giving the drug and 30, 60, and 90 minutes later, significantly increased and reached a peak at 60 minutes. Na, K, and Cl concentration was assessed by indirect potentiometry in the nasal secretion and in the plasma both before giving dichlorphenamide and 60 minutes later. Although no change was observed in the plasma, in the nasal secretion Na and Cl concentration increased and K concentration decreased. As a consequence, the gradients of Na and K between plasma and secretion decreased, and that of Cl increased. We assume analogous changes in the rate of transport through the mucosa to occur. These results thus suggest that carbonic anhydrase is involved in control of the pH of nasal secretions as well as in the electrolyte transport through the epithelium.