Salivary gland carbonic anhydrases

Carbonic anhydrases (CA) are zinc metalloenzymes that catalyze the reversible conversion of carbon dioxide and water to bicarbonate. For most mammalian cells, this reaction is essential to maintaining intracellular physiological pH. For salivary glands, it also has an important role in the regulation of the pH and buffering capacity of their secretory product, saliva, which is central to the activity of salivary digestive enzymes. This review is a chronological narrative of the discovery and distribution of CA and its isoenzymes in mammalian salivary glands and saliva and the role of CA in regulation of salivary pH via secretion of the salivary CA isoenzyme and the secretion and reabsorption of bicarbonate from the ductal lumen. The interaction of sodium/bicarbonate co-transporters and other factors in these processes is briefly described. The distribution of CA among mammalian species, salivary glands, and gland cells as determined by CA activity in saliva and gland extracts, enzyme histochemistry, and immunohistochemistry is presented in tables. The importance of salivary CA to oral health is underscored by the reduction in salivary gland and salivary CA activity by nutritional zinc deficiency and genetic variants of two of the CA isoenzymes, which cause dysgeusia and hyposalivation and are associated with increased dental caries.