Bicarbonate Transport by Salivary Gland Acinar Cells

In human saliva collected from the openings of the main salivary gland ducts, HCO 3 - concentration is about 5 mmol/l during spontaneous secretion, but increases dramatically to 40–60 mmol/l when salivation is stimulated (e.g. by the application of citric acid to the tongue; Ferguson 1975). This increased HCO 3 - output has a beneficial effect in the mouth. Oral bacteria rapidly produce acid from dietary sugars, causing an immediate drop in plaque pH in the mouth (Stephan 1940). In subjects where salivation is inhibited this drop in pH is large and sustained, whereas in normal subjects, salivation attenuates the fall in pH and reduces the duration of lowered plaque pH (Englander et al. 1959). Low plaque pH is associated with dental caries as it causes dissolution of tooth enamel (Hillam 1975; Jenkins 1978). Thus, salivary HCO 3 - appears to have a protective role, and secretion of HCO 3 - can be considered an important function of the salivary glands in man.