Abstract
The human parotid gland secretes much of the bicarbonate that enters the mouth. Prompted by studies of animal models, this study sought evidence for the expression of a functional Na +–HCO 3 − cotransporter (NBC) in human parotid acinar cells. Microfluorometric measurements of intracellular pH in isolated acini showed that the recovery from an acid load was achieved in part by HCO 3 − uptake via a Na +-dependent, DIDS-sensitive mechanism. By reverse transcriptase–polymerase chain reaction, a full-length NBC1 clone was obtained showing more than 99% homology with the human pancreatic isoform hpNBC1. Expressed in Xenopus oocytes, the electrogenicity of the transporter was detected as an inwardly directed, Na +- and HCO 3 −-dependent flux of negative charge. Immunohistochemistry using antibodies raised to NBC1 showed strong staining of the basolateral membrane of the acinar cells. Therefore, it was concluded that a functional electrogenic Na +–HCO 3 − cotransporter is expressed in the human parotid gland, and that it contributes to pH regulation in the acinar cells and could play a significant part in salivary secretion.
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