Carbonic anhydrase in mouse salivary glands and saliva: a histochemical, immunohistochemical, and enzyme activity study.

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Abstract
Mouse parotid gland and saliva were studied by histochemical, immunohistochemical, and activity measurements for carbonic anhydrase. Hansson 's histochemical reaction for carbonic anhydrase revealed positive enzyme activity in the parotid acinar cell cytoplasm and little or no reaction in the secretory granules. The luminal contents in all of the glandular duct systems also reacted positively, but the duct cells themselves were only weakly positive. Ultrastructural observations confirmed the light microscope histochemical localization and, in addition, revealed luminal content activity in intercellular ducts. Purified carbonic anhydrase isolated from mouse salivary glands was used to raise antibodies in rabbits. Localization of carbonic anhydrase by direct immunolabeling with fluorescein-coupled antibody and indirect immunoperoxidase labeling revealed enzyme localization on or in the acinar cell secretory granule membrane and not in the surrounding cytoplasm. The luminal contents of the intercalated and striated ducts were also strongly positive. Stimulation of salivary secretion with phenylephrine or pilocarpine increased the amount of carbonic anhydrase in saliva. Acetatazolamide and potassium cyanate inhibited carbonic anhydrase activity. Reasons underlying the discrepancy between the histochemical and immunolabeling localization of carbonic anhydrase are discussed. It is concluded that the parotid acinar cells of mice appear to be a significant source of carbonic anhydrase in saliva but its role is enigmatic.