Localization of an ecto-ATPase/cell-CAM 105 (C-CAM) in the rat parotid and submandibular glands

We investigated an ecto-ATPase/cell-CAM 105 (C-CAM), previously shown to be distinct from the Ca2+ pump, in rat parotid and submandibular glands. Polyclonal antibodies raised against the enzyme were employed using indirect immunofluorescence, peroxidase-anti-peroxidase (PAP), and electron microscopic immunogold labeling procedures to visualize the location of the enzyme. In the PAP-stained sections and with immunofluorescence, labeling was observed on the luminal and lateral surfaces and the intercellular canaliculi of the acinar cells of both glands. The luminal surface of the intercalated ducts was brightly stained, whereas those of the striated and excretory ducts were less prominently labeled. The basal surface of the acinar cells in the parotid gland and the lateral and basal surfaces of the duct cells were not labeled. Apparent labeling was observed on the basal surface of the submandibular acinar cells. Electron microscopy revealed that for both glands the enzyme was primarily localized along the luminal border of the acinar cells, mainly in association with microvilli, with slightly less reactivity along the intercellular canaliculi and lateral borders and relatively little along the basolateral membranes. Gold labeling was also observed on the luminal borders of the intercalated and striated ducts. Possible functions of the C-CAM include breakdown of ATP, stabilization of the microvillar membranes, cell adhesion, and involvement in secretory mechanisms.