Localization of sodium pump sites in cat salivary glands.

1. Cat submandibular glands were perfused with Locke solution containing [3H]ouabain. In some experiments additional medium was given by retrograde intraductal injection. 2. [3H]ouabain binding sites were localized by light microscopical autoradiography and the findings compared with the electron micrographs. 3. The cells of the striated ducts were heavily labelled with [3H]ouabain, predominantly in the contraluminal parts. 4. At the acinar level moderate amounts of [3H]ouabain were found in relation to the plasma membranes of the demilunar cells. The central acinar cells were found to be virtually devoid of [3H]ouabain. 5. Electron microscopy revealed that the demilunar cells possessed long, tortuous intercellular spaces separated from the secretory canaliculi by junctional complexes. In contrast, the membranes between adjacent central acinar cells were fairly straight. 6. It is concluded that the striated ducts play a dominant role in the ductal reabsorption of sodium, and that the transport is probably mediated by a (Na+ + K+)-activated ATPase. The findings on the acinar level are in agreement with the view that the primary saliva is formed predominantly by the demilunar cells. The role of a (Na+ + K+)-activated ATPase in this process is unclear.