we suggest that in acinar cells sodium ion is not only transported paracellularly but is also actively transported intracellularly into the luminal space by the ( na+ , k+ ) atpase located on the luminal plasma membranes , and that water is passively transported to the luminal space to form a plasma-like isotonic primary saliva , while in the duct cells the same ion is selectively re-absorbed intracellularly by ( na+ , k+ ) atpase found in abundance along the many infoldings of the basal plasma membranes , thus producing the hypotonic saliva .
C0007603
plasma membranes
C0007634
cells