[Water- and electrolyte secretion by salivary glands. ].
BACKGROUND
In salivary glands, fluid transport is thought to be driven osmotically in response to transepithelial salt gradients. According to the classical two-stage hypothesis of salivary secretion, an isotonic primary fluid is generated by the acinar cells and the fluid is subsequently modified by solute reabsorption and secretion as it passes along the ductal system resulted in the final, hypotonic solution.


OBJECTIVE
Very little is known about the molecular and functional nature of the transporters involved in salivary secretion, especially in human salivary glands. Therefore a systematic investigation of membrane transporters expressed also in the kidney, has been undertaken in healthy human salivary glands.


METHODS
RT-PCR and immunohistochemical analysis of different membrane transport proteins was used in rat and human salivary glands.


RESULTS
Clear evidence for the expression of aquaporin water channels in human salivary glands was found. AQP1 in the myoepithelial cells, AQP3 in the basolateral, AQP5 in the apical membrane of the acini is localized. The electroneutral NBC3 Na(+)-HCO3(-)-cotransporter is present in the apical membrane of the serous acini and of the ducts, while the NBCn1 only in the basolateral membrane of the striated duct is localized. The NHE1 Na+/H+ exchanger is present in the basolateral membrane of the acini and ducts. The vacuolar H(+)-ATPase is localized apically in the ducts, except for the intercalated duct.


CONCLUSIONS
Aquaporin water channels are likely to be involved in water secretion. The NBC3 and NBCn1 electroneutral Na(+)-HCO3(-)-cotransporters, the NHE1 Na+/H+ exchanger and the vacuolar H(+)-ATPase may play an important role in the pH regulation of salivary acinar and duct cells.
Gresz
Veronika
V
Semmelweis Egyetem, Fogorvostudományi Kar, Orálmorfológiai Csoport, Budapest. grever@net.sote.hu
D000818:Animals; D020346:Aquaporins / Q000032:analysis; D027682:Cation Transport Proteins / Q000032:analysis; D004573:Electrolytes / Q000032:analysis*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry; D026901:Membrane Transport Proteins / Q000032:analysis; D006180:Proton-Translocating ATPases / Q000032:analysis; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012463:Saliva / Q000737:chemistry* / Q000378:metabolism*; D012469:Salivary Glands / Q000737:chemistry*; D027982:Sodium-Bicarbonate Symporters / Q000032:analysis; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000032:analysis; D014867:Water / Q000737:chemistry
D020346:Aquaporins; D027682:Cation Transport Proteins; D004573:Electrolytes; D026901:Membrane Transport Proteins; C422022:SLC4A7 protein, human; C490998:SLC9A1 protein, human; C498902:Slc4a7 protein, rat; C452850:Slc9a1 protein, rat; D027982:Sodium-Bicarbonate Symporters; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; D014867:Water; D006180:Proton-Translocating ATPases