title: Immunolocalization of Na/SO4-cotransport (NaSi-1) in rat kidney.
abstract: The proximal tubule is the major site for renal reabsorption of sulphate. A sodium-dependent transport system for sulphate (NaSi-1) has recently been identified from a rat kidney cortex cDNA library. Recent work demonstrated that NaSi-1 mRNA is expressed predominantly in proximal tubules. In the present work expression along the nephron of the Na/SO4-cotransporter NaSi-1 was studied by immunofluorescence. A polyclonal antibody was raised in rabbits against a fusion protein containing a 53-amino-acid polypeptide specific for the NaSi-1 sequence. The anti-NaSi-1 polyclonal antibody specifically detected a 68-kDa protein on Western blots and, by immunofluorescence specific staining, was observed in MDCK cells transfected with the NaSi-1 cotransporter. Using rat kidney cortex slices specific NaSi-1-related immunoreactivity was detected in proximal tubules and was restricted to the apical membrane. No immunoreactivity was observed in the other nephron segments. This was confirmed by Western blot analysis using proximal tubular apical and basolateral membranes isolated by free-flow electrophoresis. The results indicate that the Na/SO4-cotransporter NaSi-1 is expressed in the apical membrane of proximal tubular cells and is therefore likely to be involved in proximal reabsorption of sulphate.
authors.affiliation: Institute of Physiology, University Zürich-Irchel, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Lötscher
authors.forename: M
authors.initials: M
authors.lastname: Custer
authors.forename: E S
authors.initials: ES
authors.lastname: Quabius
authors.forename: B
authors.initials: B
authors.lastname: Kaissling
authors.forename: H
authors.initials: H
authors.lastname: Murer
authors.forename: J
authors.initials: J
authors.lastname: Biber
mesh_terms: D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism*; D027682:Cation Transport Proteins; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D005455:Fluorescent Antibody Technique; D007150:Immunohistochemistry; D007668:Kidney / Q000378:metabolism* / Q000648:ultrastructure; D007672:Kidney Cortex / Q000378:metabolism / Q000648:ultrastructure; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism; D008969:Molecular Sequence Data; D051381:Rats; D012964:Sodium / Q000378:metabolism; D000077003:Sodium Sulfate Cotransporter; D013431:Sulfates / Q000378:metabolism; D027981:Symporters
chemical_list: D002352:Carrier Proteins; D027682:Cation Transport Proteins; D000077003:Sodium Sulfate Cotransporter; D013431:Sulfates; D027981:Symporters; D012964:Sodium