IMMUNOLOCALIZATION OF SAT-1 SULFATE OXALATE/BICARBONATE ANION-EXCHANGER IN THE RAT-KIDNEY/

The rat liver sulfate/bicarbonate/oxalate exchanger (sat-l) transports sulfate across the canalicular membrane in exchange for either bicarb onate or oxalate. Sulfate/oxalate exchange has been detected in the pr oximal tubule of the kidney, where it is probably involved in the reab sorption of filtered sulfate and the secretion of oxalate and may cont ribute to oxalate-dependent chloride reabsorption. Screening of a rena l cortex cDNA library determined that sat-1 is expressed in the rat ki dney. To evaluate this anion exchanger, the sat-1 protein was expresse d in Sf9 cells. Sodium-independent sulfate and oxalate uptake was enha nced 7.3-fold and 13.1-fold, respectively, in Sf9 cells expressing the sat-1 protein compared with cells infected with wild-type virus. We d etermined that sat-1 is glycosylated in the kidney; however, anion exc hange via sat-1 is observed despite incomplete glycosylation of sat-1 in Sf9 cells. The sat-1 protein, with an added COOH-terminal B-histidi ne tag, was purified on a metal affinity column and used to generate a nti-sat-1 monoclonal antibodies. The sat-1 protein was localized to th e basolateral membrane, but not the apical membrane, of the proximal t ubule by both Western blot analysis and immunohistochemistry. These st udies demonstrate that sulfate/oxalate exchange on the apical and baso lateral membranes of the proximal tubule represents transport on two d ifferent anion exchangers.