REGULATION OF THE TAURINE TRANSPORTER GENE IN THE S3 SEGMENT OF THE PROXIMAL TUBULE

Traditionally, bulk amino acid reabsorption in the kidney has been tho ught to be localized to the early portions of the proximal nephron. Ad ult Sprague-Dawley rats were fed diets with low, normal, and high taur ine content for two weeks. Kidneys were hybridized with an S-35-radiol abeled complementary RNA probe to the rB16a subclone encoding the extr acellular and transmembrane domains of the rat brain taurine transport er. Identical fragments were generated by RT-PCR from rat brain and ki dneys as confirmed by DNA sequencing. Hybridization was localized to t he outer zone of the medulla of all the kidneys. In the normal diet an imals, taurine transporter mRNA was localized to the S3 segment of the proximal tubule, to the loop of Henle in the medulla, and to the glom erular epithelial cell layer. With taurine restriction, taurine transp orter mRNA expression was up-regulated predominantly in the S3 segment and was virtually absent in this segment in animals supplemented with taurine. These experiments have precisely localized the rat kidney ta urine transporter gene, demonstrating regulation that is limited to th e S3 segment of the proximal tubule.