Renal osmotic stress-induced cotransporter: expression in the newborn, adult and post-ischemic rat kidney.

The renal osmotic stress-induced cotransporter (ROSIT), a new putative member of a family of organic solute transporters, is highly expressed in the kidney. Our in situ hybridization data now reveal that large amounts of ROSIT mRNA can be found in the S3 segment of the proximal tubule. In the developing kidney, ROSIT mRNA is expressed after the S-shaped body stage. Because the S3 segment is the major site of damage in the post-ischemic kidney, we evaluated alterations in ROSIT mRNA expression after ischemic acute tubular necrosis. Renal osmotic stress-induced cotransporter mRNA levels were already decreased eight hours post-ischemia. At seven days post-ischemia, ROSIT mRNA reappeared in a mosaic pattern in the regenerating S3 segment, being fully expressed three weeks after the insult except for focal areas. The exact localization of this putative osmolyte transporter in the kidney, together with that of other known osmolyte transporter will contribute to a better understanding of the mechanism of medullary osmolyte accumulation and its vectorial transport.