EFFECTS OF PARTIAL NEPHRECTOMY ON THE EXPRESSION OF OSMOLYTE TRANSPORTERS

Na+/myo-inositol cotransporter (SMIT) and Na+/Cl-/betaine-gamma-amino- n-butyric acid transporter (BGT-1) are the major osmolyte transporters that are regulated by extracellular osmolarity. We have recently show n localization and rapid regulation of the mRNAs for these transporter s in rat kidney. In the present study, we examined the expression of S MIT and BGT-1 in partial nephrectomized rats in order to assess the ch ange in local osmolarity following reduction of renal mass. Four weeks after 5/6 nephrectomy (NX), the rats were compared to sham-operated c ontrol animals (CONT). Northern analysis using RNA of whole kidney ind icated that there were little differences in the levels of SMIT and BG T-1 mRNAs between the two groups. In situ hybridization revealed that signals for both transporter mRNAs were markedly reduced in the inner medulla of the remnant kidney. In contrast, these signals in the outer medulla increased following nephrectomy. SMIT signals in the cortex i ncreased as well. Grain density, determined by counting grain number p er cell, revealed that the signals in the inner medullary collecting d ucts were markedly reduced whereas those in the thick ascending limbs of Henle (TAL) as well as macula densa cells were significantly increa sed. The signals in the TAL and macula densa were reduced by furosemid e administration. The increased expression in NX rats may reflect the increased NaCl transport and high local osmolarity in this segment.