DIFFERENTIAL UP-REGULATION OF RAT NA-K-CL COTRANSPORTER, RBSC1, MESSENGER-RNA IN THE THICK ASCENDING LIMB OF HENLE IN DIFFERENT PATHOLOGICAL CONDITIONS

Background Na-Cl cotransport across the apical membrane of epithelial cells in the thick ascending limb of the loop of Henle (TAL) plays a m ajor role in salt accumulation for hypertonic medullary interstitium. The electroneutral, rat bumetanide-sensitive sodium transporter, rBSC1 , is involved in this process. We studied the level of rBSC1 mRNA in d ehydration and cardiac failure, since sodium transport in TAL may be e nhanced in both conditions in spite of the difference in extracellular fluid accumulation. Methods. Male Sprague-Dawley rats were deprived o f water for 24 hours and myocardial infarction of about 40% of left ve ntricular circumference was induced in another group of rats that late r developed congestive heart failure (CHF). Digoxigenin-labeled cRNA p robe for rBSC1 was constructed using polymerase chain reaction (PCR), and Northern blot analysis was performed using RNAs from renal outer m edulla. By inducing a point mutation at the middle of PCR product, we compared the amount of rBSC1 transcripts in the renal cortex using com petitive PCR, since TAL represents a small fraction of the total corti cal tissue. Results. Northern analysis showed a significant increase i n rBSC1 mRNA in the renal outer medulla of both dehydrated and CHF rat s. In the renal cortex, however, the increase was noted only in CHF by competitive PCR. In situ hybridization using the riboprobe for northe rn analysis demonstrated that the transcript signal in dehydrated rats was intensified segmentally in TAL located in the inner stripe of out er medulla. Western analysis and immunohistochemistry using a specific antibody against rBSC1 confirmed the distinct segmental enhancement o f apical protein expression in dehydration and diffuse enhanced expres sion in CHF. Conclusions. rBSC1 is differentially upregulated in diffe rent pathological conditions.