NA+ H+-EXCHANGER-3 ACTIVITY AND ITS GENE IN THE SPONTANEOUSLY HYPERTENSIVE RAT-KIDNEY/

Objective To examine the mechanisms affecting proximal tubule sodium r eabsorption, we studied the gene expression and functional changes of the Na+/H+-exchanger 3 (NHE3) and its gene expression in spontaneously hypertensive rats (SHR). Methods The S1 segment of the superficial pr oximal convoluted tubules (PCT) was microdissected from collagenase-tr eated kidneys of SHR and Wistar-Kyoto (WKY) rats, The tubules were the n superfused in a HERBS-buffered solution. The intracellular pH was me asured by monitoring changes in fluorescent dye emission. By measuring the amiloride-sensitive intracellular pH recovery rate after intracel lular acid loading with NH4Cl, we estimated the NHE3 activity, Norther n blotting was performed to quantitate the NHE3 messenger RNA (mRNA) e xpression, and the NHE3 complementary DNA sequence was determined both in SHR and in WKY rat strains. Results NHE3 activity was significantl y higher in SHR than it was in WKY rats both at age 4 weeks and at age 7 weeks. Northern blot analysis showed that the mRNA expression did n ot differ significantly in the two strains at either age. Sequence ana lysis of complementary DNA of SHR NHE3 revealed five allelic variation s compared with the known wild-type sequence in Sprague-Dawley rats. T he same variations were also identified in the WKY rats. Conclusion NH E3 activity is increased in SHR compared with WKY rats of the same age , Changes in the NHE3 mRNA expression level and protein structure are not responsible for this difference between SHR and WKY rat strains.