Altered sodium pump alpha and gamma subunit gene expression in nephron segments from hypertensive rats

Objective To determine the qualitative and quantitative expression of alpha and gamma sodium pump subunits in whole kidney and nephron segment RNA fro m Sprague Dawley rats, spontaneously hypertensive rats (SHR) and Wistar-Kyo to (WKY) rats. Design A novel reverse transcription polymerase chain reaction technique wa s devised which provides accurate and precise measurement of the number of molecules of specific transcript abundance, a measurement of gene expressio n. This allows the quantitative comparison of multiple samples across multi ple subjects and, since the estimates are accurate rather than relative, ca n also be used to make quantitative comparisons across expressed genes, suc h as isoforms and subunits of the heterotrimeric renal sodium pump. Methods We examined which catalytic isoforms were expressed and then quanti fied transcript abundance in whole kidney and convoluted and straight segme nts of the proximal tubule. Results Alpha 1 and gamma transcripts, but not alpha 2, alpha 3 or alpha 4 isoforms, were consistently observed in nephron segments. Levels of alpha 1 were lower in kidney RNA from 15-16-week-old SHR than in WKY rats of the s ame age (P = 0.001), but were not different between SHR and WKY in 4-5-week -old animals. No significant difference was observed in gamma subunit abund ance in kidney RNA from 4-5-week-old animals; however, at 15-16 weeks, the expression in SHR was one-third that in WKY rats (P = 0.003). In proximal c onvoluted tubules from 4-5-week-old animals, the level of alpha 1 RNA expre ssion was lower(P = 0.03) in SHR than in WKY rats. In addition, levels of a lpha 1 in proximal straight tubule from the 4-5-week-old SHR were also lowe r than in WKY rats (P = 0.02). This difference was even greater in 15-16-we ek-old animals: in SHR, alpha 1 expression was less than 20% of the level o f expression in WKY rats (P = 0.0003), Expression of the gamma subunit exhi bited a similar pattern of downregulation in SHR, In RNA from proximal conv oluted tubules and proximal straight tubules from both 4-5- and 15-16-weeko ld animals, expression of the gamma subunit was demonstrated to be signific antly lower in SHR than in WKY rats. Conclusion The results indicate a coordinate reduction in the abundance of sodium pump alpha and gamma subunits in the proximal tubules of SHR, which occurs early during the development of hypertension. J Hyperfens 1999, 17:1 081-1087 (C) Lippincott Williams & Wilkins.