Oxidative stress and the genomic regulation of aldosterone-stimulated NHE1 activity in SHR renal proximal tubular cells

Abstract

This study evaluated the effects of aldosterone upon Na+/H+ exchange (NHE) activity in immortalized proximal tubular epithelial (PTE) cells from the spontaneously hypertensive rat (SHR) and the normotensive controls (Wistar Kyoto rat; WKY). Increases in NHE activity after exposure to aldosterone occurred in time- and concentration-dependent manner in SHR PTE cells, but not in WKY PTE cells. The aldosterone-induced increases in NHE activity were prevented by spironolactone, but not by the glucocorticoid receptor antagonist Ru 38486. The presence of the mineralocorticoid receptor transcript was confirmed by PCR and NHE1, NHE2, and NHE3 proteins were detected by immunoblot analysis. Cariporide and EIPA, but not S3226, inhibited the aldosterone-induced increase in NHE activity, indicating that NHE1 is the most likely involved NHE isoform. Pretreatment of SHR PTE cells with actinomycin D attenuated the aldosterone-induced increases in NHE activity. The SHR PTE cells had an increased rate of H2O2 production when compared with WKY PTE cells. Treatment of cells with apocynin, a NADPH oxidase inhibitor, markedly reduced the rate of H2O2 production. The aldosterone-induced increase in NHE activity SHR PTE cells was completely prevented by apocynin. In conclusion, the aldosterone-induced stimulation of NHE1 activity is a genomic event unique in SHR PTE cells, which involves the activation of the mineralocorticoid receptor, but ultimately requires the availability of H2O2 in excess.