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Inner medullary collecting duct (IMCD) cells from salt-sensitive (S) Dahl rats transport twice as much [Na.sup.+] as cells from salt-resistant (R) rats, possibly related to dysregulation of the renal epithelial sodium channel (ENaC). The effect of a high-salt diet on ENaC expression in the inner medulla of S versus R rats has not yet been studied. Young, male S and R rats were placed on a regular-salt (0.3%) or high-salt (8%) diet for 2 or 4 weeks. mRNA and protein expression of ENaC subunits were studied by real-time PCR and immunoblotting. Intracellular distribution of the subunits in the IMCD was evaluated by immunohistochemistry. On regular salt, the abundance of the mRNA of β and γENaC was higher in the medulla of S rats than R rats. This was associated with a greater protein abundance of 90 kDa γENaC and higher immunoreactivity for both α and γ ENaC. High salt did not affect mRNA abundance in either strain and decreased apical staining of βENaC in IMCD of R rats. In contrast, high salt did not affect the higher apical localization of αENaC and increased the apical membrane staining for β and γENaC in the IMCD of S rats. Expression of ENaC subunits is enhanced in the medulla of S vs. R rats on regular salt, and further increased on high salt. The persistent high expression of αENaC and increase in apical localization of β and γENaC may contribute to greater retention of sodium in S rats on a high-salt diet. Key words: kidney, salt, ENaC, real-time PCR, immunohistochemistry. Les cellules du tube collecteur medullaire interne (TCMI) des rats Dahl sensibles au sel (S) transportent deux fois plus de [Na.sup.+] que celles des rats resistants au sel (R), probablement en raison d'un dysfonctionnement du canal sodique epithelial renal (ENaC). L'effet d'une diete hypersodee sur l'expression du canal ENaC dans la partie medullaire interne des rats S versus R n'a a ce jour fait l'objet d'aucune etude. Nous avons soumis de jeunes rats S et R males a une diete contenant une quantite normale (0,3%) ou elevee (8%) de sel pendant 2 ou 4 semaines. Nous avons examinee l'expression de l'ARNm et des proteines des sous-unites de ENaC par PCR en temps reel et immunobuvardage, et nous avons evalue par immunohistochimie la distribution intracellulaire des sous-unites dans le TCMI. En condition normosodee, l'expression de l'ARNm des sous-unites β et γENaC a ete plus elevee dans la partie medullaire des rats S que des rats R. Cet effet a ete associe a un taux plus eelevee des proteeines des sous-unites γENaC de 90 kDA et a une plus forte immunoreactivitee tant pour ce qui est de β que de γENaC. La diete hypersodee n'a pas modifiee la teneur en ARNm des rats S et R, et a diminue la coloration apicale de βENaC dans le TCMI des rats R. A l'opposee, la dose eleveee de sel n'a pas influee sur la plus forte localisation apicale de γENaC, et a elle augmented la coloration apicale de β et γENaC dans le TCMI des rats S. L'expression des sous-unites ENaC est stimulee dans la partie medullaire des rats S versus R soumis a une diete normosodee, et elle augmente davantage avec une diete hypersodee. L'expression elevee persistante de αENaC et l'augmentation de la localisation apicale de β et γENaC pourraient contribuer a la plus forte retention de sodium chez les rats S soumis a une diete hypersodeee. Mots-cles: rein, sel, ENaC, PCR en temps reel, immunohistochimie. [Traduit par la Redaction], Introduction Blood pressure sensitivity to salt is seen in 40%-60% of patients with essential hypertension and in ~20%-30% of the general population (Franco and Oparil 2006). Genetic analyses of human [...]

We evaluated the effects of intracerebroventricular (icv) infusion of [Na.sup.+]-rich artificial cerebrospinal fluid (aCSF), with or without the mineralocorticoid receptor (MR) blocker spironolactone, on epithelial [Na.sup.+] channel (ENaC) subunits and regulators, such as MR, serum/glucocorticoid-inducible kinase 1, neural precursor cells expressed developmentally downregulated 4-like gene, 11[beta]-hydroxylase, and aldosterone synthase, in brain regions of Wistar rats. The effects of icv infusion of the amiloride analog benzamil on brain tissue and CSF [Na.sup.+] concentration ([[Na.sup.+]]) were also assessed. In the choroid plexus and ependyma of the anteroventral third ventricle, ENaC subunits are present in apical and basal membranes. [Na.sup.+]-rich aCSF increased [beta]-ENaC mRNA and immunoreactivity in the choroid plexus and increased [alpha]- and [beta]-ENaC immunoreactivities in the ependyma. [Na.sup.+]-rich aCSF increased [alpha]- and [beta]-ENaC-gold-labeled particles in the microvilli of the choroid plexus and in basolateral membranes of the ependyma. Spironolactone only prevented the increase in [beta]-ENaC immunoreactivity in the choroid plexus and ependyma. In the supraoptic nucleus, paraventricular nucleus, and subfornical organ, [Na.sup.+]-rich aCSF did not affect mRNA expression levels of the studied genes. Benzamil significantly increased CSF [[Na.sup.+]] in the control, but not [Na.sup.+]-rich, aCSF group. In contrast, benzamil prevented the increase in hypothalamic tissue [[Na.sup.+]] by [Na.sup.+]-rich aCSF. These results suggest that CSF [Na.sup.+] upregulates ENaC expression in the brain epithelia, but not in the neurons of hypothalamic nuclei. ENaC in the choroid plexus and ependyma appear to contribute to regulation of [Na.sup.+] homeostasis in the brain. sodium-rich artificial cerebrospinal fluid; benzamil; cerebrospinal fluid sodium concentration doi: 10.1152/ajpregu.00834.2009.

Chronic subcutaneous infusion of ouabain causes hypertension via central pathways involving angiotensin type 1 (A[T.sub.1]) receptor stimulation. The present study assessed plasma and tissue ANG I and II levels as well as A[T.sub.1] receptor and angiotensin-converting enzyme (ACE) mRNA levels and binding densities by real-time PCR and in vitro autoradiography in relevant brain nuclei and peripheral tissues (heart and kidney) in rats at 1 and/or 2 wk after start of ouabain infusion at 50 [micro]g/day. After 2 wk (but not after 1 wk), blood pressures significantly increased (+ 15 mmHg). At 2 wk, plasma ANG I and II levels were markedly suppressed by ouabain. In contrast, in the heart and kidneys, ANG I levels were not affected, and ANG II levels tended to decrease, whereas in the hypothalamus ANG II content clearly increased. At 1 wk, no changes in ACE and A[T.sub.1] receptor densities were seen. After 2 wk, there were significant decreases in AT~ receptor mRNA and densities in the organum vasculosum of the lamina terminalis (OVLT), subfornical organ (SFO), and paraventricular nucleus (PVN). ACE densities decreased only in the OVLT and SFO, but ACE mRNA showed more variable responses (decrease in OVLT vs. increase in PVN). In the kidneys, at 2 wk both A[T.sub.1] receptor and ACE densities were decreased, but mRNA abundance did not change. The heart showed no significant changes. The increase in hypothalamic ANG II content and associated decreases in central A[T.sub.1] receptor and ACE densities support the involvement of the brain renin-angiotensin system in the central hypertensive mechanism of action of ouabain. angiotensin II; angiotensin type 1 receptors; angiotensin-converting enzyme; brain; kidneys doi:10.1152/ajpheart.01148.2005