Intracellular electrolyte composition in various experimental models of hypertension: an electron microprobe study

Personalized Therapy of Hypertension: the Past and the Future

During the past 20 years, the studies on genetics or pharmacogenomics of primary hypertension provided interesting results supporting the role of genetics, but no actionable finding ready to be translated into personalized medicine. Two types of approaches have been applied: a "hypothesis-driven" approach on the candidate genes, coding for proteins involved in the biochemical machinery underlying the regulation of BP, and an "unbiased hypothesis-free" approach with GWAS, based on the randomness principles of frequentist statistics. During the past 10-15 years, the application of the latter has overtaken the application of the former leading to an enlargement of the number of previously unknown candidate loci or genes but without any actionable result for the therapy of hypertension. In the present review, we summarize the results of our hypothesis-driven approach based on studies carried out in rats with genetic hypertension and in humans with essential hypertension at the pre-hypertensive and early hypertensive stages. These studies led to the identification of mutant adducin and endogenous ouabain as candidate genetic-molecular mechanisms in both species. Rostafuroxin has been developed for its ability to selectively correct Na(+) pump abnormalities sustained by the two abovementioned mechanisms and to selectively reduce BP in rats and in humans carrying the gene variants underlying the mutant adducin and endogenous ouabain (EO) effects. A clinical trial is ongoing to substantiate these findings. Future studies should apply both the candidate gene and GWAS approaches to fully exploit the potential of genetics in optimizing the personalized therapy.

Renal Na,K-ATPase in genetic hypertension

Milan hypertensive rats (MHS) develop hypertension because of a primary renal alteration. Both apical and basolateral sodium transport are faster in membrane vesicles derived from renal tubules of MHS than in those of Milan normotensive control rats (MNS). These findings suggest that the increased renal sodium retention and concomitant development of hypertension in MHS may be linked to an altered transepithelial sodium transport. Since this transport is mainly under the control of the Na-K pump, we investigated whether an alteration of the enzymatic activity and/or protein expression of the renal Na,K-ATPase is detectable in prehypertensive MHS. We measured the Na,K-ATPase activity, Rb+ occlusion, turnover number, alpha 1- and beta 1-subunit protein abundance, and alpha 1 and beta 1 mRNA levels in microsomes from renal outer medulla of young (prehypertensive) and adult (hypertensive) MHS and in age-matched MNS. In both young and adult MHS, the Na,K-ATPase activity was significantly higher because of an enhanced number of active pump sites, as determined by Rb+ occlusion maximal binding. The higher number of pump sites was associated with a significant pretranslational increase of alpha 1 and beta 1 mRNA levels that preceded the development of hypertension in MHS. Since a molecular alteration of the cytoskeletal protein adducin is genetically associated with hypertension in MHS and is able to affect the actin-cytoskeleton and Na-K pump activity in transfected renal cells, we propose that the in vivo upregulation of Na-K pump in MHS is primary and linked to a genetic alteration of adducin.

Renal alpha-adrenergic receptors and genetic hypertension

The hypothesis has been proposed that an increase in the number of renal alpha-adrenergic receptors may contribute to the pathogenesis of genetic hypertension. Herein we review recent findings regarding expression of renal alpha 1 (alpha 1a, alpha 1b)- and alpha 2 (alpha 2a, alpha 2b)-adrenergic subtypes and we provide an updated revision of the above-stated hypothesis. Enhancement in receptor number or in post-receptor components responsible for alpha 1- and alpha 2-adrenergic-mediated sodium reabsorption in proximal tubule may contribute to sodium retention and an elevation in blood pressure. Perhaps such changes contribute to the increase in blood pressure in genetically determined hypertension in humans, although direct tests of this notion have not yet been performed.

Increased Na pump activity in the kidney cortex of the Milan hypertensive rat strain

The (Na+,K+)-ATPase activity from the kidney cortex of the Milan hypertensive rat strain (MHS) and the corresponding normotensive control (MNS) was measured both in active solubilized enzyme preparations and in isolated basolateral membrane vesicles. Kinetic analysis of the purified enzyme showed that the Vmax value was significantly higher in MHS rats. The difference between MHS and MNS was not linked to a different number of sodium pumps, but was related to the molecular activity of the enzyme. Using basolateral membrane vesicles, an increased ATP-dependent ouabain-sensitive sodium transport was also demonstrated in MHS rats. These results support the hypothesis that a higher tubular sodium reabsorption may be involved in the pathogenesis of hypertension in this rat strain.

Na+/K+/Cl(-)-cotransporter mediated Rb+ fluxes in membrane vesicles from kidneys of normotensive and hypertensive rats

This paper describes experiments to examine Rb+ fluxes via the Na+/K+/Cl- cotransporter in membrane vesicles from renal outer medulla of three strains of rat: (A) Wistar (B) Milan hypertensive (MHS) and normotensive (MNS), and (C) Sabra salt-sensitive hypertensive (SBH) and salt-resistant (SBN). Initially, Na(+)-dependent furosemide- or bumetanide-inhibited 86Rb+ fluxes were characterised using Wistar rat microsomes. The latter were partially purified on a metrizamide cushion, and assay conditions were optimized for use with microsomes from the other rats. The major result is that in microsomes from adult Milan hypertensive (MHS) rats the rate of the Na+/K+/Cl(-)-cotransporter mediated 86Rb flux at sub-saturating concentrations of Rb, appears to be significantly greater than in the normotensive (MNS) controls. The effect reflects an increased apparent Rb affinity of the cotransporter in MHS microsomes. There is no difference in maximal rate or in the apparent Na+ activation affinity of the 86Rb+ flux. In addition bumetanide appears to be a somewhat more effective inhibitor in MHS compared to MNS microsomes. The 86Rb+ flux result is compatible with a previous finding that in red cells, Na+/K+ -cotransporter mediated fluxes are increased in MHS compared to MNS. It supports the notion that the Na+/K+/Cl(-)-cotransporter in in both red cells and kidney is a genetic marker for hypertension. It is of interest that apparently more than one Na+ transport system is affected in MHS hypertensive kidneys (a) the Na+/K+/Cl- cotransporter in the thick ascending limb of Henle and (b) the Na+/H+ exchanger and/o a conductive Na(+)-pathway in brush-border membranes from proximal tubule. It is conceivable that in the hypertensive animals a common regulatory pathway (e.g., phosphorylation) or protein (e.g., cytoskeleton) is affected along the length of the nephron. In Sabra SBH and SBN rat microsomes, no difference was found for the 86Rb+ flux via the Na+/K+/Cl- cotransporter (or via a K+ channel).

Effects of high potassium or low sodium diet on vascular Na+,K+-ATPase activity and blood pressure in young spontaneously hypertensive rats

These studies were designed to investigate whether the antihypertensive effects of high potassium or low sodium diets are related to changes in vascular Na+,K+-adenosine triphosphatase (ATPase) activity. Vascular Na+,K+-ATPase was measured as ouabain-sensitive rubidium uptake in aorta incubated in buffer or plasma from spontaneously hypertensive rats (SHR) fed either a high potassium, a low sodium, or a normal diet for 2 weeks. The high potassium diet significantly increased Na+,K+-ATPase activity, whereas the low sodium diet significantly decreased activity. There was no evidence of a ouabainlike factor in plasma. The increased pump activity on the high potassium diet appeared to be due to an increase in maximum activity (Vmax) of the enzyme, rather than to an increased affinity for potassium. Potentially, an increase in Na+,K+-ATPase activity could contribute to the antihypertensive effect of potassium by hyperpolarizing the cell membrane. The decrease in vascular Na+,K+-ATPase activity on a low sodium diet probably is unrelated to its depressor effect, but it may be a homeostatic mechanism for maintaining sodium balance in the animal.