Hypertension, Na+/Ca2+ exchanger, and Na+, K+-ATPase

Mitochondrial Damage and Hypertension: Another Dark Side of Sodium Excess

PURPOSE OF REVIEW

Essential or primary hypertension (HT) is a worldwide health problem with no definitive cure. Although the exact pathogenesis of HT is not known, genetic factors, increased renin-angiotensin and sympathetic system activity, endothelial dysfunction, oxidative stress, and inflammation play a role in its development. Environmental factors such as sodium intake are also important for BP regulation, and excess sodium intake in the form of salt (NaCl, sodium chloride) increases blood pressure in salt-sensitive people. Excess salt intake increases extracellular volume, oxidative stress, inflammation, and endothelial dysfunction. Recent evidence suggests that increased salt intake also disturbs mitochondrial function both structurally and functionally which is important as mitochondrial dysfunction is associated with HT. In the current review, we have summarized the experimental and clinical data regarding the impact of salt intake on mitochondrial structure and function.

RECENT FINDINGS

Excess salt intake damage mitochondrial structure (e.g., shorter mitochondria with less cristae, increased mitochondrial fission, increased mitochondrial vacuolization). Functionally, high salt intake impairs mitochondrial oxidative phosphorylation and electron transport chain, ATP production, mitochondrial calcium homeostasis, mitochondrial membrane potential, and mitochondrial uncoupling protein function. Excess salt intake also increases mitochondrial oxidative stress and modifies Krebs cycle protein expressions. Studies have shown that high salt intake impairs mitochondrial structure and function. These maladaptive mitochondrial changes facilitate the development of HT especially in salt-sensitive individuals. High salt intake impairs many functional and structural components of mitochondria. These mitochondrial alterations along with increased salt intake promote the development of hypertension.

Relationship between high fructose corn syrup sweetened drinks, diet soft drinks, and serum sodium: NHANES 2003-2006

BACKGROUND

Consumption of high fructose corn syrup sweetened drinks and diet soft drinks has increased in the United States. However, the relationship between the intake of high fructose corn syrup sweetened drinks and diet soft drinks, and serum sodium has been scarcely studied. Our objective is to evaluate the relation between intake of high fructose corn syrup sweetened drinks and diet soft drinks, and serum sodium, and explore the possible effect modifiers in a nationally representative sample of adults from the United States.

METHODS

We conducted a cross-sectional study using data from the National Health and Nutrition Examination Survey 2003-2006. The study participants included 6989 adults aged ≥18 years. Using survey-weighted generalized linear regression analyses, we investigated the relationship between high fructose corn syrup sweetened drink, diet soft drink consumption, and serum sodium. Consumption of high fructose corn syrup sweetened drinks and diet soft drinks was evaluated through a food-frequency questionnaire.

RESULTS

Serum sodium levels increased as high fructose corn syrup sweetened drink intake increased. Serum sodium levels were higher in participants in the highest high fructose corn syrup sweetened drink consumption quantile, compared with those in the lowest high fructose corn syrup sweetened drink intake quantile (p = 0.020). The multivariate betas for serum sodium, according to the corresponding high fructose corn syrup sweetened drink intake quantiles, were 0.16, 0.19, and 0.21, respectively (P for trend = 0.051). We found no relationship between diet soft drink consumption and serum sodium after adjustment of confounding. (multivariate P > 0.05).

CONCLUSION

There was a a step-wise increase in serum sodium concentration with increasing consumption of HFCS sweetened beverages. Even moderate HFCS sweetened soft drink intake was associated with an elevated serum sodium level - a risk factor for hypertension.

Green tea could improve elderly hypertension by modulating arterial stiffness, the activity of the renin/angiotensin/aldosterone axis, and the sodium-potassium pumps in old male rats

Hypertension is a major health problem common in the elderly people. Green tea is a popular beverage recommended in folk medicine for lowering blood pressure. However, the molecular mechanisms involved in the antihypertensive effects of green tea are not fully understood. Therefore, the aim of this study was to investigate the antihypertensive effects of green tea on high-salt diet-induced hypertension in old male rats. Forty old male rats were divided into five groups: control, hypertensive, and hypertensive-green tea (2, 4, and 6 g/kg). Heart rate (HR) and systolic blood pressure (SBP) were measured. Cardiac and renal histology were also performed. Lipid profile, NO, angiotensin II (Ang II), and aldosterone were determined, and the expression of eNOS, ATIR and ATIIR, aldosterone receptor, and Atp1a1 were measured. Green tea could significantly decrease HR and SBP, lipid profiles, renin-angiotensin II-aldosterone system activity, and Ang II signaling in kidney tissue of hypertensive rats (p < .01). It also increased Atp1a1, Nrf2, and eNOS expression along with antioxidant enzymes activity and NO concentration (p < .05) and decreased NF-ĸB and iNOS expression and IL-1β levels in the heart, kidneys, and aorta of rats with hypertension. It can be concluded that green tea can improve salt-induced blood pressure by modulating the function of the renin-angiotensin-aldosterone system, enhancing the synthesis of nitric oxide in the endothelium, increasing antioxidant activity and suppressing inflammation in the heart and kidney, improving the expression of the sodium-potassium pump, and reduction in serum lipids and glucose in aged male rats. PRACTICAL APPLICATIONS: The results of this study showed that green tea could improve hypertension in elderly rats by modulating (1) the expression of the sodium-potassium pump in the heart, kidney, and aortic tissues, (2) the activity of the renin-angiotensin II-aldosterone system in kidney, (3) enhancing antioxidant and anti-inflammatory activities in the heart, aorta, and kidneys, (4) enhancing the synthesis of nitric oxide in the endothelium, and (5) lowering lipid profile. The results of these studies show that the consumption of green tea and its products can be a good candidate for the prevention of cardiovascular diseases such as hypertension in the elderly. In addition, attention to its bioactive compounds can be considered by researchers as an independent therapeutic strategy or adjunctive therapy for the treatment of hypertension.

Stabilization of F-Actin Cytoskeleton by Paclitaxel Improves the Blastocyst Developmental Competence through P38 MAPK Activity in Porcine Embryos

Changes in F-actin distribution and cortical F-actin morphology are important for blastocyst developmental competence during embryogenesis. However, the effect of paclitaxel as a microtubule stabilizer on embryonic development in pigs remains unclear. We investigated the role of F-actin cytoskeleton stabilization via P38 MAPK activation using paclitaxel to improve the developmental potential of blastocysts in pigs. In this study, F-actin enrichment and adducin expression based on blastomere fragment rate and cytokinesis defects were investigated in cleaved embryos after in vitro fertilization (IVF). Adducin and adhesive junction F-actin fluorescence intensity were significantly reduced with increasing blastomere fragment rate in porcine embryos. In addition, porcine embryos were cultured with 10 and 100 nM paclitaxel for two days after IVF. Adhesive junction F-actin stabilization and p-P38 MAPK activity in embryos exposed to 10 nM paclitaxel increased significantly with blastocyst development competence. However, increased F-actin aggregation, cytokinesis defects, and over-expression of p-P38 MAPK protein by 100 nM paclitaxel exposure disrupted blastocyst development in porcine embryos. In addition, exposure to 100 nM paclitaxel increased the misaligned α-tubulin of spindle assembly and adhesive junction F-actin aggregation at the blastocyst stage, which might be caused by p-P38 protein over-expression-derived apoptosis in porcine embryos.

Nitric Oxide Alleviated High Salt-Induced Cardiomyocyte Apoptosis and Autophagy Independent of Blood Pressure in Rats

The present study aimed to explore whether high-salt diet (HSD) could cause cardiac damage independent of blood pressure, and whether nitric oxide (NO) could alleviate high-salt–induced cardiomyocyte apoptosis and autophagy in rats. The rats received 8% HSD in vivo. H9C2 cells or primary neonatal rat cardiomyocytes (NRCM) were treated with sodium chloride (NaCl) in vitro. The levels of cleaved-caspase 3/caspase 3, cleaved-caspase 8/caspase 8, Bax/Bcl2, LC3 II/LC3 I, Beclin-1 and autophagy related 7 (ATG7) were increased in the heart of HSD rats with hypertension (HTN), and in hypertension-prone (HP) and hypertension-resistant (HR) rats. Middle and high doses (50 and 100 mM) of NaCl increased the level of cleaved-caspase 3/caspase 3, cleaved-caspase 8/caspase 8, Bax/Bcl2, LC3 II/LC3 I, Beclin-1, and ATG7 in H9C2 cells and NRCM. The endothelial NO synthase (eNOS) level was increased, but p-eNOS level was reduced in the heart of HSD rats and H9C2 cells treated with 100 mM NaCl. The level of NO was reduced in the serum and heart of HSD rats. NO donor sodium nitroprusside (SNP) reversed the increases of cleaved-caspase 3/caspase 3, cleaved-caspase 8/caspase 8, Bax/Bcl2 induced by NaCl (100 mM) in H9C2 cells and NRCM. SNP treatment attenuated the increases of cleaved-caspase 3/caspase 3, Bax/Bcl2, LC3 II/LC3 I, Beclin-1, and ATG7 in the heart, but had no effect on the blood pressure of HSD rats with HR. These results demonstrated that HSD enhanced cardiac damage independently of blood pressure. Exogenous NO supplementarity could alleviate the high salt–induced apoptosis and autophagy in cardiomyocytes.

Leptin-induced increase in blood pressure and markers of endothelial activation during pregnancy in Sprague Dawley rats is prevented by resibufogenin, a marinobufagenin antagonist

Levels of leptin and marinobufagenin (MBG), a cardiotonic steroid, are elevated in the serum of women with pre-eclampsia. Besides this, leptin administration to pregnant rats increases systolic blood pressure (SBP), urinary protein excretion and serum markers of endothelial activation. The link between leptin and MBG is unknown and it is also unclear if leptin-induced increases in blood pressure and proteinuria in the pregnant rat could be prevented by an MBG antagonist. To ascertain this link, this study investigated the effect of resibufogenin (RBG), a marinobufagenin antagonist, on leptin-induced increases in blood pressure and proteinuria during pregnancy in rats. Four groups of Sprague-Dawley rats, aged 12 weeks, were given either normal saline (CONTROL) or 120 μg/kg/day of leptin (LEP), or 120 μg/kg/day of leptin+30 μg/kg/day of resibufogenin (L + RBG) or 30 μg/kg/day of resibufogenin (RBG) from Day 1-20 of pregnancy. Systolic blood pressure and urinary protein excretion (UPE) were measured during the study period. Animals were euthanized on day 21 of pregnancy and vascular cell adhesion molecule 1, (VCAM-1), soluble intracellular cell adhesion molecule 1 (sICAM-1), E-selectin and endothelin-1 (ET-1) were estimated in the serum. SBP, UPE, VCAM-1, sICAM-1 and ET-1 were significantly higher only in the LEP group when compared with those in CONT and in L + RBG and RBG groups. The prevention by RBG of leptin-induced increases in SBP, proteinuria, and endothelial activation during pregnancy seem to suggest a potential role for MBG in leptin-induced adverse effects on blood pressure, urinary protein excretion and endothelial activity during pregnancy in the rat.

High-Sodium Diet Has Opposing Effects on Mean Arterial Blood Pressure and Cerebral Perfusion in a Transgenic Mouse Model of Alzheimer's Disease

BACKGROUND

Cerebral ionic homeostasis impairment, especially Ca2+, has been observed in Alzheimer's disease (AD) and also with hypertension. Hypertension and AD both have been implicated in impaired cerebral autoregulation. However, the relationship between the ionic homeostasis impairment in AD and hypertension and cerebral blood flow (CBF) autoregulation is not clear.

OBJECTIVE

To test the hypothesis that a high-salt diet regimen influences the accumulation of amyloid-β (Aβand CBF) and CBF, exacerbates cognitive decline, and increases the propensity to AD.

METHODS

Double transgenic mice harboring the amyloid-β protein precursor (APPswe), and presenilin-1 (PSEN1) along with control littermates, 2 months of age at initiation of special diet, were divided into 4 groups: Group A, APP/PS1 and Group B, controls fed a high-sodium (4.00%) chow diet for 3 months; Group C, APP/PS1 and Group D, controls fed a low-sodium (0.08%) regular chow diet for 3 months. Mean arterial blood pressure (MAP) and CBF were measured noninvasively using the tail MAP measurement device and magnetic resonance imaging, respectively. Aβ plaques numbers in the cortex and hippocampus of APP/PS1 were quantified.

RESULTS

In contrary to controls, APP/PS1 mice fed a high-salt diet did not show markedly elevated mean systolic and diastolic blood pressure (134±4.8 compared with 162±2.8 mmHg, and 114±5.0 compared with 137±20 mmHg, p< 0.0001). However, a high-salt diet increased CBF in both APP/PS1 and controls and did not alter the cerebral tissue integrity. Aβ plaques were significantly reduced in the cortex and hippocampus of mice fed a high-salt diet.

CONCLUSION

These data suggest that a high-salt diet differently affects MAP and CBF in APP/PS1 mice and controls.

Role of the dysfunctional ryanodine receptor - Na(+)-Ca(2+)exchanger axis in progression of cardiovascular diseases: What we can learn from pharmacological studies?

Abnormal Ca(2+)homeostasis is often associated with chronic cardiovascular diseases, such as hypertension, heart failure or cardiac arrhythmias, and typically contributes to the basic ethiology of the disease. Pharmacological targeting of cardiac Ca(2+)handling has great therapeutic potential offering invaluable options for the prevention, slowing down the progression or suppression of the harmful outcomes like life threatening cardiac arrhythmias. In this review we outline the existing knowledge on the involvement of malfunction of the ryanodine receptor and the Na(+)-Ca(2+)exchanger in disturbances of Ca(2+)homeostasis and discuss important proof of concept pharmacological studies targeting these mechanisms in context of hypertension, heart failure, atrial fibrillation and ventricular arrhythmias. We emphasize the promising results of preclinical studies underpinning the potential benefits of the therapeutic strategies based on ryanodine receptor or Na(+)-Ca(2+)exchanger inhibition.

Effect and mechanism of Salicornia bigelovii Torr. plant salt on blood pressure in SD rats

In this paper, the effect and mechanism of Salicornia bigelovii Torr. plant salt (SPS) on blood pressure in Sprague Dawley (SD) rats were investigated. The results showed that the edible salt induced hypertension, but the SPS did not. Organ indices and Hematoxylin-Eosin (HE) staining analysis indicated that SPS had a protective effect on the kidney and liver. In comparison with the edible salt-treated group, nitric oxide (NO) content, angiotensin-II (Ang-II) and endothelin-1 (ET-1) levels in the serum of the SPS-treated group had no obvious changes, but serum creatinine concentration significantly decreased. Moreover, superoxide dismutase (SOD) and Na(+)-K(+)-ATPase activity increased while malondialdehyde (MDA) content decreased in the SPS-treated group. In conclusion, a long-term high salt intake could lead to hypertension. SPS, as a salt substitute, could increase the body's antioxidant ability to protect the kidney and liver from the damage caused by a high salt intake and effectively avoid the occurrence of hypertension.

Effects of renal Na+/Ca2+ exchanger 1 inhibitor (SEA0400) treatment on electrolytes, renal function and hemodynamics in rats

BACKGROUND

Na(+)/Ca(2+) exchanger 1 (NCX1) controls intracellular Ca(2+) concentration in various cell types. In the kidney, NCX1 is expressed mainly in the distal tubular basolateral membrane as well as in vascular smooth muscle. Tubular NCX1 is involved in Ca(2+) reabsorption, and NCX1 in renal arterioles may control intraglomerular pressure. However, the functions of renal NCX1 have not been studied in vivo. Therefore, this study examined the effects of renal NCX1 blockade on water and solute metabolism, renal function and blood pressure in rats.

METHODS

Wistar-Kyoto rats were uninephrectomized, and an osmotic mini pump was implanted to infuse the remnant kidney cortex with a specific NCX1 inhibitor, SEA0400 (SEA), or vehicle for 7 days.

RESULTS

Serum Ca(2+) concentration and urinary Ca(2+) excretion were similar between the vehicle- and SEA-treated groups. However, serum phosphate was significantly decreased by 8 % in the SEA group, with similar urinary phosphate excretion between the two groups. Systolic blood pressure was higher in the SEA group (117 ± 3 vs. 126 ± 1 mmHg, n = 9-11), with a 1.6-fold increase in plasma aldosterone concentration. However, SEA significantly reduced urinary protein excretion and the glomerular sectional area by 16 and 8 %, respectively. Similar experiment in spontaneously hypertensive rats produced different results.

CONCLUSION

Renal SEA treatment reduced serum phosphate concentration, urinary protein and glomerular size with higher systemic blood pressure compared to control Wistar-Kyoto rats. Further study on renal NCX1 may be beneficial in delineating the pathophysiology of glomerular pressure control and calcium/phosphate regulations.

Exenatide induces aortic vasodilation increasing hydrogen sulphide, carbon monoxide and nitric oxide production

Background

It has been reported that GLP-1 agonist exenatide (exendin-4) decreases blood pressure. The dose-dependent vasodilator effect of exendin-4 has previously been demonstrated, although the precise mechanism is not thoroughly described. Here we have aimed to provide in vitro evidence for the hypothesis that exenatide may decrease central (aortic) blood pressure involving three gasotransmitters, namely nitric oxide (NO) carbon monoxide (CO), and hydrogen sulphide (H₂S).

Methods

We determined the vasoactive effect of exenatide on isolated thoracic aortic rings of adult rats. Two millimetre-long vessel segments were placed in a wire myograph and preincubated with inhibitors of the enzymes producing the three gasotransmitters, with inhibitors of reactive oxygen species formation, prostaglandin synthesis, inhibitors of protein kinases, potassium channels or with an inhibitor of the Na⁺/Ca²⁺-exchanger.

Results

Exenatide caused dose-dependent relaxation of rat thoracic aorta, which was evoked via the GLP-1 receptor and was mediated mainly by H₂S but also by NO and CO. Prostaglandins and superoxide free radical also play a part in the relaxation. Inhibition of soluble guanylyl cyclase significantly diminished vasorelaxation. We found that ATP-sensitive-, voltage-gated- and calcium-activated large-conductance potassium channels are also involved in the vasodilation, but that seemingly the inhibition of the KCNQ-type voltage-gated potassium channels resulted in the most remarkable decrease in the rate of vasorelaxation. Inhibition of the Na⁺/Ca²⁺-exchanger abolished most of the vasodilation.

Conclusions

Exenatide induces vasodilation in rat thoracic aorta with the contribution of all three gasotransmitters. We provide in vitro evidence for the potential ability of exenatide to lower central (aortic) blood pressure, which could have relevant clinical importance.

A novel cell-based high-throughput screen for inhibitors of HIV-1 gene expression and budding identifies the cardiac glycosides

OBJECTIVES

Highly active antiretroviral therapy (HAART) is the mainstay of treatment for HIV-1 infection. While current HAART regimens have been extremely effective, issues of associated toxicity, cost and resistance remain and there is a need for novel antiretroviral compounds to complement the existing therapy. We sought to develop a novel high-throughput method for identifying compounds that block later steps in the life cycle not targeted by current therapy.

METHODS

We designed a high-throughput screen to identify inhibitors of post-integration steps in the HIV-1 life cycle. The screening method was applied to a library of compounds that included numerous FDA-approved small molecules.

RESULTS

Among the small molecules that inhibited late stages in HIV-1 replication were members of the cardiac glycoside family. We demonstrate that cardiac glycosides potently inhibit HIV-1 gene expression, thereby reducing the production of infectious HIV-1. We demonstrate that this inhibition is dependent upon the human Na(+)/K(+)-ATPase, but independent of cardiac glycoside-induced increases in intracellular Ca(2+).

CONCLUSIONS

We have validated a novel high-throughput screen to identify small molecule inhibitors of HIV-1 gene expression, virion assembly and budding. Using this screen, we have demonstrated that a number of FDA-approved compounds developed for other purposes potently inhibit HIV-1 replication, including the cardiac glycosides. Our work indicates that the entire cardiac glycoside family of drugs shows potential for antiretroviral drug development.

Proximal nephron

The kidney plays a fundamental role in maintaining body salt and fluid balance and blood pressure homeostasis through the actions of its proximal and distal tubular segments of nephrons. However, proximal tubules are well recognized to exert a more prominent role than distal counterparts. Proximal tubules are responsible for reabsorbing approximately 65% of filtered load and most, if not all, of filtered amino acids, glucose, solutes, and low molecular weight proteins. Proximal tubules also play a key role in regulating acid-base balance by reabsorbing approximately 80% of filtered bicarbonate. The purpose of this review article is to provide a comprehensive overview of new insights and perspectives into current understanding of proximal tubules of nephrons, with an emphasis on the ultrastructure, molecular biology, cellular and integrative physiology, and the underlying signaling transduction mechanisms. The review is divided into three closely related sections. The first section focuses on the classification of nephrons and recent perspectives on the potential role of nephron numbers in human health and diseases. The second section reviews recent research on the structural and biochemical basis of proximal tubular function. The final section provides a comprehensive overview of new insights and perspectives in the physiological regulation of proximal tubular transport by vasoactive hormones. In the latter section, attention is particularly paid to new insights and perspectives learnt from recent cloning of transporters, development of transgenic animals with knockout or knockin of a particular gene of interest, and mapping of signaling pathways using microarrays and/or physiological proteomic approaches.

Systemic hypertension: the roles of salt, vascular Na+/K+ ATPase and the endogenous glycosides, ouabain and marinobufagenin

Essential hypertension has been shown to be significantly associated with an increased risk for cardiovascular disease and is not well controlled in many patients. In a large portion of people with essential hypertension, sodium intake has been shown to play a significant role in the production of their hypertension. The mechanism through which increased sodium intake manifests hypertension is unresolved and likely multifactorial. Endogenous cardiac glycosides such as endogenous ouabain (EO) and marinobufagenin have been proposed to play a role in salt-sensitive essential hypertension through their inhibition of Na/K ATPase (NKA). The normal function of the NKA pump is to extrude Na from the intracellular environment and import K. Blocking the NKA disrupts its normal maintenance function. EO is proposed to produce alteration in smooth muscle cell contractility by inhibiting the α2-isoform of NKA, altering Na in a microdomain of the cell. In this region of the plasma membrane the α2-isoform of the NKA colocalizes with another transmembrane protein, the Na/Ca exchanger (NCX). The normal function of NCX is to extrude Ca and import Na. Inhibition of NKA produces an increase in Na within the microdomain, which in turn alters the function of the NCX so that less Ca is extruded, leading to increased intracellular Ca and increased vascular contraction. EO has been shown to be synthesized and secreted by the adrenal cortex in response to chronically elevated sodium intake. The levels of EO have been shown to be significantly elevated in 40% of all untreated hypertensive patients. Marinobufagenin, another cardiac glycoside, has also been implicated as a possible cause of essential hypertension through its preferential inhibition of the α1-isoform of NKA. Antagonism of the endogenous inhibitors of NKA is currently a target of clinical research for the development of innovative antihypertensive treatments.

Hypoxic Pulmonary Vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Developmental origins of health and disease: experimental and human evidence of fetal programming for metabolic syndrome

The concept of developmental origins of health and disease has been defined as the process through which the environment encountered before birth, or in infancy, shapes the long-term control of tissue physiology and homeostasis. The evidence for programming derives from a large number of experimental and epidemiological observations. Several nutritional interventions during diverse phases of pregnancy and lactation in rodents are associated with fetal and neonatal programming for metabolic syndrome. In this paper, recent experimental models and human epidemiological studies providing evidence for the fetal programming associated with the development of metabolic syndrome and related diseases are revisited.

Attenuated renal vascular responses to acute angiotensin II infusion in smooth muscle-specific Na+/Ca2+ exchanger knockout mice

Recent studies in smooth muscle-specific Na(+)/Ca(2+) exchanger-1 knockout (NCX1(sm-/-)) mice reveal reduced arterial pressure and impaired myogenic responses compared with heterozygous littermates. In this study, we determined renal function in male anesthetized NCX1(sm-/-) mice and NCX1 heterozygous (NCX1(+/-)) littermates before and during acute ANG II infusions. Systolic blood pressure in awake mice was lower in NCX1(sm-/-) mice compared with NCX1(+/-) mice (119 ± 4 vs. 131 ± 3 mmHg, P < 0.05). Acute ANG II infusions (5 ng·min(-1)·g(-1) body wt) increased mean arterial pressure in anesthetized NCX1(+/-) (109 ± 2 to 134 ± 3 mmHg, P < 0.001, n = 8) and NCX1(sm-/-) (101 ± 8 to 129 ± 8 mmHg, P < 0.01, n = 6) mice to a similar extent (Δ25 ± 1 vs. Δ28 ± 4 mmHg, P > 0.05). In response to ANG II infusions, PAH clearance (C(PAH)) decreased from 1.39 ± 0.27 to 0.98 ± 0.22 ml·min(-1)·g(-1) (P < 0.05) and glomerular filtration rate (GFR) was reduced from 0.50 ± 0.09 to 0.32 ± 0.06 ml·min(-1)·g(-1) (P < 0.05) in NCX1(+/-) mice. In contrast, the NCX1(sm-/-) did not exhibit significant reductions in either C(PAH) (1.16 ± 0.30 to 1.22 ± 0.34 ml·min(-1)·g(-1), P > 0.05) or GFR (0.48 ± 0.08 to 0.41 ± 0.05 ml·min(-1)·g(-1), P > 0.05) during acute ANG II infusions. Using flometry to measure renal blood flow continuously, NCX1(sm-/-) mice had significantly attenuated responses to ANG II infusions (-34.2 ± 3.9%, P < 0.05) compared with those in NCX1(+/-) mice (-48 ± 2%) or in wild-type mice (-69 ± 7%). These data indicate that renal vascular responses to ANG II are attenuated in NCX1(sm-/-) mice compared with NCX1(+/-) mice and that NCX1 contributes to the renal vasoconstriction response to acute ANG II infusions.

Peritubular membrane potential in kidney proximal tubular cells of spontaneously hypertensive rats

Peritubular membrane potential in kidney proximal tubular cells of spontaneously hypertensive rats (SHR-Okamoto strain adult rats) was measured with conventional 3 mol KCl microelectrodes, in vivo. Peritubular cell membrane potential was not different in SHR (-66.5 ± 0.7 mV) as compared with normotensive control Wistar rats (-67.5 ± 1.2 mV). To test the effects of possible altered sodium membrane transport in SHR on proximal tubule peritubular membrane potential, we allowed SHR and control rats to drink 1% NaCl for two weeks. Again, proximal tubule peritubular membrane potential was not different in SHR on 1% NaCl (-67.0 ± 1.0 mV) as compared with control rats on 1% NaCl (-64.7 ± 1.3 mV). From these results we concluded that peritubular membrane potential in kidney proximal tubular cells of SHR was not different from normotensive Wistar control rats, and if some alteration of sodium transport in kidney proximal tubular cells of SHR could exist, that was not possible to evaluate from the measurements of peritubular membrane potential in kidney proximal tubular cells.

Cigarette smoke elicits relaxation of renal arteries

BACKGROUND

Epidemiological studies suggest that cigarette smoking - probably by eliciting hyperperfusion - increases glomerular filtration rate; thus, we hypothesized that cigarette smoke affects the vasomotor tone of renal arteries.

MATERIALS AND METHODS

Acute changes in the resistance index of a segmental renal artery were measured in healthy individuals during smoking. In addition, the effects of water-soluble components of cigarette smoke on the isometric tension of isolated rat renal arteries were investigated in various conditions.

RESULTS

In humans, cigarette smoking transiently reduced the resistance index of the renal artery segments (83·25 ± 5·67% of the baseline, P < 0·05). In the experimental model, water-soluble components of cigarette smoke (wCS) - either nicotinic or nicotine-free - elicited dose-dependent relaxations of rat isolated renal arteries (1% solution of nicotinic wCS: 41·18 ± 14·86% relaxation, 5% nicotinic wCS: 79·28 ± 8·91% relaxation, 10% nicotinic wCS 90·3 ± 6·1% relaxation, P < 0·05), which were not affected by removal of the endothelium, or by the soluble guanylate cyclase inhibitor oxadiazolo-quinoxalin-1, or the non specific potassium channel blocker tetraethylammonium, or the K(ATP) channel blocker glibenclamide. However, relaxations were reduced by catalase (1000 U mL⁻¹ catalase + 5% nicotinic wCS: 49·71 ± 18·4%, P < 0·05) and enhanced by superoxide dismutase (200 U mL⁻¹ SOD + 5% nicotinic wCS: 95·7 ± 2·3%, P < 0·05).

CONCLUSIONS

On the basis of these findings, we propose that cigarette smoking could contribute to the increased glomerular filtration rate observed in healthy smokers. In addition, cigarette smoke via hydrogen peroxide mediation reduces vasomotor tone of renal arteries, which could lead to hyperperfusion of kidneys.

Effects of strictosamide on mouse brain and kidney Na+, K+-ATPase and Mg2+-ATPase activities

Present study reports on the general bioactivity of strictosamide and on its effects on Na(+),K(+)-ATPase and Mg(2+)-ATPase activities of Charles River male mouse. Strictosamide is the main glycoalkaloid of Sarcocephalus latifolius (Rubiaceae) leaves and roots, used as medicinal plant in folk medicine. In this work, we studied the in vitro effects of various concentrations of strictosamide (0.25, 0.5, 1 or 2 mg/mL) and the in vivo effects of single doses (50, 100 or 200 mg/kg, i.p.) of this compound on kidney and brain Na(+),K(+)-ATPase and Mg(2+)-ATPase activities. Results of general study showed that strictosamide is slightly toxic to Charles River mouse (LD(50)=723.17 mg/kg), producing CNS depression and kidney toxicity, but the exact mechanism of these effects could not be defined. Strictosamide inhibited the in vitro and in vivo Mg(2+)-ATPase activity on kidney but had nonsignificant effect on brain. Furthermore, strictosamide had nonsignificant in vitro and in vivo effect on kidney Na(+),K(+)-ATPase activity but produced an in vivo increase of Na(+),K(+)-ATPase activity of brain, these findings suggesting that strictosamine may be related to the induction of alpha(2) isoform of Na(+),K(+)-ATPase and may account for the folk use of Sarcocephalus latifolius root infusion on hypertension.

Peripheral Resistance Modulates the Response to Volume Overload in Peritoneal Dialysis Patients

Background

Volume overload is thought to be the most important cause of hypertension in peritoneal dialysis (PD) patients. However, there is also evidence that normalization of volume overload is not always accompanied by a drop in blood pressure (BP). In the present study, we hypothesized that dysregulation of peripheral resistance due to endothelial dysfunction would constitute an important determinant of BP response in overhydrated PD patients.

Methods

We performed an observational, prospective cohort study including all prevalent PD patients at the Peking University Third Hospital between 1 June 2006 and 30 November 2006. After baseline measurements, including echocardiography and bioelectrical impedance analysis, patients fulfilling inclusion criteria were reevaluated after 2 months of follow-up. All patients that exhibited significant changes in BP and extracellular water (ECW) between 2 visits were asked to undergo a second ultrasound. These patients were then divided into group A (parallel change between BP and ECW; n = 12) and group B (paradoxical change between BP and ECW; n = 10).

Results

The cohort included 22 patients (13 males) with a mean age of 59 ± 13 years, on dialysis for 23.3 ± 32.6 months. There were no baseline differences between groups A and B. However, while patients in group A significantly increased their cardiac output, total peripheral resistance remained stable. In group B, cardiac output did not change significantly but total peripheral resistance decreased significantly.

Conclusion

In PD patients, a significant increase in fluid volume is not necessarily linked to a significant increase in BP. Rather, the change in total peripheral resistance was found to be the most important determinant of the extent to which increased fluid volume affected BP.

Functional linkage of Na+-Ca2+-exchanger to sarco/endoplasmic reticulum Ca2+ pump in coronary artery: comparison of smooth muscle and endothelial cells

An increase in cytosolic Ca(2+) concentration in coronary artery smooth muscle causes a contraction but in endothelium it causes relaxation. Na(+)-Ca(2+)-exchanger (NCX) may play a role in Ca(2+) dynamics in both the cell types. Here, the NCX-mediated (45)Ca(2+) uptake was compared in Na(+)-loaded pig coronary artery smooth muscle and endothelial cells. In both the cell types, this uptake was inhibited by KB-R7943, SEA 0400 and by monensin, but not by cariporide. Prior loading of the cells with the Ca(2+) chelator BAPTA increased the NCX-mediated (45)Ca(2+) uptake in smooth muscle but not in endothelial cells. In the presence or absence of BAPTA loading, the Na(+)-mediated (45)Ca(2+) uptake was greater in endothelial than in smooth muscle cells. In smooth muscle cells without BAPTA loading, thapsigargin diminished the NCX-mediated (45)Ca(2+) entry. This effect was not observed in endothelial cells or in either cell type after BAPTA loading. The results in the smooth muscle cells are consistent with a limited diffusional space model in which the NCX-mediated (45)Ca(2+) uptake was enhanced by chelation of cytosolic Ca(2+) or by its sequestration by the sarco/endoplasmic reticulum Ca(2+) pump (SERCA). They suggest a functional linkage between NCX and SERCA in the smooth muscle but not in the endothelial cells. The concept of a linkage between NCX and SERCA in smooth muscle was also confirmed by similar distribution of NCX and SERCA2 proteins when detergent-treated microsomes were fractionated by flotation on sucrose density gradients. Thus, the coronary artery smooth muscle and endothelial cells differ not only in the relative activities of NCX but also in its functional linkage to SERCA.

A role for benzamil-sensitive proteins of the central nervous system in the pathogenesis of salt-dependent hypertension

1. Although increasing evidence suggests that salt-sensitive hypertension is a disorder of the central nervous system (CNS), little is known about the critical proteins (e.g. ion channels or exchangers) that play a role in the pathogenesis of the disease. 2. Central pathways involved in the regulation of arterial pressure have been investigated. In addition, systems such as the renin-angiotensin-aldosterone axis, initially characterized in the periphery, are present in the CNS and seem to play a role in the regulation of arterial pressure. 3. Central administration of amiloride, or its analogue benzamil hydrochloride, has been shown to attenuate several forms of salt-sensitive hypertension. In addition, intracerebroventricular (i.c.v.) benzamil effectively blocks pressor responses to acute osmotic stimuli, such as i.c.v. hypertonic saline. Amiloride or its analogues have been shown to interact with the brain renin-angiotensin-aldosterone system (RAAS) and to effect the expression of endogenous ouabain-like compounds. Alterations of brain RAAS function and/or endobain expression could play a role in the interaction between amiloride compounds and arterial pressure. Peripheral treatments with benzamil, even at higher doses than those given centrally, have little or no effect on arterial pressure. These data provide strong evidence that benzamil-sensitive proteins (BSPs) of the CNS play a role in cardiovascular responsiveness to sodium. 4. Mineralocorticoids have been linked to human hypertension; many patients with essential hypertension respond well to pharmacological agents antagonizing the mineralocorticoid receptor and certain genetic forms of hypertension are caused by chronically elevated levels of aldosterone. The deoxycorticosterone acetate (DOCA)-salt model of hypertension is a benzamil-sensitive model that incorporates several factors implicated in the aetiology of human disease, including mineralocorticoid action and increased dietary sodium. The DOCA-salt model is ideal for investigating the role of BSPs in the pathogenesis of hypertension, because mineralocorticoid action has been shown to modulate the activity of at least one benzamil-sensitive protein, namely the epithelial sodium channel. 5. Characterizing the BSPs involved in the pathogenesis of hypertension may provide a novel clinical target. Further studies are necessary to determine which BSPs are involved and where, in the nervous system, they are located.

Hypothetical mechanism of sodium pump regulation by estradiol under primary hypertension

Causal relationship between sodium and hypertension has been proposed and various changes in Na+,K+-ATPase (sodium pump) activity have been described in established primary hypertension. A number of direct vascular effects of estradiol have been reported, including its impact on the regulation of sodium pump activity and vasomotor tone. The effects of estradiol involve the activation of multiple signaling cascades, including phosphatydil inositol-3 kinase (PI3K) and p42/44 mitogen-activated protein kinase (p42/44(MAPK)). In addition, some of the effects of estradiol have been linked to activity of cytosolic phospholipase A(2) (cPLA(2)). One possible cardioprotective mechanism of estradiol involves of the interaction between estradiol and the rennin-angiotensin system (RAS). Elevated circulating and tissue levels of angiotensin II (Ang II) have been implicated in the development of hypertension and heart failure. The aim of our investigation was to elucidate the signaling mechanisms employed by estradiol and Ang II in mediating sodium pump, in vascular smooth muscle cells (VSMC). The aim of our investigation was to elucidate the signaling mechanisms employed by estradiol and Ang II in mediating sodium pump activity/expression in VSMC, with particular emphasis on PI3K/cPLA(2)/p42/44(MAPK) signaling pathways. Our primary hypothesis is that estradiol stimulates sodium pump activity/expression in VSMC via PI3K/cPLA(2)/p42/44(MAPK) dependent mechanism and, that impaired estradiol-stimulated sodium pump activity/expression in hypertensive rodent models (i.e. SHR), Ang II-mediated vascular impairment of estradiol is related to a decrease ability of estradiol to stimulate the PI3K/cPLA(2)/p42/44(MAPK) signaling pathways. An important corollary to this hypothesis is that in hypertensive state (i.e. SHR rats) the decreasing in ACE enzyme activity and/or AT1 receptor expression caused by administration of estradiol is accompanying with abrogated ability of Ang II to decrease IRS-1/PI3K association, and consequent PI3K/cPLA(2)/p42/44(MAPK) activity and associated sodium pump activity/expression. A clear characterization of how Ang II attenuates estradiol signaling may lead to a better understanding of the molecular mechanism(s) underlying pathophysiological conditions such as hypertension and to understanding how certain pathophysiological situations affect sodium pump activity/expression in VSMC.

Ouabain modulation of cellular calcium stores and signaling

Ouabain-like factors modulate intracellular Ca2+ concentrations and Ca2+ stores. Recently, a role for Na+-K+-ATPase Na+ transport inhibition as a pivotal event in ouabain signaling was questioned (Kaunitz JD. Am J Physiol Renal Physiol 290: F995–F996, 2006). In the present study, we used a mathematical model of Ca2+ trafficking in cytoplasm and subplasmalemmal microdomains to simulate the pathways through which ouabain can affect Ca2+ signaling: inhibition of active transport by Na+-K+-ATPase α1- and α2-isoforms, activation of inositol trisphosphate (IP3) production, and increased IP3 receptor (IP3R) conductance. A fundamental prediction is that Na+-K+-ATPase inhibition favors sarcoplasmic reticulum Ca2+ store loading, whereas Src-mediated increases in IP3 production and IP3R sensitization favor store depletion. The model predicts that α2-isoform inhibition generates a peak-and-plateau pattern of cytosolic Ca2+ concentration ([Ca2+]cyt) elevation, whereas α1-isoform inhibition yields a monophasic rise. The effects of ouabain-mediated increases in IP3 production or IP3R conductance on [Ca2+]cyt depend on their relative distributions between cellular microdomains and the bulk cytoplasm. Simulations suggest that the intracellular localization of IP3 production is a pivotal determinant of the changes in compartmental Ca2+ concentrations that can be induced by ouabain. As a consequence of sequestration of the ouabain-sensitive α2-isoform into microdomains, inhibition of the α2-isoform in rodents is not predicted to significantly affect cytosolic Na+ concentration. Model simulations support the hypothesis that ouabain can enhance agonist-evoked [Ca2+]cyt transients when its predominant effect is to inhibit α2-isoform Na+ transport and, thereby, increase Ca2+ loading into sarcoplasmic reticulum stores.

Sodium and asthma: something borrowed, something new?

Some early studies have called attention to the potential contribution of sodium (both dietary and serum levels) in airway-related disease, although the picture was not entirely clear. Two recent developments may now allow a more careful consideration of this: first, the greatly improved understanding of the role of salt in hypertension (particularly the identification of subgroups of salt-sensitive individuals within the general population), and second, the recent discovery of the role of the Na(+)/Ca(2+) exchanger in smooth muscle function. Here, we first review those two developments and then apply them to airway smooth muscle and asthma.

Transgenic mice expressing Na+-K+-ATPase in smooth muscle decreases blood pressure

The Na(+)-K(+)-ATPase (NKA) is a transmembrane protein that sets and maintains the electrochemical gradient by extruding three Na(+) in exchange for two K(+). An important physiological role proposed for vascular smooth muscle NKA is the regulation of blood pressure via modulation of vascular smooth muscle contractility (5). To investigate the relations between the level of NKA in smooth muscle and blood pressure, we developed mice carrying a transgene for either the NKA alpha(1)- or alpha(2)-isoform (alpha(1 sm+) or alpha(2 sm+) mice) driven by the smooth muscle-specific alpha-actin promoter SMP8. Interestingly, both alpha-isoforms, the one contained in the transgene and the one not contained, were increased to a similar degree at both protein and mRNA levels. The total alpha-isoform protein was increased from 1.5-fold (alpha(1 sm+) mice) to 7-fold (alpha(2 sm+) mice). The increase in total NKA alpha-isoform protein was accompanied by a 2.5-fold increase in NKA activity in alpha(2 sm+) gastric antrum. Immunocytochemistry of the alpha(1)- and alpha(2)-isoforms in alpha(2 sm+) aortic smooth muscle cells indicated that alpha-isoform distributions were similar to those shown in wild-type cells. alpha(2 sm+) Mice (high expression) were hypotensive (109.9 +/- 1.6 vs. 121.3 +/- 1.4 mmHg; n = 13 and 11, respectively), whereas alpha(1 sm+) mice (low expression) were normotensive (122.7 +/- 2.5 vs. 117.4 +/- 2.3; n = 11 or 12). alpha(2 sm+) Aorta, but not alpha(1 sm+) aorta, relaxed faster from a KCl-induced contraction than wild-type aorta. Our results show that smooth muscle displays unique coordinate expression of the alpha-isoforms. Increasing smooth muscle NKA decreases blood pressure and is dependent on the degree of increased alpha-isoform expression.