The Role of Aldosterone in Renal Sodium Transport

Control of sodium appetite by hindbrain aldosterone-sensitive neurons

Mineralocorticoids play a key role in hydromineral balance by regulating sodium retention and potassium wasting. Through favoring sodium, mineralocorticoids can cause hypertension from fluid overload under conditions of hyperaldosteronism, such as aldosterone-secreting tumors. An often-overlooked mechanism by which aldosterone functions to increase sodium is through stimulation of salt appetite. To drive sodium intake, aldosterone targets neurons in the hindbrain which uniquely express 11β-hydroxysteroid dehydrogenase type 2 (HSD2). This enzyme is a necessary precondition for aldosterone-sensing cells as it metabolizes glucocorticoids - preventing their activation of the mineralocorticoid receptor. In this review, we will consider the role of hindbrain HSD2 neurons in regulating sodium appetite by discussing HSD2 expression in the brain, regulation of hindbrain HSD2 neuron activity, and the circuitry mediating the effects of these aldosterone-sensitive neurons. Reducing the activity of hindbrain HSD2 neurons may be a viable strategy to reduce sodium intake and cardiovascular risk, particularly for conditions of hyperaldosteronism.

Paradoxes in magnesium transport in type 1 Bartter's syndrome and Gitelman's syndrome: a modeling analysis

Type 1 Bartter's syndrome and Gitelman's syndrome are characterized by mutations in two key renal Na+ transporters, Na-K-2Cl cotransporter (NKCC2) and Na-Cl cotransporter (NCC). Since these two transporters play an important role in regulating magnesium (Mg2+) and calcium (Ca2+) transport in the kidney, significant alterations in the transport of these two electrolytes are observed in type 1 Bartter's syndrome and Gitelman's syndrome. In this study, we used our sex-specific computational models of renal electrolyte transport in rats to understand the complex compensatory mechanisms, in terms of alterations in tubular dimensions and ion transporter activities, that lead to Mg2+ and Ca2+ preservation or wasting in these two genetic disorders. Given the sexual dimorphism in renal transporter patterns, we also assessed how the magnitude of these alterations may differ between males and females. Model simulations showed that in type 1 Bartter's syndrome, nephron adaptations prevent salt wasting and favor Mg2+ preservation but not Ca2+, whereas in Gitelman's syndrome, those adaptations favor Ca2+ preservation over Mg2+. In addition, our models predicted that the compensatory alterations in tubular dimensions and ion transporter activities are stronger in females than in males.NEW & NOTEWORTHY Although changes in Ca2+ excretion in type 1 Bartter's syndrome and Gitelman's syndrome are well understood, Mg2+ excretion displays an interesting paradox. This computational modeling study provides insights into how renal adaptations in these two disorders impact Ca2+ and Mg2+ transport along different nephron segments. Model simulations showed that nephron adaptations favor Mg2+ preservation over Ca2+ in Bartter's syndrome and Ca2+ preservation over Mg2+ in Gitelman's syndrome and are stronger in females than in males.

Identifying KCNJ5 Mutation in Aldosterone-Producing Adenoma Patients With Baseline Characteristics Using Machine Learning Technology

Background

Primary aldosteronism is characterized by inappropriate aldosterone production, and unilateral aldosterone-producing adenoma (uPA) is a common type of PA. KCNJ5 mutation is a protective factor in uPA; however, there is no preoperative approach to detect KCNJ5 mutation in patients with uPA.

Objectives

This study aimed to provide a personalized surgical recommendation that enables more confidence in advising patients to pursue surgical treatment.

Methods

We enrolled 328 patients with uPA harboring KCNJ5 mutations (n = 158) or not (n = 170) who had undergone adrenalectomy. Eighty-seven features were collected, including demographics, various blood and urine test results, and clinical comorbidities. We designed 2 versions of the prediction model: one for institutes with complete blood tests (full version), and the other for institutes that may not be equipped with comprehensive testing facilities (condensed version).

Results

The results show that in the full version, the Light Gradient Boosting Machine outperformed other classifiers, achieving area under the curve and accuracy values of 0.905 and 0.864, respectively. The Light Gradient Boosting Machine also showed excellent performance in the condensed version, achieving area under the curve and accuracy values of 0.867 and 0.803, respectively.

Conclusions

We simplified the preoperative diagnosis of KCNJ5 mutations successfully using machine learning. The proposed lightweight tool that requires only baseline characteristics and blood/urine test results can be widely applied and can aid personalized prediction during preoperative counseling for patients with uPA.

Bioinformatic analysis of biological pathways in coronary heart disease and Alzheimer’s disease

Aim. Using bioinformatic tools, to perform a pathway enrichment analysis in Alzheimer’s disease and coronary heart disease (CHD).

Materials and methods. Genes contributing to susceptibility to CHD and Alzheimer’s disease were obtained from the public database DisGeNET (Database of Gene – Disease Associations). A pathway enrichment analysis was performed in the ClueGO Cytoscape plug-in (version 3.6.0) using hypergeometric distribution and the KEGG and Reactome databases.

Results. The identified genes contributing to susceptibility to Alzheimer’s disease and CHD are included in 69 common signaling pathways, grouped into the following subgroups: cell death signaling pathways (1); signaling pathways regulating immune responses (2); signaling pathways responsible for fatty acid metabolism (3); signaling pathways involved in the functioning of the nervous system (4), cardiovascular system (5), and endocrine system (6).

Conclusion. Following the performed analysis, we identified possible associations between processes involving genetic factors and their products in CHD and Alzheimer’s disease. In particular, we assumed that susceptibility genes involved in the implementation of these pathways regulate apoptosis, production of inflammatory cytokines and chemokines, lipid metabolism, β-amyloid formation, and angiogenesis.

Understanding the Pathobiology of Pulmonary Hypertension Due to Left Heart Disease

The development of pulmonary hypertension (PH) is common and has adverse prognostic implications in patients with heart failure due to left heart disease (LHD), and thus far, there are no known treatments specifically for PH-LHD, also known as group 2 PH. Diagnostic thresholds for PH-LHD, and clinical classification of PH-LHD phenotypes, continue to evolve and, therefore, present a challenge for basic and translational scientists actively investigating PH-LHD in the preclinical setting. Furthermore, the pathobiology of PH-LHD is not well understood, although pulmonary vascular remodeling is thought to result from (1) increased wall stress due to increased left atrial pressures; (2) hemodynamic congestion-induced decreased shear stress in the pulmonary vascular bed; (3) comorbidity-induced endothelial dysfunction with direct injury to the pulmonary microvasculature; and (4) superimposed pulmonary arterial hypertension risk factors. To ultimately be able to modify disease, either by prevention or treatment, a better understanding of the various drivers of PH-LHD, including endothelial dysfunction, abnormalities in vascular tone, platelet aggregation, inflammation, adipocytokines, and systemic complications (including splanchnic congestion and lymphatic dysfunction) must be further investigated. Here, we review the diagnostic criteria and various hemodynamic phenotypes of PH-LHD, the potential biological mechanisms underlying this disorder, and pressing questions yet to be answered about the pathobiology of PH-LHD.

Machine learning based models for prediction of subtype diagnosis of primary aldosteronism using blood test

Primary aldosteronism (PA) is associated with an increased risk of cardiometabolic diseases, especially in unilateral subtype. Despite its high prevalence, the case detection rate of PA is limited, partly because of no clinical models available in general practice to identify patients highly suspicious of unilateral subtype of PA, who should be referred to specialized centers. The aim of this retrospective cross-sectional study was to develop a predictive model for subtype diagnosis of PA based on machine learning methods using clinical data available in general practice. Overall, 91 patients with unilateral and 138 patients with bilateral PA were randomly assigned to the training and test cohorts. Four supervised machine learning classifiers; logistic regression, support vector machines, random forests (RF), and gradient boosting decision trees, were used to develop predictive models from 21 clinical variables. The accuracy and the area under the receiver operating characteristic curve (AUC) for predicting of subtype diagnosis of PA in the test cohort were compared among the optimized classifiers. Of the four classifiers, the accuracy and AUC were highest in RF, with 95.7% and 0.990, respectively. Serum potassium, plasma aldosterone, and serum sodium levels were highlighted as important variables in this model. For feature-selected RF with the three variables, the accuracy and AUC were 89.1% and 0.950, respectively. With an independent external PA cohort, we confirmed a similar accuracy for feature-selected RF (accuracy: 85.1%). Machine learning models developed using blood test can help predict subtype diagnosis of PA in general practice.

Selenoproteins and renal programming in metabolic syndrome-exposed rat offspring

Maternal metabolic syndrome (MS) during gestation and lactation leads to several cardiometabolic changes related to selenium (Se) status and selenoprotein expression in offspring. However, little is known about kidney programming and antioxidant selenoprotein status in MS pups. To gain more knowledge on this subject, two experimental groups of dam rats were used: Control (Se: 0.1 ppm) and MS (fructose 65% and Se: 0.1 ppm). At the end of lactation, Se deposits in kidneys, selenoprotein expression (GPx1, GPx3, GPx4 and selenoprotein P), oxidative balance and AMP-activated protein kinase (AMPK) and activated transcriptional factor NF-κB expression were measured. Kidney functional parameters, albuminuria, creatinine clearance, aldosteronemia, and water and electrolyte balance, were also evaluated. One week later systolic blood pressure was measured. Lipid peroxidation takes place in the kidneys of MS pups and Se, selenoproteins and NF-κB expression increased, while AMPK activation decreased. MS pups have albuminuria and low creatinine clearance which implies glomerular renal impairment with protein loss. They also present hypernatremia and hyperaldosteronemia, together with a high renal Na⁺ reabsorption, leading to a hypertensive status, which was detected in these animals one week later. Since these alterations seem to be related, at least in part, to oxidative stress, the increase in Se and selenoproteins found in the kidneys of these pups seems to be beneficial, avoiding a higher lipid oxidation. However, in order to analyze the possible global beneficial role of Se in kidneys during MS exposure, more data are necessary to document the relationships between GPx4 and NF-κB, and SelP and AMPK in kidneys.

Aldosterone nongenomically induces angiotensin II receptor dimerization in rat kidney: role of mineralocorticoid receptor and NADPH oxidase

INTRODUCTION

Previous in vitro studies demonstrated that aldosterone nongenomically induces transglutaminase (TG) and reactive oxygen species (ROS), which enhanced angiotensin II receptor (ATR) dimerization. There are no in vivo data in the kidney.

MATERIAL AND METHODS

Male Wistar rats were intraperitoneally injected with normal saline solution, or aldosterone (Aldo: 150 μg/kg BW); or received pretreatment with eplerenone (mineralocorticoid receptor (MR) blocker, Ep. + Aldo), or with apocynin (nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, Apo. + Aldo) 30 min before aldosterone. Thirty minutes after aldosterone injection, protein abundances of dimeric and monomeric forms of AT₁R and AT₂R, and protein abundances and localizations of TG2 and p47phox, a cytosolic subunit of NADPH oxidase, were determined by Western blot analysis and immunohistochemistry, respectively.

RESULTS

Protein abundances of dimeric forms of AT₁R and AT₂R were enhanced by 170% and 70%, respectively. Apocynin could block dimeric forms of both receptors while eplerenone inhibited only AT₂R. Monomeric protein levels of both receptors were maintained. Aldosterone significantly enhanced TG2 and p47phox protein abundances, which were blunted by eplerenone or apocynin. Aldosterone stimulated p47phox protein expression in both the cortex and the medulla while TG2 was induced mostly in the medulla. Eplerenone or apocynin normalized the immunoreactivity of both TG2 and p47phox.

CONCLUSIONS

This is the first in vivo study demonstrating that aldosterone nongenomically increases renal TG2 and p47phox protein expression and then activates AT₁R and AT₂R dimerizations. Aldosterone-stimulated AT₁R and AT₂R dimerizations are mediated through activation of NADPH oxidase. Aldosterone-induced AT₁R dimer formation is an MR-independent pathway, whereas the formation of AT₂R dimer is modulated in an MR-dependent manner.

An association between differential expression and genetic divergence in the Patagonian olive mouse (Abrothrix olivacea)

Recent molecular studies have found striking differences between desert-adapted species and model mammals regarding water conservation. In particular, aquaporin 4, a classical gene involved in water regulation of model species, is absent or not expressed in the kidneys of desert-adapted species. To further understand the molecular response to water availability, we studied the Patagonian olive mouse Abrothrix olivacea, a species with an unusually broad ecological tolerance that exhibits a great urine concentration capability. The species is able to occupy both the arid Patagonian steppe and the Valdivian and Magellanic forests. We sampled 95 olive mouse specimens from four localities (two in the steppe and two in the forests) and analysed both phenotypic variables and transcriptomic data to investigate the response of this species to the contrasting environmental conditions. The relative size of the kidney and the ratio of urine to plasma concentrations were, as expected, negatively correlated with annual rainfall. Expression analyses uncovered nearly 3,000 genes that were differentially expressed between steppe and forest samples and indicated that this species resorts to the "classical" gene pathways for water regulation. Differential expression across biomes also involves genes that involved in immune and detoxification functions. Overall, genes that were differentially expressed showed a slight tendency to be more divergent and to display an excess of intermediate allele frequencies, relative to the remaining loci. Our results indicate that both differential expression in pathways involved in water conservation and geographical allelic variation are important in the occupation of contrasting habitats by the Patagonian olive mouse.

Characteristics of hypertension in premature infants with and without chronic lung disease: a long-term multi-center study

BACKGROUND

Many causes for neonatal hypertension in premature infants have been described; however in some cases no etiology can be attributed. Our objectives are to describe such cases of unexplained hypertension and to compare hypertensive infants with and without chronic lung disease (CLD).

METHODS

We reviewed all cases of hypertension in premature infants referred from 18 hospitals over 16 years. Inclusion criteria were hypertension occurring at <6 months of age and birth at <37 weeks gestation; the main exclusion criterion was known secondary hypertension. Continuous variables were compared using analysis of variance. Nominal variables were compared using chi-square tests.

RESULTS

A total of 97 infants met the inclusion criteria, of whom 37 had CLD. Among these infants, hypertension presented at a mean of 11.3 ± 3.2 chronological weeks of age and a postmenstrual age of 39.6 ± 3.6 weeks. Diagnostic testing was notable for plasma renin activity (PRA) being <11 ng/mL/h in 98% of hypertensive infants. Spironolactone was effective monotherapy in 51 of 56 cases of hypertension. Hypertension resolved in all infants, with an average treatment duration of 25 weeks. Significant differences between the two groups of infants were a 0.4 kg lower birthweight and a 2.5 weeks younger gestational age at birth in those with CLD (p < 0.01, p < 0.01, respectively). Hypertension presented in those with CLD 1.8 weeks later, but at the same postmenstrual age as those without CLD (p < 0.01, p = 0.45, respectively).

CONCLUSION

Premature infants with unexplained hypertension, with and without CLD, presented at a postmenstrual age of 40 weeks with low PRA, transient time course, and a favorable response to spironolactone treatment.

The Renal Pathology of Obesity

Obesity causes various structural, hemodynamic, and metabolic alterations in the kidney. Most of these are likely to be compensatory responses to the systemic increase in metabolic demand that is seen with obesity. In some cases, however, renal injury becomes clinically apparent as a result of compensatory failure. Obesity-related glomerulopathy is the best known of such disease states. Factors that may sensitize obese individuals to renal compensatory failure and associated injury include the severity and number of obesity-associated conditions or complications, including components of metabolic syndrome, and the mismatch of body size to nephron mass, due to nephron reductions of congenital or acquired origin.

Perinatal DDT Exposure Induces Hypertension and Cardiac Hypertrophy in Adult Mice

BACKGROUND

Dichlorodiphenyltrichloroethane (DDT) was used extensively to control malaria, typhus, body lice, and bubonic plague worldwide, until countries began restricting its use in the 1970s. However, the use of DDT to control vector-borne diseases continues in developing countries. Prenatal DDT exposure is associated with elevated blood pressure in humans.

OBJECTIVE

We hypothesized that perinatal DDT exposure causes hypertension in adult mice.

METHODS

DDT was administered to C57BL/6J dams from gestational day 11.5 to postnatal day 5. Blood pressure (BP) and myocardial wall thickness were measured in male and female adult offspring. Adult mice were treated with an angiotensin converting enzyme (ACE) inhibitor, captopril, to evaluate sensitivity to amelioration of DDT-associated hypertension by ACE inhibition. We further assessed the influence of DDT exposure on the expression of mRNAs that regulate BP through renal ion transport.

RESULTS

Adult mice perinatally exposed to DDT exhibited chronically increased systolic BP, increased myocardial wall thickness, and elevated expression of mRNAs of several renal ion transporters. Captopril completely reversed hypertension in mice perinatally exposed to DDT.

CONCLUSIONS

These data demonstrate that perinatal exposure to DDT causes hypertension and cardiac hypertrophy in adult offspring. A key mechanism underpinning this hypertension is an overactivated renin angiotensin system because ACE inhibition reverses the hypertension induced by perinatal DDT exposure. Citation: La Merrill M, Sethi S, Benard L, Moshier E, Haraldsson B, Buettner C. 2016. Perinatal DDT exposure induces hypertension and cardiac hypertrophy in adult mice. Environ Health Perspect 124:1722-1727; http://dx.doi.org/10.1289/EHP164.

Achieving the Benefits of a High-Potassium, Paleolithic Diet, Without the Toxicity

The average US dietary intake of K(+) is well below the current recommended nutritional requirements. This deficiency is even more striking when comparing our current intake with that of our ancestors, who consumed large amounts of dietary K(+). K(+) deficiency has been implicated in many diseases including cardiovascular disease, kidney stones, and osteoporosis. Importantly, dietary supplementation of K(+) has favorable effects on reducing blood pressure, decreasing the risk of stroke, improving bone health, and reducing the risk of nephrolithiasis. For this comprehensive review, we scanned the literature using PubMed and MEDLINE using the following search terms: potassium intake, renal potassium excretion, and prevention of hyperkalemia. Articles were selected for inclusion if they represented primary data or review articles published between 1980 and 2015 in high-impact journals. The normal kidney has the capacity to tightly regulate K(+) homoeostasis. We discuss new findings with respect to sensing mechanisms by which the kidney maintains K(+) homeostasis in the gastrointestinal tract and distal tubule. There are widely prescribed hypertensive medications that cause hyperkalemia and thus require dietary K(+) restriction. We conclude by discussing newly approved drugs capable of binding K(+) in the gastrointestinal tract and speculate that this new pharmacology might allow diet liberalization in patients at risk for hyperkalemia, affording them the numerous benefits of a K(+)-rich diet.

Regulation of Potassium Homeostasis

Potassium is the most abundant cation in the intracellular fluid, and maintaining the proper distribution of potassium across the cell membrane is critical for normal cell function. Long-term maintenance of potassium homeostasis is achieved by alterations in renal excretion of potassium in response to variations in intake. Understanding the mechanism and regulatory influences governing the internal distribution and renal clearance of potassium under normal circumstances can provide a framework for approaching disorders of potassium commonly encountered in clinical practice. This paper reviews key aspects of the normal regulation of potassium metabolism and is designed to serve as a readily accessible review for the well informed clinician as well as a resource for teaching trainees and medical students.

Induction of FKBP51 by aldosterone in intestinal epithelium

Screening female rat distal colon preparations for aldosterone-induced genes identified the Hsp90-binding immunophilin FKBP51 as a major aldosterone-induced mRNA and protein. Limited induction of FKBP51 was observed also in other aldosterone-responsive tissues such as kidney medulla and heart. Ex vivo measurements in colonic tissue have characterized time course, dose response and receptor specificity of the induction of FKBP51. FKBP51 mRNA and protein were strongly up regulated by physiological concentrations of aldosterone in a late (greater than 2.5h) response to the hormone. Maximal increase in FKBP51 mRNA requires aldosterone concentrations that are higher than those needed to fully occupy the mineralocorticoid receptor (MR). Yet, the response is fully inhibited by the MR antagonist spironolactone and not inhibited and even stimulated by the glucocorticoid receptor (GR) antagonist RU486. These and related findings cannot be explained by a simple activation and dimerization of either MR or GR but are in agreement with response mediated by an MR-GR heterodimer. Overexpression or silencing FKBP51 in the kidney collecting duct cell line M1 had little or no effect on the aldosterone-induced increase in transepithelial Na(+) transport.

How the kidney is impacted by the perinatal maternal environment to develop hypertension

Environmental conditions during perinatal development such as maternal undernutrition, maternal glucocorticoids, placental insufficiency, and maternal sodium overload can program changes in renal Na(+) excretion leading to hypertension. Experimental studies indicate that fetal exposure to an adverse maternal environment may reduce glomerular filtration rate by decreasing the surface area of the glomerular capillaries. Moreover, fetal responses to environmental insults during early life that contribute to the development of hypertension may include increased expression of tubular apical or basolateral membrane Na(+) transporters and increased production of renal superoxide leading to enhanced Na(+) reabsorption. This review will address the role of these potential renal mechanisms in the fetal programming of hypertension in experimental models induced by maternal undernutrition, fetal exposure to glucocorticoids, placental insufficiency, and maternal sodium overload in the rat.

Effects of a selective vasopressin V2 receptor antagonist, satavaptan, on ascites recurrence after paracentesis in patients with cirrhosis

BACKGROUND & AIMS

Cirrhotic patients with recurrent ascites frequently require paracentesis despite diuretic therapy. Vasopressin receptor antagonists, by increasing free water clearance, may reduce the recurrence of ascites. To investigate the effects of the addition of a vasopressin V(2) receptor antagonist, satavaptan, to 100mg spironolactone on ascites recurrence after a large volume paracentesis in patients with liver cirrhosis irrespective of the presence of hyponatraemia.

METHODS

One hundred and fifty one cirrhotic patients with recurrent ascites with or without hyponatraemia, and normal to mildly abnormal renal function were randomised in a double-blind study to receive either 5mg (n=39), 12.5mg (n=36), 25mg (n=40) of satavaptan or placebo (n=36) for 12 weeks. Their Child-Pugh scores were 9.2+/-1.3, 8.7+/-1.7, 8.8+/-1.3, and 9.0+/-1.5, respectively.

RESULTS

Median time to first paracentesis was 23, 26, and 17 days with satavaptan 5, 12.5, and 25mg, respectively, versus 14 days with placebo (ns for all doses). The frequency of paracenteses was decreased significantly (p<0.05) in all satavaptan groups versus placebo. Mean increase in ascites was 2.82+/-0.48 L/week for placebo versus 2.12+/-0.40, 2.14+/-0.33, and 2.06+/-0.40 L/week for the 5, 12.5, and 25mg of satavaptan, respectively (ns for all doses). Similar numbers of patients experienced major adverse events in all groups. Increases in serum creatinine, orthostatic changes in systolic pressure and thirst were more common with satavaptan.

CONCLUSIONS

Satavaptan has the potential to reduce recurrence of ascites after a large volume paracentesis at doses from 5 to 25mg in cirrhotic patients with ascites.

Truncated beta epithelial sodium channel (ENaC) subunits responsible for multi-system pseudohypoaldosteronism support partial activity of ENaC

Aldosterone regulated epithelial sodium channels (ENaC) are constructed of three homologous subunits. Mutations in the alpha-, beta- and gamma-ENaC subunit genes (SCNN1A, SCNN1B and SCNN1G) are associated with multi-system pseudohypoaldosteronism (PHA), and mutations in the PY motif of carboxy-terminal region of beta and gamma subunits are associated with Liddle syndrome of hereditary hypertension. In this study we identified two frameshift mutations in the SCNN1B alleles of a female infant diagnosed with multi-system PHA inherited from her parents. This is the first case of PHA in an Ashkenazi family in Israel. The p.Glu217fs (c.648dupA in exon 4) and p.Tyr306fs (c.915delC in exon 6) mutations produce shortened beta-ENaC subunits with 253 and 317 residues respectively instead of the 640 residues present in beta-ENaC subunit. Expression of cRNAs carrying these mutations in Xenopus oocytes showed that the mutations drastically reduce but do not eliminate ENaC activity. The findings reveal that truncated beta-ENaC subunits are capable of partially supporting intracellular transport of the other two subunits to the membrane and the final assembly of a weakly active channel together with normal alpha- and gamma-ENaC subunits. Moreover, these results enhance our understanding of the long-term consequences of these types of mutations in PHA patients.

Differential regulation of H+-ATPases in MDCK-C11 cells by aldosterone and vasopressin

The objective of the present work was to characterize the biochemical activity of the proton pumps present in the C11 clone of Madin–Darby canine kidney (MDCK) cells, akin to intercalated cells of the collecting duct, as well as to study their regulation by hormones like aldosterone and vasopressin. MDCK-C11 cells from passages 78 to 86 were utilized. The reaction to determine H+-ATPase activity was started by addition of cell homogenates to tubes contained the assay medium. The inorganic phosphate (Pi) released was determined by a colorimetric method modified from that described by Fiske and Subbarow. Changes in intracellular calcium concentration in the cells was determined using the Ca2+-sensing dye fluo-4 AM. Homogenates of MDCK-C11 cells present a bafilomycin-sensitive activity (vacuolar H+-ATPase), and a vanadate-sensitive activity (H+/K+-ATPase). The bafilomycin-sensitive activity showed a pH optimum of 6.12. ATPase activity was also stimulated in a dose-dependent fashion as K+ concentration was increased between 0 and 50 mmol·L–1, with an apparent Km for the release of Pi of 0.13 mmol·L–1 and Vmax of 22.01 nmol·mg–1·min–1. Incubation of cell monolayers with 10−8 mol·L–1 aldosterone for 24 h significantly increased vacuolar H+-ATPase activity, an effect prevented by 10−5 mol·L–1 spironolactone. Vacuolar H+-ATPase activity was also stimulated by 10−11 mol·L–1 vasopressin, an effect prevented by a V1 receptor-specific antagonist. This dose of vasopressin determined a sustained rise of cytosolic ionized calcium. We conclude that (i) homogenates of MDCK-C11 cells present a bafilomycin-sensitive (H+-ATPase) activity and a vanadate-sensitive (H+/K+-ATPase) activity, and (ii) vacuolar H+-ATPase activity is activated by aldosterone through a genomic pathway and by vasopressin through V1 receptors.

Genomic and nongenomic dose-dependent biphasic effect of aldosterone on Na+/H+ exchanger in proximal S3 segment: role of cytosolic calcium

The effects of aldosterone on the intracellular pH recovery rate (pHirr) via Na+/H+ exchanger and on the [Ca2+]i were investigated in isolated rat S3 segment. Aldosterone [10(-12), 10(-10), or 10(-8) M with 1-h, 15- or 2-min preincubation (pi)] caused a dose-dependent increase in the pHirr, but aldosterone (10(-6) M with 1-h, 15- or 2-min pi) decreased it (these effects were prevented by HOE694 but not by S3226). After 1 min of aldosterone pi, there was a transient and dose-dependent increase of the [Ca2+]i and after 6-min pi there was a new increase of [Ca2+]i that persisted after 1 h. Spironolactone, actinomycin D, or cycloheximide did not affect the effects of aldosterone (15- or 2-min pi) but inhibited the effects of aldosterone (1-h pi) on pHirr and on [Ca2+]i. RU 486 prevented the stimulatory effect of aldosterone (10(-12) M, 15- or 2-min pi) on both parameters and maintained the inhibitory effect of aldosterone (10(-6) M, 15- or 2-min pi) on the pHirr but reversed its stimulatory effect on the [Ca2+]i to an inhibitory effect. The data indicate a genomic (1 h, via MR) and a nongenomic action (15 or 2 min, probably via GR) on [Ca2+]i and on the basolateral NHE1 and are compatible with stimulation of the NHE1 by increases in [Ca2+]i in the lower range (at 10(-12) M aldosterone) and inhibition by increases at high levels (at 10(-6) M aldosterone) or decreases in [Ca2+]i (at 10(-6) M aldosterone plus RU 486).

Metabolic Alkalosis, Bedside and Bench

Although significant contributions to the understanding of metabolic alkalosis have been made recently, much of our knowledge rests on data from clearance studies performed in humans and animals many years ago. This article reviews the contributions of these studies, as well as more recent work relating to the control of renal acid-base transport by mineralocorticoid hormones, angiotensin, endothelin, nitric oxide, and potassium balance. Finally, clinical aspects of metabolic alkalosis are considered.