A model of 3D-structure of H^＋, K^＋-ATPase catalytic subunit derived by homology modeling

AIM: To build a model of 3D-structure of H , K -ATPase catalytic subunit for theoretical study and anti-ulcer drug design. METHODS: The model was built on the basis of structural data from the Ca2 -ATPase. Structurally conserved regions were defined by amino acid sequence comparisons, optimum interconnecting loops were se- lected from the protein databank, and amino (N)- and carboxyl (C)-terminal ends were generated as random coil structures. Applying molecular mechanics method th…     

Isoform-specific regulation of the Na^＋-K^＋ pump by adenosine in guinea pig ventricular myocytes

Aim The present study investigated the effect of adenosine on Na^＋-K^＋ pumps in acutely isolated guinea pig （Cavia sp.） ven- tricular myocytes. Methods： The whole-cell, patch-clamp technique was used to record the Na^＋-K^＋ pump current （Ip） in acutely isolated guinea pig ventricular myocytes. Results- Adenosine inhibited the high DHO-affinity pump current （Ih） in a concentration-dependent manner, which was blocked by the selective adenosine A1 receptor antagonist DPCPX and the general protein kinase C （PKC） antagonists staurosporine, GF 109203X or the specific 6 isoform antagonist rottlerin. In addition, the inhibitory action of adenosine was mimicked by a selective A1 receptor agonist CCPA and a specific activator peptide of PKC-5, PPl14. In contrast, the selective A2A receptor agonist CGS21680 and A3 receptor agonist CMB-MECA did not affect Ih. Application of the selective A2A receptor antagonist SCH58261 and A3 receptor antagonist MRSl191 also failed to block the effect of adenosine. Furthermore, H89, a selective protein kinase A （PKA） antagonist, did not exert any effect on adenosine-induced Ih inhibition. Conclusion： The present study provides the electrophysiological evidence that adenosine can induce significant inhibition of Ih via adenosine A1 receptors and the PKC-6 isoform.     

Involvement of cAMP/cAMP-dependent protein kinase signaling pathway in regulation of Na^＋, K^＋-ATPase upon activation of opioid receptors by morphine

The depolarization of neurons induced by impairment of Na^＋ , K^＋ - ATPase activity after chronic opiate treatment has been shown to involve the development of opioid dependence. However, the mechanisms underlying changes in Na^＋ , K^＋ - ATPase activity following opioid treatment are unclear. The best - established molecular adaptation to chronic opioid exposure is up - regulation of the cAMP/PKA signaling pathway, this study, therefore, was undertaken to investigate the role of up - regulation of cAMP/ PKA signaling pathway in alteration of the mouse hippocampal Na^＋, K^＋ - ATPase activity. The results demonstrated that acute morphine treatment dose - dependently stimulated Na^＋ , K^＋ - ATPase activity. This action could be significantly suppressed by adenylyl cyclase activator forskolin, or the cAMP analogue db - cAMP. Contrary to acute morphine treatment, chronic morphine treatment significantly inhibited Na^＋ , K^＋-ATPase activity. Moreover, an additional decrease in Na^＋, K^＋ - ATPase activity was observed by naloxone precipitation. The effects of both acute and chronic morphine treatment on Na^＋, K^＋ -ATPase activity were naltrexone - reversible. The regulation of Na^＋ , K^＋ - ATPase activity by morphine was inversely correlated with intracellular cAMP accumulation. H -89, a specific PKA inhibitor, mimicked the stimulatory effect of acute morphine but antagonized the inhibitory effect of chronic morphine on Na^＋ , K^＋-ATPase activity. However, okadaic acid, a protein phosphatase inhibitor, suppressed acute morphine stimulation but potentiated chronic morphine inhibition of Na^＋, K^＋ - ATPase activity. The regulation of Na^＋ , K^＋ - ATPase activity by morphine treatment appeared to associate with the alteration in phosphorylation level, but not to be relevant to the change in abundance of Na^＋, K^＋ - ATPase.     

Involvement of cAMP/cAMP -Dependent Protein Kinase Signaling Pathwayin Regulation of Na^＋, K^＋ -ATPase upon Activation of Opioid Receptors by Morphine

Aim： The depolarization of neurons induced by impairment of Na^＋, K ^＋ - ATPase activity after chronic opiate treatment has been shown to involve the development of opioid dependence. However, the mechanisms underlying changes in Na^＋, K^＋- ATPase activity following opioid treatment are unclear. The best - established molecular adaptation to chronic opioid exposure is up - regulation of the cAMP/PKA signaling pathway, this study, therefore, was undertaken to investigate the role of up - regulation of cAMP/PKA signaling pathway in alteration of Na^＋, K^＋ - ATPase activity.     

Interaction of heavy metals with membrane Ca^2＋ channels

The objective of our study was to determine if specific types of high voltage-activated Ca^2 channels,typically found in neurons were affected differentially by MeHg,Hg^2 and Pb^2 .Expression cDNA clones of α1C,α1B or α1E subunits coding for neuronal L-,N- and R- subtypes respectively,were combined with α2b δ and β3 Ca^2 channel subunits of human neuronal origin to transfect HEK293 cells.Current was measured using whole cell voltage clamp recording techniques.It the present studies,we conclude: (1)neurotoxic heavy metals such as MeHg,Hg^2 and Pb impair the function of voltage-gated Ca^2 channels at low μmolar to sub-μmolar concentrations-concentrations in the range of which are pathologically and environmentally relevant; (2)a particular metal,i.e.Pb^2 ,may inhibit function of phenotypically distince Ca^2 channels with variable potency; (3)different metals have differing “orders of potency” at inhibiting defined populations of Ca^2 channels; (4)for “susceptible populations” of patients with either underlying diseases or genetic alter ations of Ca^2 channel function,these metals may have heightened effectiveness.As such,for these populations,environmental toxic metals could produce a more dominant neurotoxicity.     

Effects of temperature and intracellular sodium, ATP and pH on Na^＋-Ca^2＋ exchange currents of intact guinea-pig myocytes

AIM: The Na^ -Ca^2 exchange is a major pathway for removal of cytosolic Ca^2 in cardiac myocytes. There have been many re-searches reporting about the effects of temperature, intracellular sodium, ATE and pH on Na^ -Ca^2 exchange currents. But most of these researches were made with giant-patch voltage-clamp technique or with Ca^2 flux studies in sarcolemmal vesicles. During     

Steroid-like compounds in Chinese medicines promote blood circulation via inhibition of Na^＋/K^＋- ATPase

Aim:

To examine if steroid-like compounds found in many Chinese medicinal products conventionally used for the promotion of blood circulation may act as active components via the same molecular mechanism triggered by cardiac glycosides, such as ouabain.

Methods:

The inhibitory potency of ouabain and the identified steroid-like compounds on Na⁺/K⁺-ATPase activity was examined and compared. Molecular modeling was exhibited for the docking of these compounds to Na⁺/K⁺-ATPase.

Results:

All the examined steroid-like compounds displayed more or less inhibition on Na⁺/K⁺-ATPase, with bufalin (structurally almost equivalent to ouabain) exhibiting significantly higher inhibitory potency than the others. In the pentacyclic triterpenoids examined, ursolic acid and oleanolic acid were moderate inhibitors of Na⁺/K⁺-ATPase, and their inhibitory potency was comparable to that of ginsenoside Rh2. The relatively high inhibitory potency of ursolic acid or oleanolic acid was due to the formation of a hydrogen bond between its carboxyl group and the Ile322 residue in the deep cavity close to two K⁺ binding sites of Na⁺/K⁺-ATPase. Moreover, the drastic difference observed in the inhibitory potency of ouabain, bufalin, ginsenoside Rh2, and pentacyclic triterpenoids is ascribed mainly to the number of hydrogen bonds and partially to the strength of hydrophobic interaction between the compounds and residues around the deep cavity of Na⁺/K⁺-ATPase.

Conclusion:

Steroid-like compounds seem to contribute to therapeutic effects of many cardioactive Chinese medicinal products. Chinese herbs, such as Prunella vulgaris L, rich in ursolic acid, oleanolic acid and their glycoside derivatives may be adequate sources for cardiac therapy via effective inhibition on Na⁺/K⁺-ATPase.     

Effect of sugar positions in ginsenosides and their inhibitory potency on Na^＋/K^＋-ATPase activity

Aim： To determine whether ginsenosides with various sugar attachments may act as active components responsible for the cardiac therapeutic effects of ginseng and sanqi （the roots of Panax ginseng and Panax notoginseng） via the same molecular mechanism triggered by cardiac glycosides, such as ouabain and digoxin.
Methods： The structural similarity between ginsenosides and ouabain was analyzed. The inhibitory potency of ginsenosides and ouabain on Na^＋/K^＋-ATPase activity was examined and compared. Molecular modeling was exhibited for the docking of ginsenosides to Na^＋/K^＋-ATPase.
Results： Ginsenosides with sugar moieties attached only to the C-3 position of the steroid-like structure, equivalent to the sugar position in cardiac glycosides, and possessed inhibitory potency on Na^＋/K^＋-ATPase activity. However, their inhibitory potency was significantly reduced or completely abolished when a monosaccharide was linked to the C-6 or C-20 position of the steroid-like structure; replacement of the monosaccharide with a disaccharide molecule at either of these positions caused the disappearance of the inhibitory potency. Molecular modeling and docking confirmed that the difference in Na^＋/K^＋-ATPase inhibitory potency among ginsenosides was due to the steric hindrance of sugar attachment at the C-6 and C-20 positions of the steroid-like structure.
Conclusion： The cardiac therapeutic effects of ginseng and sanqi should be at least partly attributed to the effective inhibition of Na^＋/K^＋-ATPase by their metabolized ginsenosides with sugar moieties attached only to the C-3 position of the steroid-like structure.     

长寿密码=地气＋元气＋心气＋神气

几千年来,人类探寻长寿密码的行动一直都未停止。近日,有关专家组团踏上寻访中IN30位最长寿老人之路,38天时间,10个省份,破解了全国老寿星们的终极长寿密码——地气、元气、心气、神气.     

Role of Na+-K+ ATPase enzyme in vascular response of goat ruminal artery

Objective:

To study the role of Na⁺, K⁺- ATPase enzyme in the vascular response of goat ruminal artery.

Materials and Methods:

Ruminal artery was obtained in chilled aerated modified Krebs-Henseleit solution (KHS) from a local slaughterhouse and transported in ice for further processing. The endothelium intact arterial ring was mounted in a thermostatically controlled (37 ± 0.5°C) organ bath containing 20 ml of modified KHS (pH 7.4) bubbled with oxygen (95%) and CO₂ (5%) under 2g tension. An equilibration of 90 min was allowed before addition of drugs into the bath. The responses were recorded isometrically in an automatic organ bath connected to PowerLab data acquisition system. In order to examine intact functional endothelium, ACh (10 μM) was added on the 5-HT (1.0 μM) - induced sustained contractile response. Similarly, functional characterization of Na⁺, K⁺-ATPase activity was done by K⁺-induced relaxation (10 μM-10 mM) in the absence and presence of ouabain (0.1 μM/ 0.1 mM), digoxin (0.1 μM) and barium (30 μM).

Results:

ACh (10⁻⁵ M) did not produce any relaxing effect on 5-HT-induced sustained contractile response suggesting that vascular endothelium has no significant influence on the activation of sodium pump by extracellular K⁺ in ruminal artery. Low concentration of Ba²⁺ (30 μM) (IC₅₀: 0.479 mM) inhibited K⁺-induced relaxation suggesting K_ir (inward rectifier) channel in part had role in K⁺-induced vasodilatation in ruminal artery. Vasorelaxant effect of KCl (10 μM-10 mM) in K⁺-free medium is also blocked by ouabain (0.1 μM and 0.1 mM) (IC₅₀:0.398 mM and IC₃₅: 1.36 mM), but not by digoxin (0.1 μM) (IC₅₀ 0.234 mM) suggesting that ouabain sensitive Na⁺, K⁺-ATPase isoform is present in the ruminal artery.

Conclusion:

In the goat ruminal artery functional regulation of sodium pump is partly mediated by K⁺ channel and ouabain sensitive Na⁺, K⁺ ATPase.     

Magnesium lithospermate B extracted from Salvia miltiorrhiza elevats intracellular Ca2＋ level in SHSY5Y cells

Aim:

To examine if magnesium lithospermate B (MLB), a potent inhibitor of Na⁺/K⁺-ATPase, leads to the elevation of intracellular Ca²⁺ level as observed in cells treated with cardiac glycosides.

Methods:

Viability of SH-SY5Y neuroblastoma cells treated with various concentrations of ouabain or MLB was measured. Intracellular Ca²⁺ levels were visualized using Fluo4-AM (fluorescent dye) when cells were treated with ouabain or MLB in the presence or absence of KB-R7943 (Na⁺/Ca²⁺ exchanger inhibitor) and 2-APB (IP₃ receptor antagonist). Molecular modeling was conducted for the docking of ouabain or MLB to Na⁺/K⁺-ATPase. Changes of cell body and dendrite morphology were monitored under a microscope.

Results:

severe toxicity was observed in cells treated with ouabain of concentration higher than 1 μmol/L for 24 h while no apparent toxicity was observed in those treated with MLB. Intracellular Ca²⁺ levels were substantially elevated by MLB (1 μmol/L) and ouabain (1 μmol/L) in similar patterns, and significantly reduced in the presence of KB-R7943 (10 μmol/L) or 2-APB (100 μmol/L). Equivalent interaction with the binding cavity of Na⁺/K⁺-ATPase was simulated for ouabain and MLB by forming five hydrogen bonds, respectively. Treatment of ouabain (1 μmol/L), but not MLB (1 μmol/L), induced dendritic shrink of SH-SY5Y cells.

Conclusion:

Comparable to ouabain, MLB leads to the elevation of intracellular Ca²⁺ level presumably via the same mechanism by inhibiting Na⁺/K⁺-ATPase. The elevated Ca²⁺ levels seem to be supplied by Ca²⁺ influx through the reversed mode of the Na⁺/Ca²⁺ exchanger and intracellular release from endoplasmic reticulum.     

Pals-associated tight junction protein functionally links dopamine and angiotensin II to the regulation of sodium transport in renal epithelial cells

Background and purpose:

Dopamine inhibits renal cell Na⁺,K⁺-ATPase activity and cell sodium transport by promoting the internalization of active molecules from the plasma membrane, whereas angiotensin II (ATII) stimulates its activity by recruiting new molecules to the plasma membrane. They achieve such effects by activating multiple and distinct signalling molecules in a hierarchical manner. The purpose of this study was to investigate whether dopamine and ATII utilize scaffold organizer proteins as components of their signalling networks, in order to avoid deleterious cross talk.

Experimental approach:

Attention was focused on a multiple PDZ domain protein, Pals-associated tight junction protein (PATJ). Ectopic expression of PATJ in renal epithelial cells in culture was used to study its interaction with components of the dopamine signalling cascade. Similarly, expression of PATJ deletion mutants was employed to analyse its functional relevance during dopamine-, ATII- and insulin-dependent regulation of Na⁺,K⁺-ATPase.

Key results:

Dopamine receptors and components of its signalling cascade mediating inhibition of Na⁺,K⁺-ATPase interact with PATJ. Inhibition of Na⁺,K⁺-ATPase by dopamine was prevented by expression of mutants of PATJ lacking PDZ domains 2, 4 or 5; whereas the stimulatory effect of ATII and insulin on Na⁺,K⁺-ATPase was blocked by expression of PATJ lacking PDZ domains 1, 4 or 5.

Conclusions and implications:

A multiple PDZ domain protein may add functionality to G protein-coupled and tyrosine kinase receptors signalling during regulation of Na⁺,K⁺-ATPase. Signalling molecules and effectors can be integrated into a functional network by the scaffold organizer protein PATJ via its multiple PDZ domains.     

Effect of sugar positions in ginsenosides and their inhibitory potency on Na+/K+-ATPase activity

Aim:

To determine whether ginsenosides with various sugar attachments may act as active components responsible for the cardiac therapeutic effects of ginseng and sanqi (the roots of Panax ginseng and Panax notoginseng) via the same molecular mechanism triggered by cardiac glycosides, such as ouabain and digoxin.

Methods:

The structural similarity between ginsenosides and ouabain was analyzed. The inhibitory potency of ginsenosides and ouabain on Na⁺/K⁺-ATPase activity was examined and compared. Molecular modeling was exhibited for the docking of ginsenosides to Na⁺/K⁺-ATPase.

Results:

Ginsenosides with sugar moieties attached only to the C-3 position of the steroid-like structure, equivalent to the sugar position in cardiac glycosides, and possessed inhibitory potency on Na⁺/K⁺-ATPase activity. However, their inhibitory potency was significantly reduced or completely abolished when a monosaccharide was linked to the C-6 or C-20 position of the steroid-like structure; replacement of the monosaccharide with a disaccharide molecule at either of these positions caused the disappearance of the inhibitory potency. Molecular modeling and docking confirmed that the difference in Na⁺/K⁺-ATPase inhibitory potency among ginsenosides was due to the steric hindrance of sugar attachment at the C-6 and C-20 positions of the steroid-like structure.

Conclusion:

The cardiac therapeutic effects of ginseng and sanqi should be at least partly attributed to the effective inhibition of Na⁺/K⁺-ATPase by their metabolized ginsenosides with sugar moieties attached only to the C-3 position of the steroid-like structure.     

Epithelial Na⁺ channel activity in human airway epithelial cells: the role of serum and glucocorticoid-inducible kinase 1

BACKGROUND AND PURPOSE

Glucocorticoids appear to control Na⁺ absorption in pulmonary epithelial cells via a mechanism dependent upon serum and glucocorticoid-inducible kinase 1 (SGK1), a kinase that allows control over the surface abundance of epithelial Na⁺ channel subunits (α-, β- and γ-ENaC). However, not all data support this model and the present study re-evaluates this hypothesis in order to clarify the mechanism that allows glucocorticoids to control ENaC activity.

EXPERIMENTAL APPROACH

Electrophysiological studies explored the effects of agents that suppress SGK1 activity upon glucocorticoid-induced ENaC activity in H441 human airway epithelial cells, whilst analyses of extracted proteins explored the associated changes to the activities of endogenous protein kinase substrates and the overall/surface expression of ENaC subunits.

KEY RESULTS

Although dexamethasone-induced (24 h) ENaC activity was dependent upon SGK1, prolonged exposure to this glucocorticoid did not cause sustained activation of this kinase and neither did it induce a coordinated increase in the surface abundance of α-, β- and γ-ENaC. Brief (3 h) exposure to dexamethasone, on the other hand, did not evoke Na⁺ current but did activate SGK1 and cause SGK1-dependent increases in the surface abundance of α-, β- and γ-ENaC.

CONCLUSIONS AND IMPLICATIONS

Although glucocorticoids activated SGK1 and increased the surface abundance of α-, β- and γ-ENaC, these responses were transient and could not account for the sustained activation of ENaC. The maintenance of ENaC activity did, however, depend upon SGK1 and this protein kinase must therefore play an important but permissive role in glucocorticoid-induced ENaC activation.     

Loss of Ca2+-mediated ion transport during colitis correlates with reduced ion transport responses to a Ca2+-activated K+ channel opener

Background and purpose:

Epithelial surface hydration is critical for proper gut function. However, colonic tissues from individuals with inflammatory bowel disease or animals with colitis are hyporesponsive to Cl⁻ secretagogues. The Cl⁻ secretory responses to the muscarinic receptor agonist bethanechol are virtually absent in colons of mice with dextran sodium sulphate (DSS)-induced colitis. Our aim was to define the mechanism underlying this cholinergic hyporesponsiveness.

Experimental approach:

Colitis was induced by 4% DSS water, given orally. Epithelial ion transport was measured in Ussing chambers. Colonic crypts were isolated and processed for mRNA expression via RT-PCR and protein expression via immunoblotting and immunolocalization.

Key results:

Expression of muscarinic M₃ receptors in colonic epithelium was not decreased during colitis. Short-circuit current (I_SC) responses to other Ca²⁺-dependent secretagogues (histamine, thapsigargin, cyclopiazonic acid and calcium ionophore) were either absent or severely attenuated in colonic tissue from DSS-treated mice. mRNA levels of several ion transport molecules (a Ca²⁺-regulated Cl⁻ channel, the intermediate-conductance Ca²⁺-activated K⁺ channel, the cystic fibrosis transmembrane conductance regulator, the Na⁺/K⁺-ATPase pump or the Na⁺/K⁺/2Cl⁻ co-transporter) were not reduced in colonic crypts from DSS-treated mice. However, protein expression of Na⁺/K⁺-ATPase α1 subunits was decreased twofold during colitis. Activation of Ca²⁺-activated K⁺ channels increased I_SC significantly less in DSS colons compared with control, as did the protein kinase C activator, phorbol 12-myristate 13-acetate.

Conclusions and implications:

Decreased Na⁺/K⁺-ATPase expression probably contributes to overall epithelial hyporesponsiveness during colitis, while dysfunctional K⁺ channels may account, at least partially, for lack of epithelial secretory responses to Ca²⁺-mediated secretagogues.     

AMP-activated protein kinase (AMPK)-dependent and -independent pathways regulate hypoxic inhibition of transepithelial Na(+) transport across human airway epithelial cells

BACKGROUND AND PURPOSE

Pulmonary transepithelial Na⁺ transport is reduced by hypoxia, but in the airway the regulatory mechanisms remain unclear. We investigated the role of AMPK and ROS in the hypoxic regulation of apical amiloride-sensitive Na⁺ channels and basolateral Na⁺K⁺ ATPase activity.

EXPERIMENTAL APPROACH

H441 human airway epithelial cells were used to examine the effects of hypoxia on Na⁺ transport, AMP : ATP ratio and AMPK activity. Lentiviral constructs were used to modify cellular AMPK abundance and activity; pharmacological agents were used to modify cellular ROS.

KEY RESULTS

AMPK was activated by exposure to 3% or 0.2% O₂ for 60 min in cells grown in submerged culture or when fluid (0.1 mL·cm⁻²) was added to the apical surface of cells grown at the air–liquid interface. Only 0.2% O₂ activated AMPK in cells grown at the air–liquid interface. AMPK activation was associated with elevation of cellular AMP : ATP ratio and activity of the upstream kinase LKB1. Hypoxia inhibited basolateral ouabain-sensitive I_sc (I_ouabain) and apical amiloride-sensitive Na⁺ conductance (G_Na+). Modification of AMPK activity prevented the effect of hypoxia on I_ouabain (Na⁺K⁺ ATPase) but not apical G_Na+. Scavenging of superoxide and inhibition of NADPH oxidase prevented the effect of hypoxia on apical G_Na+ (epithelial Na⁺ channels).

CONCLUSIONS AND IMPLICATIONS

Hypoxia activates AMPK-dependent and -independent pathways in airway epithelial cells. Importantly, these pathways differentially regulate apical Na⁺ channels and basolateral Na⁺K⁺ ATPase activity to decrease transepithelial Na⁺ transport. Luminal fluid potentiated the effect of hypoxia and activated AMPK, which could have important consequences in lung disease conditions.     

Enhancing the potency of lithospermate B for inhibiting Na+/K+-ATPase activity by forming transition metal ion complexes

Aim:

To determine whether replacing Mg²⁺ in magnesium lithospermate B (Mg-LSB) isolated from danshen (Salvia miltiorrhiza) with other metal ions could affect its potency in inhibition of Na⁺/K⁺-ATPase activity.

Methods:

Eight metal ions (Na⁺, K⁺, Mg²⁺, Cr³⁺, Mn²⁺, Co²⁺, Ni²⁺, and Zn²⁺) were used to form complexes with LSB. The activity of Na⁺/K⁺-ATPase was determined by measuring the amount of inorganic phosphate (Pi) liberated from ATP. Human adrenergic neuroblastoma cell line SH-SY5Y was used to assess the intracellular Ca²⁺ level fluctuation and cell viability. The metal binding site on LSB and the binding mode of the metal-LSB complexes were detected by NMR and visible spectroscopy, respectively.

Results:

The potencies of LSB complexed with Cr³⁺, Mn²⁺, Co²⁺, or Ni²⁺ increased by approximately 5 times compared to the naturally occurring LSB and Mg-LSB. The IC₅₀ values of Cr-LSB, Mn-LSB, Co-LSB, Ni-LSB, LSB, and Mg-LSB in inhibition of Na⁺/K⁺-ATPase activity were 23, 17, 26, 25, 101, and 128 μmol/L, respectively. After treatment of SH-SY5Y cells with the transition metal-LSB complexes (25 μmol/L), the intracellular Ca²⁺ level was substantially elevated, and the cells were viable for one day. The transition metals, as exemplified by Co²⁺, appeared to be coordinated by two carboxylate groups and one carbonyl group of LSB. Titration of LSB against Co²⁺ demonstrated that the Co-LSB complex was formed with a Co²⁺:LSB molar ratio of 1:2 or 1:1, when [Co²⁺] was less than half of the [LSB] or higher than the [LSB], respectively.

Conclusion:

LSB complexed with Cr³⁺, Mn²⁺, Co²⁺, or Ni²⁺ are stable, non-toxic and more potent in inhibition of Na⁺/K⁺-ATPase. The transition metal-LSB complexes have the potential to be superior substitutes for cardiac glycosides in the treatment of congestive heart failure.     

Effects of peroxisome proliferator-activated receptor γ agonists on Na+ transport and activity of the kinase SGK1 in epithelial cells from lung and kidney

Background and purpose:

Peroxisome proliferator-activated receptor γ (PPARγ) agonists, such as rosiglitazone and pioglitazone, sensitize cells to insulin, and are therefore used to treat type 2 diabetes. However, in some patients, these drugs induce oedema, and the present study tests the hypothesis that this side effect reflects serum and glucocorticoid-inducible kinase 1 (SGK1)-dependent enhancement of epithelia Na⁺ absorption.

Experimental approach:

Na⁺ absorbing epithelial cells (H441 cells, mpkCCD cells) on permeable membranes were mounted in Ussing chambers, and the effects of rosiglitazone (2 µM) and pioglitazone (10 µM) on transepithelial Na⁺ absorption were quantified electrometrically. Changes in SGK1 activity were assessed by monitoring phosphorylation of residues within an endogenous protein.

Key results:

Both cell types absorbed Na⁺ via an electrogenic process that was enhanced by insulin. In mpkCCD cells, this stimulation of Na⁺ transport was associated with increased activity of SGK1, whereas insulin regulated Na⁺ transport in H441 cells through a mechanism that did not involve activation of this kinase. Rosiglitazone and pioglitazone had no discernible effect on transepithelial Na⁺ absorption in unstimulated or insulin-stimulated cells and failed to alter cellular SGK1 activity.

Conclusions and implications:

Our results do not support the view that PPARγ agonists stimulate epithelial Na⁺ absorption or alter the control of cellular SGK1 activity. It is therefore likely that other mechanisms are involved in PPARγ-mediated fluid retention, and a better understanding of these mechanisms may help with the identification of patients likely to develop oedema or heart failure when treated with these drugs.