Effect of chronic obstructive pulmonary disease on calcium pump ATPase expression in human diaphragm.

We have previously demonstrated that human diaphragm remodeling elicited by severe chronic obstructive pulmonary disease (COPD) is characterized by a fast-to-slow myosin heavy chain isoform transformation. To test the hypothesis that COPD-induced diaphragm remodeling also elicits a fast-to-slow isoform shift in the sarcoendoplasmic reticulum Ca(2+) ATPase (SERCA), the other major ATPase in skeletal muscle, we obtained intraoperative biopsies of the costal diaphragm from 10 severe COPD patients and 10 control subjects. We then used isoform-specific monoclonal antibodies to characterize diaphragm fibers with respect to the expression of SERCA isoforms. Compared with control diaphragms, COPD diaphragms exhibited a 63% decrease in fibers expressing only fast SERCA (i.e., SERCA1; P < 0.001), a 190% increase in fibers containing both fast and slow SERCA isoforms (P < 0.01), and a 19% increase (P < 0.05) in fibers expressing only the slow SERCA isoform (i.e., SERCA2). Additionally, immunoblot experiments carried out on diaphragm homogenates indicated that COPD diaphragms expressed only one-third the SERCA1 content noted in control diaphragms; in contrast, COPD and control diaphragms did not differ with respect to SERCA2 content. The combination of these histological and immunoblot results is consistent with the hypothesis that diaphragm remodeling elicited by severe COPD is characterized by a fast-to-slow SERCA isoform transformation. Moreover, the combination of these SERCA data and our previously reported myosin heavy chain isoform data (Levine S, Nguyen T, Kaiser LR, Rubinstein NA, Maislin G, Gregory C, Rome LC, Dudley GA, Sieck GC, and Shrager JB. Am J Respir Crit Care Med 168: 706-713, 2003) suggests that diaphragm remodeling elicited by severe COPD should decrease ATP utilization by the diaphragm.     

Effects of static magnetic field on specific adenosine-5′-triphosphatase activities and bioelectrical and biomechanical properties in the rat diaphragm muscle

In this study, we aimed to clarify the effects of chronically applied static magnetic field (200 Gauss) on specific ATPase activities and bioelectrical and biomechanical responses in the isolated rat diaphragm muscle. The mean activities of Na⁺-K⁺ ATPase and Ca²⁺ ATPase determined from the diaphragm homogenates were significantly higher in the magnetic field exposed group (n = 20), but that of Mg²⁺ ATPase was nonsignificantly lower compared to the control group (n = 13). Resting membrane potential, amplitude of muscle action potential, and overshoot values (mean ± SE) in the control group were found to be ?76.5 ± 0.6, 100 ± 0.8, and 23.5 ± 0.6 mV, respectively; these values were determined to be ?72.8 ± 0.4, 90.3 ± 0.5, and 17.2 ± 0.4 mV in the magnetic field-exposed group, respectively. The latency was determined to increase in the experimental group, and all the above-mentioned bioelectrical differences between the groups were significant statistically. Force of muscle twitch was found to decrease significantly in the magnetic field-exposed group, and this finding was attributed to the augmenting effect of magnetic field on Ca²⁺ ATPase activity. These results suggest that magnetic field exposure changes specific ATPase activities and, thence, bioelectrical and biomechanical properties in the rat diaphragm muscle. © 1995 Wiley-Liss, Inc.     

Different neuronal Na+/K+‐ATPase isoforms are involved in diverse signaling pathways

Inhibition of rat neuronal Na⁺/K⁺‐ATPase α3 isoform at low (100 nM) ouabain concentration led to activation of MAP kinase cascade via PKC and PIP₃ kinase. In contrast to ouabain‐sensitive α3 isoform of Na⁺/K⁺‐ATPase, an ouabain‐resistant α1 isoform (inhibition with 1 mM of ouabain) of Na⁺/K⁺‐ATPase regulates MAP kinase via Src kinase dependent reactions. Using of Annexin V‐FITC apoptotic test to determine the cells with early apoptotic features allows to conclude that α3 isoform stimulates and α1 suppresses apoptotic process in cerebellum neurons. These data are the first demonstration showing participation of ouabain‐resistant (α1) and ouabain‐sensitive (α3) Na⁺/K⁺‐ATPase isoforms in diverse signaling pathways in neuronal cells. Copyright © 2010 John Wiley & Sons, Ltd.     

Ca-transport in sea urchin unfertilized eggs: Regulation by endogenous sulfated polysaccharides and K

Previous data from our laboratory showed that the reticulum of the sea cucumber smooth muscle body wall retains both a sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) and a sulfated polysaccharide. In this invertebrate, the transport of Ca²⁺ by the SERCA is naturally inhibited by these endogenous sulfated polysaccharides. The inhibition is reverted by K⁺ leading to an enhancement of the Ca²⁺ transport rate. We now show that vesicles derived from the endoplasmic reticulum of unfertilized eggs from the sea urchin Arbacia lixula retain a SERCA that is able to transport Ca²⁺ at the expense of ATP hydrolysis. As described for the sea cucumber SERCA isoform, the enzyme from the sea urchin is activated by K⁺ but not by Li⁺ and is inhibited by thapsigargin, a specific inhibitor of SERCA. A new sulfated polysaccharide was identified in the sea urchin eggs reticulum composed mainly by galactose, glucose, hexosamine and manose. After extraction and purification, this sulfated polysaccharide was able to inhibit the mammal SERCA isoform found in rabbit skeletal muscle and the inhibition is reversed by K⁺. These data suggest that the regulation of the SERCA pump by K⁺ and sulfated polysaccharides is not restricted to few marine invertebrates but is widespread.     

Role of the Na+,K+-ATPase α2 isoform in the positive inotropic effect of ouabain and marinobufagenin in the rat diaphragm

It was found that ouabain and marinobufagenin, specific inhibitors of Na⁺,K⁺-ATPase, increased the contraction of the isolated rat diaphragm by ～15% (positive inotropic effect) at EC₅₀ = 1.2 ± 0.3 nM and 0.3 ± 0.1 nM, respectively, which was indicative of the participation of the ouabain-sensitive Na⁺,K⁺-ATPase α2 isoform. Analysis of the dose-response curves for the effect of ouabain on the resting membrane potential of muscle fibers in the absence and in the presence of 100 nM acetylcholine (hyperpolarizing the membrane) showed the presence of two pools of Na⁺,K⁺-ATPase α2 that differed in affinity for ouabain. Only the high-affinity pool (IC₅₀ ～ 9 nM) mediates the hyperpolarizing effect of nanomolar concentrations of acetylcholine. Most likely, it is this pool of that is involved in the positive inotropic effect of ouabain, which can be a mechanism of regulation of the muscle function by circulating endogenous inhibitors of Na⁺,K⁺-ATPase.     

Role of phospholemman and the 70 kDa inhibitor protein in regulating Na/K ATPase activity in pulmonary artery smooth muscle cells under U46619 stimulation

Treatment of bovine pulmonary smooth muscle cells with U46619 inhibited the Na⁺/K⁺ ATPase activity in two parallel pathways: one of which is mediated via glutathionylation of the pump and the other by augmenting the inhibitory activity of the 70 kDa inhibitor protein of Na⁺/K⁺ ATPase. Although phospholemman deglutathionylates the pump leading to its activation, the inhibitor is responsible for irreversible inhibition of Na⁺/K⁺ ATPase in an isoform specific manner during treatment of the cells with U46619.     

Sodium or potassium efflux ATPase: A fungal, bryophyte, and protozoal ATPase

The K⁺ and Na⁺ concentrations in living cells are strictly regulated at almost constant concentrations, high for K⁺ and low for Na⁺. Because these concentrations correspond to influx-efflux steady states, K⁺ and Na⁺ effluxes and the transporters involved play a central role in the physiology of cells, especially in environments with high Na⁺ concentrations where a high Na⁺ influx may be the rule. In eukaryotic cells two P-type ATPases are crucial in these homeostatic processes, the Na,K-ATPase of animal cells and the H⁺-ATPase of fungi and plants. In fungi, a third P-type ATPase, the ENA ATPase, was discovered nineteen years ago. Although for many years it was considered to be exclusively a fungal enzyme, it is now known to be present in bryophytes and protozoa. Structurally, the ENA (from exitus natru: exit of sodium) ATPase is very similar to the sarco/endoplasmic reticulum Ca²⁺ (SERCA) ATPase, and it probably exchanges Na⁺ (or K⁺) for H⁺. The same exchange is mediated by Na⁺ (or K⁺)/H⁺ antiporters. However, in eukaryotic cells these antiporters are electroneutral and their function depends on a ΔpH across the plasma membrane. Therefore, the current notion is that the ENA ATPase is necessary at high external pH values, where the antiporters cannot mediate uphill Na⁺ efflux. This occurs in some fungal environments and at some points of protozoa parasitic cycles, which makes the ENA ATPase a possible target for controlling fungal and protozoan parasites. Another technological application of the ENA ATPase is the improvement of salt tolerance in flowering plants.     

Sodium plus Potassium-Activated, Ouabain-Inhibited AdenosineTriphosphatase from a Fraction of Rat Skeletal Muscle, and Lack of Insulin Effect on It

An ATPase, activated by Na⁺ plus K⁺ in the presence of Mg⁺⁺ and inhibited by ouabain, has been obtained from rat skeletal muscle. Unlike ATPase's with similar properties obtained from other preparations, this ATPase was found only in the fraction containing fragmented sarcoplasmic reticulum. It is suggested that in rat skeletal muscle this ATPase may reside in sarcoplasmic reticulum and not in sarcolemma. This ATPase differed in its pH optimum and in its cation sensitivity from that of rat brain and from that of human muscle reported by Samaha and Gergely (1965, 1966). Because insulin accelerates Na⁺ efflux from muscle, efforts were made to determine whether or not this effect of insulin could be attributed to increased Na⁺ + K⁺-activated ATPase activity. Insulin, administered either in vivo or in vitro, had no demonstrable effect on the enzyme system, nor did it protect against inhibition by ouabain.     

Na+,K+-ATPase Na+ Affinity in Rat Skeletal Muscle Fiber Types

Previous studies in expression systems have found different ion activation of the Na⁺/K⁺-ATPase isozymes, which suggest that different muscles have different ion affinities. The rate of ATP hydrolysis was used to quantify Na⁺,K⁺-ATPase activity, and the Na⁺ affinity of Na⁺,K⁺-ATPase was studied in total membranes from rat muscle and purified membranes from muscle with different fiber types. The Na⁺ affinity was higher (K _m lower) in oxidative muscle compared with glycolytic muscle and in purified membranes from oxidative muscle compared with glycolytic muscle. Na⁺,K⁺-ATPase isoform analysis implied that heterodimers containing the β₁ isoform have a higher Na⁺ affinity than heterodimers containing the β₂ isoform. Immunoprecipitation experiments demonstrated that dimers with α₁ are responsible for approximately 36% of the total Na,K-ATPase activity. Selective inhibition of the α₂ isoform with ouabain suggested that heterodimers containing the α₁ isoform have a higher Na⁺ affinity than heterodimers containing the α₂ isoform. The estimated K _m values for Na⁺ are 4.0, 5.5, 7.5 and 13 mM for α₁β₁, α₂β₁, α₁β₂ and α₂β₂, respectively. The affinity differences and isoform distributions imply that the degree of activation of Na⁺,K⁺-ATPase at physiological Na⁺ concentrations differs between muscles (oxidative and glycolytic) and between subcellular membrane domains with different isoform compositions. These differences may have consequences for ion balance across the muscle membrane.     

Mechanism of reduced colonic contractility in experimental colitis: role of sarcoplasmic reticulum pump isoform-2

Inflammatory bowel diseases (IBD) such as Crohn’s disease and ulcerative colitis are inflammatory disorders associated with decreased colonic contractility. Here we show that, in experimental colitis in rat induced by trinitrobenzenesulfonic acid, there is a decrease in contraction in response to carbamoylcholine and the sarco/endoplasmic reticulum Ca⁺² (SERCA) pump inhibitor thapsigargin. However, the decrease in contractility may occur due to decrease in the SERCA pump levels or their inactivation. Therefore, we examined the protein and mRNA levels for SERCA2 isoform, which is predominant isoform in colonic smooth muscle. There was a decrease in the levels of SERCA2 protein and mRNA levels in inflamed colonic muscle. These findings suggest that decreased SERCA pump levels is responsible for a decrease in the Ca⁺² stores in the sarco/endoplasmic reticulum that causes a decrease in the contractility in colonic smooth muscle leading to poor bowel movements.     

Na+ Dysregulation Coupled with Ca2+ Entry through NCX1 Promotes Muscular Dystrophy in Mice

Unregulated Ca²⁺ entry is thought to underlie muscular dystrophy. Here, we generated skeletal-muscle-specific transgenic (TG) mice expressing the Na⁺-Ca²⁺ exchanger 1 (NCX1) to model its identified augmentation during muscular dystrophy. The NCX1 transgene induced dystrophy-like disease in all hind-limb musculature, as well as exacerbated the muscle disease phenotypes in δ-sarcoglycan (Sgcd^−/−), Dysf^−/−, and mdx mouse models of muscular dystrophy. Antithetically, muscle-specific deletion of the Slc8a1 (NCX1) gene diminished hind-limb pathology in Sgcd^−/− mice. Measured increases in baseline Na⁺ and Ca²⁺ in dystrophic muscle fibers of the hind-limb musculature predicts a net Ca²⁺ influx state due to reverse-mode operation of NCX1, which mediates disease. However, the opposite effect is observed in the diaphragm, where NCX1 overexpression mildly protects from dystrophic disease through a predicted enhancement in forward-mode NCX1 operation that reduces Ca²⁺ levels. Indeed, Atp1a2^+/− (encoding Na⁺-K⁺ ATPase α2) mice, which have reduced Na⁺ clearance rates that would favor NCX1 reverse-mode operation, showed exacerbated disease in the hind limbs of NCX1 TG mice, similar to treatment with the Na⁺-K⁺ ATPase inhibitor digoxin. Treatment of Sgcd^−/− mice with ranolazine, a broadly acting Na⁺ channel inhibitor that should increase NCX1 forward-mode operation, reduced muscular pathology.     

A model for the generation of localized transient [Na] elevations in vascular smooth muscle

We present a stochastic computational model to study the mechanism of signaling between a source and a target ionic transporter, both localized on the plasma membrane (PM). In general this requires a nanometer-scale cytoplasmic space, or nanodomain, between the PM and a peripheral organelle to reflect ions back towards the PM. Specifically we investigate the coupling between Na⁺ entry via the transient receptor potential canonical channel 6 (TRPC6) and the Na⁺/Ca²⁺ exchanger (NCX), a process which is essential for reloading the sarcoplasmic reticulum (SR) via the sarco/endoplasmic reticulum Ca²⁺ATPase (SERCA) and maintaining Ca²⁺ oscillations in activated vascular smooth muscle. Having previously modeled the flow of Ca²⁺ between reverse NCX and SERCA during SR refilling, this quantitative approach now allows us to model the upstream linkage of Na⁺ entry through TRPC6 to reversal of NCX. We have implemented a random walk (RW) Monte Carlo (MC) model with simulations mimicking a diffusion process originating at the TRPC6 within PM-SR junctions. The model calculates the average Na⁺ in the nanospace and also produces profiles as a function of distance from the source. Our results highlight the necessity of a strategic juxtaposition of the relevant ion translocators as well as other physical structures within the nanospaces to permit adequate Na⁺ build-up to initiate NCX reversal and Ca²⁺ influx to refill the SR.     

Properties of (Na+ + K+)-activated ATPase in rat liver plasma membranes enriched with bile canaliculi

Liver plasma membranes enriched in bile canaliculi were isolated from rat liver by a modification of the technique of Song et al. (J. Cell Biol. (1969) 41, 124–132) in order to study the possible role of ATPase in bile secretion. Optimum conditions for assaying (Na⁺ + K⁺)-activated ATPase in this membrane fraction were defined using male rats averaging 220 g in weight. (Na⁺ + K⁺)-activated ATPase activity was documented by demonstrating specific cation requirements for Na⁺ and K⁺, while the divalent cation, Ca²⁺, and the cardiac glycosides, ouabain and scillaren, were inhibitory. (Na⁺ + K⁺)-activated ATPase activity averaged 10.07 ± 2.80 μmol P_i/mg protei per h compared to 50.03 ± 11.41 for Mg²⁺-activated ATPase and 58.66 ± 10.07 for 5′-nucleotidase. Concentrations of ouabain and scillaren which previously inhibited canalicular bile secretion in the isolated perfused rat liver produced complete inhibition of (Na⁺ + K⁺)-activated ATPase without any effect on Mg²⁺-activated ATPase. Both (Na⁺ + K⁺)-activated ATPase and Mg²⁺-activated ATPase demonstrated temperature dependence but differed in temperature optima. Temperature induced changes in specific activity of (Na⁺ + K⁺)-activated ATPase directly paralleled previously demonstrated temperature optima for bile secretion. These studies indicate that (Na⁺ + K⁺)-activated ATPase is present in fractions of rat liver plasma membranes that are highly enriched in bile canaliculi and provide a model for further study of the effects of various physiological and chemical modifiers of bile secretion and cholestasis.     

Eicosapentaenoic acid enhances myo-inositol uptake in cultured human aortic smooth muscle cells

The effects of elevated glucose and Eicosapentaenoic acid (EPA, 20:5) on myoinositol uptake in human aortic smooth muscle cells (HASMC) were evaluated. Myo-inositol incorporation into HASMC was dependent on an active transport system via Na⁺−K⁺ ATPase activity based on the results with Na⁺ deprivation and Ouabain (5 mM). Although glucose (27.5, 55 mM) inhibited 2-[³H] myo-inositol uptake, the addition of EPA (3×10⁴ M) prevented glucose-mediated inhibition. In addition, EPA potentiated Na⁺−K⁺ ATPase activity of HASMC. Since EPA decrease glucose-mediated inhibition of myo-inositol uptake, this agent might ameliorate aortic smooth muscle cell function associated with diabetes.     

23Na Magnetic Resonance Imaging of the Lower Leg of Acute Heart Failure Patients during Diuretic Treatment

Objective

Na⁺ can be stored in muscle and skin without commensurate water accumulation. The aim of this study was to assess Na⁺ and H₂O in muscle and skin with MRI in acute heart failure patients before and after diuretic treatment and in a healthy cohort.

Methods

Nine patients (mean age 78 years; range 58–87) and nine age and gender-matched controls were studied. They underwent ²³Na/¹H-MRI at the calf with a custom-made knee coil. Patients were studied before and after diuretic therapy. ²³Na-MRI gray-scale measurements of Na⁺-phantoms served to quantify Na⁺-concentrations. A fat-suppressed inversion recovery sequence was used to quantify H₂O content.

Results

Plasma Na⁺-levels did not change during therapy. Mean Na⁺-concentrations in muscle and skin decreased after furosemide therapy (before therapy: 30.7±6.4 and 43.5±14.5 mmol/L; after therapy: 24.2±6.1 and 32.2±12.0 mmol/L; p˂0.05 and p˂0.01). Water content measurements did not differ significantly before and after furosemide therapy in muscle (p = 0.17) and only tended to be reduced in skin (p = 0.06). Na⁺-concentrations in calf muscle and skin of patients before and after diuretic therapy were significantly higher than in healthy subjects (18.3±2.5 and 21.1±2.3 mmol/L).

Conclusions

²³Na-MRI shows accumulation of Na⁺ in muscle and skin in patients with acute heart failure. Diuretic treatment can mobilize this Na⁺-deposition; however, contrary to expectations, water and Na⁺-mobilization are poorly correlated.     

Thapsigargin decreases the Na+- Ca2 + exchanger mediated Ca2 + entry in pig coronary artery smooth muscle

Na⁺- Ca^2 + exchanger (NCX) has been proposed to play a role in refilling the sarco/endoplasmic reticulum (SER) Ca^2 + pool along with the SER Ca^2 + pump (SERCA). Here, SERCA inhibitor thapsigargin was used to determine the effects of SER Ca^2 + depletion on NCX–SERCA interactions in smooth muscle cells cultured from pig coronary artery. The cells were Na⁺-loaded and then placed in either a Na⁺-containing or in a Na⁺-substituted solution. Subsequently, the difference in Ca^2 + entry between the two groups was examined and defined as the NCX mediated Ca^2 + entry. The NCX mediated Ca^2 + entry in the smooth muscle cells was monitored using two methods: Ca^2 +sensitive fluorescence dye Fluo-4 and radioactive Ca^2 +. Ca^2 +-entry was greater in the Na⁺-substituted cells than in the Na⁺-containing cells when measured by either method. This difference was established to be NCX-mediated as it was sensitive to the NCX inhibitors. Thapsigargin diminished the NCX mediated Ca^2 + entry as determined by either method. Immunofluorescence confocal microscopy was used to determine the co-localization of NCX1 and subsarcolemmal SERCA2 in the cells incubated in the Na⁺-substituted solution with or without thapsigargin. SER Ca^2 + depletion with thapsigargin increased the co-localization between NCX1 and the subsarcolemmal SERCA2. Thus, inhibition of SERCA2 leads to blockade of constant Ca^2 + entry through NCX1 and also increases proximity between NCX1 and SERCA2. This blockade of Ca^2 + entry may protect the cells against Ca^2 +-overload during ischemia–reperfusion when SERCA2 is known to be damaged.     

Silencing SERCA1b in a few fibers stimulates growth in the entire regenerating soleus muscle

The neonatal isoform of the sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 1 (SERCA1b) is a dominant Ca²⁺ pump in the young fibers of regenerating muscle. In vivo transfection of about 1% of the fibers with SERCA1b RNAi plasmid resulted in no apparent change in the transfected fibers, but enhanced the increase of fresh weight and fiber size in the whole regenerating rat soleus muscle, until the normal size was reached. Co-transfection of calcineurin inhibitor cain/cabin-1 with SERCA1b RNAi was sufficient to cut down the widespread growth stimulation, but the subsequent transfection of cain into the SERCA1b RNAi transfected muscle did not inhibit muscle growth. The SERCA1b RNAi preferably upregulated the expression of the NFAT reporter lacZ compared to controls when co-transfected into the fibers. Notably, perimuscular injection of interleukin-4 (IL-4) antibody but not that of an unrelevant antibody completely abolished the growth-promoting effect of SERCA1b RNAi. This indicates that silencing SERCA1b in a few fibers stimulates the calcineurin-NFAT-IL-4 pathway and fiber growth in the whole regenerating soleus. These results suggest the presence of an autocrine–paracrine coordination of growing muscle fibers, and put forward a new method to stimulate skeletal muscle regeneration.     

Effects of monovalent cations on Ca uptake by skeletal and cardiac muscle sarcoplasmic reticulum

Ca²⁺ transport by the sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase (SERCA) is sensitive to monovalent cations. Possible K⁺ binding sites have been identified in both the cytoplasmic P-domain and the transmembrane transport-domain of the protein. We measured Ca²⁺ transport into SR vesicles and SERCA ATPase activity in the presence of different monovalent cations. We found that the effects of monovalent cations on Ca²⁺ transport correlated in most cases with their direct effects on SERCA. Choline⁺, however, inhibited uptake to a greater extent than could be accounted for by its direct effect on SERCA suggesting a possible effect of choline on compensatory charge movement during Ca²⁺ transport. Of the monovalent cations tested, only Cs⁺ significantly affected the Hill coefficient of Ca²⁺ transport (n_H). An increase in n_H from ∼2 in K⁺ to ∼3 in Cs⁺ was seen in all of the forms of SERCA examined. The effects of Cs⁺ on the maximum velocity of Ca²⁺ uptake were also different for different forms of SERCA but these differences could not be attributed to differences in the putative K⁺ binding sites of the different forms of the protein.     

Glutathione S‐transferase π complexes with and stimulates Na+,K+‐ATPase

Glutathione S‐transferase (GST) was found to complex with the Na⁺,K⁺‐ATPase as shown by binding assay using quartz crystal microbalance. The complexation was obstructed by the addition of antiserum to the α‐subunit of the Na⁺,K⁺‐ATPase, suggesting the specificity of complexation between GST and the Na⁺,K⁺‐ATPase. Co‐immunoprecipitation experiments, using the anti‐α‐subunit antiserum to precipitate the GST‐Na⁺,K⁺‐ATPase complex and then using antibodies specific to an isoform of GST to identify the co‐precipitated proteins, revealed that GSTπ was complexed with the Na⁺,K⁺‐ATPase. GST stimulated the Na⁺,K⁺‐ATPase activity up to 1.4‐fold. The level of stimulation exhibited a saturable dose–response relationship with the amount of GST added, although the level of stimulation varied depending on the content of GSTπ in the lots of GST received from supplier. The stimulation was also obtained when recombinant GSTπ was used, confirming the results. When GST was treated with reduced glutathione, GST activity was greatly stimulated, whereas the level of stimulation of the Na⁺,K⁺‐ATPase activity was similar to that when untreated GST was added. When GST was treated with H₂O₂, GST activity was greatly diminished while the stimulation of the Na⁺,K⁺‐ATPase activity was preserved. The results suggest that GSTπ complexes with the Na⁺,K⁺‐ATPase and stimulates the latter independent of its GST activity. Copyright © 2012 John Wiley & Sons, Ltd.     

The disparity between effects of vanadate (V) and vanadyl (IV) ions on (Na+-K+)-ATPase and K+-phosphatase in skeletal muscle

On crude membrane fractions of skeletal musccle, vanadyl (IV) and vanadate (V) compounds inhibited the membrane (Na⁺K⁺)-ATPase and neutral (K⁺-)p-nitrophenylphosphatase equally with K_i 4×10^?8 mol.1^?1. Only vanadate (V) inhibited significantly the muscle (Na⁺K⁺)ATPase with K_i 1×10^?6 mol.1^?1, whereas vanadyl (IV) ions were almost without effect. Extracellular application of both forms of vanadium failed to inhibit the electrogenic (Na⁺K⁺) pump in intact mouse diaphragm fibres.