Modulation of the Na,K-ATPase by Magnesium Ions

A Soluble Expression Construct of the Isolated Catalytic Domain of Plasmodium falciparum ATP4 Exhibits ATPase Activity Independent of a γ-Phosphate Receiving Aspartate

The sodium/proton-exchanging ATPase of Plasmodium falciparum malaria parasites, PfATP4, is an emerging drug target. Inhibition results in detrimental cell swelling due to cytosolic accumulation of sodium and alkalization. PfATP4 is a sodium-releasing type II P-type ATPase restricted to apicomplexan parasites. Experimental data on structure-function relationships of the isolated protein are absent. Here, we produced and purified the soluble catalytic domain of PfATP4 and evaluated kinetic properties by in vitro phosphate colorimetry. The protein exhibited Mg2+-dependent ATPase activity at the same order of magnitude as the native cellular PfATP4 and was insensitive to the presence of sodium. AlphaFold 3-based structure and ATP/Mg2+ interaction predictions identified key residues of the nucleotide binding domain (Lys619, Lys652, Arg703). Replacement of the lysines by methionine decreased the enzymatic activity to one quarter. Individual mutation of the putative Mg2+-coordinating Asp865 of the phosphorylation domain was tolerated, while a joint replacement with Asp869 decreased ATPase again to one quarter. Mutation of the putative γ-phosphate receiving Asp451 maintained the rate of Pi release. Our data attribute typical functional roles for P-type ATPases to the basic and acidic residues of the soluble PfATP4 catalytic domain and show that its ATP hydrolysis is independent of phosphorylation of Asp451.

4-amino-3-(phenylselanyl) benzenesulfonamide attenuates intermittent cold stress-induced fibromyalgia in mice: Targeting to the Nrf2-NFκB axis

Stress is widely recognized as the primary environmental factor associated with chronic pain conditions, including fibromyalgia. A recent study demonstrated the potential antinociceptive effects of 4-amino-3-(phenylselanyl) benzenesulfonamide (4-APSB) in acute nociceptive animal models due to its antioxidant and anti-inflammatory properties. However, the efficacy of 4-APSB in managing chronic painful conditions, such as fibromyalgia, has not been explored so far. This study investigated the pharmacological effects of 4-APSB in an experimental model of fibromyalgia induced by intermittent cold stress (ICS). Male and female mice were divided into Control, ICS, 4-APSB, and ICS + 4-APSB. After the ICS, the animals were treated with 4-APSB (1 mg kg-1) or vehicle by the intragastric route until the tenth day. The behavioral tasks were performed on days 5, 8, and 10. The findings showed a negative correlation between paw withdrawal threshold and Nrf2 or NFκB mRNA expression levels caused by ICS exposure. The 4-APSB suppressed the nociceptive signs and a depressive like-phenotype in male and female mice exposed to ICS. 4-APBS normalized the elevated levels of TBARS and the up-regulation of Nrf2 and NFκB expression in the cerebral cortex of ICS-exposed mice. This compound also modulated the oxidative stress in the spinal cord of female mice. The 4-APSB attenuated the inhibition of Na+, K+ - ATPase activity in the central nervous system (CNS) of female mice exposed to ICS. 4-APSB attenuated behavioral and redox imbalance triggered by the ICS model in male and female mice, suggesting its beneficial effects for treating fibromyalgia in both sexes.

Kinetic properties of gill (Na+, K+)-ATPase in the Pacific whiteleg shrimp Penaeus vannamei (Decapoda, Penaeidae)

The whiteleg marine shrimp Penaeus vannamei, originally from the Eastern Pacific Ocean, now inhabits tropical waters across Asia and Central and Southern America. This benthic species exhibits rapid growth, wide salinity and temperature tolerance, and disease resistance. These physiological traits have led to extensive research on its osmoregulatory mechanisms, including next-generation sequencing, transcriptomic analyses, and lipidomic responses. In crustaceans, osmotic and ionic homeostasis is primarily maintained by the membrane-bound metalloenzyme (Na+, K+)-ATPase. However, little is known about how various ligands modulate this enzyme in P. vannamei. Here, we examined the kinetic characteristics of the gill (Na+, K+)-ATPase to get biochemical insights into its modulation. A prominent immunoreactive band of ~120 kDa, corresponding to the (Na+, K+)-ATPase alpha-subunit, was identified. The enzyme exhibited two ATP hydrolyzing sites with K0.5 = 0.0003 ± 0.00002 and 0.05 ± 0.003 mmol L-1 and was stimulated by low sodium ion concentrations. Potassium and ammonium ions also stimulated enzyme activity with similar K0.5 values of 0.08 ± 0.004 and 0.06 ± 0.003 mmol L-1, respectively. Ouabain inhibition profile suggested a single enzyme isoform with a KI value of 2.10 ± 0.16 mmol L-1. Our findings showed significant kinetic differences in the (Na+, K+)-ATPase in Penaeus vannamei compared to marine and freshwater crustaceans. We expect our results to enhance understanding of the modulation of gill (Na+, K+)-ATPase in Penaeus vannamei and to provide a valuable tool for studying the shrimp's biochemical acclimation to varying salinity conditions.

Primary amino acid sequences of decapod (Na+, K+)-ATPase provide evolutionary insights into osmoregulatory mechanisms

Decapod Crustacea exhibit a marine origin, but many taxa have occupied environments ranging from brackish to fresh water and terrestrial habitats, overcoming their inherent osmotic challenges. Osmotic and ionic regulation is achieved by the gill epithelia, driven by two active ATP-hydrolyzing ion transporters, the basal (Na+, K+)-ATPase and the apical V(H+)-ATPase. The kinetic characteristic of gill (Na+, K+)-ATPase and the mRNA expression of its α subunit have been widely studied in various decapod species under different salinity challenges. However, the evolution of the primary structure has not been explored, especially considering the functional modifications associated with decapod phylogeny. Here, we proposed a model for the topology of the decapod α subunit, identifying the sites and motifs involved in its function and regulation, as well as the patterns of its evolution assuming a decapod phylogeny. We also examined both the amino acid substitutions and their functional implications within the context of biochemical and physiological adaptation. The α-subunit of decapod crustaceans shows greater conservation (∼94% identity) compared to the β-subunit (∼40%). While the binding sites for ATP and modulators are conserved in the decapod enzyme, the residues involved in the α-β interaction are only partially conserved. In the phylogenetic context of the complete sequence of (Na+, K+)-ATPase α-subunit, most substitutions appear to be characteristic of the entire group, with specific changes for different subgroups, especially among brachyuran crabs. Interestingly, there was no consistent separation of α-subunit partial sequences related to habitat, suggesting that the convergent evolution for freshwater or terrestrial modes of life is not correlated with similar changes in the enzyme's primary amino acid sequence.

Influence of Anticholinesterase Drugs on Activity and Properties of Na+,K+-ATPase in Rat Erythrocytes under Stress Caused by Intense Physical Exercise

We studied the effect of intramuscular injection of physostigmine and neostigmine on Na+,K+-ATPase activity in erythrocytes of rats subjected to intense physical exercise. Both anticholinesterase drugs had a significant effect on the development of the stress response, which was expressed in a decrease in the manifestation of its individual components such as the concentration of ascorbic acid in the adrenal glands, stress-related erythrocyte polycythemia, and LPO indicators. Anticholinesterase drugs reverse the stress-induced decrease in Na+,K+-ATPase activity, as well as changes in its magnesium-dependent properties. There were no changes in the activity of the studied enzyme in the erythrocyte ghosts. We associate the observed differences with the correction of the functions of the cholinergic components of the hypothalamic-pituitary-adrenal axis leading to the development of a hypoergic type stress reaction.

(Na+, K+)- ATPase kinetics in Macrobrachium pantanalense: highlighting intra- and interspecific variation within the Macrobrachium amazonicum complex

The Macrobrachium amazonicum complex is composed of at least the Macrobrachium amazonicum and Macrobrachium pantanalense species, with the latter described from specimens originally identified as part of an endemic M. amazonicum population in the Brazilian Pantanal region. While there may be a reproductive barrier between these two Macrobrachium species, both are phylogenetically close, with small genetic distance. However, there is currently no available biochemical information of Macrobrachium pantanalense (Na+, K+)-ATPase. Here, we report the kinetic characteristics of the gill (Na+, K+)-ATPase in two populations of M. pantanalense from Baiazinha Lagoon (Miranda, MS, Brazil) and Araguari River (Uberlândia, MG, Brazil), and compare them with Macrobrachium amazonicum populations from the Paraná-Paraguay River Basin. (Na+, K+)-ATPase activities were 67.9 ± 3.4 and 93.3 ± 4.1 nmol Pi min-1 mg-1 protein for the Baiazinha Lagoon and Araguari River populations, respectively. Two ATP hydrolyzing sites were observed for the Araguari River population while a single ATP site was observed for the Baiazinha Lagoon shrimps. Compared to the Araguari River population, a 3-fold greater apparent affinity for Mg2+ and Na+ was estimated for the Baiazinha Lagoon population, but no difference in K+ affinity and ouabain inhibition was seen. The kinetic differences observed in the gill (Na+, K+)-ATPase between the two populations of M. pantanalense, compared with those of various M. amazonicum populations, highlight interspecific divergence within the Macrobrachium genus, now examined from a biochemical perspective.

Elemental mass spectrometry to study metallo-transcriptomic changes during the in vitro degeneration of the retinal pigment epithelium

Trace elements play crucial roles in cellular biology. Their improper homeostasis may contribute to the progress of eye diseases, exacerbated during ageing. The retinal pigment epithelium (RPE) is progressively deteriorated during age-related neurodegeneration and metal homeostasis may be compromised. In this study, elemental mass spectrometry (MS) was combined with cellular and molecular biology techniques to identify changes in trace elements during the in vitro degeneration of human RPE cells. Cells were collected at 21, 91, and 133 days and processed for RNA sequencing; Ca, Na, P, Mg, and Cu quantification by flow injection analysis and inductively coupled plasma-MS; and protein analysis by immunocytochemistry. Four-month-old RPE cultures showed depigmentation, impaired barrier function, and antioxidant protection, manifesting signs of epithelial-to-mesenchymal transition. Na and P significantly increased in the cytosol of degenerated RPE cells (from 15 ± 20 to 13495 ± 638 ng·µg-1 and from 30.6 ± 9.5 to 116.8 ± 16.8 ng·µg-1, respectively). Mg decreased in both the cytosol and insoluble fraction of cells (from 2.83 ± 0.40 to 1.58 ± 0.56 ng·µg-1 and from 247.57 ± 11.06 to 30 ± 8 ng·g-1, respectively), while P and Cu decreased in the insoluble fraction after 133 days in culture (from 9471 ± 1249 to 4555 ± 985 ng·µg-1 and from 2251 ± 79 to 1054 ± 235 ng·g-1, respectively), along with changes in metal-dependent antioxidant enzymes and Cu transporters. This RPE model reflected metal homeostatic changes, providing additional perspectives on effects of metal regulation during ageing.

Comparison of bicarbonate Ringer's solution with lactated Ringer's solution among postoperative outcomes in patients with laparoscopic right hemihepatectomy: a single-centre randomised controlled trial

The study was aimed to investigate the positive impact of bicarbonate Ringer's solution on postoperative outcomes in patients who underwent laparoscopic right hemihepatectomy. Patients in the two groups were infused with lactated Ringer's solution (LRS, n = 38) and the bicarbonate Ringer's solution (BRS, n = 38) at a rate of 5 ml·kg-1·h-1. The stroke volume was monitored and 200 ml of hydroxyethyl starch with 130/0.4 sodium chloride injection (Hes) of a bolus was given in the first 5-10 min. The main outcome was to test lactic acid (LAC) concentration before and after surgery. The concentrations of LAC in the LRS group were higher than in the BRS group at 2 h after operation began, at the end of the operation and 2 h after the operation. Overall, the parameters including pH, base excess (BE), HCO3-, aspartate transaminase (AST) and alanine transaminase (ALT) were improved. The values of bilirubin in the LRS group were higher and albumin were lower than in the BRS group at post-operation 1st and 2nd day (P<0.05). The time of prothrombin time (PT) and activated partial thromboplastin time (APTT) in the LRS group were longer than that in the BRS group at post-operation 1st and 2nd day (P<0.05). Likewise, the concentrations of Mg2+, Na+ and K+ also varied significantly. The length of hospital was reduced, and the incidence of premature ventricular contractions (P = 0.042) and total complications (P = 0.016) were lower in group BRS. TRIAL REGISTRATION: The study was registered at clinicalTrials.gov with the number ChiCTR2000038077 on 09/09/2020.

Cytosolic actin isoforms form networks with different rheological properties that indicate specific biological function

The implications of the existence of different actins expressed in epithelial cells for network mechanics and dynamics is investigated by microrheology and confocal imaging. γ-actin predominately found in the apical cortex forms stiffer networks compared to β-actin, which is preferentially organized in stress fibers. We attribute this to selective interactions with Mg2+-ions interconnecting the filaments' N-termini. Bundling propensity of the isoforms is different in the presence of Mg2+-ions, while crosslinkers such as α-actinin, fascin, and heavy meromyosin alter the mechanical response independent of the isoform. In the presence of myosin, β-actin networks show a large number of small contraction foci, while γ-actin displays larger but fewer foci indicative of a stronger interaction with myosin motors. We infer that subtle changes in the amino acid sequence of actin isoforms lead to alterations of the mechanical properties on the network level with potential implications for specific biological functions.

Differential effects of cobalt ions in vitro on gill (Na+, K+)-ATPase kinetics in the Blue crab Callinectes danae (Decapoda, Brachyura)

We used the gill (Na+, K+)-ATPase as a molecular marker to provide a comprehensive kinetic analysis of the effects of Co2+in vitro on the modulation of K+-phosphatase activity in the Blue crab Callinectes danae. Co2+ can stimulate or inhibit K+-phosphatase activity. With Mg2+, K+-phosphatase activity is almost completely inhibited by Co2+. Co2+ stimulates K+-phosphatase activity similarly to Mg2+ although with a ≈4.5-fold greater affinity. At saturating Mg2+ concentrations, Mg2+ displaces bound Co2+ from the Mg2+-binding site in a concentration dependent manner, but Co2+ cannot displace Mg2+ from its binding site even at millimolar concentrations. Saturation by Co2+ of the Mg2+ binding site does not affect pNPP recognition by the enzyme. Substitution of Mg2+ by Co2+ slightly increases enzyme affinity for K+ and NH4+. Independently of Mg2+, inhibition by ouabain or sodium ions is unaffected by Co2+. Investigation of gill (Na+, K+)-ATPase K+-phosphatase activity provides a reliable tool to examine the kinetic effects of Co2+ with and without Na+ and ATP. Given that the toxic effects of Co2+ at the molecular level are poorly understood, these findings advance our knowledge of the mechanism of action of Co2+ on the crustacean gill (Na+, K+)-ATPase.

The Na+,K+-ATPase and its stoichiometric ratio: some thermodynamic speculations

 Almost seventy years after its discovery, the sodium-potassium adenosine triphosphatase (the sodium pump) located in the cell plasma membrane remains a source of novel mechanistic and physiologic findings. A noteworthy feature of this enzyme/transporter is its robust stoichiometric ratio under physiological conditions: it sequentially counter-transports three sodium ions and two potassium ions against their electrochemical potential gradients per each hydrolyzed ATP molecule. Here we summarize some present knowledge about the sodium pump and its physiological roles, and speculate whether energetic constraints may have played a role in the evolutionary selection of its characteristic stoichiometric ratio.

Implementation of the medical emergencies in eating disorders in adults guidance on non-specialist units

The Royal College of Psychiatrists recently published data showing an 84% increase in UK hospital admissions for eating disorders over the past 5 years, highlighting the importance of the college's new Medical Emergencies in Eating Disorders (MEED) guidance. This includes a 79% increase among adults, many of whom are admitted to general medical wards that do not have input from expert eating disorder services. Consequently, the multidisciplinary nutrition support team, nutrition specialist nurses and dietitians have a potentially vital role in implementing MEED to ensure that the appropriate nutritional, fluid and electrolyte management is in place for safe refeeding and avoidance of the potentially harmful underfeeding syndrome. Furthermore, the guidance includes special recommendations for the use of nasogastric feeding in eating disorder patients, which requires input from experts in this field, including specialist nurses and dietitians. This article focuses on the implementation of MEED on hospital wards that do not have input from specialist eating disorders services.

Physiology of a Forgotten Electrolyte-Magnesium Disorders

Magnesium (Mg²⁺) is the second most common intracellular cation and the fourth most abundant element on earth. However, Mg²⁺ is a frequently overlooked electrolyte and often not measured in patients. While hypomagnesemia is common in 15% of the general population, hypermagnesemia is typically only found in preeclamptic women after Mg²⁺ therapy and in patients with ESRD. Mild to moderate hypomagnesemia has been associated with hypertension, metabolic syndrome, type 2 diabetes mellitus, CKD, and cancer. Nutritional Mg²⁺ intake and enteral Mg²⁺ absorption are important for Mg²⁺ homeostasis, but the kidneys are the key regulators of Mg²⁺ homeostasis by limiting urinary excretion to less than 4% while the gastrointestinal tract loses over 50% of the Mg²⁺ intake in the feces. Here, we review the physiological relevance of Mg²⁺, the current knowledge of Mg²⁺ absorption in the kidneys and the gut, the different causes of hypomagnesemia, and a diagnostic approach on how to assess Mg²⁺ status. We highlight the latest discoveries of monogenetic conditions causing hypomagnesemia, which have enhanced our understanding of tubular Mg²⁺ absorption. We will also discuss external and iatrogenic causes of hypomagnesemia and advances in the treatment of hypomagnesemia.

Measurements of Na+-occluded intermediates during the catalytic cycle of the Na+/K+-ATPase provide novel insights into the mechanism of Na+ transport

The Na⁺/K⁺-ATPase is an integral plasma membrane glycoprotein of all animal cells that couples the exchange of intracellular Na⁺ for extracellular K⁺ to the hydrolysis of ATP. The asymmetric distribution of Na⁺ and K⁺ is essential for cellular life and constitutes the physical basis of a series of fundamental biological phenomena. The pumping mechanism is explained by the Albers-Post model. It involves the presence of gates alternatively exposing Na⁺/K⁺-ATPase transport sites to the intracellular and extracellular sides and includes occluded states in which both gates are simultaneously closed. Unlike for K⁺, information is lacking about Na⁺-occluded intermediates, as occluded Na⁺ was only detected in states incapable of performing a catalytic cycle, including two Na⁺-containing crystallographic structures. The current knowledge is that intracellular Na⁺ must bind to the transport sites and become occluded upon phosphorylation by ATP to be transported to the extracellular medium. Here, taking advantage of epigallocatechin-3-gallate to instantaneously stabilize native Na⁺-occluded intermediates, we isolated species with tightly bound Na⁺ in an enzyme able to perform a catalytic cycle, consistent with a genuine occluded state. We found that Na⁺ becomes spontaneously occluded in the E1 dephosphorylated form of the Na⁺/K⁺-ATPase, exhibiting positive interactions between binding sites. In fact, the addition of ATP does not produce an increase in Na⁺ occlusion as it would have been expected; on the contrary, occluded Na⁺ transiently decreases, whereas ATP lasts. These results reveal new properties of E1 intermediates of the Albers-Post model for explaining the Na⁺ transport pathway.

Magnesium stable isotope composition, but not concentration, responds to obesity and early insulin-resistant conditions in minipig

Hypomagnesemia is frequently associated with type 2 diabetes and generally correlates with unfavorable disease progression, but the magnesium status in pre-diabetic conditions remains unclear. Here, the magnesium metabolism is scrutinized in a minipig model of obesity and insulin resistance by measuring variations of the metallome—the set of inorganic elements—and the magnesium stable isotope composition in six organs of lean and obese minipigs raised on normal and Western-type diet, respectively. We found that metallomic variations are most generally insensitive to lean or obese phenotypes. The magnesium stable isotope composition of plasma, liver, kidney, and heart in lean minipigs are significantly heavier than in obese minipigs. For both lean and obese minipigs, the magnesium isotope composition of plasma and liver were negatively correlated to clinical phenotypes and plasma lipoproteins concentration as well as positively correlated to hyperinsulinemic-euglycemic clamp output. Because the magnesium isotope composition was not associated to insulin secretion, our results suggest that it is rather sensitive to whole body insulin sensitivity, opening perspectives to better comprehend the onset of insulin-resistant diabetic conditions.

The Roles and Pathogenesis Mechanisms of a Number of Micronutrients in the Prevention and/or Treatment of Chronic Hepatitis, COVID-19 and Type-2 Diabetes Mellitus

A trace element is a chemical element with a concentration (or other measures of an amount) that is very low. The essential TEs, such as copper (Cu), selenium (Se), zinc (Zn), iron (Fe) and the electrolyte magnesium (Mg) are among the most commonly studied micronutrients. Each element has been shown to play a distinctive role in human health, and TEs, such as iron (Fe), zinc (Zn) and copper (Cu), are among the essential elements required for the organisms' well-being as they play crucial roles in several metabolic pathways where they act as enzyme co-factors, anti-inflammatory and antioxidant agents. Epidemics of infectious diseases are becoming more frequent and spread at a faster pace around the world, which has resulted in major impacts on the economy and health systems. Different trace elements have been reported to have substantial roles in the pathogenesis of viral infections. Micronutrients have been proposed in various studies as determinants of liver disorders, COVID-19 and T2DM risks. This review article sheds light on the roles and mechanisms of micronutrients in the pathogenesis and prevention of chronic hepatitis B, C and E, as well as Coronavirus-19 infection and type-2 diabetes mellitus. An update on the status of the aforementioned micronutrients in pre-clinical and clinical settings is also briefly summarized.

Effect of Fe3+ on Na,K-ATPase: Unexpected activation of ATP hydrolysis

Iron is a key element in cell function; however, its excess in iron overload conditions can be harmful through the generation of reactive oxygen species (ROS) and cell oxidative stress. Activity of Na,K-ATPase has been shown to be implicated in cellular iron uptake and iron modulates the Na,K-ATPase function from different tissues. In this study, we determined the effect of iron overload on Na,K-ATPase activity and established the role that isoforms and conformational states of this enzyme has on this effect. Total blood and membrane preparations from erythrocytes (ghost cells), as well as pig kidney and rat brain cortex, and enterocytes cells (Caco-2) were used. In E1-related subconformations, an enzyme activation effect by iron was observed, and in the E2-related subconformations enzyme inhibition was observed. The enzyme's kinetic parameters were significantly changed only in the Na⁺ curve in ghost cells. In contrast to Na,K-ATPase α2 and α3 isoforms, activation was not observed for the α1 isoform. In Caco-2 cells, which only contain Na,K-ATPase α1 isoform, the FeCl₃ increased the intracellular storage of iron, catalase activity, the production of H₂O₂ and the expression levels of the α1 isoform. In contrast, iron did not affect lipid peroxidation, GSH content, superoxide dismutase and Na,K-ATPase activities. These results suggest that iron itself modulates Na,K-ATPase and that one or more E1-related subconformations seems to be determinant for the sensitivity of iron modulation through a mechanism in which the involvement of the Na, K-ATPase α3 isoform needs to be further investigated.

Functional characterization of Legionella pneumophila Cu+ transport ATPase. The activation by Cu+ and ATP

Cu⁺-ATPases are integral membrane proteins belonging to the IB subfamily of the P-type ATPases that couple Cu⁺ transport to the hydrolysis of ATP. As some structural and functional particularities arise for Cu⁺-ATPases, several authors suggest that some of the reaction steps of the Albers-Post model postulated for other P-ATPases may be different. In this work we describe a functional characterization of Legionella pneumophila Cu⁺-ATPase (LpCopA), the first P_IB-ATPase whose structure was determined by X-ray crystallography. Cu⁺-ATPase activity of the enzyme presents a maximum at ∼37 °C and pH 6.6-6.8. Phospholipids enhance LpCopA Cu⁺-ATPase activity in a non-essential mode where optimal activity is achieved at an asolectin molar fraction of 0.15 and an amphiphile-protein ratio of ~30,000. As described for other P-ATPases, Mg²⁺ acts as an essential activator. Furthermore, Cu⁺-ATPase activity dependence on [Cu⁺] and [ATP] can both be described by a sum of two hyperbolic functions. Based on that, and the [Cu⁺] and [ATP] dependencies of the best fitting parameters of the hyperbolae pointed above, we propose a minimal reaction scheme for the catalytic mechanism that shares the basic reaction steps of the Albers-Post model for P-type ATPases. The reaction scheme postulated contemplates two different binding affinities for a single ATP (apparent affinities of 0.66 and 550 μM at [Cu⁺] → ∞) and binding of at least 2 Cu⁺ with different affinities as well (apparent affinities of 1.4 and 102.5 μM at [ATP] → ∞).

Bioabsorbable metal zinc differentially affects mitochondria in vascular endothelial and smooth muscle cells

Zinc is an essential trace element having various structural, catalytic and regulatory interactions with an estimated 3000 proteins. Zinc has drawn recent attention for its use, both as pure metal and alloyed, in arterial stents due to its biodegradability, biocompatibility, and low corrosion rates. Previous studies have demonstrated that zinc metal implants prevent the development of neointimal hyperplasia, which is a common cause of restenosis following coronary intervention. This suppression appears to be smooth muscle cell-specific, as reendothelization of the neointima is not inhibited. To better understand the basis of zinc's differential effects on rat aortic smooth muscle (RASMC) versus endothelial (RAENDO) cells, we conducted a transcriptomic analysis of both cell types following one-week continuous treatment with 5 µM or 50 µM zinc. This analysis indicated that genes whose protein products regulate mitochondrial functions, including oxidative phosphorylation and fusion/fission, are differentially affected by zinc in the two cell types. To better understand this, we performed Seahorse metabolic flux assays and quantitative imaging of mitochondrial networks in both cell types. Zinc treatment differently affected energy metabolism and mitochondrial structure/function in the two cell types. For example, both basal and maximal oxygen consumption rates were increased by zinc in RASMC but not in RAENDO. Zinc treatment increased apparent mitochondrial fusion in RASMC cells but increased mitochondrial fission in RAENDO cells. These results provide some insight into the mechanisms by which zinc treatment differently affects the two cell types and this information is important for understanding the role of zinc treatment in vascular cells and improving its use in biodegradable metal implants.

Effect of Detergents on Activity and Magnesium-Dependent Properties of Different Isoforms of Na+,K+-ATPase in the Crude Membrane Fraction of Rat Cerebral Cortex

We studied the effect of various detergents (Tween-20, Triton X-100, and sodium deoxycholate) on activity and magnesium-dependent properties of Na⁺,K⁺-ATPase of the crude membrane fraction of rat cerebral cortex. All studied detergents significantly increased activity of the studied enzyme in a concentration-dependent manner. Sodium deoxycholate provided significantly higher values Na⁺,K⁺-ATPase activity (by ≈50%) than Triton X-100 and Tween-20. In the presence of Triton X-100, a changed pattern of the dependence of enzyme activity on the concentration of magnesium ions in the incubation solution was noted. Separate measurement of activities of Na⁺,K⁺-ATPase isoforms made it possible to assume that changes in magnesium-dependent properties are due to the predominant effect of Triton X-100 on ouabain-sensitive α2- and α3-isoforms.

Sex-specific associations of plasma metals and metal mixtures with glucose metabolism: An occupational population-based study in China

Studies with multi-pollutant approach on the relationships between multiple metals and fasting plasma glucose (FPG) are limited. Few studies are available on the potential sex-specific associations between metal exposures and glucose metabolism. We explored the associations between 22 plasma metals and FPG level among the 769 participants from the manganese-exposed workers healthy cohort in China. We applied a sparse partial least squares (sPLS) regression followed by ordinary least-squares regression to evaluate multi-pollutant association. Bayesian kernel machine regression (BKMR) model was used to deal with metal mixtures and evaluate their joint effects on FPG level. In the sPLS model, negative associations on FPG levels were observed for plasma iron (belta = -0.066), cobalt (belta = -0.075), barium (belta = -0.109), and positive associations for strontium (belta = 0.082), and selenium (belta = 0.057) in men, which overlapped with the results among the overall participants. Among women, plasma copper (belta = 0.112) and antimony (belta = 0.137) were positively associated with elevated FPG level. Plasma magnesium was negatively associated with FPG level in both sexes (belta = -0.071 in men and belta = -0.144 in women). The results of overlapped for plasma magnesium was selected as the significant contributor to decreasing FPG level in the multi-pollutant, single-metal, and multi-metal models. BKMR model showed a significantly negative over-all effect of six metal mixtures (magnesium, iron, cobalt, selenium, strontium and barium) on FPG level among the overall participants from all the metals fixed at 50th percentile. In summary, our findings underline the probable role of metals in glucose homeostasis with potential sex-dependent heterogeneities, and suggest more researches are needed to explore the sex-specific associations of metal exposures with risk of diabetes.

High-magnesium exposure to bullfrog heart causes ST segment elevation

Hypermagnesemia occurs in elderly people or patients with renal insufficiency after excessive ingestion of magnesium-containing laxatives. In addition to typical electrocardiogram (ECG) findings caused by conduction defects, changes in the ST segments and T waves are also observed in patients with severe hypermagnesemia. This suggested the involvement of similar pathophysiology to acute myocardial infarction, as we previously demonstrated using burn-induced subepicardial injury model in frog hearts. In the present study, by exposing the bullfrog heart to high-magnesium solution, we reproduced prominent ST segment changes in ECG as actually observed in patients with severe hypermagnesemia. In addition to the great increase in the T waves, the ECG showed a marked elevation of the ST segments and the cardiac action potential demonstrated a marked shift of the resting membrane potential to the depolarized side. High-magnesium exposure did not affect the abundance of Na⁺/K⁺-ATPase proteins. However, the pharmacological stimulation of Na⁺/K⁺-ATPase activity by insulin quickly retrieved the elevated ST segments in ECG. From these results, the functional blockade of Na⁺/K⁺-ATPase activity by magnesium ions was thought to be responsible for generating the potassium concentration gradient and the subsequent ST segment changes.

Mechanisms coupling sodium and magnesium reabsorption in the distal convoluted tubule of the kidney

Hypomagnesaemia is a common feature of renal Na+ wasting disorders such as Gitelman and EAST/SeSAME syndrome. These genetic defects specifically affect Na+ reabsorption in the distal convoluted tubule, where Mg2+ reabsorption is tightly regulated. Apical uptake via TRPM6 Mg2+ channels and basolateral Mg2+ extrusion via a putative Na+ -Mg2+ exchanger determines Mg2+ reabsorption in the distal convoluted tubule. However, the mechanisms that explain the high incidence of hypomagnesaemia in patients with Na+ wasting disorders of the distal convoluted tubule are largely unknown. In this review, we describe three potential mechanisms by which Mg2+ reabsorption in the distal convoluted tubule is linked to Na+ reabsorption. First, decreased activity of the thiazide-sensitive Na+ /Cl- cotransporter (NCC) results in shortening of the segment, reducing the Mg2+ reabsorption capacity. Second, the activity of TRPM6 and NCC are determined by common regulatory pathways. Secondary effects of NCC dysregulation such as hormonal imbalance, therefore, might disturb TRPM6 expression. Third, the basolateral membrane potential, maintained by the K+ permeability and Na+ -K+ -ATPase activity, provides the driving force for Na+ and Mg2+ extrusion. Depolarisation of the basolateral membrane potential in Na+ wasting disorders of the distal convoluted tubule may therefore lead to reduced activity of the putative Na+ -Mg2+ exchanger SLC41A1. Elucidating the interconnections between Mg2+ and Na+ transport in the distal convoluted tubule is hampered by the currently available models. Our analysis indicates that the coupling of Na+ and Mg2+ reabsorption may be multifactorial and that advanced experimental models are required to study the molecular mechanisms.

Magnesium in Obesity, Metabolic Syndrome, and Type 2 Diabetes

Magnesium (Mg²⁺) deficiency is probably the most underestimated electrolyte imbalance in Western countries. It is frequent in obese patients, subjects with type-2 diabetes and metabolic syndrome, both in adulthood and in childhood. This narrative review aims to offer insights into the pathophysiological mechanisms linking Mg²⁺ deficiency with obesity and the risk of developing metabolic syndrome and type 2 diabetes. Literature highlights critical issues about the treatment of Mg²⁺ deficiency, such as the lack of a clear definition of Mg²⁺ nutritional status, the use of different Mg²⁺ salts and dosage and the different duration of the Mg²⁺ supplementation. Despite the lack of agreement, an appropriate dietary pattern, including the right intake of Mg²⁺, improves metabolic syndrome by reducing blood pressure, hyperglycemia, and hypertriglyceridemia. This occurs through the modulation of gene expression and proteomic profile as well as through a positive influence on the composition of the intestinal microbiota and the metabolism of vitamins B1 and D.

Slowing Development Facilitates Arabidopsis mgt Mutants to Accumulate Enough Magnesium for Pollen Formation and Fertility Restoration

Magnesium (Mg) is an abundant and important cation in cells. Plants rely on Mg transporters to take up Mg from the soil, and then Mg is transported to anthers and other organs. Here, we showed that MGT6+/- plants display reduced fertility, while mgt6 plants are fertile. MGT6 is expressed in the anther at the early stages. Pollen mitosis and intine formation are impaired in aborted pollen grains (PGs) of MGT6+/- plants, which is similar to the defective pollen observed in mgt5 and mgt9 mutants. These results suggest that Mg deficiency leads to pollen abortion in MGT6+/- plants. Our data showed that mgt6 organs including buds develop significantly slower and mgt6 stamens accumulate a higher level of Mg, compared with wild-type (WT) and MGT6+/- plants. These results indicate that slower bud development allows mgt6 to accumulate sufficient amounts of Mg in the pollen, explaining why mgt6 is fertile. Furthermore, we found that mgt6 can restore fertility of mgt5, which has been reported to be male sterile due to defects in Mg transport from the tapetum to microspores and that an additional Mg supply can restore its fertility. Interestingly, mgt5 fertility is recovered when grown under short photoperiod conditions, which is a well-known factor regulating plant fertility. Taken together, these results demonstrate that slow development is a general mechanism to restore mgts fertility, which allows other redundant magnesium transporter (MGT) members to transport sufficient Mg for pollen formation.

SARS-CoV-2: influence of phosphate and magnesium, moderated by vitamin D, on energy (ATP) metabolism and on severity of COVID-19

The use of vitamin D to reduce the severity of COVID-19 complications is receiving considerable attention, backed by encouraging data. Its purported mode of action is as an immune modulator. Vitamin D, however, also affects the metabolism of phosphate and Mg, which may well play a critical role in SARS-CoV-2 pathogenesis. SARS-CoV-2 may induce a cytokine storm that drains ATP whose regeneration requires phosphate and Mg. These minerals, however, are often deficient in conditions that predispose people to severe COVID-19, including older age (especially males), diabetes, obesity, and usage of diuretics. Symptoms observed in severe COVID-19 also fit well with those seen in classical hypophosphatemia and hypomagnesemia, such as thrombocytopenia, coagulopathy, dysfunction of liver and kidneys, neurologic disturbances, immunodeficiency, failure of heart and lungs, delayed weaning from a respirator, cardiac arrhythmia, seizures, and, finally, multiorgan failure. Deficiencies of phosphate and Mg can be amplified by kidney problems commonly observed in patients with COVID-19 resulting in their wastage into urine. Available data show that phosphate and Mg are deficient in COVID-19, with phosphate showing a remarkable correlation with its severity. In one experiment, patients with COVID-19 were supplemented with a cocktail of vitamin D3, Mg, and vitamin B12, with very encouraging results. We, thus, argue that patients with COVID-19 should be monitored and treated for phosphate and Mg deficiencies, ideally already in the early phases of infection. Supplementation of phosphate and Mg combined with vitamin D could also be implemented as a preventative strategy in populations at risk.

The Effect of Low Magnesium Concentration on Ictal Discharges In A Non-Synaptic Model

Magnesium (Mg[Formula: see text] is an essential mineral for several cellular functions. The concentration of this ion below the physiological concentration induces recurrent neuronal discharges both in slices of the hippocampus and in neuronal cultures. These epileptiform discharges are initially sensitive to the application of [Formula: see text]-methyl-D-aspartate (NMDA) receptor antagonists, but these antagonists may lose their effectiveness with prolonged exposure to low [Mg[Formula: see text]], when extracellular Ca[Formula: see text] reduction occurs, typical of ictal periods, indicating the absence of synaptic connections. The study herein presented aimed at investigating the effect of reducing the [Mg[Formula: see text]] during the induction of Nonsynaptic Epileptiform Activities (NSEA). As an experimental protocol, NSEA were induced in rat hippocampal dentate gyrus (DG), using a bath solution containing high-K[Formula: see text] and zero-added-Ca[Formula: see text]. Additionally, computer simulations were performed using a mathematical model that represents electrochemical characteristics of the tissue of the DG granular layer. The experimental results show that the reduction of [Mg[Formula: see text]] causes an increase in the duration of the ictal period and a reduction in the interictal period, intensifying epileptiform discharges. The computer simulations suggest that the reduction of the Mg[Formula: see text] level intensifies the epileptiform discharges by a joint effect of reducing the surface charge screening and reducing the activity of the Na/K pump.

Partial Reactions of the Na,K-ATPase: Determination of Activation Energies and an Approach to Mechanism

Abstract

Kinetic experiments were performed with preparations of kidney Na,K-ATPase in isolated membrane fragments or reconstituted in vesicles to obtain information of the activation energies under turnover conditions and for selected partial reactions of the Post-Albers pump cycle. The ion transport activities were detected with potential or conformation sensitive fluorescent dyes in steady-state or time-resolved experiments. The activation energies were derived from Arrhenius plots of measurements in the temperature range between 5 °C and 37 °C. The results were used to elaborate indications of the respective underlying rate-limiting reaction steps and allowed conclusions to be drawn about possible molecular reaction mechanisms. The observed consequent alteration between ligand-induced reaction and conformational relaxation steps when the Na,K-ATPase performs the pump cycle, together with constraints set by thermodynamic principles, provided restrictions which have to be met when mechanistic models are proposed. A model meeting such requirements is presented for discussion.

Graphic Abstract

Microneedle-Assisted Percutaneous Transport of Magnesium Sulfate

OBJECTIVE

In vitro diffusion experiments were performed to assess the permeation of magnesium sulfate across pig skin.

METHODS

The mean thickness of the dermatomed porcine skin was 648 ± 12 µm. Magnesium concentration was measured using inductively coupled plasma-optical emission spectroscopy. Transdermal flux of magnesium sulfate across MN-treated and untreated porcine skin was obtained from the slope of the steady-state linear portion of cumulative amount versus time curve.

RESULTS

Statistical analysis of the results was done with Student's t-test. The transdermal flux of magnesium sulfate across microneedle-treated porcine skin was 134.19 ± 2.4 µg/cm2/h and transdermal flux across untreated porcine skin was 4.64 ± 0.05 µg/cm2/h. Confocal microscopy was used to visualize the microchannels created by a solid microneedle roller (500 µm).

CONCLUSION

From our confocal microscopy studies, it was evident that the 500 μm long microneedles disrupted the stratum corneum and created microchannels measuring 191 ± 37 µm. The increase in transdermal flux across the microneedle-treated skin was statistically significant compared to that of controls, i.e., without the application of microneedles. With the application of microneedles, the transdermal flux of magnesium permeated over 12 h was approximately 33-fold higher in comparison to passive diffusion across an intact stratum corneum.

NaCl cotransporter activity and Mg2+ handling by the distal convoluted tubule

The genetic disease Gitelman syndrome, knockout mice, and pharmacological blockade with thiazide diuretics have revealed that reduced activity of the NaCl cotransporter (NCC) promotes renal Mg²⁺ wasting. NCC is expressed along the distal convoluted tubule (DCT), and its activity determines Mg²⁺ entry into DCT cells through transient receptor potential channel subfamily M member 6 (TRPM6). Several other genetic forms of hypomagnesemia lower the drive for Mg²⁺ entry by inhibiting activity of basolateral Na⁺-K⁺-ATPase, and reduced NCC activity may do the same. Lower intracellular Mg²⁺ may promote further Mg²⁺ loss by directly decreasing activity of Na⁺-K⁺-ATPase. Lower intracellular Mg²⁺ may also lower Na⁺-K⁺-ATPase indirectly by downregulating NCC. Lower NCC activity also induces atrophy of DCT cells, decreasing the available number of TRPM6 channels. Conversely, a mouse model with increased NCC activity was recently shown to display normal Mg²⁺ handling. Moreover, recent studies have identified calcineurin and uromodulin (UMOD) as regulators of both NCC and Mg²⁺ handling by the DCT. Calcineurin inhibitors paradoxically cause hypomagnesemia in a state of NCC activation, but this may be related to direct effects on TRPM6 gene expression. In Umod^-/- mice, the cause of hypomagnesemia may be partly due to both decreased NCC expression and lower TRPM6 expression on the cell surface. This mini-review discusses these new findings and the possible role of altered Na⁺ flux through NCC and ultimately Na⁺-K⁺-ATPase in Mg²⁺ reabsorption by the DCT.

Hemolymph composition, gene expressions in the gills, and thus the survival of euryhaline crabs are controlled by ambient minor cations according to osmotic condition-dependent manner

Na+ and Cl- are the most abundant dissolved ions in seawater, constituting ~ 85% of total ions. They significantly affect the osmolality of body fluids of marine invertebrates. Seawater also contains minor ions such as Mg2+, Ca2+, K+, and SO4 2- , but their effects on marine organisms are unclear. This study analyzed the effects of Mg2+, Ca2+, and K+ (ambient minor cations) on survival, hemolymph ionic composition, and gene expression in the gills of three euryhaline crabs: Helice tridens, Macrophthalmus japonicus, and Chiromantes dehaani. Ambient minor cations were required for survival of H. tridens and M. japonicus under isosmotic conditions with seawater. The ambient minor cations also affected the osmolality and ionic composition of hemolymph by regulating expressions of specific genes in the gills required for Na+ uptake, such as Na+/K+ ATPase, cytoplasmic carbonic anhydrase, and Na+/H+ exchanger. Administration of carbonic anhydrase and Na+/H+ exchanger inhibitors increased the survival rate even if ambient minor cations did not exist. In contrast, under hypo-osmotic conditions, ambient minor cations had different effects on crabs, a lethal effect on M. japonicus, and an increase of the hemolymph K+ concentration in H. tridens and M. japonicus. It is thus concluded that the effects of ambient minor cations are osmolality-dependent. In contrast, in C. dehaani, the hemolymph ionic composition and survival rate were hardly affected by ambient minor cations, probably reflecting the habitat of this species. These results strongly indicated that C. dehaani is less susceptive to ambient minor cations compared to H. tridens and M. japonicus.

Biochemical Characterization and Allosteric Modulation by Magnesium of (Na+, K+)-ATPase Activity in the Gills of the Red Mangrove Crab Goniopsis cruentata (Brachyura, Grapsidae)

We provide a kinetic characterization of (Na⁺, K⁺)-ATPase activity in a posterior gill microsomal fraction from the grapsid crab Goniopsis cruentata. (Na⁺, K⁺)-ATPase activity constitutes 95% of total ATPase activity, and sucrose density centrifugation reveals an ATPase activity peak between 25 and 35% sucrose, distributed into two, partially separated protein fractions. The (Na⁺, K⁺)-ATPase α-subunit is localized throughout the ionocyte cytoplasm and has an M_r of ≈ 10 kDa and hydrolyzes ATP obeying cooperative kinetics. Low (V_M = 186.0 ± 9.3 nmol Pi min^-1 mg^-1 protein and K_0.5 = 0.085 ± 0.004 mmol L^-1) and high (V_M = 153.4 ± 7.7 nmol Pi min^-1 mg^-1 protein and K_0.5 = 0.013 ± 0.0006 mmol L^-1) affinity ATP binding sites were characterized. At low ATP concentrations, excess Mg²⁺ stimulates the enzyme, triggering exposure of a high-affinity binding site that accounts for 50% of (Na⁺, K⁺)-ATPase activity. Stimulation by Mg²⁺ (V_M = 425.9 ± 25.5 nmol Pi min^-1 mg^-1 protein, K_0.5 = 0.16 ± 0.01 mmol L^-1), K⁺ (V_M = 485.3 ± 24.3 nmol Pi min^-1 mg^-1 protein, K_0.5 = 0.9 ± 0.05 mmol L^-1), Na⁺ (V_M = 425.0 ± 23.4 nmol Pi min^-1 mg^-1 protein, K_0.5 = 5.1 ± 0.3 mmol L^-1) and NH₄⁺ (V_M = 497.9 ± 24.9 nmol Pi min^-1 mg^-1 protein, K_0.5 = 9.7 ± 0.5 mmol L^-1) obeys cooperative kinetics. Ouabain inhibits up to 95% of ATPase activity with K_I = 196.6 ± 9.8 µmol L^-1. This first kinetic characterization of the gill (Na⁺, K⁺)-ATPase in Goniopsis cruentata enables better comprehension of the biochemical underpinnings of osmoregulatory ability in this semi-terrestrial mangrove crab.

Inosine protects against impairment of memory induced by experimental model of Alzheimer disease: a nucleoside with multitarget brain actions

RATIONALE

Inosine is a naturally occurring purine nucleoside formed by adenosine breakdown. This nucleoside is reported to exert potent effects on memory and learning, possibly through its antioxidant and anti-inflammatory actions.

OBJECTIVE

The objective is to evaluate the effects of inosine on the behavioral and neurochemical parameters in a rat model of Alzheimer's disease (AD) induced by streptozotocin (STZ).

METHODS

Adult male rats were divided into four groups: control (saline), STZ, STZ plus inosine (50 mg/kg), and STZ plus inosine (100 mg/kg). STZ (3 mg/kg) was administered by bilateral intracerebroventricular injection. The animals were treated intraperitoneally with inosine for 25 days. Memory, oxidative stress, ion pump activities, acetylcholinesterase (AChE), and choline acetyltransferase (ChAT) activities and expression were evaluated in the cerebral cortex and hippocampus.

RESULTS

The memory impairment induced by STZ was prevented by inosine. An increase in the Na⁺, K⁺-ATPase, and Mg-ATPase activities and a decrease in the Ca²⁺-ATPase activity were induced by STZ in the hippocampus and cerebral cortex, and inosine could prevent these alterations in ion pump activities. Inosine also prevented the increase in AChE activity and the alterations in AChE and ChAT expression induced by STZ. STZ increased the reactive oxygen species, nitrite levels, and superoxide dismutase activity and decreased the catalase and glutathione peroxidase activities. Inosine treatment conferred protection from these oxidative alterations in the brain.

CONCLUSIONS

Our findings demonstrate that inosine affects brain multiple targets suggesting that this molecule may have therapeutic potential against cognitive deficit and tissue damage in AD.

Dietary magnesium deficiency impaired intestinal structural integrity in grass carp (Ctenopharyngodon idella)

Grass carp (223.85–757.33 g) were fed diets supplemented with magnesium (73.54–1054.53 mg/kg) for 60 days to explore the impacts of magnesium deficiency on the growth and intestinal structural integrity of the fish. The results demonstrated that magnesium deficiency suppressed the growth and damaged the intestinal structural integrity of the fish. We first demonstrated that magnesium is partly involved in (1) attenuating antioxidant ability by suppressing Nrf2 signalling to decrease antioxidant enzyme mRNA levels and activities (except CuZnSOD mRNA levels and activities); (2) aggravating apoptosis by activating JNK (not p38MAPK) signalling to upregulate proapoptotic protein (Apaf-1, Bax and FasL) and caspase-2, -3, -7, -8 and -9 gene expression but downregulate antiapoptotic protein (Bcl-2, IAP and Mcl-1b) gene expression; (3) weakening the function of tight junctional complexes (TJs) by promoting myosin light chain kinase (MLCK) signalling to downregulate TJ gene expression [except claudin-7, ZO-2b and claudin-15 gene expression]. Additionally, based on percent weight gain (PWG), against reactive oxygen species (ROS), against caspase-9 and claudin-3c in grass carp, the optimal dietary magnesium levels were calculated to be 770.38, 839.86, 856.79 and 811.49 mg/kg, respectively.

Effect of lansoprazole on human sperm motility, sperm viability, seminal nitric oxide production, and seminal calcium chelation

Lansoprazole is a proton-pump inhibitor that is commonly used to treat many gastric illnesses. However, little is known about its effect on sperm function. Here, we investigated the in vitro effect of LP on human sperm motility, viability, nitric oxide (NO) production, and the ability of LP to chelate seminal calcium. Seventy-two semen samples from normozoospermic men were tested in this study. The effects of LP at 0.375, 0.75, 1.5, and 3 μg/mL on sperm motility and viability as well as at 3 μg/mL on NO production and calcium chelation in semen were assessed. Lansoprazole at 3 μg/mL significantly decreased total and progressive sperm motility (P = 0.0021, P = 0.0256, respectively), but not sperm viability (P = 0.8763). In addition, semen samples supplemented with 3 μg/mL LP had insignificant changes (P = 0.9085) in nitrite concentrations. Moreover, LP exhibited a significant (P < 0.0001) calcium chelation effect in semen. In conclusion, LP reduced sperm motility, but not viability. The reduction in sperm motility may be due to the calcium chelating effect of LP and/or decreased Na⁺/K⁺-ATPase activity, but not an alteration in NO production. Besides, none of the tested parameters was found to be correlated with male age.

Serum trace elements in insulin-dependent and non-insulin-dependent diabetes: a comparative study

BACKGROUND

Diabetes mellitus is associated with imbalance in body trace elements. The aim of the current investigation was to compare the levels of trace elements (Zn, Mg, Mn, Cu, Na, K, Fe, Ca, Cr, and Se) in insulin dependent (IDDM) and non-insulin dependent (NIDDM) diabetes.

METHODS

A total of 100 patients with diabetes (40 IDDM and 60 NIDDM) and 50 healthy subjects were recruited in the study from both genders. Biochemical measures include glucose, lipids, and HbA1C.

RESULTS

The results showed that Zn, Mg, Cu and Cr were significant lower in patients with diabetes compared to the control group (P<0.01). In addition, Zn and Cr were significantly lower in IDDM than NIDDM (P<0.05). Moreover, Zn and Mg levels were inversely correlated with HbA1c in IDDM and NIDDM (P<0.05). Zn was inversely correlated with fasting blood glucose in IDDM (P<0.05). Finally, no correlation between trace element levels with BMI was found (P>0.05).

CONCLUSION

Disturbance in trace element profile among IDDM and NIDDM is similar.

A Kinetic Characterization of the Gill (Na+, K+)-ATPase from the Semi-terrestrial Mangrove Crab Cardisoma guanhumi Latreille, 1825 (Decapoda, Brachyura)

We provide a kinetic characterization of (Na⁺, K⁺)-ATPase activity in a posterior gill microsomal fraction from the semi-terrestrial mangrove crab Cardisoma guanhumi. Sucrose density gradient centrifugation reveals two distinct membrane fractions showing considerable (Na⁺, K⁺)-ATPase activity, but also containing other microsomal ATPases. The (Na⁺, K⁺)-ATPase, notably immuno-localized to the apical region of the epithelial pillar cells, and throughout the pillar cell bodies, has an M _r of around 110 kDa and hydrolyzes ATP with V _M = 146.8 ± 6.3 nmol Pi min^-1 mg protein^-1 and K _M = 0.05 ± 0.003 mmol L^-1 obeying Michaelis-Menten kinetics. While stimulation by Na⁺ (V _M = 139.4 ± 6.9 nmol Pi min^-1 mg protein^-1, K _M = 4.50 ± 0.22 mmol L^-1) also follows Michaelis-Menten kinetics, modulation of (Na⁺, K⁺)-ATPase activity by MgATP (V _M = 136.8 ± 6.5 nmol Pi min^-1 mg protein^-1, K _0.5 = 0.27 ± 0.04 mmol L^-1), K⁺ (V _M = 140.2 ± 7.0 nmol Pi min^-1 mg protein^-1, K _0.5 = 0.17 ± 0.008 mmol L^-1), and NH₄⁺ (V _M = 149.1 ± 7.4 nmol Pi min^-1 mg protein^-1, K _0.5 = 0.60 ± 0.03 mmol L^-1) shows cooperative kinetics. Ouabain (K _I = 52.0 ± 2.6 µmol L^-1) and orthovanadate (K _I = 1.0 ± 0.05 µmol L^-1) inhibit total ATPase activity by around 75%. At low Mg²⁺ concentrations, ATP is an allosteric modulator of the enzyme. This is the first study to provide a kinetic characterization of the gill (Na⁺, K⁺)-ATPase in C. guanhumi, and will be useful in better comprehending the biochemical underpinnings of osmoregulatory ability in a semi-terrestrial mangrove crab.

RH421 binds into the ATP-binding site on the Na+/K+-ATPase

The Na⁺/K⁺-ATPase plays a key role in ion transport across the plasma membrane of all animal cells. The voltage-sensitive styrylpyrimidium dye RH421 has been used in several laboratories for monitoring of Na⁺/K⁺-ATPase kinetics. It is known, that RH421 can interact with the enzyme and it can influence its activity at micromolar concentrations, but structural details of this interaction are only poorly understood. Experiments with isolated large cytoplasmic loop (C45) of Na⁺/K⁺-ATPase revealed that RH421 can interact with this part of the protein with dissociation constant 1μM. The Trp-to-RH421 FRET performed on six single-tryptophan mutants revealed that RH421 binds directly into the ATP-binding site. This conclusion was further supported by results from molecular docking, site-directed mutagenesis and by competitive experiments using ATP. Experiments with C45/DPPC mixture revealed that RH421 can bind to both C45 and lipids, but only the former interaction was influenced by the presence of ATP.

The Central Role of Biometals Maintains Oxidative Balance in the Context of Metabolic and Neurodegenerative Disorders

Traditionally, oxidative stress as a biological aspect is defined as an imbalance between the free radical generation and antioxidant capacity of living systems. The intracellular imbalance of ions, disturbance in membrane dynamics, hypoxic conditions, and dysregulation of gene expression are all molecular pathogenic mechanisms closely associated with oxidative stress and underpin systemic changes in the body. These also include aspects such as chronic immune system activation, the impairment of cellular structure renewal, and alterations in the character of the endocrine secretion of diverse tissues. All of these mentioned features are crucial for the correct function of the various tissue types in the body. In the present review, we summarize current knowledge about the common roots of metabolic and neurodegenerative disorders induced by oxidative stress. We discuss these common roots with regard to the way that (1) the respective metal ions are involved in the maintenance of oxidative balance and (2) the metabolic and signaling disturbances of the most important biometals, such as Mg²⁺, Zn²⁺, Se²⁺, Fe²⁺, or Cu²⁺, can be considered as the central connection point between the pathogenesis of both types of disorders and oxidative stress.