A robust fluorescence-based assay for human erythrocyte Ca++ efflux suitable for high-throughput inhibitor screens.

Intracellular calcium is maintained at very low concentrations through the action of PMCA Ca++ extrusion pumps. Although much of our knowledge about these Ca++ extrusion pumps derives from studies with human erythrocytes, kinetic studies of Ca++ transport for these cells are limited to radioisotope flux measurements. Here, we developed a robust, microplate-based assay for erythrocyte Ca++ efflux using extracellular fluorescent Ca++ indicators. We optimized Ca++ loading with the A23187 ionophore, established conditions for removal of the ionophore, and adjusted fluorescent dye sensitivity by addition of extracellular EGTA to allow continuous tracking of Ca++ efflux. Efflux kinetics were accelerated by glucose and inhibited in a dose-dependent manner by the nonspecific inhibitor vanadate, revealing that Ca++ pump activity can be tracked in a 384-well microplate format. These studies enable radioisotope-free kinetic measurements of the Ca++ pump and should facilitate screens for specific inhibitors of this essential transport activity.

Cardiotoxicity of (-)-borneol, (+)-borneol, and isoborneol in zebrafish embryos is associated with Na+ /K+ -ATPase and Ca2+ -ATPase inhibition.

Borneol is an example of traditional Chinese medicine widely used in Asia. There are different isomers of chiral borneol in the market, but its toxicity and effects need further study. In this study, we used zebrafish embryos to examine the effects of exposure to three isomers of borneol [(-)-borneol, (+)-borneol, and isoborneol] on heart development and the association with Na+ /K+ -ATPase from 4 h post-fertilization (4 hpf). The results showed that the three isomers of borneol increased mortality and decreased hatching rate when the zebrafish embryo developed to 72 hpf. All three isomers of borneol (0.01-1.0 mM) significantly reduced heart rate from 48 to 120 hpf and reduced the expression of genes related to Ca2+ -ATPase (cacna1ab and cacna1da) and Na+ /K+ -ATPase (atp1b2b, atp1a3b, and atp1a2). At the same time, the three isomers of borneol significantly reduced the activities of Ca2+ -ATPase and Na+ /K+ -ATPase at 0.1 to 1.0 mM. (+)-Borneol caused the most significant reduction (p < 0.05), followed by isoborneol and (-)-borneol. Na+ /K+ -ATPase was mainly expressed in otic vesicles and protonephridium. All three isomers of borneol reduced Na+ /K+ -ATPase mRNA expression, but isoborneol was the most significant (p < 0.01). Our results indicated that (+)-borneol was the least toxic of the three isomers while the isoborneol showed the most substantial toxic effect, closely related to effects on Na+ /K+ -ATPase.

Phospholamban deficiency does not alter skeletal muscle SERCA pumping efficiency or predispose mice to diet-induced obesity.

The sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) pump is a major contributor to skeletal muscle Ca2+ homeostasis and metabolic rate. SERCA activity can become adaptively uncoupled by its regulator sarcolipin (SLN) to increase the energy demand of Ca2+ pumping, preventing excessive obesity and glucose intolerance in mice. Several other SERCA regulators bear structural and functional resemblance to SLN, including phospholamban (PLN). Here, we sought to examine whether endogenous levels of skeletal muscle PLN control SERCA Ca2+ pumping efficiency and whole body metabolism. Using PLN-null mice ( Pln-/-), we found that soleus (SOL) muscle's SERCA pumping efficiency (measured as an apparent coupling ratio: Ca2+ uptake/ATP hydrolysis) was unaffected by PLN. Expression of Ca2+-handling proteins within the SOL, including SLN, were comparable between Pln-/- and wild-type (WT) littermates, as were fiber-type characteristics. Not surprisingly then, Pln-/- mice developed a similar degree of diet-induced obesity and glucose intolerance as WT controls when given a "Western" high-fat diet. Lack of an excessively obesogenic phenotype of Pln-/- could not be explained by compensation from skeletal muscle SLN or brown adipose tissue uncoupling protein-1 content. In agreement with several other reports, our study lends support to the notion that PLN serves a functionally distinct role from that of SLN in skeletal muscle physiology.

Bromine inhalation mimics ischemia-reperfusion cardiomyocyte injury and calpain activation in rats.

Halogens are widely used, highly toxic chemicals that pose a potential threat to humans because of their abundance. Halogens such as bromine (Br2) cause severe pulmonary and systemic injuries; however, the mechanisms of their toxicity are largely unknown. Here, we demonstrated that Br2 and reactive brominated species produced in the lung and released in blood reach the heart and cause acute cardiac ultrastructural damage and dysfunction in rats. Br2-induced cardiac damage was demonstrated by acute (3-24 h) increases in circulating troponin I, heart-type fatty acid-binding protein, and NH2-terminal pro-brain natriuretic peptide. Transmission electron microscopy demonstrated acute (3-24 h) cardiac contraction band necrosis, disruption of z-disks, and mitochondrial swelling and disorganization. Echocardiography and hemodynamic analysis revealed left ventricular (LV) systolic and diastolic dysfunction at 7 days. Plasma and LV tissue had increased levels of brominated fatty acids. 2-Bromohexadecanal (Br-HDA) injected into the LV cavity of a normal rat caused acute LV enlargement with extensive disruption of the sarcomeric architecture and mitochondrial damage. There was extensive infiltration of neutrophils and increased myeloperoxidase levels in the hearts of Br2- or Br2 reactant-exposed rats. Increased bromination of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) and increased phosphalamban after Br2 inhalation decreased cardiac SERCA activity by 70%. SERCA inactivation was accompanied by increased Ca2+-sensitive LV calpain activity. The calpain-specific inhibitor MDL28170 administered within 1 h after exposure significantly decreased calpain activity and acute mortality. Bromine inhalation and formation of reactive brominated species caused acute cardiac injury and myocardial damage that can lead to heart failure. NEW & NOTEWORTHY The present study defines left ventricular systolic and diastolic dysfunction due to cardiac injury after bromine (Br2) inhalation. A calpain-dependent mechanism was identified as a potential mediator of cardiac ultrastructure damage. This study not only highlights the importance of monitoring acute cardiac symptoms in victims of Br2 exposure but also defines calpains as a potential target to treat Br2-induced toxicity.

HIF-1 regulation of miR-29c impairs SERCA2 expression and cardiac contractility.

The principal regulator of cellular response to low oxygen is hypoxia-inducible factor (HIF)-1, which is stabilized in several forms of heart failure. Our laboratory developed a mouse strain in which a stable form of HIF-1 can be inducibly expressed in cardiomyocytes. Strikingly, these mice show a rapid decrease in cardiac contractility and a rapid loss of SERCA2 protein, which is also seen in heart failure. Interestingly, while the SERCA2 transcript decreased, it did not fully account for the observed decrease in protein. We therefore investigated whether HIF-1-regulated microRNA could impair SERCA translation. Multiple screening analyses identified the microRNA miR-29c to be substantially upregulated upon HIF-1 induction and to have complementarity to SERCA, and therefore be a potential regulator of SERCA2 expression in hypoxia. Subsequent evaluation confirmed that miR-29c reduced SERCA2 expression and Ca2+ reuptake. Additionally, administration of an antagonist sequence (antimir) improved cardiac contractility and SERCA2 expression in HIF transgenic mice. To extend the significance of these findings, we examined miR-29c expression in physiological hypoxia. Surprisingly, miR-29c decreased in these settings. We also treated mice with antimir before infarction to see if further suppression of miR-29c could improve cardiac function. While no improvement in contractility or SERCA2 was observed, reduction of heart size after infarction indicated that the antimir could modulate cardiac physiology. These results demonstrate that while a HIF-1-regulated microRNA, miR-29c, can reduce SERCA2 expression and contractility, additional factors in the ischemic milieu may limit these effects. Efforts to develop miRNA-based therapies will need to explore and account for these additional countervailing effects. NEW & NOTEWORTHY Our study demonstrated hypoxia-inducible factor-1-dependent upregulation of miR-29c, which, in turn, inhibited SERCA2 expression and reduced cardiac contractility in a transgenic overexpression system. Interestingly, these results were not recapitulated in a murine myocardial infarction model. These results underscore the complexity of the pathological environment and highlight the need for therapeutic target validation in physiologically relevant models.

Cadmium-calcium interference in the Rhinella arenarum oviduct.

Given that the cadmium (Cd) toxicity could be due to its interference with the calcium (Ca) homeostasis, the aim of this work was to study the effect of Cd over the presence, distribution and volume density (Vv) of Ca and Ca-ATPase in the secretory cells of the pars preconvoluta (PPC) and the pars convoluta (pc) in Rhinella arenarum. The severe effect of the xenobiotic (CdCl2 2.5 mg/kg) in sexually matured females was evaluated. Co-localization, as well as a marked reduction of Ca and Ca-ATPase, was observed in treated animals, in the areas analyzed, compared to control. Low calcium deposits were found in the secreting granules (SG) of the epithelial (ESC) and glandular secretory cells (GSC), while an increase in their cytoplasm and intracellular space was observed. The Ca-ATPase in treated and control animals was detected at the SG and the plasmatic membrane of the ESC and GSC. In relation to the Vv estimates, a substantial reduction of Ca deposits and Ca-ATPase activity was observed in the treated group, with respect to the control. Both amounts of Vv of Ca and Ca-ATPase activity were higher in PPC than in pc, and, higher in ESC than in GSC. These results were associated with the Cd concentration in the oviductal PC, determining that it is a bioaccumulator organ. Thus, this work demonstrated that the Cd interacted with Ca-ATPase, leading to an increase of cytosolic Ca, which is responsible for the possible disruptions in cellular metabolism.

SERCA2a was serotonylated and may regulate sino-atrial node pacemaker activity.

The modulation of sino-atrial node (SAN) automaticity is an essential mechanism of heart rate generation that is still not completely understood. Recent studies highlighted the importance of protein serotonylation by intracellular 5-HT during varies physiological actions. Nevertheless, the functional role of protein serotonylation in controlling SAN automaticity is largely unexplored. In this study, we screened the cardiomyocytes proteins and found that sarco(endo)plasmic reticulum Ca ATPase type 2a (SERCA2a) can be serotonylated. Simulation studies using mathematical SAN cell model showed that variation of Ca2+ affinity of SERCA2a pump cause either tachycardia or bradycardia.

Cadmium inhibits motility, activities of plasma membrane Ca(2+)-ATPase and axonemal dynein-ATPase of human spermatozoa.

Cd(2+) has been associated with decreased sperm motility in individuals exposed to this element, such as smokers. Among other factors, this lowered motility could be the result of inhibition exerted by Cd(2+) on the activity of the sperm ATPases associated with sperm motility. In this study, we evaluated the plasma membrane Ca(2+)-ATPase and the axonemal dynein-ATPase activities as well as sperm motility, in the presence of different free Cd(2+) concentrations in the assay media. It was found that spermatozoa incubated for 5 h in a medium containing 25 nm free Cd(2+) showed a significant inhibition of progressive motility, reaching values even lower at higher Cd(2+) concentrations. In addition, it was found that the activity of the plasma membrane Ca(2+)-ATPase reached maximal inhibition at 50 nm free Cd(2+), with a K50% inhibition of 18.3 nm free Cd(2+). The dynein-ATPase activity was maximally inhibited by 25 nm free Cd(2+) in the assay medium, with a K50% inhibition of 11.3 nm Cd(2+). Our results indicate that the decreased activity of the sperm ATPases might have a critical importance in the biochemical mechanisms underlying the decreased sperm motility of individuals exposed to Cd(2+).

Synthetic phosphopeptides enable quantitation of the content and function of the four phosphorylation states of phospholamban in cardiac muscle.

We have studied the differential effects of phospholamban (PLB) phosphorylation states on the activity of the sarcoplasmic reticulum Ca-ATPase (SERCA). It has been shown that unphosphorylated PLB (U-PLB) inhibits SERCA and that phosphorylation of PLB at Ser-16 or Thr-17 relieves this inhibition in cardiac sarcoplasmic reticulum. However, the levels of the four phosphorylation states of PLB (U-PLB, P16-PLB, P17-PLB, and doubly phosphorylated 2P-PLB) have not been measured quantitatively in cardiac tissue, and their functional effects on SERCA have not been determined directly. We have solved both problems through the chemical synthesis of all four PLB species. We first used the synthetic PLB as standards for a quantitative immunoblot assay, to determine the concentrations of all four PLB phosphorylation states in pig cardiac tissue, with and without left ventricular hypertrophy (LVH) induced by aortic banding. In both LVH and sham hearts, all phosphorylation states were significantly populated, but LVH hearts showed a significant decrease in U-PLB, with a corresponding increase in the ratio of total phosphorylated PLB to U-PLB. To determine directly the functional effects of each PLB species, we co-reconstituted each of the synthetic peptides in phospholipid membranes with SERCA and measured calcium-dependent ATPase activity. SERCA inhibition was maximally relieved by P16-PLB (the most highly populated PLB state in cardiac tissue homogenates), followed by 2P-PLB, then P17-PLB. These results show that each PLB phosphorylation state uniquely alters Ca(2+) homeostasis, with important implications for cardiac health, disease, and therapy.

Ocean acidification induces biochemical and morphological changes in the calcification process of large benthic foraminifera.

Large benthic foraminifera are significant contributors to sediment formation on coral reefs, yet they are vulnerable to ocean acidification. Here, we assessed the biochemical and morphological impacts of acidification on the calcification of Amphistegina lessonii and Marginopora vertebralis exposed to different pH conditions. We measured growth rates (surface area and buoyant weight) and Ca-ATPase and Mg-ATPase activities and calculated shell density using micro-computer tomography images. In A. lessonii, we detected a significant decrease in buoyant weight, a reduction in the density of inner skeletal chambers, and an increase of Ca-ATPase and Mg-ATPase activities at pH 7.6 when compared with ambient conditions of pH 8.1. By contrast, M. vertebralis showed an inhibition in Mg-ATPase activity under lowered pH, with growth rate and skeletal density remaining constant. While M. vertebralis is considered to be more sensitive than A. lessonii owing to its high-Mg-calcite skeleton, it appears to be less affected by changes in pH, based on the parameters assessed in this study. We suggest difference in biochemical pathways of calcification as the main factor influencing response to changes in pH levels, and that A. lessonii and M. vertebralis have the ability to regulate biochemical functions to cope with short-term increases in acidity.

Expression of sarcoplasmic-endoplasmic reticulum Ca-ATPase isoforms in masticatory muscles.

The aim of this study was to characterize the sarcoplasmic-endoplasmic reticulum Ca-ATPase (SERCA) isoforms in rabbit masticatory muscles compared with those in fast-twitch muscle. It was hypothesized that combined expression of the SERCA isoforms in fast- and slow-twitch muscles accounts for lower Ca-ATPase activity. SERCA was isolated by differential centrifugation, the isoforms were determined by ELISA, and the activity of each isoform was measured using a colorimetric method. Activity was tested for significance by anova, and the distribution of isoforms was assessed using the chi-square test (P < 0.05) and correlated to SERCA activity using Spearman's rank correlation. SERCA1 was predominant (90.5%) in fast-twitch muscle, whereas a mixture of SERCA isoforms was found in masticatory muscles: 62-78% was SERCA2, 20-37% was SERCA1, and the SERCA3 content was negligible. Depressor muscles showed a significantly higher content (77.8%) of SERCA2, and elevator muscles showed a higher content (35.4%) of SERCA1. Elevator muscles showed higher expression of SERCA2a (58%), and depressor muscles showed higher expression of SERCA2b (20%). The SERCA1 content was mainly SERCA1a and significantly higher for elevator muscles (33%), whereas depressor muscles showed a higher content of SERCA1b (4%). The SERCA1 content of fast-twitch muscle was mainly SERCA1a (88.5%). It is concluded that the mixture of different SERCA isoforms, along with a substantial content of SERCA2b, in masticatory muscles would support lower Ca-ATPase activity and calcium transport.

Thiazolium salt mimics the non-coenzyme effects of vitamin B1 in rat synaptosomes.

Long-term studies have confirmed a causal relationship between the development of neurodegenerative processes and vitamin B1 (thiamine) deficiency. However, the biochemical mechanisms underlying the high neurotropic activity of thiamine are not fully understood. At the same time, there is increasing evidence that vitamin B1, in addition to its coenzyme functions, may have non-coenzyme activities that are particularly important for neurons. To elucidate which effects of vitamin B1 in neurons are due to its coenzyme function and which are due to its non-coenzyme activity, we conducted a comparative study of the effects of thiamine and its derivative, 3-decyloxycarbonylmethyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazolium chloride (DMHT), on selected processes in synaptosomes. The ability of DMHT to effectively compete with thiamine for binding to thiamine-binding sites on the plasma membrane of synaptosomes and to participate as a substrate in the thiamine pyrophosphokinase reaction was demonstrated. In experiments with rat brain synaptosomes, unidirectional effects of DMHT and thiamine on the activity of the pyruvate dehydrogenase complex (PDC) and on the incorporation of radiolabeled [2-14C]pyruvate into acetylcholine were demonstrated. The observed effects of thiamine and DMHT on the modulation of acetylcholine synthesis can be explained by suggesting that both compounds, which interact in cells with enzymes of thiamine metabolism, are phosphorylated and exert an inhibitory/activating effect (concentration-dependent) on PDC activity by affecting the regulatory enzymes of the complex. Such effects were not observed in the presence of structural analogues of thiamine and DMHT without a 2-hydroxyethyl substituent at position 5 of the thiazolium cycle. The effect of DMHT on the plasma membrane Ca-ATPase was similar to that of thiamine. At the same time, DMHT showed high cytostatic activity against neuroblastoma cells.

Targeting calcium regulators as therapy for heart failure: focus on the sarcoplasmic reticulum Ca-ATPase pump.

Impaired myocardial Ca2+ cycling is a critical contributor to the development of heart failure (HF), causing changes in the contractile function and structure remodeling of the heart. Within cardiomyocytes, the regulation of sarcoplasmic reticulum (SR) Ca2+ storage and release is largely dependent on Ca2+ handling proteins, such as the SR Ca2+ ATPase (SERCA2a) pump. During the relaxation phase of the cardiac cycle (diastole), SERCA2a plays a critical role in transporting cytosolic Ca2+ back to the SR, which helps to restore both cytosolic Ca2+ levels to their resting state and SR Ca2+ content for the next contraction. However, decreased SERCA2a expression and/or pump activity are key features in HF. As a result, there is a growing interest in developing therapeutic approaches to target SERCA2a. This review provides an overview of the regulatory mechanisms of the SERCA2a pump and explores potential strategies for SERCA2a-targeted therapy, which are being investigated in both preclinical and clinical studies.

Spatial Distribution of Calcium Sparks Determines Their Ability to Induce Afterdepolarizations in Human Atrial Myocytes.

Analysis of the spatio-temporal distribution of calcium sparks showed a preferential increase in sparks near the sarcolemma in atrial myocytes from patients with atrial fibrillation (AF), linked to higher ryanodine receptor (RyR2) phosphorylation at s2808 and lower calsequestrin-2 levels. Mathematical modeling, incorporating modulation of RyR2 gating, showed that only the observed combinations of RyR2 phosphorylation and calsequestrin-2 levels can account for the spatio-temporal distribution of sparks in patients with and without AF. Furthermore, we demonstrate that preferential calcium release near the sarcolemma is key to a higher incidence and amplitude of afterdepolarizations in atrial myocytes from patients with AF.

Cadmium-induced ultrastructural changes and apoptosis in the gill of freshwater mussel Anodonta woodiana.

This study investigated the acute toxicity of cadmium (Cd) to the freshwater mussel Anodonta woodiana. The freshwater mussels were exposed to five concentrations of Cd (0 mg/L, 8.43 mg/L, 16.86 mg/L, 33.72 mg/L, and 67.45 mg/L) for up to 96 h. The 24-h, 48-h, 72-h, and 96-h LC50 values for Cd were estimated as 562.3 mg/L, 331.1 mg/L, 182.0 mg/L, and 134.9 mg/L, respectively. Caspase-3, caspase-8, caspase-9, and Ca-ATPase activities; protein and H2O2 levels; DNA fragmentation; and ultrastructure of the gill were also investigated. The activities of caspase-3 and caspase-9 in mussels were increased by Cd in a dose-dependent manner, where higher doses of Cd (33.72 mg/L and 67.45 mg/L) significantly increased the enzyme activities compared to the controls (P < 0.05). The caspase-8 activity was significantly depressed by a low dose of Cd (8.43 mg/L) but was clearly induced by higher doses of Cd (16.86 mg/L, 33.72 mg/L, and 67.45 mg/L) (P < 0.05). The Ca-ATPase activity and H2O2 levels were elevated and reached maximum values under the medium dose of Cd (16.86 mg/L). However, protein levels were decreased by Cd in an inverse dose-dependent manner. In the gills of the mussels, Cd treatment induced DNA fragmentation as demonstrated by DNA ladders observed via agarose gel electrophoresis. Moreover, ultrastructural alterations in gill cells of mussels treated with Cd (16.86 mg/L and 67.45 mg/L) for 96 h were observed by electronic microscopy. The ultrastructure abnormalities were characterized by the following features: (1) a disordered arrangement and breaking off of microvilli of epithelial cells; (2) chromatin condensed near the nuclear membrane and the appearances of extremely irregular nuclei, some with a fingerlike shape and an unclear, swollen, invaginated, or ruptured nuclear membrane and apoptotic bodies; (3) swollen and vacuolating mitochondria, some with disintegrated or missing cristae; (4) a disintegrated rough endoplasmic reticulum containing different sizes of vesicles; and (5) shrinking and deformation of Golgi bodies with decreased vesicle numbers. Our results demonstrated that Cd could activate caspase-3, caspase-8, caspase-9, and Ca-ATPase; cause ultrastructural changes; and produce DNA fragmentation in the mussels investigated. Based on the information obtained through this study, it is reasonable to conclude that Cd can induce apoptosis in the gills of the mussels, eventually leading to tissue damage.

ER stress and calcium-dependent arrhythmias.

The sarcoplasmic reticulum (SR) plays the key role in cardiac function as the major source of Ca2+ that activates cardiomyocyte contractile machinery. Disturbances in finely-tuned SR Ca2+ release by SR Ca2+ channel ryanodine receptor (RyR2) and SR Ca2+ reuptake by SR Ca2+-ATPase (SERCa2a) not only impair contraction, but also contribute to cardiac arrhythmia trigger and reentry. Besides being the main Ca2+ storage organelle, SR in cardiomyocytes performs all the functions of endoplasmic reticulum (ER) in other cell types including protein synthesis, folding and degradation. In recent years ER stress has become recognized as an important contributing factor in many cardiac pathologies, including deadly ventricular arrhythmias. This brief review will therefore focus on ER stress mechanisms in the heart and how these changes can lead to pro-arrhythmic defects in SR Ca2+ handling machinery.

Effect of sodium lactate as cryostabilizer on physico-chemical attributes of croaker (Johnius gangeticus) muscle protein.

Effect of sodium lactate as cryostabilizer on physico-chemical attributes of croaker (Johnius gangeticus) fish muscle protein was studied during freezing and frozen (-20 ± 2°C) storage for 3 months. Minced meat was mixed with 4% sucrose, 4% sorbitol, and 0.3% sodium tri poly phosphate (STPP) (T1), minced meat was mixed with 6% (w/v) sodium lactate and 0.3% STPP (T2) and control (C) was without any additive. The decreasing rate of Ca(2+) ATPase activity, thaw drip, water holding capacity and relative viscosity in T1 and T2 samples from that of C was significantly lower, indicating higher protective effect of additives. In case of cryoprotectant treated samples, the degradation of myosin heavy chain was much lower than that of C which prevents the aggregation and subsequent insolubilization of myosin during frozen storage. The sodium lactate prevented Ca(2+)ATPase activity more than that of sucrose/sorbitol during isothermal storage at -20 ± 2°C for 3 months. This inferred that sodium lactate can effectively be used as an alternative cryostabilizer to sucrose/sorbitol for stabilization of croaker muscle protein native structure.

SERCA stimulation: A potential approach in therapeutics.

sarco-endoplasmic reticulum Ca-ATPase (SERCA) is the major transporter present in sarco-endoplasmic reticulum (SR/ER), transporting calcium back into SR/ER from cytosol. The calcium-sequestering activity of SERCA facilitates relaxation in both cardiac and skeletal tissue. ER stress is one of the etiological factors in various diseases such as neurodegenerative diseases and diabetes. Disrupted calcium handling can cause ER stress. In the cardiac tissue, impairment of systolic and diastolic function can cause various cardiovascular diseases. SERCA ensures the proper calcium handling in cells and may act as a therapeutic target for the disease associated with dysregulation of calcium ions. This review examines the principle of calcium ion handling through SERCA and its role in various diseases.

Mitochondrial Function and Dysfunction in Dilated Cardiomyopathy.

Cardiac tissue requires a persistent production of energy in order to exert its pumping function. Therefore, the maintenance of this function relies on mitochondria that represent the "powerhouse" of all cardiac activities. Mitochondria being one of the key players for the proper functioning of the mammalian heart suggests continual regulation and organization. Mitochondria adapt to cellular energy demands via fusion-fission events and, as a proof-reading ability, undergo mitophagy in cases of abnormalities. Ca2+ fluxes play a pivotal role in regulating all mitochondrial functions, including ATP production, metabolism, oxidative stress balance and apoptosis. Communication between mitochondria and others organelles, especially the sarcoplasmic reticulum is required for optimal function. Consequently, abnormal mitochondrial activity results in decreased energy production leading to pathological conditions. In this review, we will describe how mitochondrial function or dysfunction impacts cardiac activities and the development of dilated cardiomyopathy.

Copper exposure and seawater acidification interaction: Antagonistic effects on biomarkers in the zooxanthellate scleractinian coral Mussismilia harttii.

Coral reefs are threatened by global and local impacts, such as ocean acidification (OA) and metal contamination. Toxicity of metals, such as copper (Cu), is expected to be enhanced with OA. However, the interaction between these environmental stressors is still poorly evaluated. In the present study, the interactive effects of seawater acidification and increasing Cu concentrations were evaluated in a zooxanthellate scleractinian coral (Mussismilia harttii), using biochemical biomarkers involved in the coral calcification process and the photosynthetic metabolism of endosymbionts. Corals were kept under control conditions (no seawater acidification and no Cu addition in seawater) or exposed to combined treatments of reduced seawater pH (8.1, 7.8, 7.5 and 7.2) and environmentally relevant concentrations of dissolved Cu (measured: 1.0, 1.6, 2.3 and 3.2 µg/L) in a mesocosm system. After 15- and 35-days exposure, corals were analyzed for photochemical efficiency (Fv/Fm), chlorophyll a content, Ca-ATPase and carbonic anhydrase (CA) activity. Results showed that 76% of the interactions between reduced seawater pH and increasing Cu concentrations were antagonistic. Only 24% of these interactions were additive or synergistic. In general, the combination of stressors had no significant deleterious effects in the photosynthetic metabolism of endosymbionts or Ca-ATPase activity. In fact, the lowest dissolved Cu concentration tested had a consistent positive effect on Ca-ATPase activity in corals facing any of the reduced seawater pH conditions tested. In turn, potentially deleterious effects on acid-base balance in M. harttii, associated with changes in CA activity, were intensified by the combination of stressors. Findings reported here indicate that Cu toxicity in future OA scenarios can be less severe than previously suggested in this coral holobiont.