Movement Of Ca2 Research Articles

Dynamic Calcium Movement Inside Cardiac Sarcoplasmic Reticulum During Release

Intra-sarcoplasmic reticulum (SR) free [Ca] ([Ca](SR)) provides the driving force for SR Ca release and is a key regulator of SR Ca release channel gating during normal SR Ca release or arrhythmogenic spontaneous Ca release events. However, little is known about [Ca](SR) spatiotemporal dynamics. To directly measure local [Ca](SR) with subsarcomeric spatiotemporal resolution during both normal global SR Ca release and spontaneous Ca sparks and to evaluate the quantitative implications of spatial [Ca](SR) gradients. Intact and permeabilized rabbit ventricular myocytes were subjected to direct simultaneous measurement of cytosolic [Ca] and [Ca](SR) and FRAP (fluorescence recovery after photobleach). We found no detectable [Ca](SR) gradients between SR release sites (junctional SR) and Ca uptake sites (free SR) during normal global Ca release, clear spatiotemporal [Ca](SR) gradients during isolated Ca blinks, faster intra-SR diffusion in the longitudinal versus transverse direction, 3- to 4-fold slower diffusion of fluorophores in the SR than in cytosol, and that intra-SR Ca diffusion varies locally, dependent on local SR connectivity. A computational model clarified why spatiotemporal gradients are more detectable in isolated local releases versus global releases and provides a quantitative framework for understanding intra-SR Ca diffusion. Intra-SR Ca diffusion is rapid, limiting spatial [Ca](SR) gradients during excitation-contraction coupling. Spatiotemporal [Ca](SR) gradients are apparent during Ca sparks, and these observations constrain models of dynamic Ca movement inside the SR. This has important implications for myocyte SR Ca handling, synchrony, and potentially arrhythmogenic spontaneous contraction.

Abscisic acid triggers whole-plant and fruit-specific mechanisms to increase fruit calcium uptake and prevent blossom end rot development in tomato fruit

Calcium (Ca) uptake into fruit and leaves is dependent on xylemic water movement, and hence presumably driven by transpiration and growth. High leaf transpiration is thought to restrict Ca movement to low-transpiring tomato fruit, which may increase fruit susceptibility to the Ca-deficiency disorder, blossom end rot (BER). The objective of this study was to analyse the effect of reduced leaf transpiration in abscisic acid (ABA)-treated plants on fruit and leaf Ca uptake and BER development. Tomato cultivars Ace 55 (Vf) and AB2 were grown in a greenhouse environment under Ca-deficit conditions and plants were treated weekly after pollination with water (control) or 500 mg l(-1) ABA. BER incidence was completely prevented in the ABA-treated plants and reached values of 30-45% in the water-treated controls. ABA-treated plants had higher stem water potential, lower leaf stomatal conductance, and lower whole-plant water loss than water-treated plants. ABA treatment increased total tissue and apoplastic water-soluble Ca concentrations in the fruit, and decreased Ca concentrations in leaves. In ABA-treated plants, fruit had a higher number of Safranin-O-stained xylem vessels at early stages of growth and development. ABA treatment reduced the phloem/xylem ratio of fruit sap uptake. The results indicate that ABA prevents BER development by increasing fruit Ca uptake, possibly by a combination of whole-plant and fruit-specific mechanisms.

Cellular prion protein is implicated in the regulation of local Ca2+ movements in cerebellar granule neurons

The cellular prion protein (PrP(C)) is a cell-surface glycoprotein mainly expressed in the CNS. The structural conversion of PrP(C) generates the prion, the infectious agent causing transmissible spongiform encephalopathies, which are rare and fatal diseases affecting animals and humans. Despite decades of intensive research, the mechanism of prion-associated neurodegeneration and the physiologic role of PrP(C) are still obscure. Recent evidence, however, supports the hypothesis that PrP(C) may be involved in the control of Ca(2+) homeostasis. Given the universal significance of Ca(2+) as an intracellular messenger for both the life and death of cells, this possibility may help explain the complex, often controversial, dataset accumulated on PrP(C) physiology, and the events leading to prion-associated neuronal demise. In this study, we have compared local Ca(2+) movements in cerebellar granule neurons (CGN) derived from wild-type (WT), or PrP-knockout (KO), mice, by means of the Ca(2+)-sensitive photo-probe, aequorin, genetically targeted to specific intracellular domains and delivered to CGN by lentiviral vectors. The use of an aequorin that localizes to the cytosolic domains proximal to the plasma membrane has allowed us to demonstrate that there was a dramatic increase of store-operated Ca(2+) entry in PrP-KO CGN compared to WT neurons. Notably, this phenotype was rescued upon restoring PrP(C) expression. The Ca(2+)-phenotype of PrP-KO neurons can in part be explained by the lower expression of two major Ca(2+)-extruding proteins, namely the plasma membrane and the sarco-endoplasmic reticulum Ca(2+)-ATPases. The lower sarco-endoplasmic reticulum Ca(2+)-ATPase content may also contribute to explain why PrP-KO CGN accumulated less Ca(2+) in the endoplasmic reticulum than the WT counterpart.

Ca2+ Overload and Sarcoplasmic Reticulum Instability in tric-a Null Skeletal Muscle

The sarcoplasmic reticulum (SR) of skeletal muscle contains K(+), Cl(-), and H(+) channels may facilitate charge neutralization during Ca(2+) release. Our recent studies have identified trimeric intracellular cation (TRIC) channels on SR as an essential counter-ion permeability pathway associated with rapid Ca(2+) release from intracellular stores. Skeletal muscle contains TRIC-A and TRIC-B isoforms as predominant and minor components, respectively. Here we test the physiological function of TRIC-A in skeletal muscle. Biochemical assay revealed abundant expression of TRIC-A relative to the skeletal muscle ryanodine receptor with a molar ratio of TRIC-A/ryanodine receptor ∼5:1. Electron microscopy with the tric-a(-/-) skeletal muscle showed Ca(2+) overload inside the SR with frequent formation of Ca(2+) deposits compared with the wild type muscle. This elevated SR Ca(2+) pool in the tric-a(-/-) muscle could be released by caffeine, whereas the elemental Ca(2+) release events, e.g. osmotic stress-induced Ca(2+) spark activities, were significantly reduced likely reflecting compromised counter-ion movement across the SR. Ex vivo physiological test identified the appearance of "alternan" behavior with isolated tric-a(-/-) skeletal muscle, i.e. transient and drastic increase in contractile force appeared within the decreasing force profile during repetitive fatigue stimulation. Inhibition of SR/endoplasmic reticulum Ca(2+ ATPase) function could lead to aggravation of the stress-induced alternans in the tric-a(-/-) muscle. Our data suggests that absence of TRIC-A may lead to Ca(2+) overload in SR, which in combination with the reduced counter-ion movement may lead to instability of Ca(2+) movement across the SR membrane. The observed alternan behavior with the tric-a(-/-) muscle may reflect a skeletal muscle version of store overload-induced Ca(2+) release that has been reported in the cardiac muscle under stress conditions.

ATRIBUTOS QUÍMICOS DE SOLO CULTIVADO COM DIFERENTES CULTURAS DE COBERTURA

  The effect of cover crops annually implanted in the summer, since 2001, under no-tillage system, on the soil chemical attributes was evaluated. The experiment was carried out in Embrapa Rice & Beans, in Santo Antônio de Goiás, GO, Brazil, in a Dystrophic Red Latosol (Red Oxisol). Brachiaria brizantha, corn (Zea mays L.) associated with B. brizantha, pigeon pea, millet, Panicum maximum, sorghum, Stylosanthes guianensis, and sunn hemp were used as cover crops. Sixty days after the cut of the cover crops, common bean crop was implanted, under a central pivot sprinkler irrigation system. In November 2001, 2005, and 2006, soil samples were collected in the depths of 0-5 cm, 5-10 cm, and 10-20 cm. Immediately after the 2005 sampling, it was applied 4,000 kg ha-1 of dolomitic lime, in all the experimental area. Cover crops affected soil pH and magnesium content in the superficial layer. Soil under millet showed higher phosphorus content in subsuperficial layers, in relation to the initial values. The soil P and Cu contents were higher in the subsuperficial layers, while the other chemical attributes were higher in the superficial layer. There was movement of Ca and Mg in the soil profile, one year after the application of lime in the soil surface. KEY-WORDS: No-tillage system; grasses; Leguminosae; soil fertility.

Signal transduction, plasma membrane calcium movements, and pigment translocation in freshwater shrimp chromatophores

Crustacean color change results from the differential translocation of chromatophore pigments, regulated by neurosecretory peptides like red pigment concentrating hormone (RPCH) that, in the red ovarian chromatophores of the freshwater shrimp Macrobrachium olfersi, triggers pigment aggregation via increased cytosolic cGMP and Ca(2+) of both smooth endoplasmatic reticulum (SER) and extracellular origin. However, Ca(2+) movements during RPCH signaling and the mechanisms that regulate intracellular [Ca(2+)] are enigmatic. We investigate Ca(2+) transporters in the chromatophore plasma membrane and Ca(2+) movements that occur during RPCH signal transduction. Inhibition of the plasma membrane Ca(2+)-ATPase by La(3+) and indirect inhibition of the Na(+)/Ca(2+) exchanger by ouabain induce pigment aggregation, revealing a role for both in Ca(2+) extrusion. Ca(2+) channel blockade by La(3+) or Cd(2+) strongly inhibits slow-phase RPCH-triggered aggregation during which pigments disperse spontaneously. L-type Ca(2+) channel blockade by gabapentin markedly reduces rapid-phase translocation velocity; N- or P/Q-type blockade by ω-conotoxin MVIIC strongly inhibits RPCH-triggered aggregation and reduces velocity, effects revealing RPCH-signaled influx of extracellular Ca(2+). Plasma membrane depolarization, induced by increasing external K(+) from 5 to 50 mM, produces Ca(2+)-dependent pigment aggregation, whereas removal of K(+) from the perfusate causes pigment hyperdispersion, disclosing a clear correlation between membrane depolarization and pigment aggregation; K(+) channel blockade by Ba(2+) also partially inhibits RPCH action. We suggest that, during RPCH signal transduction, Ca(2+) released from the SER, together with K(+) channel closure, causes chromatophore membrane depolarization, leading to the opening of predominantly N- and/or P/Q-type voltage-gated Ca(2+) channels, and a Ca(2+)/cGMP cascade, resulting in pigment aggregation.

Involvement of NMDA Receptor in the Modulation of Excitatory and Inhibitory Amino Acid Neurotransmitters Release in Cortical Neurons

The purpose of this paper was to examine the function of N-methyl-D-aspartate (NMDA) glutamate receptor in cortical neurons on amino acid neurotransmitters release as well as the fraction of neurons implicated in the response of this receptor. Local stimulation of these cells at different concentrations of NMDA, agonist of this ionotropic glutamate receptor, produced a dose dependent release of aspartate, glutamate, glycine and GABA. These effects were blocked by DAP5, an antagonist of the NMDA receptor. The amino acid Ca(2+) dependent release mediated by the NMDA receptor, is induced by the opening of voltage-dependent Ca(2+) channels that this receptor promotes. Ca(++) movements were explored in single cells loaded with fura-2. When single cells were stimulated with 100 microM NMDA, the calcium recording performed showed that 82% of the cells responded to this agonist increasing the intracellular calcium concentration, although the amplitude of these increments was variable. The results suggest that NMDA-elicited neurotransmitter release from cortical neurons involves Ca(2+)-dependent and Ca(2+)-independent components, as well as neuron depolarisation, and different VDCC subtypes of N, P/Q or L depending of the amino acid neurotransmitter release elicited by this receptor.

Effect of m-3M3FBS on Ca(superscript 2+) Movement in PC3 Human Prostate Cancer Cells

The effect of 2,4,6-trimethyl-N-(meta-3-trifluoromethyl-phenyl)-benzenesulfonamide (m-3M3FBS), a presumed phospholipase C activator, on cytosolic free Ca²⁺ concentrations ([Ca²⁺]i) in PC3 human prostate cancer cells is unclear. This study explored whether m-3M3FBS changed basal [Ca²⁺]i levels in suspended PC3 cells by using fura-2 as a Ca²⁺-sensitive fluorescent dye. M-3M3FBS at concentrations between 10-50 microM increased [Ca²⁺]i in a concentration-dependent manner. The Ca²⁺ signal was reduced by 60% by removing extracellular Ca²⁺. M-3M3FBS-induced Ca²⁺ influx was inhibited by the store-operated Ca²⁺ channel blockers nifedipine, econazole and SK&F96365, and by the phospholipase A2 inhibitor aristolochic acid. In Ca²⁺-free medium, 30 microM m-3M3FBS pretreatment greatly inhibited the [Ca²⁺]i rise induced by the endoplasmic reticulum Ca²⁺ pump inhibitor thapsigargin or BHQ. Conversely, pretreatment with thapsigargin, BHQ or cyclopiazonic acid reduced the major part of m-3M3FBS-induced [Ca²⁺]i rise. Inhibition of phospholipase C with U73122 did not much alter m-3M3FBS-induced [Ca²⁺]i rise. Collectively, in PC3 cells, m-3M3FBS induced [Ca²⁺]i rises by causing phospholipase C-independent Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ influx via store-operated Ca²⁺ channels.

Soil Nutrients Flow In A Tropical Semi-Deciduous Forest Ecosystem In Ghana

Primary and some secondary nutrient labile fractions concentrations of dissolved soil nutrients (Ca, Mg, K, N. Av. P and NO) were determined in cocoa plantation (DC), secondary forest (DS) and primary forest (FB) land uses in Dwinyan watershed in Ghana. Zero-tensioned lysimeters were buried at 0-15, 15-30 cm, 30-45 cm and 45-60 cm soil depths in the three land uses during the rainy season (March-September). The soil remained relatively moist throughout the study period. The highest soil moisture values recorded for DC and DS land uses were higher than that for TB. The primary forest exhibited a gentle rise and fall of its soil moisture. The volumes of soil leachate at monthly harvests in the land uses were higher in the 0-15 cm soil depth and highest for TBfollowed by DC and DS was least. Movement of Ca in solution in the land use was highest in DC (190 mg ml-I)at 0-15 cm soil depthfollowed by DS (174 mg m[-I) at 0-15 cm. Magnesium was highest in the DC (61 mg ml-I) at 0-15 cm followed by DC (33 mg m[-I) at 45-60 cm. Whilst N concentration in DC decreased with increasing soil depth, N03 increased with increasing soil depth. AvailableP showed the trend for N except in TB where at 0-15 cm lower P concentration was recorded for the other soil depths. Potassium did not show a clear pattern. In DC and TB land uses, the trend of nutrient insolution was Ca > Mg > N03 > K > N> P and in DS, Ca > Mg > N03 > N> K> P The variation in soil moisture regime due to different quantities of precipitation and litter build up at the soil urface may greatly influence concentrations of mineral nutrients to flow in soil solution to fertilize lowlands. Keywords: Landuse, leachate, nutrients, watershed, zero-tensioned lysimter

Contribution of Intestine, Bone, Kidney, and Dialysis to Extracellular Fluid Calcium Content

Calcium (Ca) balance is the net of Ca intake and output from the body over a period of time. The concept of Ca balance does not consider the redistribution of Ca that often occurs in patients with chronic kidney disease (CKD), especially those who are on dialysis, which is often in the form of soft tissue and/or vascular calcification. In this article, we consider movement of Ca with respect to the extracellular fluid (ECF) and develop a mathematical formulation for Ca homeostasis with respect to the ECF that includes input and output from the diet, the bone, the kidney, and dialysis. We consider calcium homeostasis in healthy individuals and in patients with excess parathyroid hormone, excess 1,25-dihydroxyvitamin D(3), and metabolic acidosis; patients who have CKD and are not on dialysis; and, finally, patients who have CKD and are on dialysis. On the basis of a number of assumptions, dialysis patients with a daily intake of >37.5 mmol of elemental Ca (1.5 g) have movement of Ca into the ECF even without supplemental activated vitamin D. Addition of activated vitamin D, which increases intestinal Ca absorption and can increase resorption of Ca from bone, leads to the movement of Ca into the ECF at virtually all levels of intake; however, there are numerous unanswered questions regarding Ca homeostasis in patients with CKD, including how much of the Ca, administered as a phosphate binder, is absorbed and what is the fate of this absorbed Ca. Until these pressing questions are answered with well-designed experiments, we do not know whether we are doing more harm than good for our dialysis patients by administering additional Ca as a phosphate binder, especially when they also receive activated vitamin D.

Deficiency of MIP/MTMR14 phosphatase induces a muscle disorder by disrupting Ca2+ homeostasis

The intracellular Ca(2+) concentration ([Ca(2+)](i)) in skeletal muscles must be rapidly regulated during the excitation-contraction-relaxation process. However, the signalling components involved in such rapid Ca(2+) movement are not fully understood. Here we report that mice deficient in the newly identified PtdInsP (phosphatidylinositol phosphate) phosphatase MIP/MTMR14 (muscle-specific inositol phosphatase) show muscle weakness and fatigue. Muscles isolated from MIP/MTMR14(-/-) mice produced less contractile force, had markedly prolonged relaxation and showed exacerbated fatigue relative to normal muscles. Further analyses revealed that MIP/MTMR14 deficiency resulted in spontaneous Ca(2+) leakage from the internal store - the sarcoplasmic reticulum. This was attributed to decreased metabolism (dephosphorylation) and the subsequent accumulation of MIP/MTMR14 substrates, especially PtdIns(3,5)P(2) and PtdIns (3,4)P(2). Furthermore, we found that PtdIns(3,5)P(2) and PtdIns(3,4)P(2) bound to, and directly activated, the Ca(2+) release channel (ryanodine receptor 1, RyR1) of the sarcoplasmic reticulum. These studies provide the first evidence that finely controlled PtdInsP levels in muscle cells are essential for maintaining Ca(2+) homeostasis and muscle performance.

Exploring Functional β-Cell Heterogeneity In Vivo Using PSA-NCAM as a Specific Marker

BackgroundThe mass of pancreatic β-cells varies according to increases in insulin demand. It is hypothesized that functionally heterogeneous β-cell subpopulations take part in this process. Here we characterized two functionally distinct groups of β-cells and investigated their physiological relevance in increased insulin demand conditions in rats.MethodsTwo rat β-cell populations were sorted by FACS according to their PSA-NCAM surface expression, i.e. βhigh and βlow-cells. Insulin release, Ca2+ movements, ATP and cAMP contents in response to various secretagogues were analyzed. Gene expression profiles and exocytosis machinery were also investigated. In a second part, βhigh and βlow-cell distribution and functionality were investigated in animal models with decreased or increased β-cell function: the Zucker Diabetic Fatty rat and the 48 h glucose-infused rat.ResultsWe show that β-cells are heterogeneous for PSA-NCAM in rat pancreas. Unlike βlow-cells, βhigh-cells express functional β-cell markers and are highly responsive to various insulin secretagogues. Whereas βlow-cells represent the main population in diabetic pancreas, an increase in βhigh-cells is associated with gain of function that follows sustained glucose overload.ConclusionOur data show that a functional heterogeneity of β-cells, assessed by PSA-NCAM surface expression, exists in vivo. These findings pinpoint new target populations involved in endocrine pancreas plasticity and in β-cell defects in type 2 diabetes.

Na+-Stimulated Na+/H+ Exchange and an Unfavorable Ca2+ Homeostasis Initiate the Cycloxygenase-2 Inhibitors-Induced Apoptotic Signals in Colonic Epithelial Cells During the Early Stage of Colon Carcinogenesis

Evidence suggests that nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit cycloxygenase (COX) and production of the proinflammatory prostaglandin, PGE2, and thus prevent carcinogenesis in the colon. Indeed, one of the specific COX-2 inhibitors, celecoxib, had been accepted by the US FDA for the treatment of familial adenomatous polyposis. However, the molecular mechanism of such inhibition is not clear, although apoptosis appears to be the dominant antiproliferative end effect. The present study delineates the intracellular ionic milieu in the colonocytes that could generate strong apoptotic signals where DMH-induced carcinogenesis was studied in the initiation stage in rats and its regression with the COX inhibitors. While DMH treatment produced a significant elevation in the Na+/H+ exchanger activity and resultant proton efflux, this was reversed by the NSAIDs, particularly so with celecoxib and etoricoxib compared to aspirin. Similarly, the intracellular pH was changed, with more alkalosis noted in DMH, which was reversed by NSAIDs. Also, an intracellular Ca2+ build up was noted by Fura 2 AM, which was also supported by a reduced Ca2+ ATPase and an enhanced inward movement of Ca2+. Further, mitochondrial dysfunction-related cyt C release, increased DNA ladder formation, activation of caspase-3, and cleavage product of poly (ADP-ribose) polymerase (PARP) were not seen in DMH but well noted in NSAIDs. Our results indicate that NSAIDs can induce apoptosis through a change in the colonic Na+/H+ exchange, intracellular pH, and an unfavorable Ca2+ homeostasis.

DYSREGULATION OF Ca2+ MOVEMENT IN PLATELETS FROM PATIENTS WITH ACUTE ISCHAEMIC STROKE

1. Platelets play a pivotal role during acute ischaemic stroke. An increase in cytosolic Ca(2+) concentrations ([Ca(2+)](i)) triggers intracellular signal transduction, leading to platelet aggregation and thrombosis. In the present study, we examined the differences between platelets from acute ischaemic stroke patients and at-risk controls in terms of the increase in platelet [Ca(2+)](i). 2. Thirty-one patients with acute ischaemic stroke and 27 at-risk controls were enrolled in the present study. Platelet [Ca(2+)](i) was measured using the fluorescent dye fura-2 after stimulation with 100 micromol/L arachidonic acid (AA), 10 micromol/L ADP, 1 micromol/L platelet-activation factor (PAF) and 0.1 U/mL thrombin. 3. Basal [Ca(2+)](i) was higher in the stroke group compared with at-risk controls, irrespective of the presence or absence of extracellular Ca(2+). In Ca(2+)-containing medium, both PAF and ADP, but not AA and thrombin, significantly increased platelet [Ca(2+)](i) in the stroke group compared with the at-risk controls. However, in Ca(2+)-free medium, only PAF significantly increased platelet [Ca(2+)](i) in the stroke group compared with the at-risk controls. Basal [Ca(2+)](i) and PAF-induced platelet [Ca(2+)](i) increases were still higher in the stroke group at the subacute stage than in the at-risk controls. 4. The results of the present study provide direct evidence that Ca(2+) signalling in platelets from acute ischaemic stroke patients was altered in response to particular stimuli. The dysregulation of Ca(2+) movement in platelets may persist up to the subacute stage of ischaemic stroke.

Compartmentalized signalling: Ca2+ compartments, microdomains and the many facets of Ca2+ signalling

Ca(2+) regulates a multitude of cellular processes and does so by partitioning its actions in space and time. In this review, we discuss how Ca(2+) responses are constructed from small quantal (elementary) events that have the potential to propagate to produce large pan-cellular responses. We review how Ca(2+) is compartmentalized both physically and functionally, and describe how each organelle has its own distinct Ca(2+)-handling properties. We explain how coordination of the movement of Ca(2+) between organelles is used to shape and hone Ca(2+) signals. Finally, we provide a number of specific examples of where compartmentation and localization of Ca(2+) are crucial to cell function.

Microhandling of vesicular glutamate uptake modulate feeding in broilers

Glutamate (Glu), the major excitatory neurotransmitter in vertebrate central nervous system, is actively taken up and stored in synaptic vesicles. On the arrival of an action potential to the pre-synaptic membrane and the subsequent opening of the voltage-gated calcium channels and movement of Ca(2+) into the neuron, these small vesicles fuse with the pre-synaptic membrane to release the neurotransmitter content into the synaptic cleft. Because it has previously been shown that intracerebroventricular (ICV) glutamate plays a role in feed intake in broilers, the manipulation of its vesicular concentration could affect feeding behaviour. On the contrary, research on vesicular glutamate transporters has, so far, been carried out on mammalian species. In the present study, we aim to examine the effect of Chicago sky blue 6B (CSB6B), a glutamate vesicular uptake inhibitor, on feed intake and latency to start feeding in a commercial strain of meat type chickens. To do this, four experiments have been designed to investigate the effect of ICV injection of saline, glutamate, as a general agonist for glutamate receptors, CSB6B and the combination of Glu and CSB6B. The findings indicate that CSB6B increases feed intake and decreases the latency to start feeding in 24-h-feed-deprived Ross 208 broilers.

Activation of (Na++K+)-ATPase Modulates Cardiac L-Type Ca2+Channel Function

Cellular Ca(2+) signaling underlies diverse vital biological processes, including muscle contractility, memory encoding, fertilization, cell survival, and cell death. Despite extensive studies, the fundamental control mechanisms that regulate intracellular Ca(2+) movement remain enigmatic. We have found recently that activation of the (Na(+)+K(+))-ATPase markedly potentiates intracellular Ca(2+) transients and contractility of rat heart cells. Little is known about the pathway responsible for the activation of the (Na(+)+K(+))-ATPase-initiated Ca(2+) signaling. Here, we demonstrate a novel mechanism in which activation of the (Na(+)+K(+))-ATPase is coupled to increased L-type Ca(2+) channel function through a signaling cascade involving Src and ERK1/2 but not well established regulators of the channel, such as adrenergic receptor system or activation of PKA or CaMKII. We have also identified Ser(1928), a phosphorylation site for the alpha1 subunit of the L-type Ca(2+) channel that may participate in the activation of the (Na(+)+K(+))-ATPase-mediated Ca(2+) signaling. The findings reported here uncover a novel molecular cross-talk between activation of the (Na(+)+K(+))-ATPase and L-type Ca(2+) channel and provide new insights into Ca(2+) signaling mechanisms for deeper understanding of the nature of cellular Ca(2+) handling in heart.

Causes and control of calcium deficiency disorders in vegetables: a review

SummaryThe aim of this study was to provide an overview of the causes and control of calcium (Ca)-deficiency disorders in vegetables. Ca-deficiency is usually related to the inability of the plant to translocate adequate Ca to the affected part. Many vegetables develop unique symptoms: for example blackheart in celery, tipburn in lettuce, chervil, onion, fennel, chinese cabbage and other cabbages, blossom end rot (BER) in tomato. Ca-deficiency disorders in vegetables can be controlled by various means. The growing medium influences the development of Ca-deficiency symptoms in plants. Restriction of the root volume is one factor that favours the development of Ca-deficiency symptoms in leafy vegetables, but reduces the incidence of BER in pepper. Ca-deficiency can also be avoided by using reasonable levels of nitrogen in the nutrient solution. Cations depress Ca-uptake and distribution, while anions depress the development of tipburn in plants. Ca-deficiency can be avoided by using the recommended level of salinity for each crop. Too high a salinity level increases the symptoms of Ca-deficiency in plants. Watering helps to prevent Ca-deficiency injury, as when growing vegetables outdoors. Maintaining an optimum soil moisture level helps to promote adequate movement of Ca to the roots and into the plant. A low relative humidity during the day-time increases the Ca-contents of leaves in leafy vegetables with an open growing point, but reduces the Ca contents of fruit and the inner leaves of leafy vegetables with a closed growing point. Avoiding too long a duration of supplementary lighting, too high a light intensity, and the use of high-pressure sodium lamps can prevent Ca-deficiency injury in plants. Shading may influence the incidence of BER, by reducing the appearance of symptoms of BER. Growing plants under a far-red wavelength filter helps to prevent Ca-deficiency disorders. Avoiding high or low temperatures also prevents Ca-deficiency injury. A negative DIF value (DIF = the difference between the day-time and night-time temperatures; a negative DIF means the night temperature is higher than the day temperature) may influence the incidence of tipburn injury by reducing its appearance. Air flow to the affected parts of plants can help to avoid the symptoms of Ca-deficiency. Ca sprays also help to prevent Ca-deficiency disorders in plants. Mulches can be used to protect plants against Ca-deficiency. Some crop varieties are less susceptible to Ca-deficiency. The plant growth regulator, Cultar (paclobutrazol, an inhibitor of gibberellin-biosynthesis), may influence the symptoms of Ca-deficiency in plants by reducing the appearance of the disorders. Planting a little later than the optimum date can avoid Ca-deficiency symptoms in leafy vegetables in Nordic countries. Harvesting a little earlier than the optimum date can also avoid Ca deficiency- symptoms in leafy vegetables.

A modified, rapid fluorometric method for the quantification of mitochondrial calcium

Background: Calcium is an important cellular mediator in numerous physiological processes. Under pathological conditions, large influxes of Ca 2+ into mitochondria may occur, leading to activation of “cell-death” pathways. Although there are several methods by which to monitor mitochondrial Ca 2+ [Ca 2+ ] m in vitro, current methods for quantifying [Ca 2+ ] m in the living animal are limited. Purpose: Herein, we describe a rapid and simple method by which to quantify the levels of total [Ca 2+ ] m in situ. Methods: The method relies on the presence of inhibitors of Ca 2+ influx and efflux to prevent movement of Ca 2+ during mitochondrial isolation followed by the lysing of the organelles to liberate the cation. Total [Ca 2+ ] m is quantified using the fluorescent probe Calcium Green 5-N. Results: A standard linear relationship between calcium green 5-N fluorescence signal intensity as a result of increasing concentrations of Cacl2 indicates that the amount of mitochondria in the assay mixture does not interfere with the fluorescent signal. A significant increase in Ca 2+ was observed, presumably due to the release of both bound and free Ca 2+ from the mitochondria in response to Triton X-100 exposure. The pH of samples from both DNP- and DMSO- treated animals remained unaltered after solubilization with Triton X-100. Conclusion: The method is sensitive to in vivo perturbations, as demonstrated by decreases in [Ca 2+ ] m following administration of the uncoupling agent 2, 4-dinitrophenol. doi : 10.5214/ans.0972.7531.2009.160204 Competing interests: None. Source of Funding: None Received Date: 09 March 2009 Revised Date: 31 March 2009 Accepted Date: 18 April 2009

Mitochondrial dysfunction activates cyclooxygenase 2 expression in cultured normal human chondrocytes

Mitochondrial alterations play a key role in the pathogenesis of osteoarthritis (OA). This study evaluated a potential role of mitochondrial respiratory chain (MRC) dysfunction in the inflammatory response of normal human chondrocytes. Commonly used inhibitors of the MRC were utilized to induce mitochondrial dysfunction in normal human chondrocytes. Levels of prostaglandin E(2) (PGE(2)) protein and expression of cyclooxygenase 2 (COX-2) and COX-1 messenger RNA (mRNA) and protein were analyzed. To identify the underlying mechanisms responsible for PGE(2) liberation, reactive oxygen species (ROS) were measured. Inhibitors of ROS, including vitamin E, and inhibitors of mitochondrial Ca(2+) and NF-kappaB were used to test their effects on the MRC. Antimycin A and oligomycin (inhibitors of mitochondrial complexes III and V, respectively) significantly increased the levels of PGE(2) (mean +/- SEM 505 +/- 132 pg/50,000 cells and 288 +/- 104 pg/50,000 cells, respectively, at 24 hours versus a basal level of 29 +/- 9 pg/50,000 cells; P < 0.05) and increased the expression of COX-2 at both the mRNA and protein levels. Expression of COX-1 did not show any modulation with either inhibitor. Further experiments revealed that antimycin A and oligomycin induced a marked increase in the levels of ROS. Production of PGE(2) and expression of COX-2 protein were inhibited by antioxidants, vitamin E, and mitochondrial Ca(2+) and NF-kappaB inhibitors. The response to blockers of mitochondrial Ca(2+) movement showed that ROS production was dependent on mitochondrial Ca(2+) accumulation. These results strongly suggest that, in human chondrocytes, the inhibition of complexes III and V of the MRC induces an inflammatory response, which could be especially relevant in relation to PGE(2) production via mitochondrial Ca(2+) exchange, ROS production, and NF-kappaB activation. These data may prove valuable for a better understanding of the participation of mitochondria in the pathogenesis of OA.