Interaction of polyamines or their precursors with the calcium-controlled secretion of peroxidase by sugarbeet cells

Summary Three polyamines tested (cadaverine, spermidine and spermine) and their 2 precursors (the amino acids arginine and ornithine) inhibit the Ca²⁺-mediated secretion of peroxidases by sugarbeet cells in suspension culture at concentrations ranging from 10^–15 to 10^–5M. In the absence of exogenous Ca²⁺, spermine added at higher concentrations mimics the activatory effect of Ca²⁺, the other polyamines being without effect.Supported by the Belgian FRFC (grant No. 2.9009.75 to T.G.) and the Swiss National Foundation for Scientific Research (grant No. 3.140-0.81 to C.P. and H.G.).     

Neuronal calcium signaling: function and dysfunction

Calcium (Ca²⁺) is an universal second messenger that regulates the most important activities of all eukaryotic cells. It is of critical importance to neurons as it participates in the transmission of the depolarizing signal and contributes to synaptic activity. Neurons have thus developed extensive and intricate Ca²⁺ signaling pathways to couple the Ca²⁺ signal to their biochemical machinery. Ca²⁺ influx into neurons occurs through plasma membrane receptors and voltage-dependent ion channels. The release of Ca²⁺ from the intracellular stores, such as the endoplasmic reticulum, by intracellular channels also contributes to the elevation of cytosolic Ca²⁺. Inside the cell, Ca²⁺ is controlled by the buffering action of cytosolic Ca²⁺-binding proteins and by its uptake and release by mitochondria. The uptake of Ca²⁺ in the mitochondrial matrix stimulates the citric acid cycle, thus enhancing ATP production and the removal of Ca²⁺ from the cytosol by the ATP-driven pumps in the endoplasmic reticulum and the plasma membrane. A Na⁺/Ca²⁺ exchanger in the plasma membrane also participates in the control of neuronal Ca²⁺. The impaired ability of neurons to maintain an adequate energy level may impact Ca²⁺ signaling: this occurs during aging and in neurodegenerative disease processes. The focus of this review is on neuronal Ca²⁺ signaling and its involvement in synaptic signaling processes, neuronal energy metabolism, and neurotransmission. The contribution of altered Ca²⁺ signaling in the most important neurological disorders will then be considered.     

Sulfhydryl oxidation induces calcium release from fragmented sarcoplasmic reticulum even in the presence of glutathione

Alcian blue and plumbagin induced transient Ca²⁺ release from fragmented sarcoplasmic reticulum. Dithiothreitol (DTT) and glutathione (GSH) partially blocked Ca²⁺ release induced by these oxidizing compounds. Pretreatment of alcian blue and plumbagin with DTT or GSH for more than 1 min was required to abolish the ability of the oxidizing compounds to release Ca²⁺. Mg²⁺ and ruthenium red completely blocked alcian blue-and plumbagin-induced Ca²⁺ release. These results suggest that oxidation of sulfhydryls on Ca²⁺ release channels induces Ca²⁺ release even in the presence of GSH in situ.     

Sr2+ can become incorporated into an agonist-sensitive,cytoplasmic Ca2+ store in a cell line derived from the equine sweat gland epithelium

We have explored the properties of a Ca²⁺-dependent cell-signalling pathway that becomes active when cultured equine sweat gland cells are stimulated with ATP. The ATP-regulated, Ca²⁺-influx pathway allowed Sr²⁺ to enter the cytoplasm but permitted only a minimal influx of Ba²⁺. Experiments in which cells were repeatedly stimulated with ATP suggested that Sr²⁺, but not Ba²⁺, could become incorporated into the agonist-sensitive, cytoplasmic Ca²⁺ store. Further evidence for this was provided by experiments using ionomycin, a Ca²⁺ ionophore which has no affinity for Sr²⁺.     

ATP-induced Ca<Superscript>2+</Superscript>-signalling mechanisms in the regulation of mesenchymal stem cell migration

The ability of cells to migrate to the destined tissues or lesions is crucial for physiological processes from tissue morphogenesis, homeostasis and immune responses, and also for stem cell-based regenerative medicines. Cytosolic Ca²⁺ is a primary second messenger in the control and regulation of a wide range of cell functions including cell migration. Extracellular ATP, together with the cognate receptors on the cell surface, ligand-gated ion channel P2X receptors and a subset of G-protein-coupled P2Y receptors, represents common autocrine and/or paracrine Ca²⁺ signalling mechanisms. The P2X receptor ion channels mediate extracellular Ca²⁺ influx, whereas stimulation of the P2Y receptors triggers intracellular Ca²⁺ release from the endoplasmic reticulum (ER), and activation of both type of receptors thus can elevate the cytosolic Ca²⁺ concentration ([Ca²⁺]_c), albeit with different kinetics and capacity. Reduction in the ER Ca²⁺ level following the P2Y receptor activation can further induce store-operated Ca²⁺ entry as a distinct Ca²⁺ influx pathway that contributes in ATP-induced increase in the [Ca²⁺]_c. Mesenchymal stem cells (MSC) are a group of multipotent stem cells that grow from adult tissues and hold promising applications in tissue engineering and cell-based therapies treating a great and diverse number of diseases. There is increasing evidence to show constitutive or evoked ATP release from stem cells themselves or mature cells in the close vicinity. In this review, we discuss the mechanisms for ATP release and clearance, the receptors and ion channels participating in ATP-induced Ca²⁺ signalling and the roles of such signalling mechanisms in mediating ATP-induced regulation of MSC migration.     

Ca2+ release-activated Ca2+ (CRAC) current, structure, and function

Store-operated Ca²⁺ entry describes the phenomenon that connects a depletion of internal Ca²⁺ stores to an activation of plasma membrane-located Ca²⁺ selective ion channels. Tremendous progress towards the underlying molecular mechanism came with the discovery of the two respective limiting components, STIM and Orai. STIM1 represents the ER-located Ca²⁺ sensor and transmits the signal of store depletion to the plasma membrane. Here it couples to and activates Orai, the highly Ca²⁺-selective pore-forming subunit of Ca²⁺ release-activated Ca²⁺ channels. In this review, we focus on the molecular steps that these two proteins undergo from store-depletion to their coupling, the activation, and regulation of Ca²⁺ currents.     

Calcium binding, structural stability and guanylate cyclase activation in GCAP1 variants associated with human cone dystrophy

Guanylate cyclase activating protein 1 (GCAP1) is a neuronal Ca²⁺ sensor (NCS) that regulates the activation of rod outer segment guanylate cyclases (ROS-GCs) in photoreceptors. In this study, we investigated the Ca²⁺-induced effects on the conformation and the thermal stability of four GCAP1 variants associated with hereditary human cone dystrophies. Ca²⁺ binding stabilized the conformation of all the GCAP1 variants independent of myristoylation. The myristoylated wild-type GCAP1 was found to have the highest Ca²⁺ affinity and thermal stability, whereas all the mutants showed decreased Ca²⁺ affinity and significantly lower thermal stability in both apo and Ca²⁺-loaded forms. No apparent cooperativity of Ca²⁺ binding was detected for any variant. Finally, the nonmyristoylated mutants were still capable of activating ROS-GC1, but the measured cyclase activity was shifted toward high, nonphysiological Ca²⁺ concentrations. Thus, we conclude that distorted Ca²⁺-sensor properties could lead to cone dysfunction.     

Cytosolic free Ca2+ in insulin secreting cells and its regulation by isolated organelles

Summary The role of Ca²⁺ in secretagogue-induced insulin release is documented not only by the measurements of⁴⁵Ca fluxes in pancreatic islets, but also, by direct monitoring of cytosolic free Ca²⁺, [Ca²⁺]_i. As demonstrated, using the fluorescent indicator quin 2, glyceraldehyde, carbamylcholine and alanine raise [Ca²⁺]_i in the insulin secreting cell line RINm5F, whereas glucose has a similar effect in pancreatic islet cells. The regulation of cellular Ca²⁺ homeostasis by organelles from a rat insulinoma, was investigated with a Ca²⁺ selective electrode. The results suggest that both the endoplasmic reticulum and the mitochondria participate in this regulation, albeit at different Ca²⁺ concentrations. By contrast, the secretory granules do not appear to be involved in the short-term regulation of [Ca²⁺]_i. Evidence is presented that inositol 1,4,5-trisphosphate, which is shown to mobilize Ca²⁺ from the endoplasmic reticulum, is acting as an intracellular mediator in the stimulation of insulin release.     

The cell cycle: a new entry in the field of Ca2+ signaling

Ca²⁺ signaling plays a crucial role in virtually all cellular processes, from the origin of new life at fertilization to the end of life when cells die. Both the influx of external Ca²⁺ through Ca²⁺-permeable channels and its release from intracellular stores are essential to the signaling function. Intracellular Ca²⁺ is influenced by mitogenic factors which control the entry and progression of the cell cycle; this is a strong indication for a role of Ca²⁺ in the control of the cycle, but surprisingly, the possibility of such a role has only been paid scant attention in the literature. Substantial progress has nevertheless been made in recent years in relating Ca²⁺ and the principal decoder of its information, calmodulin, to the modulation of various cycle steps. The aim of this review is to critically discuss the evidence for a role of Ca²⁺ in the cell cycle and to discuss Ca²⁺-dependent pathways regulating cell growth and differentiation. Received 2 March 2005; received after revision 9 May 2005; accepted 24 May 2005     

The Ca2+-transport ATPases in smooth muscle

Summary A calmodulin stimulated Ca²⁺-transport ATPase which has many of the characteristics of the erythrocyte type Ca²⁺-transport ATPase has been purified from smooth muscle. In particular, the effect of calmodulin on these transport enzymes is mimiced by partial proteolysis and antibodies against erythrocyte Ca²⁺-transport ATPase also bind to the smooth muscle (Ca²⁺+Mg²⁺)ATPase. A correlation between the distribution of the calmodulin stimulated (Ca²⁺+Mg²⁺)ATPase and (Na⁺+K⁺)ATPase activities in smooth muscle membranes separated by density gradient centrifugation suggests a plasmalemmal distribution of this (Ca²⁺+Mg²⁺)ATPase. A phosphoprotein intermediate in smooth muscle which strongly resembles the corresponding phosphoprotein in sarcoplasmic reticulum of skeletal muscle may indicate the presence in smooth muscle of a similar type of Ca²⁺-transport ATPase.     

Darier’s disease: a calcium-signaling perspective

Ca²⁺ influx evoked across the plasma membrane upon internal store depletion is essential for a myriad of cellular functions including gene expression, cell proliferation, differentiation and even apoptosis. Darier’s disease (DD), an autosomal dominant inherited disorder of the skin, arising due to mutations in the isoform 2 of the sarco (endo) plasmic reticulum Ca²⁺ ATPase (SERCA2), exemplifies an anomaly of Ca²⁺ signaling disturbances. Owing to loss of function mutations in SERCA2, keratinocytes in DD patients have a reduced pool of endoplasmic reticulum (ER) Ca²⁺. Importantly, the status of ER Ca²⁺ is critical for the activation of a class of plasma membrane Ca²⁺ channels referred to as store operated Ca²⁺ channels (SOCs). The widely expressed transient receptor potential (TRP) family of channels is proposed to be SOCs. In this review we discuss DD from the viewpoint of Ca²⁺ signaling and present a potential role for TRPC1 in the disease pathogenesis. Received 30 August 2007; received after revision 17 October 2007; accepted 6 November 2007     

The role of calcium in aggregation and development ofDictyostelium

Changes in cytosolic Ca²⁺ play an important role in a wide array of cell types and the control of its concentration depends upon the interplay of many cellular constituents. Resting cells maintain cytosolic calcium ([Ca²⁺]_i) at a low level in the face of steep gradients of extracellular and sequestered Ca²⁺. Many different signals can provoke the opening of calcium channels in the plasma membrane or in intracellular compartments and cause rapid influx of Ca²⁺ into the cytosol and elevation of [Ca²⁺]_i. After such stimulation Ca²⁺ ATPases located in the plasma membrane and in the membranes of intracellular stores rapidly return [Ca²⁺]_i to its basal level. Such responses to elevation of [Ca²⁺]_i are a part of an important signal transduction mechanism that uses calcium (often via the binding protein calmodulin) to mediate a variety of cellular actions responsive to outside influences.     

Blockade by zinc ions of K+-induced contraction and calcium in guinea pigTaenia coli

Preincubation with 0.3 mM Zn²⁺ markedly inhibited both the tonic response and Ca²⁺ binding at low affinity sites induced by K⁺ (60 mM), with smaller effects on the phasic response and the high affinity Ca²⁺ sites, inTaenia coli. However, when the muscle was kept in Zn²⁺-containing medium following the first stimulation with the K⁺, the phasic response and the high affinity Ca²⁺ sites were more severely inhibited during the second stimulation with K⁺. This probably indicates that Zn²⁺ reduced the tonic tension response to K⁺ mainly by inhibiting Ca²⁺ influx at the cell membranes ofTaenia coli. However, when Zn²⁺ is continuously present, Ca²⁺ is not supplied at the storage sites and is not available for the phasic response to a second stimulation with K⁺.     

Experiments on the mechanism of the inhibition of mitochondrial Ca2+ transport by La3+ and ruthenium red

Summary The effects of La³⁺ and ruthenium red on the energy-linked uptake of Ca²⁺ mediated by a synthetic neutral Ca²⁺ ionophore have been investigated in rat liver mitochondria. The results indicate that unspecific surface charge effects do not play a major role in the mechanism of inhibition of mitochondrial Ca²⁺ transport by La³⁺ and ruthenium red.Acknowledgments. The authors are indebted to Prof. W. Simon, ETH Zurich, for having provided samples of the synthetic neutral Ca²⁺ ligand, and to M. Mattenberger for the valuable technical assistence. The work was supported by a grant of the Swiss Nationalfonds (grant No. 3.1720.75).     

Cytosolic calcium in platelet activation

Experiments with permeabilised platelets, and with intact platelets loaded with fluorescent Ca²⁺-indicators, over the past several years have greatly extended our knowledge and understanding of cytosolic Ca²⁺ as a platelet activator and its interactions with other cytosolic regulators. This article outlines insights, gained from the use of the fluorescent dyes, into maintenance and restoration of basal [Ca²⁺]_i, mechanisms of receptor-mediated Ca²⁺-mobilisation and quantitation of [Ca²⁺]_i/response relations in intact human platelets.     

Involvement of thiols in the induction of inward current induced by silver in frog skeletal muscle membrane

Exposure of voltage-clamped frog skeletal muscle fibres to silver caused a maintained inward current which could be carried by Ca²⁺, Mg²⁺ or Na⁺. Inorganic Ca²⁺ channel blockers and dithiothreitol (SH reducing agent) diminished this current, but a Na⁺ channel blocker did not. Thus, silver activates the Ca²⁺ channel by acting on SH groups in a Ca²⁺ channel protein.     

Peroxovanadate inhibits Ca2+ release from mitochondria

Mitochondria contain a specific Ca²⁺ release pathway which operates when oxidized mitochondrial pyridine nucleotides are hydrolyzed. NAD⁺ hydrolysis and therefore Ca²⁺ release is possible when some vicinal thiols are cross-linked. Here we report that the thiol oxidant peroxovanadate inhibits the specific Ca²⁺ release pathway. In mitochondria, peroxovanadate causes a complete loss of reduced glutathione, which is not accompanied by formation of glutathione disulfide, and a partial loss of protein thiols. In model reactions, peroxovanadate oxidizes reduced glutathione predominantly to the sulfonate derivative, but does not react with glutathione disulfide. When the vicinal thiols relevant for Ca²⁺ release are cross-linked, Ca²⁺ release is no longer inhibited by peroxovanadate. Conversely, pretreatment of mitochondria with peroxovanadate makes them insensitive to compounds promoting the disulfide state. These results suggest that peroxovanadate inhibits the prooxidant-induced Ca²⁺ release from mitochondria by (i) depleting mitochondria of reduced glutathione and (ii) oxidizing the vicinal thiols relevant for Ca²⁺ release to a state higher than disulfide, presumably the sulfonate state. The findings provide further insight into the regulation of Ca²⁺ release from intact mitochondria, and may be relevant for a better understanding of the action of peroxovanadate in cells, where the compound can be insulin mimetic. Received 28 March 2002; received after revision 8 May 2002; accepted 15 May 2002     

Pharmacological inhibition of store-operated calcium entry in MDA-MB-468 basal A breast cancer cells: consequences on calcium signalling,cell migration and proliferation

Store-operated Ca²⁺ entry is a pathway that is remodelled in a variety of cancers, and altered expression of the components of store-operated Ca²⁺ entry is a feature of breast cancer cells of the basal molecular subtype. Studies of store-operated Ca²⁺ entry in breast cancer cells have used non-specific pharmacological inhibitors, complete depletion of intracellular Ca²⁺ stores and have mostly focused on MDA-MB-231 cells (a basal B breast cancer cell line). These studies compared the effects of the selective store-operated Ca²⁺ entry inhibitors Synta66 and YM58483 (also known as BTP2) on global cytosolic free Ca²⁺ ([Ca²⁺]_CYT) changes induced by physiological stimuli in a different breast cancer basal cell line model, MDA-MB-468. The effects of these agents on proliferation as well as serum and epidermal growth factor (EGF) induced migration were also assessed. Activation with the purinergic receptor activator adenosine triphosphate, produced a sustained increase in [Ca²⁺]_CYT that was entirely dependent on store-operated Ca²⁺ entry. The protease activated receptor 2 activator, trypsin, and EGF also produced Ca²⁺ influx that was sensitive to both Synta66 and YM58483. Serum-activated migration of MDA-MB-468 breast cancer cells was sensitive to both store-operated Ca²⁺ inhibitors. However, proliferation and EGF-activated migration was differentially affected by Synta66 and YM58483. These studies highlight the need to define the exact mechanisms of action of different store-operated calcium entry inhibitors and the impact of such differences in the control of tumour progression pathways.     

Calcium signaling in plants

Changes in the cytosolic concentration of calcium ions ([Ca²⁺]_i) play a key second messenger role in signal transduction. These changes are visualized by making use of either Ca²⁺-sensitive fluorescent dyes or the Ca²⁺-sensitive photoprotein, aequorin. Here we describe the advances made over the last 10 years or so, which have conclusively demonstrated a second messenger role for [Ca²⁺]_i in a few model plant systems. Characteristic changes in [Ca²⁺]_i have been seen to precede the responses of plant cells and whole plants to physiological stimuli. This has had a major impact on our understanding of cell signaling in plants. The next challenge will be to establish how the Ca²⁺ signals are encrypted and decoded in order to provide specificity, and we discuss the current understanding of how this may be achieved.     

The action of the peptidoleukotriene LTD4 on intracellular calcium in rat mesangial cells

The dose-dependent effect of CGP 45715A on the LTD₄-induced Ca²⁺ response of glomerular mesangial cells has been studied. Our results demonstrate that the LTD₄-dependent increase in the cytosolic Ca²⁺ concentration primarily involves an InsP₃-mediated release of Ca²⁺ from intracellular storage sites and to a minor extent an enhanced influx of Ca²⁺ through receptor-operated Ca²⁺ channels located in the plasma membrane. The action of CGP 45715A on the Ca²⁺ response is an inhibitory one and is convincingly explained by a displacement of LTD₄ from its receptor site(s). The contractile effect of LTD₄ on pulmonary smooth muscle is proposed to be mainly caused by a receptor-mediated hydrolysis of phosphatidylinositol-4,5-bisphosphate.