[Calcium signaling in plants].
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Calcium↗
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A calcium signaling cascade essential for myosin thick filament assembly in Xenopus myocytes.
Spontaneous calcium release from intracellular stores occurs during myofibrillogenesis, the process of sarcomeric protein assembly in striated muscle. Preventing these Ca2+ transients disrupts sarcomere formation, but the signal transduction cascade has not been identified. Here we report that specific blockade of Ca2+ release from the ryanodine receptor (RyR) activated Ca2+ store blocks transients and disrupts myosin thick filament (A band) assembly. Inhibition of an embryonic Ca2+/calmodulin-dependent myosin light chain kinase (MLCK) by blocking the ATP-binding site, by allosteric phosphorylation, or by intracellular delivery of a pseudosubstrate peptide, also disrupts sarcomeric organization. The results indicate that both RyRs and MLCK, which have well-described calcium signaling roles in mature muscle contraction, have essential developmental roles during construction of the contractile apparatus.
Actin Cytoskeleton↗
Netrin-1 induces axon branching in developing cortical neurons by frequency-dependent calcium signaling pathways.
A single axon can innervate multiple targets by collateral branching. Axon branching is thus essential for establishing CNS connectivity. However, surprisingly little is known about the mechanisms by which branching is regulated. Axons often stop elongating before branches develop and anatomical and molecular data suggest that axon branching occurs independent of axon outgrowth. We found that netrin-1 dramatically increases cortical axon branching. Here, we sought to identify intracellular signaling components involved in netrin-1-induced axon branching. Using live cell imaging of dissociated developing cortical neurons, we show that netrin-1 rapidly increases the frequency of repetitive calcium transients. These transients are often restricted to small regions of the axon. Simultaneous imaging of calcium activity and development of axon branches revealed that Ca2+ transients coincide spatially and temporally with protrusion of branches from the axon. Remarkably, fully formed branches with motile growth cones could develop de novo within 20 min. Netrin-1-induced Ca2+ transients involve release from intracellular stores and Ca2+ signaling is essential for netrin-1-induced axon branching. Using techniques to overexpress or suppress kinase activity, we find that calcium/calmodulin-dependent protein kinase II (CaMKII) and mitogen-activated protein kinase (MAPK) are major downstream targets of the netrin-1 calcium signaling pathway and are required for axon branching. CaMKII, but not MAPK, is also involved in axon outgrowth. The role of CaMKII and MAPKs in axon branching is consistent with the sensitivity of these kinases to changes in the frequency Ca2+ transients. Together, these novel findings define calcium signaling mechanisms required for development of new axon branches promoted by a guidance cue.
1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
Inhibition of calcium signaling in descending vasa recta endothelia by ANG II.
The intracellular calcium ([Ca(2+)](i)) response of outer medullary descending vasa recta (OMDVR) endothelia to ANG II was examined in fura 2-loaded vessels. Abluminal ANG II (10(-8) M) caused [Ca(2+)](i) to fall in proportion to the resting [Ca(2+)](i) (r = 0. 82) of the endothelium. ANG II (10(-8) M) also inhibited both phases of the [Ca(2+)](i) response generated by bradykinin (BK, 10(-7) M), 835 +/- 201 versus 159 +/- 30 nM (peak phase) and 169 +/- 26 versus 103 +/- 14 nM (plateau phase) (means +/- SE). Luminal ANG II reduced BK (10(-7) M)-stimulated plateau [Ca(2+)](i) from 180 +/- 40 to 134 +/- 22 nM without causing vasoconstriction. Abluminal ANG II added to the bath after luminal application further reduced [Ca(2+)](i) to 113 +/- 9 nM and constricted the vessels. After thapsigargin (TG) pretreatment, ANG II (10(-8) M) caused [Ca(2+)](i) to fall from 352 +/- 149 to 105 +/- 37 nM. This effect occurred at a threshold ANG II concentration of 10(-10) M and was maximal at 10(-8) M. ANG II inhibited both the rate of Ca(2+) entry into [Ca(2+)](i)-depleted endothelia and the rate of Mn(2+) entry into [Ca(2+)](i)-replete endothelia. In contrast, ANG II raised [Ca(2+)](i) in the medullary thick ascending limb and outer medullary collecting duct, increasing [Ca(2+)](i) from baselines of 99 +/- 33 and 53 +/- 11 to peaks of 200 +/- 47 and 65 +/- 11 nM, respectively. We conclude that OMDVR endothelia are unlikely to be the source of ANG II-stimulated NO production in the medulla but that interbundle nephrons might release Ca(2+)-dependent vasodilators to modulate vasomotor tone in vascular bundles.
Angiotensin II↗
Impact of cytoplasmic calcium buffering on the spatial and temporal characteristics of intercellular calcium signals in astrocytes.
The impact of calcium buffering on the initiation and propagation of mechanically elicited intercellular Ca2+ waves was studied using astrocytes loaded with different exogenous, cell membrane-permeant Ca2+ chelators and a laser scanning confocal or video fluorescence microscope. Using an ELISA with a novel antibody to BAPTA, we showed that different cell-permeant chelators, when applied at the same concentrations, accumulate to the same degree inside the cells. Loading cultures with BAPTA, a high Ca2+ affinity chelator, almost completely blocked calcium wave occurrence. Chelators having lower Ca2+ affinities had lesser affects, as shown in their attenuation of both the radius of spread and propagation velocity of the Ca2+ wave. The chelators blocked the process of wave propagation, not initiation, because large [Ca2+]i increases elicited in the mechanically stimulated cell were insufficient to trigger the wave in the presence of high Ca2+ affinity buffers. Wave attenuation was a function of cytoplasmic Ca2+ buffering capacity; i.e., loading increasing concentrations of low Ca2+ affinity buffers mimicked the effects of lesser quantities of high-affinity chelators. In chelator-treated astrocytes, changes in calcium wave properties were independent of the Ca2+-binding rate constants of the chelators, of chelation of other ions such as Zn2+, and of effects on gap junction function. Slowing of the wave could be completely accounted for by the slowing of Ca2+ ion diffusion within the cytoplasm of individual astrocytes. The data obtained suggest that alterations in Ca2+ buffering may provide a potent mechanism by which the localized spread of astrocytic Ca2+ signals is controlled.
Animals↗
Changes in calcium signalling, gravitropism, and statocyte ultrastructure in pea roots induced by calcium channel blockers.
The effect of Ca2+ channel blockers (D600 and nicardipine) were investigated in our experiments on 5-day seedlings of pea. Nicardipine had more inhibiting effect on root elongation than D600. The Ca2+ channel blockers (CCB) depressed gravitropic response in roots. In root statocytes, the destruction of the polar arrangement of cell organelles and other changes were induced by 10(-5) M D600 or nicardipine treatment for 12 h. At ultrastructural level, there were observed a lack of polarity, pronounced vacuolization, and changes in dictyosome structure in treated statocytes. Cytochemical study indicated that Ca2+ ions were concentrated in the intracellular organelles and cell walls in statocytes treated with CCB similar to untreated control. The data suggest that the effects of the CCB that demonstrated the correlation between the loss of polarity in statocytes and altered root gravitropism may be functionally related to systems that regulate Ca2+ homeostasis, particularly Ca2+ channels.
Calcium↗
cAMP potentiates ATP-evoked calcium signaling in human parotid acinar cells.
In salivary acinar cells, intracellular calcium ([Ca(2+)](i)) signaling plays an important role in eliciting fluid secretion through the activation of Ca(2+)-activated ionic conductances. Ca(2+) and cAMP have synergistic effects on fluid secretion such that peak secretion is elicited following activation of both parasympathetic and sympathetic pathways. We have recently demonstrated that cAMP exerts effects on Ca(2+) release, through protein kinase A (PKA)-mediated phosphorylation of inositol 1,4,5-trisphosphate receptors (InsP(3)R) in mouse parotid acinar cells. To extend these findings, in the present study cross-talk between Ca(2+) signaling and cAMP pathways in human parotid acinar cells was investigated. In human parotid acinar cells, carbachol stimulation evoked increases in the [Ca(2+)](i) and the initial peak amplitude was enhanced following PKA activation, consistent with reports from mouse parotid. Stimulation with ATP also evoked an increase in [Ca(2+)](i). The ATP-evoked Ca(2+) elevation was largely dependent on extracellular Ca(2+), suggesting the involvement of the P2X family of purinergic receptors. Pharmacological elevation of cAMP resulted in a approximately 5-fold increase in the peak [Ca(2+)](i) change evoked by ATP stimulation. This enhanced [Ca(2+)](i) increase was not dependent on intracellular release from InsP(3)R or ryanodine receptors, suggesting a direct effect on P2XR. Reverse transcription-polymerase chain reaction and Western blot analysis confirmed the presence of P2X(4)R and P2X(7)R mRNA and protein in human parotid acinar cells. ATP-activated cation currents were studied using whole cell patch clamp techniques in HEK-293 cells, a null background for P2XR. Raising cAMP resulted in a approximately 4.5-fold enhancement of ATP-activated current in HEK-293 cells transfected with P2X(4)R DNA but had no effects on currents in cells expressing P2X(7)R. These data indicate that in human parotid acinar cells, in addition to modulation of Ca(2+) release, Ca(2+) influx through P2X(4)R may constitute a further locus for the synergistic effects of Ca(2+) and PKA activation.
Adenosine Triphosphate↗
Network regulation of calcium signal in stomatal development.
AIM: Each cell is the production of multiple signal transduction programs involving the expression of thousands of genes. This study aims to gain insights into the gene regulation mechanisms of stomatal development and will investigate the relationships among some signaling transduction pathways. METHODS: Nail enamel printing was conducted to observe the stomatal indices of wild type and 10 mutants (plant hormone mutants, Pi-starvation induced CaM mutants and Pi-starvation-response mutant) in Arabidopsis, and their stomatal indices were analyzed by ANOVA. We analyzed the stomatal indices of 10 Arabidopsis mutants were analyzed by a model PRGE (potential relative effect of genes) to research relations among these genes. RESULTS: In wild type and 10 mutants, the stomatal index did not differ with respect to location on the lower epidermis. Compared with wild type, the stomatal indices of 10 mutants all decreased significantly. Moreover, significant changes and interactions might exist between some mutant genes. CONCLUSION: It was the stomatal intensity in Arabidopsis might be highly sensitive to most mutations in genome. While the effect of many gene mutations on the stomatal index might be negative, we also could assume the stomatal development was regulated by a signal network in which one signal transduction change might influence the stomatal development more or less, and the architecture might be reticulate. Furthermore, we could speculate that calcium was a hub in stomatal development signal regulation network, and other signal transduction pathways regulated stomatal development by influencing or being influenced by calcium signal transduction pathways.
Arabidopsis↗
[The calcium signal in the physiology of the secretory process. I].
The author gives an account of contemporary knowledge and hypotheses on the role of calcium as the second messenger signalizing stimulation of the secretory cell by a specific secretagogue stimulus. The basic structures from which calcium ions are released into the cytosol are the endoplasmatic reticulum, secretory granules and the cell membrane. The author discusses also the importance of mitochondria which act as an intracellular calcium reservoir. An important source of calcium for activation of the secretory process is also the extracellular space. Oscillation of the electric tension of the membrane of the excitable cell which causes temporary opening of the calcium channels participates also in the rise of this ion concentration in the cytosol; in the majority of endocrine systems, however, only in the second stage of the secretory process. In the reparative stage the intracellular reserves are resaturated with calcium. The ratio of the intra- and extracellular source depends probably on the type of secretory cell and the secretagogue stimulus. The author refers to some of her own clinical investigations where it did not prove possible to demonstrate the inhibiting action of calcium current blockers in the secretory process of excitable systems. Based on theoretical findings and hypotheses, she explains the inhibitory action of acute hypercalcaemia on some hormonal functions. In the review attention is paid to the function of calmodulin which is a mediator of the calcium signal and probably the site of interaction of some calciotropic substances.
Animals↗
Regulation of prolactin, thyrotropin subunit, and gonadotropin subunit gene expression by pulsatile or continuous calcium signals.
We investigated the importance of calcium (Ca2+) influx in increasing the steady state concentrations of mRNAs coding for the pituitary peptides PRL, alpha, and TSH, LH, and FSH beta-subunits. Adult female rat pituitaries were dissociated, plated for 48 h, then inserted into perifusion chambers. Secretory responses were measured after 2 and 22 h of perifusion, and after 24 h, the cells were recovered, total RNA was extracted, and mRNAs were assayed by dot blot hybridization. The first experiment examined the effect of the Ca2+ channel blocker verapamil (100 microM) on the stimulatory action of pulsatile TRH (4 nM; 60-min interval) or GnRH (100 pM; 60-min interval) on pituitary mRNAs. TRH pulses induced a significant increase (49-56%) in PRL, alpha, and TSH beta mRNAs. Similarly, GnRH pulses stimulated a rise in alpha (64%) and FSH beta (50%) mRNAs, but not LH beta. The effects of pulsatile TRH or GnRH were eliminated when verapamil was added to the medium, suggesting that Ca2+ influx is critical to the stimulatory action of TRH or GnRH. The second experiment examined the effect of pulsatile vs. continuous increases in intracellular Ca2+ on pituitary mRNA expression. Pulsatile Ca2+ signals were produced by giving 60-min pulses of 50 mM KCl, Bay K 8644 (10 microM), or Bay K 8644 (10 microM; in the presence of 10 mM KCl in the injectate) and vehicle pulses to controls. Continuous increases in intracellular Ca2+ were induced by perifusion with medium containing the Ca2+ ionophore A23187 (20 microM), and these groups were compared to that receiving continuous verapamil. Pulsatile increases in Ca2+ influx (KCl or Bay K 8644) stimulated significant elevations in all mRNAs studied (36-74% increase vs. controls), with the exception of TSH beta. The magnitude of the mRNA responses to pulsatile Ca2+ (vs. controls) was similar to that observed after TRH and GnRH pulses. In contrast, only LH beta was increased by A23187 (42% increase vs. controls; P < 0.05). PRL and alpha mRNAs were selectively diminished by A23187 (57% and 83% decreases vs. controls, respectively; P < 0.05) and verapamil (67% and 60%; P < 0.05). The data show that expression of these pituitary genes is regulated by Ca2+ and that a pulsatile Ca2+ signal is required to stimulate PRL, alpha, and FSH beta (but not LH beta).(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Calcium signaling pathways in the enteric nervous system.
The intracellular calcium level is an important regulator of cellular functioning, and its tight regulation occurs at several levels. Influx of extracellular calcium occurs via voltage-gated channels in response to a depolarization, and "capacitative" extracellular calcium occurs with cellular calcium depletion. Intracellular release of calcium also occurs through both the inositol trisphosphate- and ryanodine-sensitive stores of calcium. The following will detail these events and recent discoveries in Ca2+ signaling, and will specifically focus on their role in the functioning of the enteric nervous system.
Animals↗
Calcium signalling: the ups and downs of protein kinase C.
Oscillations in intracellular calcium levels control a plethora of physiological processes, but how they are decoded by a cell remains unclear. In a recent study, advances in FRET technology have been used to describe how calcium oscillations are decoded through phase-locked oscillations in substrate phosphorylation catalysed by protein kinase C.
Animals↗
Oxidative stress-induced calcium signalling in Aspergillus nidulans.
The effects of oxidative stress on levels of calcium ion (Ca(2+)) in Aspergillus nidulans were measured using strains expressing aequorin in the cytoplasm (Aeq(cyt)) and mitochondria (Aeq(mt)). When oxidative stress was induced by exposure to 10-mM H(2)O(2), the mitochondrial calcium response (Ca(mt)(2+)) was greater than the change in cytoplasmic calcium (Ca(c)(2+)). The Ca(mt)(2+) response to H(2)O(2) was dose dependent, while the increase in [Ca(c)(2+)] did not change with increasing H(2)O(2). The increase in both [Ca(c)(2+)] and [Ca(mt)(2+)] in response to oxidative stress was enhanced by exposure of cells to Ca(2+). The presence of chelator in the external medium only partially inhibited the Ca(mt)(2+) and Ca(c)(2+) responses to oxidative stress. Reagents that alter calcium fluxes had varied effects on the Ca(mt)(2+) response to peroxide. Ruthenium red blocked the increase in [Ca(mt)(2+)], while neomycin caused an even greater increase in [Ca(mt)(2+)]. Treatment with ruthenium red and neomycin had no effect on the Ca(c)(2+) response. Bafilomycin A and oligomycin had no effect on either the mitochondrial or cytoplasmic response. Inhibitors of both voltage-regulated calcium channels and intracellular calcium release channels inhibited the Ca(2+)-dependent component of the Ca(mt)(2+) response to oxidative stress. We conclude that the more significant Ca(2+) response to oxidative stress occurs in the mitochondria and that both intracellular and extracellular calcium pools can contribute to the increases in [Ca(c)(2+)] and [Ca(mt)(2+)] induced by oxidative stress.
Aequorin↗
Calcium signaling: a historical account.
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Animals↗
Fc epsilon RI signaling of mast cells activates intracellular production of hydrogen peroxide: role in the regulation of calcium signals.
Earlier studies, including our own, revealed that activation of mast cells is accompanied by production of reactive oxygen species (ROS) that help to mediate the release of the inflammatory mediators, including histamine and eicosanoids. However, little is known about the mechanisms of ROS production, including the species of oxidants produced. In this study we show that in both the RBL-2H3 mast cell line and bone marrow-derived mast cells, FcepsilonRI cross-linking stimulates intracellular oxidative burst, including hydrogen peroxide (H(2)O(2)) production, as defined with the oxidant-sensitive dyes dichlorofluorescein and scopoletin and the selective scavenger ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one). The oxidative burst was observed immediately after stimulation and was most likely due to an NAD(P)H oxidase. Experiments using selective pharmacological inhibitors demonstrated that activation of tyrosine kinases and phosphatidylinositol-3-kinase is required for induction of the oxidative burst. Blockade of the oxidative burst by diphenyleneiodonium impaired the release of preformed granular mediators, such as histamine and beta-hexosaminidase, and the secretion of newly synthesized leukotriene C(4), whereas selective scavenging H(2)O(2) by ebselen impaired leukotriene C(4) secretion, but not degranulation. Sustained elevation of cytosolic calcium through store-operated calcium entry was totally abolished when ROS production was blocked. In contrast, selective depletion of H(2)O(2) caused a considerable decrease and delay of the calcium response. Finally, tyrosine phosphorylation of phospholipase Cgamma and the linker for activation of T cells, an event required for calcium influx, was suppressed by diphenyleneiodonium and ebselen. These studies demonstrate that activation of the intracellular oxidative burst is an important regulatory mechanism of mast cell responses.
Adaptor Proteins, Signal Transducing↗
Calcium signalling and control of cell proliferation by tyrosine kinase receptors (review).
Most peptidic growth factors (GFs) that act as mitogens for different cell types bind to tyrosine kinase receptors (RTKs) and trigger complex intracellular signal transduction pathways finally leading to cell proliferation. Among the early events induced by GFs, cytosolic calcium increase plays a key role, and in particular calcium entry from extracellular medium appears to be a widespread signal. Even if a great amount of data has been provided during the last decades, several issues remain to be fully clarified: the nature of the calcium-permeable channels involved, their regulation by intracellular messengers, and the mechanisms underlying calcium-dependent cell proliferation. This review focuses on the relationship between calcium signals and angiogenesis, a process in which endothelial cell proliferation, mainly triggered by basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF), is a critical step.
Animals↗
Dopamine D1 and D2 receptor Co-activation generates a novel phospholipase C-mediated calcium signal.
Although dopamine D1 and D2 receptors belong to distinct subfamilies of dopamine receptors, several lines of evidence indicate that they are functionally linked. However, a mechanism for this linkage has not been elucidated. In this study, we demonstrate that agonist stimulation of co-expressed D1 and D2 receptors resulted in an increase of intracellular calcium levels via a signaling pathway not activated by either receptor alone or when only one of the co-expressed receptors was activated by a selective agonist. Calcium signaling by D1-D2 receptor co-activation was abolished following treatment with a phospholipase C inhibitor but not with pertussis toxin or inhibitors of protein kinase A or protein kinase C, indicating coupling to the G(q) pathway. We also show, by co-immunoprecipitation from rat brain and from cells co-expressing the receptors, that D1 and D2 receptors are part of the same heteromeric protein complex and, by immunohistochemistry, that these receptors are co-expressed and co-localized within neurons of human and rat brain. This demonstration that D1 and D2 receptors have a novel cellular function when co-activated in the same cell represents a significant step toward elucidating the mechanism of the functional link observed between these two receptors in brain.
Animals↗
Regulation of calcium signalling by docosahexaenoic acid in human T-cells. Implication of CRAC channels.
We elucidated the role of docosahexaenoic acid (DHA) on the increases in free intracellular calcium concentrations, [Ca(2+)]i, in human (Jurkat) T-cell lines. DHA evoked an increase in [Ca(2+)]i in a dose-dependent manner in these cells. Anti-CD3 antibody, known to stimulate increases in Ca(2+) from endoplasmic reticulum (ER) via the production of inositol trisphosphate, also evoked increases in [Ca(2+)]i in Jurkat T-cells. We also used thapsigargin which inhibits Ca(2+)-ATPase of the ER and, therefore, increases Ca(2+) in the cytosol. Interestingly, addition of DHA during the thapsigargin-induced peak response exerted an additive effect on the increases in [Ca(2+)]i in human T-cells, indicating that the mechanisms of action of these two agents are different. However, the DHA-induced calcium response was not observed when this agent was added during the anti-CD3-induced calcium peak, though its addition resulted in a prolonged and sustained calcium response as a function of time, suggesting that DHA recruits calcium, in part, from the ER pool and the prolonged response may be due to Ca(2+) influx. In the medium containing 0% Ca(2+), the DHA-evoked response on the increases in [Ca(2+)]i was significantly curtailed as compared to that in 100% Ca(2+) medium, supporting the notion that the response of the DHA is also due, in part, to the opening of calcium channels. Furthermore, preincubation of cells with tyrphostin A9, an inhibitor of Ca(2+) release-activated Ca(2+) (CRAC) channels also significantly curtailed the DHA-induced sustained response on the increases in [Ca(2+)]i in these cells. These results suggest that DHA induces an increase in [Ca(2+)]i via the ER pool and the opening of CRAC channels in human T-cells.
Antibodies↗