Understanding Of Ca Research Articles

HIV-1 capsid and viral DNA integration.

HIV-1 capsid protein (CA)-independently or by recruiting host factors-mediates several key steps of virus replication in the cytoplasm and nucleus of the target cell. Research in the recent years have established that CA is multifunctional and genetically fragile of all the HIV-1 proteins. Accordingly, CA has emerged as a validated and high priority therapeutic target, and the first CA-targeting antiviral drug was recently approved for treating multi-drug resistant HIV-1 infection. However, development of next generation CA inhibitors depends on a better understanding of CA's known roles, as well as probing of CA's novel roles, in HIV-1 replication. In this timely review, we present an updated overview of the current state of our understanding of CA's multifunctional role in HIV-1 replication-with a special emphasis on CA's newfound post-nuclear roles, highlight the pressing knowledge gaps, and discuss directions for future research.

Abstract 472: Organizations Unite in “Call-Push-Shock” Movement to Impact Public Understanding That Drives Action

Introduction: The incidence of OHCA in the U.S. is high (>350,000); the survival rate is low, about 1 in 10. Less than half of victims receive bystander CPR (39%) or treatment with an AED (6%) before EMS arrival. Consumer research indicates the public’s motivation to learn CPR/AED skills and help in emergencies increases with understanding of CA and the impact of bystander action. Two tested messages resonate most with the public: CPR/AED use can double or triple the chance of survival, and CA can happen to a loved one. Hypothesis: An inclusive national movement of organizations using unified, co-branded and tested messaging in a coordinated, multi-channel social media campaign could improve targeted reach and, over time, public understanding of CA and the importance of bystander action. Creating a gold standard for educational content on CA could improve message retention and motivation to act over time. Methods: We created a movement through consistent messaging in a user-friendly toolkit. We built a landing page (CallPushShock.org) and co-sponsored a social media campaign on CA and the importance of bystander action. We launched the campaign during CPR-AED Awareness Week (June 2018). We invited other organizations to join for SCA Awareness Month (Oct 2018), providing co-branded social media assets (Facebook/Twitter posts, videos, infographic) and posting schedules to all partners. Social media analytics were used to measure the reach of the campaign. Results: The campaign launched in June, attracting 20 partners by October. Combined co-sponsor results for June were: News release: 548,464 headline impressions (PR Web); hashtag (#callpushshock) impressions: 243,345 (Keyhole); FB reach: 86,134; Twitter impressions: 25,107; YouTube views: 351; e-news opens: 4,226 (MailChimp, Constant Contact); landing page: 1,291 users (Google). [ Oct 2018 and June 2019 results in development, reflecting extended partner reach.] Conclusion: A social media campaign, leveraging consumer-tested messaging used by multiple organizations in a unified, consistent movement can be effective in improving targeted reach and educational outcomes. A sustained effort is needed to determine campaign impact in improving public understanding of CA and bystander action over time.

What Drives Symbiotic Calcium Signalling in Legumes? Insights and Challenges of Imaging

We review the contribution of bioimaging in building a coherent understanding of Ca signalling during legume-bacteria symbiosis. Currently, two different calcium signals are believed to control key steps of the symbiosis: a Ca gradient at the tip of the legume root hair is involved in the development of an infection thread, while nuclear Ca oscillations, the hallmark signal of this symbiosis, control the formation of the root nodule, where bacteria fix nitrogen. Additionally, different Ca spiking signatures have been associated with specific infection stages. Bioimaging is intrinsically a cross-disciplinary area that requires integration of image recording, processing and analysis. We used experimental examples to critically evaluate previously-established conclusions and draw attention to challenges caused by the varying nature of the signal-to-noise ratio in live imaging. We hypothesise that nuclear Ca spiking is a wide-range signal involving the entire root hair and that the Ca signature may be related to cytoplasmic streaming.

Effect of early neonatal development and delayed feeding post-hatch on jejunal and ileal calcium and phosphorus transporter genes expression in broiler chickens

Calcium (Ca) and phosphorus (P) are essential minerals involved in many biological processes including bone development and mineralization. Plasma concentration of both minerals is tightly regulated, and Ca and P homeostasis is maintained via intestinal absorption, bone storage and exchange, and renal reabsorption. In the current broiler production systems, chicks are deprived of food and water for up to 72 h due to uneven hatching, hatchery procedures, and transportation time to farms. Post-hatch (PH) feed delay results in lower body and organ weight, higher feed conversion ratio and mortality, and delayed PH growth and GIT development. Little is known about the effects of early neonatal development and delayed or immediate feeding PH on Ca and P transporters. Therefore, the aim of the present study was to characterize expression patterns of Ca and P transporter genes in small intestine during the first 2 wk PH in chickens fed immediately after hatch (FED) or subjected to 48 h delayed feeding (NOTFED). Expression of all Ca and P transporters in jejunum and ileum was significantly (P < 0.05) affected by age. Among Ca transporter genes, only mRNA expression of Calbidin D28k in jejunum and Ca sensing receptor (CaSR) in ileum were significantly (P < 0.05) affected by delay in feed access. For P transporter genes' expression, only P transporter type III (PIT1) mRNA was significantly affected by age, delay in feed access, and their interaction (P < 0.05). In summary, we have shown, for the first time, early developmental changes of Ca and P transporter genes in broiler chickens. Results suggest that an increase in gene expression of some of the transporters corresponds with the switch from yolk to high starch diet. Overall, our results can be helpful in better understanding of Ca and P homeostasis in broilers.

Ca(2+) signaling initiated by canonical transient receptor potential channels in dendritic development.

The spatial patterns of dendritic structures diverge in different types of neurons as adaptations to their unique functions. Although different intracellular mechanisms underlying dendritic morphogenesis have been suggested, it is evident that the elevation in intracellular Ca(2+) levels plays a major role in the process. Canonical transient receptor potential (TRPC) channels, known to be non-selective Ca(2+)-permeable cation channels, act as environmental detectors to sense and transduce extracellular signals into different intracellular responses, including the regulation of dendritic growth, via Ca(2+) influx. Here, we review recent advances in the understanding of Ca(2+) signaling, especially signals mediated by Ca(2+) influx via TRPC channels, and the underlying molecular events in dendritic development.

Calcium Signaling Alterations, Oxidative Stress, and Autophagy in Aging

Aging is a multi-factorial process that may be associated with several functional and structural deficits which can evolve into degenerative diseases. In this review, we present data that may depict an expanded view of molecular aging theories, beginning with the idea that reactive oxygen species (ROS) are the major effectors in this process. In addition, we have correlated the importance of autophagy as a neuroprotective mechanism and discussed a link between age-related molecules, Ca(2+) signaling, and oxidative stress. There is evidence suggesting that alterations in Ca(2+) homeostasis, including mitochondrial Ca(2+) overload and alterations in electron transport chain (ETC) complexes, which increase cell vulnerability, are linked to oxidative stress in aging. As much as Ca(2+) signaling is altered in aged cells, excess ROS can be produced due to an ineffective coupling of mitochondrial respiration. Damaged mitochondria might not be removed by the macroautophagic system, which is hampered in aging by lipofuscin accumulation, boosting ROS generation, damaging DNA, and, ultimately, leading to apoptosis. This process can lead to altered protein expression (such as p53, Sirt1, and IGF-1) and progress to cell death. This cycle can lead to increased cell vulnerability in aging and contribute to an increased susceptibility to degenerative processes. A better understanding of Ca(2+) signaling and molecular aging alterations is important for preventing apoptosis in age-related diseases. In addition, caloric restriction, resveratrol and autophagy modulation appear to be predominantly cytoprotective, and further studies of this process are promising in age-related disease therapeutics.

Calcium influx pathways in breast cancer: opportunities for pharmacological intervention

Ca(2+) influx through Ca(2+) permeable ion channels is a key trigger and regulator of a diverse set of cellular events, such as neurotransmitter release and muscle contraction. Ca(2+) influx is also a regulator of processes relevant to cancer, including cellular proliferation and migration. This review focuses on calcium influx in breast cancer cells as well as the potential for pharmacological modulators of specific Ca(2+) influx channels to represent future agents for breast cancer therapy. Altered expression of specific calcium permeable ion channels is present in some breast cancers. In some cases, such changes can be related to breast cancer subtype and even prognosis. In vitro and in vivo models have now helped identify specific Ca(2+) channels that play important roles in the proliferation and invasiveness of breast cancer cells. However, some aspects of our understanding of Ca(2+) influx in breast cancer still require further study. These include identifying the mechanisms responsible for altered expression and the most effective therapeutic strategy to target breast cancer cells through specific Ca(2+) channels. The role of Ca(2+) influx in processes beyond breast cancer cell proliferation and migration should become the focus of studies in the next decade.

Macromineral requirements for the maintenance and growth of Boer crossbred kids 1

Advances in mineral nutrition of goats have been made during the last decade, especially in our understanding of Ca and P requirements. However, few studies have focused on the mineral requirements of crossbred Boer goats in their growth phase. Our objective for this study was to determine the macromineral (Ca, P, Mg, K, and Na) requirements for the maintenance and growth of intact, male three-fourths Boer × one-fourth Saanen kids (n = 34; 20.5 ± 0.24 kg of initial BW). Two trials were conducted: 1 for maintenance and 1 for growth requirements. In the maintenance trial, 28 kids were used. The baseline (BL) group consisted of 7 randomly selected kids averaging 21.2 ± 0.36 kg BW and 122 d old. The remaining kids (n = 21; age 168 ± 5 d) were randomly allocated into 7 slaughter groups (blocks) including 3 animals distributed among 3 amounts of DMI (treatments: ad libitum and restricted to 70 or 40% of ad libitum intake). Animals in a group were slaughtered when the ad libitum-treatment kid in the block reached 35 kg BW. The BL and ad libitum-fed groups in the maintenance trial were also part of the growth trial. Therefore, in the growth trial, 20 kids fed for ad libitum intake were used as follows: 7 kids slaughtered at 21.2 ± 0.36 kg BW (BL), 6 kids slaughtered at 28.2 ± 0.39 kg BW (intermediate slaughter), and 7 kids slaughtered at 35.6 ± 0.36 kg BW. Empty whole bodies of the kids (head + feet, hide, internal organs + blood, and carcass) were weighed, ground, mixed, and subsampled for chemical analyses. Daily maintenance requirements, calculated using the comparative slaughter technique (P < 0.001), were estimated as 32.3 ± 1.1 mg Ca, 30.8 ± 1.2 mg P, 1.31 ± 0.5 mg Mg, 8.41 ± 3.0 mg K, and 5.14 ± 1.0 mg Na/kg of empty BW (EBW). Net requirements for growth increased from 6.2 to 6.6 g Ca, 5.3 to 5.4 g P, and 0.29 to 0.30 g Mg and decreased from 1.20 to 1.07 g K and 0.65 to 0.59 g Na/kg of EBW gain for kids from 20 to 35 kg BW. This study indicated that the net mineral requirements for Boer crossbred goat kids may be different from those of purebred or other genotypes, and more data are needed for goats in general.

Distribution of calcium (Ca) and magnesium (Mg) in the leaves of Brassica rapa under varying exogenous Ca and Mg supply.

Leafy vegetable Brassica crops are an important source of dietary calcium (Ca) and magnesium (Mg) and represent potential targets for increasing leaf Ca and Mg concentrations through agronomy or breeding. Although the internal distribution of Ca and Mg within leaves affects the accumulation of these elements, such data are not available for Brassica. The aim of this study was to characterize the internal distribution of Ca and Mg in the leaves of a vegetable Brassica and to determine the effects of altered exogenous Ca and Mg supply on this distribution. Brassica rapa ssp. trilocularis 'R-o-18' was grown at four different Ca:Mg treatments for 21 d in a controlled environment. Concentrations of Ca and Mg were determined in fully expanded leaves using inductively coupled plasma-mass spectrometry (ICP-MS). Internal distributions of Ca and Mg were determined in transverse leaf sections at the base and apex of leaves using energy-dispersive X-ray spectroscopy (EDS) with cryo-scanning electron microscopy (cryo-SEM). Leaf Ca and Mg concentrations were greatest in palisade and spongy mesophyll cells, respectively, although this was dependent on exogenous supply. Calcium accumulation in palisade mesophyll cells was enhanced slightly under high Mg supply; in contrast, Mg accumulation in spongy mesophyll cells was not affected by Ca supply. The results are consistent with Arabidopsis thaliana and other Brassicaceae, providing phenotypic evidence that conserved mechanisms regulate leaf Ca and Mg distribution at a cellular scale. The future study of Arabidopsis gene orthologues in mutants of this reference B. rapa genotype will improve our understanding of Ca and Mg homeostasis in plants and may provide a model-to-crop translation pathway for targeted breeding.

TRPM2 Cation Channels, Oxidative Stress and Neurological Diseases: Where Are We Now?

The Na+ and Ca(2+)-permeable melastatin related transient receptor potential 2 (TRPM2) channels can be gated either by ADP-ribose (ADPR) in concert with Ca(2+) or by hydrogen peroxide (H(2)O(2)), an experimental model for oxidative stress, binding to the channel's enzymatic Nudix domain. Since the mechanisms that lead to TRPM2 gating in response to ADPR and H(2)O(2) are not understood in neuronal cells, I summarized previous findings and important recent advances in the understanding of Ca(2+) influx via TRPM2 channels in different neuronal cell types and disease processes. Considering that TRPM2 is activated by oxidative stress, mediated cell death and inflammation, and is highly expressed in brain, the channel has been investigated in the context of central nervous system. TRPM2 plays a role in H(2)O(2) and amyloid β-peptide induced striatal cell death. Genetic variants of the TRPM2 gene confer a risk of developing Western Pacific amyotropic lateral sclerosis and parkinsonism-dementia complex and bipolar disorders. TRPM2 also contributes to traumatic brain injury processes such as oxidative stress, inflammation and neuronal death. There are a limited number of TRPM2 channel blockers and they seem to be cell specific. For example, ADPR-induced Ca(2+) influx in rat hippocampal cells was not blocked by N-(p-amylcinnomoyl)anthralic acid (ACA), the IP(3) receptor inhibitor 2-aminoethoxydiphenyl borate or PLC inhibitor flufenamic acid (FFA). However, the Ca(2+) entry in rat primary striatal cells was blocked by ACA and FFA. In conclusion TRPM2 channels in neuronal cells can be gated by either ADPR or H(2)O(2). It seems to that the exact relationship between TRPM2 channels activation and neuronal cell death still remains to be determined.

Structure and Functional Analysis of a Ca2+ Sensor Mutant of the Na+/Ca2+ Exchanger

The mammalian Na(+)/Ca(2+) exchanger, NCX1.1, serves as the main mechanism for Ca(2+) efflux across the sarcolemma following cardiac contraction. In addition to transporting Ca(2+), NCX1.1 activity is also strongly regulated by Ca(2+) binding to two intracellular regulatory domains, CBD1 and CBD2. The structures of both of these domains have been solved by NMR spectroscopy and x-ray crystallography, greatly enhancing our understanding of Ca(2+) regulation. Nevertheless, the mechanisms by which Ca(2+) regulates the exchanger remain incompletely understood. The initial NMR study showed that the first regulatory domain, CBD1, unfolds in the absence of regulatory Ca(2+). It was further demonstrated that a mutation of an acidic residue involved in Ca(2+) binding, E454K, prevents this structural unfolding. A contradictory result was recently obtained in a second NMR study in which Ca(2+) removal merely triggered local rearrangements of CBD1. To address this issue, we solved the crystal structure of the E454K-CBD1 mutant and performed electrophysiological analyses of the full-length exchanger with mutations at position 454. We show that the lysine substitution replaces the Ca(2+) ion at position 1 of the CBD1 Ca(2+) binding site and participates in a charge compensation mechanism. Electrophysiological analyses show that mutations of residue Glu-454 have no impact on Ca(2+) regulation of NCX1.1. Together, structural and mutational analyses indicate that only two of the four Ca(2+) ions that bind to CBD1 are important for regulating exchanger activity.

Use of foliar Ca/Sr discrimination and 87Sr/86Sr ratios to determine soil Ca sources to sugar maple foliage in a northern hardwood forest

Calcium/strontium and 87Sr/86Sr ratios in foliage can be used to determine the relative importance of different soil sources of Ca to vegetation, if the discrimination of Ca/Sr by the plant between nutrient sources and foliage is known. We compared these tracers in the foliage of sugar maple (Acer saccharum) to the exchange fraction and acid leaches of soil horizons at six study sites in the White Mountains of New Hampshire, USA. In a previous study, sugar maple was shown to discriminate for Ca compared to Sr in foliage formation by a factor of 1.14 ± 0.12. After accounting for the predicted 14% shift in Ca/Sr, foliar Ca/Sr and 87Sr/86Sr ratios closely match the values in the Oie horizon at each study site across a 3.6-fold variation in foliar Ca/Sr ratios. Newly weathered cations, for which the Ca/Sr and 87Sr/86Sr ratios are estimated from acid leaches of soils, can be ruled out as a major Ca source to current foliage. Within sites, the 87Sr/86Sr ratio of the soil exchange pool in the Oa horizon and in the 0–10 cm and 10–20 cm increments of the mineral soil are similar to the Oie horizon and sugar maple foliar values, suggesting a common source of Sr in all of the actively cycling pools, but providing no help in distinguishing among them as sources to foliage. The Ca/Sr ratio in the soil exchange pool, however, decreases significantly with depth, and based on this variation, the exchange pool below the forest floor can be excluded as a major Ca source to the current sugar maple foliage. This study confirms that internal recycling of Ca between litter, organic soil horizons and vegetation dominate annual uptake of Ca in northern hardwood ecosystems. Refinement of our understanding of Ca and Sr uptake and allocation in trees allows improvement in the use of Ca/Sr and 87Sr/86Sr ratios to trace Ca sources to plants.

Multiple calcium binding sites make calmodulin multifunctional

Protein-protein or protein-ion interactions with multisite proteins are essential to the regulation of intracellular and extracellular events. There is, however, limited understanding of how ligand-multisite protein interactions selectively regulate the activities of multiple protein targets. In this paper, we focus on the important calcium (Ca(2+)) binding protein calmodulin (CaM), which has four Ca(2+) ion binding sites and regulates the activity of over 30 other proteins. Recent progress in structural studies has led to significant improvements in the understanding of Ca(2+)-CaM-dependent regulation mechanisms. However, no quantitative model is currently available that can fully explain how the structural diversity of protein interaction surfaces leads to selective activation of protein targets. In this paper, we analyze the multisite protein-ligand binding mechanism using mathematical modelling and experimental data for Ca(2+)-CaM-dependent protein targets. Our study suggests a potential mechanism for selective and differential activation of Ca(2+)-CaM targets by the same CaM molecules, which are involved in a variety of intracellular functions. The close agreement between model predictions and experimental dose-response curves for CaM targets available in the literature suggests that such activation is due to the selective activity of CaM conformations in complexes with variable numbers of Ca(2+) ions. Although the paper focuses on the Ca(2+)-CaM pair as a particularly data rich example, the proposed model predictions are quite general and can easily be extended to other multisite proteins. The results of the study may therefore be proposed as a general explanation for multifunctional target regulation by multisite proteins.

Calcium signaling complexes in microdomains of polarized secretory cells

The highly polarized nature of epithelial cells in exocrine glands necessitates targeting, assembly into complexes and confinement of the molecules comprising the Ca 2+ signaling apparatus, to cellular microdomains. Such high degree of polarized localization has been shown for all Ca 2+ signaling molecules tested, including G protein coupled receptors and their associated proteins, Ca 2+ pumps, Ca 2+ influx channels at the plasma membrane and Ca 2+ release channels in the endoplasmic reticulum. Although the physiological significance of polarized Ca 2+ signaling is clear, little is known about the mechanism of targeting, assembly and retention of Ca 2+ signaling complexes in cellular microdomains. The present review attempts to summarize the evidence in favor of polarized expression of Ca 2+ signaling proteins at the apical pole of secretory cells with emphasis on the role of scaffolding proteins in the assembly and function of the Ca 2+ signaling complexes. The consequence of polarized enrichment of Ca 2+ signaling complexes at the apical pole is generation of an apical to basal pole gradient of cell responsiveness that, at low physiological agonist concentrations, limits Ca 2+ spikes to the apical pole, and when a Ca 2+ wave occurs, it always propagates from the apical to the basal pole. Our understanding of Ca 2+ signaling in microdomains is likely to increase rapidly with the application of techniques to controllably and selectively disrupt components of the complexes and apply high resolution recording techniques, such as TIRF microscopy to this problem.

06/02377 Energy-based ecological optimization for a generalized irreversible Carnot refrigerator: Zhu, X. et al. Journal of the Energy Institute, 2006, 79, (1), 42–46.

The calcium (Ca+2) molecules being an important intracellular messenger are involved in various signal transduction mechanisms in plants. Many external stimuli such as drought, cold, heat stress, metalloid stress (copper (Cu), cadmium (Cd), nickel (Ni), and arsenic), flooding, and salinity stress increase the free Ca+2 ions in the cytosol. The H+/Ca+2 antiporters and Ca+2-ATPases actively transport the cytosolic Ca+2 in intracellular organelles or apoplasts. Increase in Ca+2 concentration is sensed by calcium-binding proteins or Ca+2-sensors which lead to activation of CDPKs (Calcium-dependent protein kinases). These CDPKs regulate various genes responsive to stress to show phenotypic responses against stress stimuli. Hormonal signaling and their crosstalk with Ca+2 have been studied extensively but a thorough understanding of Ca+2 in stress tolerance is limited. This review describes the various aspects of Ca+2 involvement in sensing stress stimuli, signal transduction, role against various stress factors (including temperature extreme, salinity, flooding, metalloids, and drought), the role of Ca+2 in the regulation of physiological processes, and Ca+2-ATPase.

Hypoxia stimulates Ca 2+ release from intracellular stores in astrocytes via cyclic ADP ribose-mediated activation of ryanodine receptors

The ability of O 2 levels to regulate Ca 2+ signalling in non-excitable cells is poorly understood, yet crucial to our understanding of Ca 2+-dependent cell functions in physiological and pathological situations. Here, we demonstrate that hypoxia mobilizes Ca 2+ from an intracellular pool in primary cultures of cortical astrocytes. This pool can also be mobilized by bradykinin, which acts via phospholipase C and inositol trisphosphate production. By contrast, hypoxic Ca 2+ mobilization utilizes ryanodine receptors, which appear to be either present on the same intracellular pool, or on a separate but functionally coupled pool. Hypoxic activation of ryanodine receptors requires formation of cyclic ADP ribose, since hypoxic Ca 2+ mobilization was fully prevented by nicotinamide (which inhibits ADP ribosyl cyclase) or by 8-Br-cADP ribose, an antagonist of cyclic ADP ribose. Our results demonstrate for the first time the involvement of cyclic ADP ribose in hypoxic modulation of Ca 2+ signalling in the central nervous system, and suggest that this modulator of ryanodine receptors may play a key role in the function of astrocytes under conditions of fluctuating O 2 levels.

Calcium signalling: Past, present and future

Ca 2+ is a universal second messenger controlling a wide variety of cellular reactions and adaptive responses. The initial appreciation of Ca 2+ as a universal signalling molecule was based on the work of Sydney Ringer and Lewis Heilbrunn. More recent developments in this field were critically influenced by the invention of the patch clamp technique and the generation of fluorescent Ca 2+ indicators. Currently the molecular Ca 2+ signalling mechanisms are being worked out and we are beginning to assemble a reasonably complete picture of overall Ca 2+ homeostasis. Furthermore, investigations of organellar Ca 2+ homeostasis have added complexity to our understanding of Ca 2+ signalling. The future of the Ca 2+ signalling field lies with detailed investigations of the integrative function in vivo and clarification of the pathology associated with malfunctions of Ca 2+ signalling cascades.

Blossom-End Rot: A Calcium Deficiency

Blossom-end rot (BER) is a common physiological disorder that occurs on the fruit of tomato (Lycopersicon esculentumMill.), pepper (Capsicum annuumL.), eggplant (Solanum melongenaL.), and watermelon [Citrullus lanatus(Thunb.) Matsun & Nakai]. BER may occur in all the tomato-producing areas of the world and has been shown to create losses up to 50%. BER is related to many factors including: high salinity, high magnesium (Mg), ammonium (NH4), and/or potassium (K) concentration, inadequate xylem tissue development, accelerated growth rate, unfavorable moisture relationships (high, low, or fluctuating), low soluble soil calcium (Ca), high temperature, and high and low transpiration, but the underlying cause of this disorder is an inadequate amount of Ca in the blossom-end of the fruit. Although it is widely accepted that a local Ca deficiency plays an important role in the induction of BER, there are also some claims that Ca deficiency is not the cause of BER as a critical level of Ca for BER induction has not been found. To prevent BER from occurring, an understanding of Ca in the soil, uptake and translocation of Ca, and the factors affecting these processes, is necessary.

Recent advances in the regulation of plant calcium channels: evidence for regulation by G-proteins, the cytoskeleton and second messengers

Important aspects of the regulatory properties of plant calcium channels have been discovered during the past few years. These include the control of plasma membrane-bound channels by regulatory proteins and the characterization of a plethora of intracellular calcium release channels. Deciphering the mechanisms of regulation of different Ca 2+ channels and the probable co-operation of their activities in response to various stimuli is leading to a better understanding of Ca 2+-signalling processes in higher plants.

Imaging of caffeine-inducible release of intracellular calcium in cultured embryonic mouse telencephalic neurons.

To gain a better understanding of Ca(2+)-induced Ca2+ release in central neurons, we have studied the increase in intracellular Ca2+ concentration ([Ca2+]i) induced by application of caffeine to cells cultured from embryonic mouse telencephalon (hippocampus or cortex). The magnitudes and distributions of changes in [Ca2+]i in neuron somata were measured by quantitative video microscopy. We observed that application of caffeine to pyramidally shaped neurons typically initiated an increase in [Ca2+]i in the cytoplasmic region between the nucleus and the base of a major dendrite. [Ca2+] in this region increased over a period of 3 to 6 s and was followed by, with a slight delay, a surge of Ca2+ that moved across the soma and into or over the nucleus. Similar Ca2+ responses to caffeine were observed in Ca(2+)-containing and nominally Ca(2+)-free external solutions, suggesting that caffeine was inducing Ca2+ release from intracellular stores. Ca2+ responses to caffeine were potentiated by inducing a tonic Ca2+ influx through N-methyl-D-aspartate (NMDA)-type glutamate receptors activated by 0.3 microM glutamate and multiple responses to caffeine could be elicited by using this Ca2+ influx to refill the intracellular stores. Ryanodine inhibition of caffeine-induced Ca2+ release was use- and concentration-dependent; the median effective concentration EC50 for ryanodine declined from 22 microM for the first application of caffeine to 20 nM for the fourth. We conclude, based on these responses to caffeine, that ryanodine-sensitive mechanisms of intracellular Ca2+ release are active in hippocampal and cortical neurons and may be involved in generation of directed Ca2+ waves that engulf the nucleus.