Calcium Channels, OST1 and Stomatal Defence: Current Status and Beyond

Stomatal immunity is regulated by pathogen-associated molecular patterns (PAMPs)- and abscisic acid (ABA)-triggered signalling in different ways. Cytoplasmic Ca²⁺ signature in the guard cells plays a vital function in stomatal immunity, but the mechanism of Ca²⁺ import is unknown. It has been very recently established that the hyperosmolality-gated calcium-permeable channels (OSCAs) and cyclic nucleotide-gated channels (CNGCs) are responsible for the influx of Ca²⁺ in the cytoplasm, which are activated after BIK1-mediated phosphorylation and ABA interaction during PAMPs- and ABA-triggered stomatal immunity in plants, respectively. Further, ABA-triggered OPEN STOMATA1 (OST1) causes the disassembly of microtubules in the guard cells besides activation of S-type anion channels (SLAC1) for the efflux of cytoplasmic anions that leads to stomata closure.

Electroactive Hydroxyapatite/Carbon Nanofiber Scaffolds for Osteogenic Differentiation of Human Adipose-Derived Stem Cells

Traditional bone defect treatments are limited by an insufficient supply of autologous bone, the immune rejection of allogeneic bone grafts, and high medical costs. To address this medical need, bone tissue engineering has emerged as a promising option. Among the existing tissue engineering materials, the use of electroactive scaffolds has become a common strategy in bone repair. However, single-function electroactive scaffolds are not sufficient for scientific research or clinical application. On the other hand, multifunctional electroactive scaffolds are often complicated and expensive to prepare. Therefore, we propose a new tissue engineering strategy that optimizes the electrical properties and biocompatibility of carbon-based materials. Here, a hydroxyapatite/carbon nanofiber (HAp/CNF) scaffold with optimal electrical activity was prepared by electrospinning HAp nanoparticle-incorporated polyvinylidene fluoride (PVDF) and then carbonizing the fibers. Biochemical assessments of the markers of osteogenesis in human adipose-derived stem cells (h-ADSCs) cultured on HAp/CNF scaffolds demonstrate that the material promoted the osteogenic differentiation of h-ADSCs in the absence of an osteogenic factor. The results of this study show that electroactive carbon materials with a fibrous structure can promote the osteogenic differentiation of h-ADSCs, providing a new strategy for the preparation and application of carbon-based materials in bone tissue engineering.

Glucose Uptake Is Increased by Estradiol Dipropionate in L6 Skeletal Muscle Cells

GLUT4 is an important glucose transporter, which is closely related to insulin resistance and type 2 diabetes. In this study, we investigated the mechanism of Estradiol Dipropionate (EDP) on uptake of glucose in L6 skeletal muscle cells. In our study, we confirmed that EDP promoted uptake of glucose in L6 skeletal muscle cells in both normal and insulin resistant models. Western blot indicated that EDP accelerated GLUT4 expression and significantly activated AMPK and PKC phosphorylation; the expression of GLUT4 was significantly inhibited by AMPK inhibitor compound C and PKC inhibitor Gö6983, but not by Wortmannin (Akt inhibitor). Meanwhile, EDP boosted GLUT4 expression, and also increased intracellular Ca²⁺ levels. In the presence of 2 mM, 0 mM extracellular Ca²⁺ and 0 mM extracellular Ca²⁺ + BAPTA-AM, the involvement of intracellular Ca²⁺ levels contribute to EDP-induced GLUT4 expression and fusion with plasma membrane. Therefore, this study investigated whether EDP promoted GLUT4 expression through AMPK and PKC signaling pathways, thereby enhancing GLUT4 uptake of glucose and fusion into plasma membrane in L6 skeletal muscle cells. In addition, both EDP induced GLUT4 translocation and uptake of glucose were Ca²⁺ dependent. These findings suggested that EDP may be potential drug for the treatment of type 2 diabetes.

Enhancement production of lipid and unsaturation of fatty acids in Cryptococcus humicola via addition of calcium ion

Lipids synthesized by oleaginous yeasts are considered to be the best candidates for biodiesel production. Cryptococcus humicola as an oleaginous yeast accumulated lipid in cells. In order to optimize the conditions for lipid production, different carbon and nitrogen sources were used and metals were added into the medium. Ca²⁺ addition increased the lipid production greatly. Xylose and peptone were optimal carbon source and nitrogen source, respectively for lipid accumulation. Response surface experiment results revealed that the accumulation of lipid could be maximized when the xylose, peptone and Ca²⁺ concentration was 61 g/L, 4.31 g/L, 0.67 mmol/L. C16 and C18 fatty acid account for about 91% of the total fatty acids. The most abundant fatty acid was oleic acid (42.68%), followed by palmitic acid (29.7%) and stearic acid (13.87%). The addition of Ca²⁺ increased the content of unsaturated fatty acids (such as C16:1 and C18:1) and improved the unsaturation of fatty acids. Quantitative real time PCR analysis revealed that expression of genes related to lipid biosynthesis showed up-regulated by Ca²⁺ treatment. This study provided a strategy for increase in lipid production and content of unsaturated fatty acids.

The interaction of TRPV1 and lipids: Insights into lipid metabolism

Transient receptor potential vanilloid 1 (TRPV1), a non-selective ligand-gated cation channel with high permeability for Ca²⁺, has received considerable attention as potential therapeutic target for the treatment of several disorders including pain, inflammation, and hyperlipidemia. In particular, TRPV1 regulates lipid metabolism by mechanisms that are not completely understood. Interestingly, TRPV1 and lipids regulate each other in a reciprocal and complex manner. This review surveyed the recent literature dealing with the role of TRPV1 in the hyperlipidemia-associated metabolic syndrome. Besides TRPV1 structure, molecular mechanisms underlying the regulatory effect of TRPV1 on lipid metabolism such as the involvement of uncoupling proteins (UCPs), ATP-binding cassette (ABC) transporters, peroxisome proliferation-activated receptors (PPAR), sterol responsive element binding protein (SREBP), and hypoxia have been discussed. Additionally, this review extends our understanding of the lipid-dependent modulation of TRPV1 activity through affecting both the gating and the expression of TRPV1. The regulatory role of different classes of lipids such as phosphatidylinositol (PI), cholesterol, estrogen, and oleoylethanolamide (OEA), on TRPV1 has also been addressed.

Interaction of Gamma-Aminobutyric Acid and Ca2+ on Phenolic Compounds Bioaccumulation in Soybean Sprouts under NaCl Stress

NaCl stress can enhance the accumulation of phenolic compounds in soybean during germination. In the present study, effects of gamma-aminobutyric acid (GABA) and Ca²⁺ on the biosynthesis of phenolic compounds in soybean sprouts germinated with NaCl stress were investigated. Results showed that addition of Ca²⁺ increased the content of total phenolics, phenolic acids, and isoflavonoids in soybean sprouts by ca. 15%, 7%, and 48%, respectively, through enhancing the activities of three key enzymes involved in the biosynthesis. On the other hand, addition of LaCl₃, a calcium channel blocker, inhibited the synthesis of phenolic compounds, indicating that Ca²⁺ plays an important role in the synthesis of these compounds in soybean sprouts. Addition of GABA can increase the content of Ca²⁺ in soybean sprouts by ca. 20% and alleviate the inhibition of LaCl₃ on phenolics biosynthesis in soybean sprouts. Similarly, addition of Ca²⁺ can reverse the inhibition of 3-mercaptopropionate, an inhibitor of endogenous GABA synthesis, on the biosynthesis of phenolic compounds in soybean sprouts under NaCl stress. To conclude, both GABA and Ca²⁺ can enhance the biosynthesis of phenolic compounds in soybean sprouts and there was an interaction between their effects on the promotion of phenolic compounds biosynthesis.

Roles of Glutamate Receptor-Like Channels (GLRs) in Plant Growth and Response to Environmental Stimuli

Plant glutamate receptor-like channels (GLRs) are the homologues of ionotropic glutamate receptors (iGluRs) that mediate neurotransmission in mammals, and they play important roles in various plant-specific physiological processes, such as pollen tube growth, sexual reproduction, root meristem proliferation, internode cell elongation, stomata aperture regulation, and innate immune and wound responses. Notably, these biological functions of GLRs have been mostly linked to the Ca²⁺-permeable channel activity as GLRs can directly channel the transmembrane flux of Ca²⁺, which acts as a key second messenger in plant cell responses to both endogenous and exogenous stimuli. Thus, it was hypothesized that GLRs are mainly involved in Ca²⁺ signaling processes in plant cells. Recently, great progress has been made in GLRs for their roles in long-distance signal transduction pathways mediated by electrical activity and Ca²⁺ signaling. Here, we review the recent progress on plant GLRs, and special attention is paid to recent insights into the roles of GLRs in response to environmental stimuli via Ca²⁺ signaling, electrical activity, ROS, as well as hormone signaling networks. Understanding the roles of GLRs in integrating internal and external signaling for plant developmental adaptations to a changing environment will definitely help to enhance abiotic stress tolerance.

Suppression of PD-L1 release from small extracellular vesicles promotes systemic anti-tumor immunity by targeting ORAI1 calcium channels

Blockade of immune checkpoints as a strategy of cancer cells to overcome the immune response has received ample attention in cancer research recently. In particular, expression of PD-L1 by various cancer cells has become a paradigm in this respect. Delivery of PD-L1 to its site of action occurs either by local diffusion, or else by transport via small extracellular vesicles (sEVs, commonly referred to as exosomes). Many steps of sEVs formation, their packaging with PD-L1 and their release into the extracellular space have been studied in detail. The likely dependence of release on Ca²⁺ -signaling, however, has received little attention. This is surprising, since the intracellular Ca²⁺ -concentration is known as a prominent regulator of many secretory processes. Here, we report on the roles of three Ca²⁺ -dependent proteins in regulating release of PD-L1-containing sEVs, as well as on the growth of tumors in mouse models. We show that sEVs release in cancer cell lines is Ca²⁺ -dependent and the knockdown of the gene coding the Ca²⁺ -channel protein ORAI1 reduces Ca²⁺ -signals and release of sEVs. Consequently, the T cell response is reinvigorated and tumor progression in mouse models is retarded. Furthermore, analysis of protein expression patterns in samples from human cancer tissue shows that the ORAI1 gene is significantly upregulated. Such upregulation is identified as an unfavorable prognostic factor for survival of patients with non-small-cell lung cancer. We show that reduced Ca²⁺ -signaling after knockdown of ORAI1 gene also compromises the activity of melanophilin and Synaptotagmin-like protein 2, two proteins, which are important for correct localization of secretory organelles within cancer cells and their transport to sites of exocytosis. Thus, the Ca²⁺ -channel ORAI1 and Ca²⁺ -dependent proteins of the secretion pathway emerge as important targets for understanding and manipulating immune checkpoint blockade by PD-L1.

cGAS-STING Pathway Performance in the Vulnerable Atherosclerotic Plaque

The important role of Ca2+ in pathogenic store-operated calcium entry (SOCE) is well-established. Among the proteins involved in the calcium signaling pathway, Stromal interacting molecule 1 (STIM1) is a critical endoplasmic reticulum transmembrane protein. STIM1 is activated by the depletion of calcium stores and then binds to another calcium protein, Orai1, to form a channel through which the extracellular Ca2+ can enter the cytoplasm to replenish the calcium store. Multiple studies have shown that increased STIM1 facilitates the aberrant proliferation and apoptosis of vascular smooth cells (VSMC) and macrophages which can promote the formation of rupture-prone plaque. Together with regulating the cytosolic Ca2+ concentration, STIM1 also activates STING through altered intracellular Ca2+ concentration, a critical pro-inflammatory molecule. The cGAS-STING pathway is linked with cellular proliferation and phenotypic conversion of VSMC and enhances the progression of atherosclerosis plaque. In summary, we conclude that STIM1/cGAS-STING is involved in the progression of AS and plaque vulnerability.

Essential role of lysosomal Ca2+-mediated TFEB activation in mitophagy and functional adaptation of pancreatic β-cells to metabolic stress

Although the role of pancreatic β-cell macroautophagy/autophagy is well known, that of β-cell mitophagy is unclear. We investigated the changes of lysosomal Ca²⁺ by mitochondrial or metabolic stress that can modulate TFEB activation and, additionally, the role of TFEB-induced mitophagy in β-cell function. Mitochondrial or metabolic stress induces mitophagy, which is mediated by lysosomal Ca²⁺ release, increased cytosolic [Ca²⁺] and subsequent TFEB activation. Lysosomal Ca²⁺ release is replenished by ER→lysosome Ca²⁺ refilling through ER Ca²⁺ exit channels, which is important for the increase of cytosolic [Ca²⁺] and mitophagy by mitochondria stressors. High-fat diet (HFD) feeding augments pancreatic β-cell mitophagy, probably as an adaptation to metabolic stress. HFD-induced increase ofβ-cell mitophagy is reduced by tfeb KO, leading to increased ROS and decreased mitochondrial complex activity or oxygen consumption in tfeb-KO islets. In tfeb Δβ-cell mice, HFD-induced glucose intolerance and β-cell dysfunction are aggravated. Expression of mitophagy receptor genes including Optn or Calcoco2 is increased by mitochondrial or metabolic stressors in a TFEB-dependent manner, likely contributing to increased mitophagy. These results suggest that lysosomal Ca²⁺ release in conjunction with ER→lysosome Ca²⁺ refilling is important for TFEB activation and mitophagy induction, which contributes to pancreatic β-cell adaptation to metabolic stress.

High-performance optical control of GPCR signaling by bistable animal opsins MosOpn3 and LamPP in a molecular property-dependent manner

Optical control of G protein-coupled receptor (GPCR) signaling is a highly valuable approach for comprehensive understanding of GPCR-based physiologies and controlling them precisely. However, optogenetics for GPCR signaling is still developing and requires effective and versatile tools with performance evaluation from their molecular properties. Here, we systematically investigated performance of two bistable opsins that activate Gi/Go-type G protein (mosquito Opn3 (MosOpn3) and lamprey parapinopsin (LamPP)) in optical control in vivo using Caenorhabditis elegans. Transgenic worms expressing MosOpn3, which binds 13-cis retinal to form photopigments, in nociceptor neurons showed light-induced avoidance responses in the presence of all-trans retinal, a retinal isomer ubiquitously present in every tissue, like microbial rhodopsins and unlike canonical vertebrate opsins. Remarkably, transgenic worms expressing MosOpn3 were ~7,000 times more sensitive to light than transgenic worms expressing ChR2 in this light-induced behavior, demonstrating the advantage of MosOpn3 as a light switch. LamPP is a UV-sensitive bistable opsin having complete photoregenerative ability by green light. Accordingly, transgenic worms expressing LamPP in cholinergic motor neurons stopped moving upon violet light illumination and restored coordinate movement upon green light illumination, demonstrating color-dependent control of behavior using LamPP. Furthermore, we applied molecular engineering to produce MosOpn3-based tools enabling light-dependent upregulation of cAMP or Ca²⁺ levels and LamPP-based tool enabling clamping cAMP levels color dependently and context independently, extending their usability. These findings define the capacity of two bistable opsins with similar retinal requirement as ChR2, providing numerous strategies for optical control of various GPCR-based physiologies as well as GPCR signaling itself.

Signaling Transduction of ABA, ROS, and Ca2+ in Plant Stomatal Closure in Response to Drought

Drought is a global threat that affects agricultural production. Plants have evolved several adaptive strategies to cope with drought. Stomata are essential structures for plants to control water status and photosynthesis rate. Stomatal closure is an efficient way for plants to reduce water loss and improve survivability under drought conditions. The opening and closure of stomata depend on the turgor pressure in guard cells. Three key signaling molecules, including abscisic acid (ABA), reactive oxygen species (ROS), and calcium ion (Ca²⁺), play pivotal roles in controlling stomatal closure. Plants sense the water-deficit signal mainly via leaves and roots. On the one hand, ABA is actively synthesized in root and leaf vascular tissues and transported to guard cells. On the other hand, the roots sense the water-deficit signal and synthesize CLAVATA3/EMBRYO-SURROUNDING REGION RELATED 25 (CLE25) peptide, which is transported to the guard cells to promote ABA synthesis. ABA is perceived by pyrabactin resistance (PYR)/PYR1-like (PYL)/regulatory components of ABA receptor (RCAR) receptors, which inactivate PP2C, resulting in activating the protein kinases SnRK2s. Many proteins regulating stomatal closure are activated by SnRK2s via protein phosphorylation. ABA-activated SnRK2s promote apoplastic ROS production outside of guard cells and transportation into the guard cells. The apoplastic H₂O₂ can be directly sensed by a receptor kinase, HYDROGEN PEROXIDE-INDUCED CA²⁺ INCREASES1 (HPCA1), which induces activation of Ca²⁺ channels in the cytomembrane of guard cells, and triggers an increase in Ca²⁺ in the cytoplasm of guard cells, resulting in stomatal closure. In this review, we focused on discussing the signaling transduction of ABA, ROS, and Ca²⁺ in controlling stomatal closure in response to drought. Many critical genes are identified to have a function in stomatal closure under drought conditions. The identified genes in the process can serve as candidate genes for genetic engineering to improve drought resistance in crops. The review summarizes the recent advances and provides new insights into the signaling regulation of stomatal closure in response to water-deficit stress and new clues on the improvement of drought resistance in crops.

DORN1 Is Involved in Drought Stress Tolerance through a Ca2+-Dependent Pathway

Water shortages caused by climate change seriously threaten the survival and production of plants and are also one of the major environmental pressures faced by plants. DORN1 was the first identified purinoceptor for the plant response to extracellular ATP. It has been established that DORN1 could play key roles in a series of biological activities in plants. However, the biological roles of DORN1 and the mechanism remain unclear under drought stress conditions in plants. Here, DORN1 was targeted for knockout by using the CRISPR/Cas 9 system. It was found that the loss function of DORN1 resulted in a significant decrease in the effective quantum yield of PSII [Y(II)], the photochemical quenching coefficient (qP), and the rate of photosynthetic electron transport through PSII (ETR), which reflected plants' photochemical efficiency. Whereas Y_(NO) values showed obvious enhancement under drought stress conditions. Further experimental results showed that the Y_(II), q_P, and ETR, which reflect plants' photochemical efficiency, increased significantly with CaCl₂ treatment. These results indicated that the drought tolerance of the mutant was decreased, and the exogenous application of calcium ions could effectively promote the drought tolerance of the dorn1 mutant. Transpiration loss controlled by stomata is closely related to drought tolerance, further, we examined the transpirational water loss in dorn1 and found that it was greater than wild-type (WT). Besides, the dorn1 mutant's stomatal aperture significantly increased compared with the WT and the stomata of dorn1 mutant plants tend to close after CaCl₂ treatment. Taken together, our results show that DORN1 plays a key role in drought stress tolerance in plants, which may depend on calcium and calcium-related signaling pathways.

Mitochondrial Ca2+ uniporter haploinsufficiency enhances long-term potentiation at hippocampal mossy fibre synapses

Long-term changes in synaptic strength form the basis of learning and memory. These changes rely upon energy-demanding mechanisms, which are regulated by local Ca2+ signalling. Mitochondria are optimised for providing energy and buffering Ca2+. However, our understanding of the role of mitochondria in regulating synaptic plasticity is incomplete. Here, we have used optical and electrophysiological techniques in cultured hippocampal neurons and ex vivo hippocampal slices from mice with haploinsufficiency of the mitochondrial Ca2+ uniporter (MCU+/-) to address whether reducing mitochondrial Ca2+ uptake alters synaptic transmission and plasticity. We found that cultured MCU+/- hippocampal neurons have impaired Ca2+ clearance, and consequently enhanced synaptic vesicle fusion at presynapses occupied by mitochondria. Furthermore, long-term potentiation (LTP) at mossy fibre (MF) synapses, a process which is dependent on presynaptic Ca2+ accumulation, is enhanced in MCU+/- slices. Our results reveal a previously unrecognised role for mitochondria in regulating presynaptic plasticity of a major excitatory pathway involved in learning and memory.

Alleviating Neuroinflammation through Photothermal Conjugated Polymer Nanoparticles by Regulating Reactive Oxygen Species and Ca2+ Signaling

Neuroinflammation is one of the important manifestations of the amyloid β peptide (Aβ) protein-induced neurotoxic signaling pathway in which the aggregation of Aβ causes an increase in reactive oxygen species (ROS) and Ca²⁺ concentration. Here, near-infrared (NIR) photothermal-responsive conjugated polymer nanoparticles were designed to regulate ROS and Ca²⁺ signaling to alleviate neuroinflammation. Under 808 nm laser irradiation, the nanoparticles effectively penetrated the blood-brain barrier (BBB) and reduced the aggregation of Aβ and partially disaggregated the aggregates outside the cell, thereby reducing ROS content which downregulated the oxidative stress damage to cells. Meanwhile, the nanoparticles reduced the concentration of Ca²⁺ by inhibiting the transient receptor potential melastatin-related 2 (TRPM2) ion channel inside the cell. Ultimately, the concentration of inflammatory factor tumor necrosis factor-α was decreased. This study provides an effective strategy to reduce neuroinflammation by simultaneously regulating ROS and Ca²⁺ signaling.

Rootstock effects on bitter pit incidence in 'Honeycrisp' apples are associated with changes in fruit's cell wall chemical properties

Bitter pit (BP) is a physiological disorder of apples that often appears during or after cold storage. Despite being defined as a calcium deficiency disorder, BP is a complex process that is not only affected by the total Ca²⁺ content in the fruit but also by the proper cellular Ca²⁺ homeostasis and partitioning. Early investigations have also suggested that rootstocks could affect BP development and severity. In the present study, rootstock effects on BP development were assessed on 'Honeycrisp' trees that were grafted on 14 different rootstocks (B.10, G.11, G.202, G.214, G.30, G.41, G.935, G.969, M.26 EMLA, M.9, V.1, V.5, V.6, and V.7). We evaluated BP incidence at harvest, and three months after cold storage for four, and three growing seasons, respectively. BP incidence was significantly reduced in 'Honeycrisp' trees on B.10 compared to other rootstocks, whereas trees on V.6 showed the highest percentage of BP at harvest and after cold storage. 'Honeycrisp' apples were collected from three different rootstocks (B.10, G.41, and V.6) two months after cold storage and evaluated for mineral nutrient composition, Ca²⁺ homeostasis, and cell wall properties, e.g., pectin content, pectin de-esterification rate and pectin methylesterase (PME) activity. Water-soluble and insoluble pectin content was markedly higher in fruits from B.10 than in G.41 and V.6. We also observed increased PME enzyme activity and a greater degree of water-insoluble pectin de-esterification in 'Honeycrisp' apples from V.6 compared to those from B.10. A significantly higher Ca²⁺ was found in the fruits from B.10 than G.41 and V.6. Higher Ca²⁺ and lower Mg²⁺ levels were also observed in the cell wall and water-insoluble pectin fractions of the fruits from B.10 compared to G.41 and V.6. However, the ratio of cell wall-bound Ca²⁺ to total Ca²⁺ was lower in B.10 compared to G.41 and V.6. Together, our results indicate that the tolerance of B.10 to BP could be attributed to a reduced PME activity and lower pectin de-esterification level, which in turn reduced the amount of Ca²⁺ cross-linked with pectin, and probably increased the apoplastic free calcium concentrations that is essential for maintaining cell membrane integrity and reducing BP development.

Mitochondrial VDAC1: A Potential Therapeutic Target of Inflammation-Related Diseases and Clinical Opportunities

The multifunctional protein, voltage-dependent anion channel 1 (VDAC1), is located on the mitochondrial outer membrane. It is a pivotal protein that maintains mitochondrial function to power cellular bioactivities via energy generation. VDAC1 is involved in regulating energy production, mitochondrial oxidase stress, Ca²⁺ transportation, substance metabolism, apoptosis, mitochondrial autophagy (mitophagy), and many other functions. VDAC1 malfunction is associated with mitochondrial disorders that affect inflammatory responses, resulting in an up-regulation of the body’s defensive response to stress stimulation. Overresponses to inflammation may cause chronic diseases. Mitochondrial DNA (mtDNA) acts as a danger signal that can further trigger native immune system activities after its secretion. VDAC1 mediates the release of mtDNA into the cytoplasm to enhance cytokine levels by activating immune responses. VDAC1 regulates mitochondrial Ca²⁺ transportation, lipid metabolism and mitophagy, which are involved in inflammation-related disease pathogenesis. Many scientists have suggested approaches to deal with inflammation overresponse issues via specific targeting therapies. Due to the broad functionality of VDAC1, it may become a useful target for therapy in inflammation-related diseases. The mechanisms of VDAC1 and its role in inflammation require further exploration. We comprehensively and systematically summarized the role of VDAC1 in the inflammatory response, and hope that our research will lead to novel therapeutic strategies that target VDAC1 in order to treat inflammation-related disorders.

[Alleviating effect of exogenous melatonin and calcium on the peroxidation damages of cucumber under high temperature stress]

To explore whether there is an interaction between melatonin (MT) and calcium (Ca²⁺) in regulating heat tolerance of plants, we analyzed the response of endogenous MT and Ca²⁺ to heat stress, and examined the effect of MT and Ca²⁺ on the reactive oxygen (ROS) accumulation, antioxidant system, and transcripts of heat shock factor (HSF) and heat shock proteins (HSPs) of cucumber seedlings under high temperature stress. Seedlings were foliar sprayed with 100 μmol·L^-1 MT, 10 mmol·L^-1 CaCl₂, 3 mmol·L^-1 ethylene glycol tetraacetic acid (EGTA, Ca²⁺ chelating agent) +100 μmol·L^-1 MT, 0.05 mmol·L^-1 chlorpromazine (calmodulin antagonist, CPZ) +100 μmol·L^-1 MT, 100 μmol·L^-1 p-chlorophenylalanine (p-CPA, inhibitor of MT) +10 mmol·L^-1 CaCl₂ or deionized water (H₂O), respectively. The results showed that both endogenous MT and Ca²⁺ in cucumber seedlings were induced by high temperature stress. The seedlings treated with exogenous MT showed significant increases in the mRNA expression of calmodulin (CaM), calcium-dependent protein kinase (CDPK5), calcineurin B-like protein (CBL3) and CBL interacting protein kinase (CIPK2) compared with the control at normal temperature. The mRNA levels of tryptophane decarboxylase (TDC), 5-hydroxytryptamine-N-acetyltransferase (SNAT) and N-acetyl-5-hydroxytryptamine methyltransferase (ASMT), key genes of MT biosynthesis and endogenous MT content were also induced by Ca²⁺ in cucumber seedlings. Exogenous MT and CaCl₂ alleviated the heat-induced oxidative damage through increasing antioxidant ability, reducing the accumulation of reactive oxygen species (ROS), and upregulating the mRNA abundances of HSF7, HSP70.1 and HSP70.11, as evidenced by mild thermal damage symptoms, lower heat injury index and electrolyte leakage under heat stress. The positive effect of MT-induced antioxidant capacity and mRNA expression of HSPs was removed by adding EGTA and CPZ in stressed seedlings. Similarly, the mitigating role of Ca²⁺ in the peroxidation damage to high temperature stress was reversed by p-CPA. These results suggested that both MT and Ca²⁺ could induce heat tolerance of cucumber seedlings, which had crosstalk in the process of heat stress signal transduction.

Exogenous Ca2+ priming can improve peanut photosynthetic carbon fixation and pod yield under early sowing scenarios in the field

Harnessing cold-resilient and calcium-enriched peanut production technology are crucial for high-yielding peanut cultivation in high-latitude areas. However, there is limited field data about how exogenous calcium (Ca²⁺) application would improve peanut growth resilience during exposure to chilling stress at early sowing (ES). To help address this problem, a two-year field study was conducted to assess the effects of exogenous foliar Ca²⁺ application on photosynthetic carbon fixation and pod yield in peanuts under different sowing scenarios. We measured plant growth indexes, leaf photosynthetic gas exchange, photosystems activities, and yield in peanuts. It was indicated that ES chilling stress at the peanut seedling stage led to the reduction of Pn, g_s, Tr, Ls, WUE, respectively, and the excessive accumulation of non-structural carbohydrates in leaves, which eventually induced a chilling-dependent feedback inhibition of photosynthesis due mainly to weaken growth/sink demand. While exogenous Ca²⁺ foliar application improved the export of nonstructural carbohydrates, and photosynthetic capacity, meanwhile activated cyclic electron flow, thereby enhancing growth and biomass accumulation in peanut seedlings undergoing ES chilling stress. Furthermore, ES combined with exogenous Ca²⁺ application can significantly enhance plant chilling resistance and peanut yield ultimately in the field. In summary, the above results demonstrated that exogenous foliar Ca²⁺ application restored the ES-linked feedback inhibition of photosynthesis, enhancing the growth/sink demand and the yield of peanuts.

Calcium Channels in Retinal Function and Disease

Voltage-gated Ca2+ (Cav) channels play pivotal roles in regulating gene transcription, neuronal excitability, and neurotransmitter release. To meet the spatial and temporal demands of visual signaling, Cav channels exhibit unusual properties in the retina compared to their counterparts in other areas of the nervous system. In this article, we review current concepts regarding the specific subtypes of Cav channels expressed in the retina, their intrinsic properties and forms of modulation, and how their dysregulation could lead to retinal disease.

[Effect of acupuncture on expression of endoplasmic reticulum Ca2+ and Caspase-12 protein in hippocampal neurons of rats with convulsive brain injury]

OBJECTIVE

To observe the effect of acupuncture on endoplasmic reticulum calcium, apoptosis number and Caspase-12 protein expression in hippocampal neurons of convulsive rats, so as to explore its mechanisms underlying improvement of convulsion.

METHODS

SD rats were randomly divided into normal control, model and acupuncture groups, with 36 rats in each group. Rats in the normal control group received intraperitoneal injection (i.p.) of normal saline (2 mL), and those of the other 2 groups received i.p. of pentylenetetrazole (50 mg/kg) for establishing convulsion model. Manual acupuncture stimulation was applied to "Baihui"(GV20) and "Dazhui"(GV14) for 30 min after modeling. The hippocampal tissues were taken at 2, 12 and 48 h after modeling. The endoplasmic reticulum Ca²⁺ concentration (optical density, OD) was detected by using fluorescence probe technique and laser confocal microscopy, and the number of apoptosis of hippocampal neurons at the 3 time points detected by using terminal-deoxynucleoitidyl transferase mediated nick end labeling (TUNEL) stain. The expression of Caspase-12 protein in hippocampus at 3 time points was observed by immunohistochemistry.

RESULTS

In comparison with the normal group, the number of apoptotic cells of hippocampal neurons and the expression levels of Caspase-12 protein in hippocampus at 2, 12 and 48 h after seizures were obviously increased (P<0.01), and the OD value of Ca²⁺ at 3 time points significantly decreased (P<0.01) in the model group.Following acupuncture intervention, the increased levels of the number of apoptotic cells of hippocampal neurons and the expression of Caspase-12 protein in hippocampus at 3 time points and the decreased levels of OD value of Ca²⁺ at 3 time points were reversed in the acupuncture group (P<0.05, P<0.01).

CONCLUSION

Acupuncture intervention is effective in reducing the apoptosis of hippocampal neurons in convulsion rats, which may be related to its functions in down-regulating Caspase-12 expression and promoting influx of Ca²⁺ in the hippocampal neurons.

Ca2+ mediates transcription factor PuDof2.5 and suppresses stone cell production in pear fruits

Stone cells are sclerenchyma cells formed by deposition of lignin, which is the most significant factor limiting the quality of pears. Ca²⁺ was known to inhibit stone cells in pear fruits, but the underlying molecular mechanism remains unclear. Our study revealed that exogenous CaCl₂ (Ca²⁺) treatment of "Nanguo" pear (Pyrus ussuriensis) suppressed the synthesis of lignin and stone cell production. We further analysed the transcriptomes using RNA-seq, identified a transcription factor, PuDof2.5, and its targets gene PuPRX42-like (lignin polymerase gene) expression decreased in CaCl₂-treated samples, which are involved in suppressing lignin biosynthesis in pear fruit. PuDof2.5 was found to bind directly to the PuPRX42-like promoter and induced its transcription. Taken together, our results revealed that Ca²⁺ modulated the key lignin biosynthetic transcription factor PuDof2.5 to suppress stone cell production in pear fruits.

Influence of Ca2+ on Early Degradation of Cast-In-Situ Mortar Induced by Sulfate-Magnesium Multiple Combined Attack

Early degradation of cast-in-situ concrete induced by multiple internal-external sulfate combined attacks significantly affects the development of concrete strength. An experimental study regarding the effects of Ca²⁺ on the early degradation of cast-in-situ mortars subjected to internal-external sulfate and magnesium combined attacks is investigated in this paper. In particular, a specific method for accurately simulating the degradation of cast-in-situ structures was proposed in this experiment. Physical properties (including weight, size changes, and porosity), mechanical properties (including flexural strength and compressive strength), sulfate concentration, and microstructural properties were monitored during 28 days of immersion. The results show that an internal sulfate and magnesium combined attack (ISA-IMA) obviously retards the development of early strength and accelerates the degradation induced by external sulfate attack (ESA). The diffusion path of sulfate ions from outside is blocked by flake-shaped magnesium hydrates, delaying the penetration of external sulfate attacks. However, it is far from neutralizing the strength loss induced by an internal magnesium attack (IMA) at an early age. Premixed excessive Ca²⁺ would improve the strength development and pore structure of concrete or mortar, enhancing durability against corrosive conditions.

Vasorelaxant Effect of Trachelospermi caulis Extract on Rat Mesenteric Resistance Arteries

Background: Trachelospermi caulis (T. caulis) has been used as a traditional herbal medicine in Asian countries. Although it is well known that T. caulis has beneficial effects, no sufficient research data are available on the cardiovascular effect of T. caulis. We investigated whether T. caulis extract has vascular effects in rat resistance arteries in this study. Methods: To examine whether T. caulis extract affects vascular reactivity, we measured isometric tension of rat mesenteric resistance arteries using a multi-wire myograph system. T. caulis extract was administered after arteries were pre-contracted with high K⁺ (70 mM) or phenylephrine (5 µM). Vanillin, a single active component of T. caulis, was used to treat mesenteric arteries. Results: T. caulis extract caused vascular relaxation in a concentration-dependent manner, which was endothelium-independent. To further identify the mechanism, we incubated the arteries in Ca²⁺-free solution containing high K⁺, followed by a cumulative administration of CaCl₂ (0.01–2.0 mM) with or without T. caulis extract (250 µg/mL). The treatment of T. caulis extract decreased contractile responses induced by the addition of Ca²⁺, which suggested that the extracellular Ca²⁺ influx was inhibited by the T. caulis extract. Moreover, an active compound of T. caulis extract, vanillin, also induced vasodilation in mesenteric resistance arteries. Conclusion: T. caulis extract and its active compound, vanillin, concentration-dependently induced vascular relaxation in mesenteric resistance arteries. These results suggest that the administration of T. caulis extract could help decrease blood pressure.

Expression of the Calcium-Binding Protein CALB1 Is Induced and Controls Intracellular Ca2+ Levels in Senescent Cells

In response to many stresses, such as oncogene activation or DNA damage, cells can enter cellular senescence, a state of proliferation arrest accompanied by a senescence-associated secretory phenotype (SASP). Cellular senescence plays a key role in many physiopathological contexts, including cancer, aging and aging-associated diseases, therefore, it is critical to understand how senescence is regulated. Calcium ions (Ca²⁺) recently emerged as pivotal regulators of cellular senescence. However, how Ca²⁺ levels are controlled during this process is barely known. Here, we report that intracellular Ca²⁺ contents increase in response to many senescence inducers in immortalized human mammary epithelial cells (HMECs) and that expression of calbindin 1 (CALB1), a Ca²⁺-binding protein, is upregulated in this context, through the Ca²⁺-dependent calcineurin/NFAT pathway. We further show that overexpression of CALB1 buffers the rise in intracellular Ca²⁺ levels observed in senescent cells. Finally, we suggest that increased expression of Ca²⁺-binding proteins calbindins is a frequent mark of senescent cells. This work thus supports that, together with Ca²⁺channels, Ca²⁺-binding proteins modulate Ca²⁺ levels and flux during cellular senescence. This opens potential avenues of research to better understand the role of Ca²⁺ and of Ca²⁺-binding proteins in regulating cellular senescence.

The p53 and Calcium Regulated Actin Rearrangement in Model Cells

Long-term cellular stress maintains high intracellular Ca²⁺ concentrations which ultimately initiates apoptosis. Our interest is focused on how the gelsolin (GSN) and junctional mediating and regulating Y protein (JMY) play important roles in stress response. Both of these proteins can bind p53 and actin. We investigated using in vitro fluorescence spectroscopy and found that the p53 competes with actin in GSN to inhibit p53–JMY complex formation. A high Ca²⁺ level initializes p53 dimerization; the dimer competes with actin on JMY, which can lead to p53–JMY cotransport into the nucleus. Here we investigated how the motility and division rate of HeLa cells changes due to low-voltage electroporation of GSN or JMY in scratching assays. We revealed that JMY inhibits their motion, but that it can accelerate the cell division. GSN treatment slows down cell division but does not affect cell motility. HeLa cells fully recovered the gap 20 h after the electroporation with JMY and then started to release from the glass slides. Taken together, our in vitro results indicate that GSN and JMY may play an important role in the cellular stress response.

Two-pore channels: going with the flows

In recent years, our understanding of the structure, mechanisms and functions of the endo-lysosomal TPC (two-pore channel) family have grown apace. Gated by the second messengers, NAADP and PI(3,5)P₂, TPCs are an integral part of fundamental signal-transduction pathways, but their array and plasticity of cation conductances (Na⁺, Ca²⁺, H⁺) allow them to variously signal electrically, osmotically or chemically. Their relative tissue- and organelle-selective distribution, together with agonist-selective ion permeabilities provides a rich palette from which extracellular stimuli can choose. TPCs are emerging as mediators of immunity, cancer, metabolism, viral infectivity and neurodegeneration as this short review attests.

Activation of STIM1/Orai1‑mediated SOCE in sepsis‑induced myocardial depression

Unbalanced Ca2⁺ homeostasis serves an essential role in the occurrence and development of septic myocardial injury. However, the mechanism of Ca2⁺ homeostasis in septic myocardial depression is poorly understood due to the complexity of Ca2⁺ transporters in excitable cells. It was therefore hypothesized that cardiac dysfunction, myocardial injury and cardiac apoptosis in septic myocardial depression are associated with elevated intracellular Ca2⁺ concentrations caused by stromal interaction molecule 1 (STIM1)/Orai calcium release‑activated calcium modulator 1 (Orai1)‑mediated store‑operated Ca2⁺ entry (SOCE). A septic myocardial depression model was established using the cecal ligation and puncture operation (CLP) in mice and was simulated in H9C2 cells via lipopolysaccharide (LPS) stimulation. Cardiac function, myocardial injury, cardiac apoptosis and the expression levels of Bax, Bcl‑2, STIM1 and Orai1 were quantified in vivo at 6, 12 and 24 h. Changes in the intracellular Ca2⁺ concentration, SOCE and the distribution of STIM1 were assessed in vitro within 6 h. The morphological changes of heart tissue were observed by hematoxylin‑eosin staining. Myocardial cellular apoptosis was determined by TUNEL method. The expression of Bax, Bcl‑2, STIM1 and Orai1 were visualized by western blot. Cytosolic calcium concentration and SOCE were evaluated by confocal microscopy. The results demonstrated that cardiac contractile function was significantly reduced at 6 h and morphological changes in cardiac tissues, as well as the myocardial apoptosis rate, were markedly increased at 6, 12 and 24 h following CLP. mRNA and protein expression levels of Bax/Bcl‑2 were significantly enhanced at 6 and 12 h and glycosylation of Orai1 in the myocardium of septic mice was significantly increased at 6 h following CLP. The intracellular Ca2⁺ concentration, SOCE, was significantly increased at 1‑2 h and the clustering and distribution of STIM1 were markedly changed in H9C2 cells at 1 and 2 h. These findings suggested that myocardial dysfunction, cardiac injury and myocardial depression may be related to increased intracellular Ca2⁺ concentration resulting from STIM1/Orai1‑mediated SOCE, which may provide a potential method to alleviate septic myocardial depression.

The role of metal ions in the Golgi apparatus

The Golgi apparatus is a membrane-bound organelle that functions as a central role in the secretory pathway. Since the discovery of the Golgi apparatus, its structure and function have attracted ever-increasing attention from researchers. Recently, it has been demonstrated that metal ions are necessary for the Golgi apparatus to maintain its proper structure and functions. Given that metal ions play an important role in various biological processes, their abnormal homeostasis is related to many diseases. Therefore, in this paper, we reviewed the uptake and release mechanisms of the Golgi apparatus Ca²⁺ , Cu, and Zn²⁺ . Furthermore, we describe the diseases associated with Golgi apparatus Ca²⁺ , Cu, and Zn²⁺ imbalance.

Effects of arginase inhibition on myocardial Ca2+ and contractile responses

Nitric oxide (NO) is thought to increase cardiac contractility by increasing cytosolic Ca²⁺ concentration ([Ca²⁺ ]_cyt ) during excitation. Alternatively, NO could increase the sensitivity of the contractile response to [Ca²⁺ ]_cyt (Ca²⁺ sensitivity). Arginase regulates NO production by competing with NO synthase (NOS), and thus, arginase inhibition should increase cardiac contractility by increasing NO production. We hypothesized that arginase inhibition increases cardiac contractility by increasing both [Ca²⁺ ]_cyt and Ca²⁺ sensitivity. [Ca²⁺ ]_cyt and contractile (sarcomere length [SL] shortening) responses to electrical stimulation were measured simultaneously in isolated rat cardiomyocytes using an IonOptix system. In the same cardiomyocytes, measurements were obtained at baseline, following 3-min exposure to an arginase inhibitor (S-[2-boronoethyl]-l-cysteine; BEC) and following 3-min exposure to BEC plus a NOS inhibitor (N^G -nitro-l-arginine-methyl ester; l-NAME). These responses were compared to time-matched control cardiomyocytes that were untreated. Compared to baseline, BEC increased the amplitude and the total amount of evoked [Ca²⁺ ]_cyt , and the extent and velocity of SL shortening in cardiomyocytes, whereas addition of l-NAME mitigated these effects. The [Ca²⁺ ]_cyt at 50% contraction and relaxation were not different across treatment groups indicating no effect of BEC on Ca²⁺ sensitivity. The [Ca²⁺ ]_cyt and SL shortening responses in time-matched controls did not vary with time. Arginase inhibition by BEC significantly increased the amplitude and the total amount of evoked [Ca²⁺ ]_cyt , and the extent and velocity of SL shortening in cardiomyocytes, but did not affect Ca²⁺ sensitivity. These effects of BEC were mitigated by l-NAME. Together, these results indicate an effect of NO on [Ca²⁺ ]_cyt responses that then increase the contractile response of cardiomyocytes.

Connecting the dots between cell populations, whole-brain activity, and behavior

Simultaneously manipulating and monitoring both microscopic and macroscopic brain activity in vivo and identifying the linkage to behavior are powerful tools in neuroscience research. These capabilities have been realized with the recent technical advances of optogenetics and its combination with fMRI, here termed "opto-fMRI." Opto-fMRI allows for targeted brain region-, cell-type-, or projection-specific manipulation and targeted Ca 2 + activity measurement to be linked with global brain signaling and behavior. We cover the history, technical advances, applications, and important considerations of opto-fMRI in anesthetized and awake rodents and the future directions of the combined techniques in neuroscience and neuroimaging.

Sulfur dioxide improves drought tolerance through activating Ca2+ signaling pathways in wheat seedlings

Sulfur dioxide (SO₂) and drought are two important co-occurring abiotic stresses affecting the growth and productivity of plants. Here, we will investigate the role of Ca²⁺ in regulating antioxidant defense during drought or SO₂/drought stress, and the effect of SO₂ pretreatment on the physiological response of wheat seedlings to drought stress. The results showed that exogenous Ca²⁺ increased the activities of SOD, CAT and POD, and reduced the contents of H₂O₂ and MDA in drought-treated wheat seedlings, suggesting Ca²⁺ could improve drought tolerance by promoting antioxidant defense in plants. Moreover, exogenous Ca²⁺ up-regulated the expression of two stress-responsive transcription factor (TF) genes, ERF1 and MYB30, to cope with drought stress. Exposure of wheat seedlings to 10 mg m^-3 SO₂ significantly enhanced the activities of SOD, CAT and POD. The contents of H₂O₂ and MDA remained at control levels, showing that SO₂ at this concentration led to an activation of the antioxidant defense system and did not cause oxidative damage to the seedlings. Furthermore, 10 mg m^-3 SO₂ pretreatment increased the expression of CCaMK and CPK10, enhanced the activities of SOD and POD, and reduced the accumulation of H₂O₂ and MDA in drought-treated wheat seedlings, showing a role of SO₂ in protection of plants against drought stress. However, with removal of Ca²⁺ by spraying EGTA on the SO₂-pretreated wheat seedlings, the expression of transcription factor genes and activities of antioxidant enzymes were decreased, and the contents of H₂O₂ and MDA enhanced to the level of drought treatment alone, suggesting a role of Ca²⁺ in the SO₂-induced alleviation of drought stress. Together, these results indicated that exogenous Ca²⁺ increased defense-related gene expression and enzyme activity in response to drought stress, and that pre-exposure to appropriate levels of SO₂ could improve drought tolerance through activation of Ca²⁺ signaling pathways in plants. This study would provide new strategy for enhancing plant resistance to environmental stress.

Human coronary microvascular contractile dysfunction associates with viable synthetic smooth muscle cells

AIMS

Coronary microvascular smooth muscle cells (SMCs) respond to luminal pressure by developing myogenic tone (MT), a process integral to the regulation of microvascular perfusion. The cellular mechanisms underlying poor myogenic reactivity in patients with heart valve disease are unknown and form the focus of this study.

METHODS AND RESULTS

Intramyocardial coronary micro-arteries (IMCAs) isolated from human and pig right atrial (RA) appendage and left ventricular (LV) biopsies were studied using pressure myography combined with confocal microscopy. All RA- and LV-IMCAs from organ donors and pigs developed circa 25% MT. In contrast, 44% of human RA-IMCAs from 88 patients with heart valve disease had poor (<10%) MT yet retained cell viability and an ability to raise cytoplasmic Ca2+ in response to vasoconstrictor agents. Comparing across human heart chambers and species, we found that based on patient medical history and six tests, the strongest predictor of poor MT in IMCAs was increased expression of the synthetic marker caldesmon relative to the contractile marker SM-myosin heavy chain. In addition, high resolution imaging revealed a distinct layer of longitudinally aligned SMCs between ECs and radial SMCs, and we show poor MT was associated with disruptions in these cellular alignments.

CONCLUSION

These data demonstrate the first use of atrial and ventricular biopsies from patients and pigs to reveal that impaired coronary MT reflects a switch of viable SMCs towards a synthetic phenotype, rather than a loss of SMC viability. These arteries represent a model for further studies of coronary microvascular contractile dysfunction.

A narrative review on the biology of piezo1 with platelet-rich plasma in cardiac cell regeneration

Cardiomyocyte regeneration following cardiac damage is challenging to study because of the inflammatory process, the multiplication of cells in the stroma, and the creation of scar tissue. In addition to the initial damage, the subsequent decrease in cardiac myocytes adds to heart failure. Piezo1 is remarkably understudied in the heart, which may be related to its recent discovery. Despite this, Piezo1 is expressed in a variety of cardiovascular cell populations, notably epithelial cells (EC), cardiac fibroblasts (CF), and cardiac myocytes (CM), in both animal and human samples, with fibroblasts expressing more than myocytes. Researchers have recently shown that disrupting Piezo1 signaling causes defects in zebrafish developing the outflow tract (OFT) and aortic valves. Platelet plasma membranes may provide lipid substrates, such as phosphatidylinositol bisphosphate, that aid in activating the piezo 1 ion channel in the cardiovascular system. In addition, CXC chemokine ligand 8/CXC chemokine receptor 1/2 (CXCL8-CXCR1/2) signaling was identified to establish the proliferation of coronary endothelial cells during cardiac regeneration. Notably, all these pathways are calcium-dependent, and cell proliferation and angiogenesis were necessary to recover myocardial cells. This review will examine the most current findings to understand further how platelet-rich plasma (PRP) and the piezo 1 channel might aid in cardiomyocyte regeneration.

Let's shape again: the concerted molecular action that builds the pollen tube

The pollen tube is being subjected to control by a complex network of communication that regulates its shape and the misfunction of a single component causes specific deformations. In flowering plants, the pollen tube is a tubular extension of the pollen grain required for successful sexual reproduction. Indeed, maintaining the unique shape of the pollen tube is essential for the pollen tube to approach the embryo sac. Many processes and molecules (such as GTPase activity, phosphoinositides, Ca²⁺ gradient, distribution of reactive oxygen species and nitric oxide, nonuniform pH values, organization of the cytoskeleton, balance between exocytosis and endocytosis, and cell wall structure) play key and coordinated roles in maintaining the cylindrical shape of pollen tubes. In addition, the above factors must also interact with each other so that the cell shape is maintained while the pollen tube follows chemical signals in the pistil that guide it to the embryo sac. Any intrinsic changes (such as erroneous signals) or extrinsic changes (such as environmental stresses) can affect the above factors and thus fertilization by altering the tube morphology. In this review, the processes and molecules that enable the development and maintenance of the unique shape of pollen tubes in angiosperms are presented emphasizing their interaction with specific tube shape. Thus, the purpose of the review is to investigate whether specific deformations in pollen tubes can help us to better understand the mechanism underlying pollen tube shape.

Interaction of background Ca2+ influx, sarcoplasmic reticulum threshold and heart failure in determining propensity for Ca2+ waves in sheep heart

Ventricular arrhythmias can cause death in heart failure (HF). A trigger is the occurrence of Ca²⁺ waves which activate a Na⁺ -Ca²⁺ exchange (NCX) current, leading to delayed after-depolarisations and triggered action potentials. Waves arise when sarcoplasmic reticulum (SR) Ca²⁺ content reaches a threshold and are commonly induced experimentally by raising external Ca²⁺ , although the mechanism by which this causes waves is unclear and was the focus of this study. Intracellular Ca²⁺ was measured in voltage-clamped ventricular myocytes from both control sheep and those subjected to rapid pacing to produce HF. Threshold SR Ca²⁺ content was determined by applying caffeine (10  mM) following a wave and integrating wave and caffeine-induced NCX currents. Raising external Ca²⁺ induced waves in a greater proportion of HF cells than control. The associated increase of SR Ca²⁺ content was smaller in HF due to a lower threshold. Raising external Ca²⁺ had no effect on total influx via the L-type Ca²⁺ current, I_Ca-L , and increased efflux on NCX. Analysis of sarcolemmal fluxes revealed substantial background Ca²⁺ entry which sustains Ca²⁺ efflux during waves in the steady state. Wave frequency and background Ca²⁺ entry were decreased by Gd³⁺ or the TRPC6 inhibitor BI 749327. These agents also blocked Mn²⁺ entry. Inhibiting connexin hemi-channels, TRPC1/4/5, L-type channels or NCX had no effect on background entry. In conclusion, raising external Ca²⁺ induces waves via a background Ca²⁺ influx through TRPC6 channels. The greater propensity to waves in HF results from increased background entry and decreased threshold SR content. KEY POINTS: Heart failure is a pro-arrhythmic state and arrhythmias are a major cause of death. At the cellular level, Ca²⁺ waves resulting in delayed after-depolarisations are a key trigger of arrhythmias. Ca²⁺ waves arise when the sarcoplasmic reticulum (SR) becomes overloaded with Ca²⁺ . We investigate the mechanism by which raising external Ca²⁺ causes waves, and how this is modified in heart failure. We demonstrate that a novel sarcolemmal background Ca²⁺ influx via the TRPC6 channel is responsible for SR Ca²⁺ overload and Ca²⁺ waves. The increased propensity for Ca²⁺ waves in heart failure results from an increase of background influx, and a lower threshold SR content. The results of the present study highlight a novel mechanism by which Ca²⁺ waves may arise in heart failure, providing a basis for future work and novel therapeutic targets.

Regulation of Ca2+ for Cancer Cell Apoptosis through Photothermal Conjugated Nanoparticles

Ca²⁺ overload is caused by the abnormal accumulation of Ca²⁺, which is a potential therapeutic strategy for inhibiting tumor growth. However, due to the limited intracellular Ca²⁺ concentration, its anticancer effect is non-significant. Herein, near-infrared (NIR)-responsive nanoparticles NPs-PCa (DPPC-DSPE-PEG2000-NH₂@PDPP@CaO₂@DOX) were designed and prepared to achieve photothermal trigger of Ca²⁺ release, thereby increasing intracellular Ca²⁺ content. Furthermore, the nanoparticles convert light to heat to activate the transient receptor potential cation channel subfamily V member 1 (TRPV1) ion channels, allowing external Ca²⁺ to flow into the cells, further increasing the Ca²⁺ concentration. NPs-PCa nanoparticles overcome the limitation of insufficient concentration by increasing Ca²⁺ in both internal and external approaches. Meanwhile, an imbalance of intracellular Ca²⁺ induces mitochondrial dysfunction and ultimately results in cancer cell death. This study provides an effective strategy for inhibiting breast cancer tumor growth by regulating Ca²⁺ concentration.

Crosstalk between Ca2+ and Other Regulators Assists Plants in Responding to Abiotic Stress

Plants have evolved many strategies for adaptation to extreme environments. Ca²⁺, acting as an important secondary messenger in plant cells, is a signaling molecule involved in plants' response and adaptation to external stress. In plant cells, almost all kinds of abiotic stresses are able to raise cytosolic Ca²⁺ levels, and the spatiotemporal distribution of this molecule in distant cells suggests that Ca²⁺ may be a universal signal regulating different kinds of abiotic stress. Ca²⁺ is used to sense and transduce various stress signals through its downstream calcium-binding proteins, thereby inducing a series of biochemical reactions to adapt to or resist various stresses. This review summarizes the roles and molecular mechanisms of cytosolic Ca²⁺ in response to abiotic stresses such as drought, high salinity, ultraviolet light, heavy metals, waterlogging, extreme temperature and wounding. Furthermore, we focused on the crosstalk between Ca²⁺ and other signaling molecules in plants suffering from extreme environmental stress.

Synaptotagmin-1 is a bidirectional Ca2+ sensor for neuronal endocytosis

Precise and efficient coupling of endocytosis to exocytosis is critical for neurotransmission. The activity-dependent facilitation of endocytosis has been well established for efficient membrane retrieval; however, whether neural activity clamps endocytosis to avoid excessive membrane retrieval remains debatable with the mechanisms largely unknown. The present work provides compelling evidence that synaptotagmin-1 (Syt1) functions as a primary bidirectional Ca²⁺ sensor to promote slow, small-sized clathrin-mediated endocytosis but inhibit the fast, large-sized bulk endocytosis during elevated neural activity, the disruption of which leads to inefficient vesicle recycling under mild stimulation but excessive membrane retrieval following sustained neurotransmission. Thus, Syt1 serves as a fine-tuning Ca²⁺ sensor to ensure both efficient and precise coupling of endocytosis to exocytosis in response to different neural activities.

Exocytosis and endocytosis are tightly coupled. In addition to initiating exocytosis, Ca²⁺ plays critical roles in exocytosis–endocytosis coupling in neurons and nonneuronal cells. Both positive and negative roles of Ca²⁺ in endocytosis have been reported; however, Ca²⁺ inhibition in endocytosis remains debatable with unknown mechanisms. Here, we show that synaptotagmin-1 (Syt1), the primary Ca²⁺ sensor initiating exocytosis, plays bidirectional and opposite roles in exocytosis–endocytosis coupling by promoting slow, small-sized clathrin-mediated endocytosis but inhibiting fast, large-sized bulk endocytosis. Ca²⁺-binding ability is required for Syt1 to regulate both types of endocytic pathways, the disruption of which leads to inefficient vesicle recycling under mild stimulation and excessive membrane retrieval following intense stimulation. Ca²⁺-dependent membrane tubulation may explain the opposite endocytic roles of Syt1 and provides a general membrane-remodeling working model for endocytosis determination. Thus, Syt1 is a primary bidirectional Ca²⁺ sensor facilitating clathrin-mediated endocytosis but clamping bulk endocytosis, probably by manipulating membrane curvature to ensure both efficient and precise coupling of endocytosis to exocytosis.

Transient Receptor Potential Vanilloid1 (TRPV1) Channel Opens Sesame of T Cell Responses and T Cell-Mediated Inflammatory Diseases

Transient receptor potential vanilloid1 (TRPV1) was primarily expressed in sensory neurons, and could be activated by various physical and chemical factors, resulting in the flow of extracellular Ca2+ into cells. Accumulating data suggest that the TRPV1 is expressed in some immune cells and is a novel regulator of the immune system. In this review, we highlight the structure and biological features of TRPV1 channel. We also summarize recent findings on its role in modulating T cell activation and differentiation as well as its protective effect in T cell-mediated inflammatory diseases and potential mechanisms.

Microtiter plate with built-in oxygen sensors: a novel approach to investigate the dynamics of Pseudomonas aeruginosa growth suppression in the presence of divalent cations and antibiotics

The depletion of dissolved oxygen in a defined synthetic medium can be measured in real time, using a micro-well plate format, associated with a fluorescent plate reader. This technology is appropriate for investigating the effect of antibiotics on cell kinetics because there is a direct correlation between the latter and the amount of dissolved oxygen in the medium of an assay. In this study, the metabolic activity of the opportunistic human pathogen Pseudomonas aeruginosa PA01 was investigated using the OxoPlate OP96U optical sensor technology. The response of P. aeruginosa to aminoglycoside antibiotics when Ca²⁺and Mg²⁺ ions are present in the Evans defined synthetic medium was measured. The results revealed that the effect of antibiotics on P. aeruginosa is influenced by the concentration of divalent cations present in the test medium, although the efficiency of Ca²⁺ in supressing antibiotic activity was found to be greater than that of Mg²⁺. By comparison to tobramycin, the effect of amikacin is largely inhibited by the Ca²⁺and Mg²⁺concentrations. The study results underscore that the reliability of the observation of growth inhibitors is enhanced by the oxygen consumption measurements. Thus, the OxoPlate OP96U system is proven to be an accurate method to test the effectiveness of antibiotic treatments against P. aeruginosa.

Two-Pore Channels Regulate Inter-Organellar Ca2+ Homeostasis in Immune Cells

Two-pore channels (TPCs) are ligand-gated cation-selective ion channels that are preserved in plant and animal cells. In the latter, TPCs are located in membranes of acidic organelles, such as endosomes, lysosomes, and endolysosomes. Here, we focus on the function of these unique ion channels in mast cells, which are leukocytes that mature from myeloid hematopoietic stem cells. The cytoplasm of these innate immune cells contains a large number of granules that comprise messenger substances, such as histamine and heparin. Mast cells, along with basophil granulocytes, play an essential role in anaphylaxis and allergic reactions by releasing inflammatory mediators. Signaling in mast cells is mainly regulated via the release of Ca2+ from the endoplasmic reticulum as well as from acidic compartments, such as endolysosomes. For the crosstalk of these organelles TPCs seem essential. Allergic reactions and anaphylaxis were previously shown to be associated with the endolysosomal two-pore channel TPC1. The release of histamine, controlled by intracellular Ca2+ signals, was increased upon genetic or pharmacologic TPC1 inhibition. Conversely, stimulation of TPC channel activity by one of its endogenous ligands, namely nicotinic adenine dinucleotide phosphate (NAADP) or phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2), were found to trigger the release of Ca2+ from the endolysosomes; thereby improving the effect of TPC1 on regulated mast cell degranulation. In this review we discuss the importance of TPC1 for regulating Ca2+ homeostasis in mast cells and the overall potential of TPC1 as a pharmacological target in anti-inflammatory therapy.

Vasodilatory Effect of Alpinia officinarum Extract in Rat Mesenteric Arteries

Background: Alpinia officinarum (A. officinarum) is known to exhibit a beneficial effect for anti-inflammatory, anti-oxidant, and anti-hyperlipidemic effects. However, no sufficient research data are available on the cardiovascular effect of A. officinarum. Thus, in this study, we investigate whether A. officinarum extract has direct effects on vascular reactivity. Methods: To examine whether A. officinarum extract affects vascular functionality, we measured isometric tension in rat mesenteric resistance arteries using a wire myograph. After arteries were pre-contracted with high-K⁺ (70 mM), phenylephrine (5 µM), or U46619 (1 µM), A. officinarum extract was treated. Results: A. officinarum extract induced vasodilation in a concentration-dependent manner, and this effect was endothelium independent. To further investigate the mechanism, we incubated arteries in a Ca²⁺-free and high-K⁺ solution, followed by the cumulative addition of CaCl₂ (0.01–2.5 mM) with or without A. officinarum extract (30 µg/mL). Pre-treatment of A. officinarum extract reduced the contractile responses induced by cumulative administration of Ca²⁺, which suggests that extracellular Ca²⁺ influx was inhibited by the treatment of A. officinarum extract. These results were associated with a reduction in phosphorylated MLC₂₀ in VSMCs treated with A. officinarum extract. Furthermore, eucalyptol, an active compound of A. officinarum extract, had a similar effect as A. officinarum extract, which causes vasodilation in mesenteric resistance arteries. Conclusion: A. officinarum extract and its active compound eucalyptol induce concentration-dependent vasodilation in mesenteric resistance arteries. These results suggest that administration of A. officinarum extract could exert beneficial effects to treat high blood pressure.

CD137 Signal Mediates Cardiac Ischemia-Reperfusion Injury by Regulating the Necrosis of Cardiomyocytes

The injury of cardiomyocytes after ischemia-reperfusion is the main reason of cardiac dysfunction. Necrosis is one of the methods of programmed cell death and cardiomyocyte necrosis occurs in the process of reperfusion. The activation of CD137 signal is involved in various diseases. In vivo experiments proved that CD137^-/- mice have less heart damage than wild-type mice after ischemia-reperfusion. In vitro experiments, we found that after inhibiting the CD137 signal, the degree of necrosis of HL-1 cells was reduced and it was caused by reducing the Ca2 + overload in the mitochondria, which caused the reduction of mPTP opening. Ca2 + overload in mitochondria induced by activation of CD137 signal was caused by increased Ca2 + released into mitochondria by activation of IP3R and increased MCU level. These results indicate that CD137 signaling aggravates cardiac ischemia-reperfusion injury by inducing myocardial cell necrosis.

Pharmacodynamic Mechanism of Kuanxiong Aerosol for Vasodilation and Improvement of Myocardial Ischemia

OBJECTIVE

To explore the effect of Kuanxiong Aerosol (KXA) on isoproterenol (ISO)-induced myocardial injury in rat models.

METHODS

Totally 24 rats were radomly divided into control, ISO, KXA low-dose and high-dose groups according to the randomized block design method, and were administered by intragastric administration for 10 consecutive days, and on the 9th and 10th days, rats were injected with ISO for 2 consecutive days to construct an acute myocardial ischemia model to evaluate the improvement of myocardial ischemia by KXA. In addition, the diastolic effect of KXA on rat thoracic aorta and its regulation of ion channels were tested by in vitro vascular tension test. The influence of KXA on the expression of calcium-CaM-dependent protein kinase II (CaMK II)/extracellular regulated protein kinases (ERK) signaling pathway has also been tested.

RESULTS

KXA significantly reduced the ISO-induced increase in ST-segment, interventricular septal thickness, cardiac mass index and cardiac tissue pathological changes in rats. Moreover, the relaxation of isolated thoracic arterial rings that had been precontracted using norepinephrine (NE) or potassium chloride (KCl) was increased after KXA treatment in an endothelium-independent manner, and was attenuated by preincubation with verapamil, but not with tetraethylammonium chloride, 4-aminopyridine, glibenclamide, or barium chloride. KXA pretreatment attenuated vasoconstriction induced by CaCl2 in Ca2+-free solutions containing K+ or NE. In addition, KXA pretreatment inhibited accumulation of Ca2+ in A7r5 cells mediated by KCl and NE and significantly decreased p-CaMK II and p-ERK levels.

CONCLUSION

KXA may inhibit influx and release of calcium and activate the CaMK II/ERK signaling pathway to produce vasodilatory effects, thereby improving myocardial injury.

Melanocortin-4 receptor complexity in energy homeostasis,obesity and drug development strategies

The melanocortin-4 receptor (MC4R) has been critically investigated for the past two decades, and novel findings regarding MC4R signalling and its potential exploitation in weight loss therapy have lately been emphasized. An association between MC4R and obesity is well established, with disease-causing mutations affecting 1% to 6% of obese patients. More than 200 MC4R variants have been reported, although conflicting results as to their effects have been found in different cohorts. Most notably, some MC4R gain-of-function variants seem to rescue obesity and related complications via specific pathways such as beta-arrestin (ß-arrestin) recruitment. Broadly speaking, however, dysfunctional MC4R dysregulates satiety and induces hyperphagia. The picture at the mechanistic level is complicated as, in addition to the canonical G stimulatory pathway, the ß-arrestin signalling pathway and ions (particularly calcium) seem to interact with MC4R signalling to contribute to or alleviate obesity pathogenesis. Thus, the overall complexity of the MC4R signalling spectra has broadened considerably, indicating there is great potential for the development of new drugs to manage obesity and its related complications. Alpha-melanocyte-stimulating hormone is the major endogenous MC4R agonist, but structure-based ligand discovery studies have identified possible superior and selective agonists that can improve MC4R function. However, some of these agonists characterized in vitro and in vivo confer adverse effects in patients, as demonstrated in clinical trials. In this review, we provide a comprehensive insight into the genetics, function and regulation of MC4R and its contribution to obesity. We also outline new approaches in drug development and emerging drug candidates to treat obesity.

The Sarcoplasmic Reticulum of Skeletal Muscle Cells: A Labyrinth of Membrane Contact Sites

The sarcoplasmic reticulum of skeletal muscle cells is a highly ordered structure consisting of an intricate network of tubules and cisternae specialized for regulating Ca2+ homeostasis in the context of muscle contraction. The sarcoplasmic reticulum contains several proteins, some of which support Ca2+ storage and release, while others regulate the formation and maintenance of this highly convoluted organelle and mediate the interaction with other components of the muscle fiber. In this review, some of the main issues concerning the biology of the sarcoplasmic reticulum will be described and discussed; particular attention will be addressed to the structure and function of the two domains of the sarcoplasmic reticulum supporting the excitation-contraction coupling and Ca2+-uptake mechanisms.

Melatonin Mediates Osteoblast Proliferation Through the STIM1/ORAI1 Pathway

Based on the positive correlation between bone mineral density and melatonin levels in blood, this study confirmed that melatonin supplementation prevents postmenopausal osteoporosis. We further confirmed that melatonin promotes an increase in intracellular calcium concentrations through the STIM1/ORAI1 pathway, thereby inducing the proliferation of osteoblasts. Introduction: Osteoporosis (OP) is a progressive, systemic bone disease that is one of the main causes of disability and death in elderly female patients. As an amine hormone produced by the human pineal gland, melatonin plays an important role in regulating bone metabolism. This study intends to investigate the relationship between melatonin levels in human blood and bone density and to suggest the efficacy of melatonin in treating osteoporosis by performing in vivo and in vitro experiments. Methods: We used liquid chromatography-tandem mass spectrometry to determine the serum melatonin levels in postmenopausal women with osteoporosis and young women with a normal bone mass. The bone density, BV/TV, Tb.Th, Tb.Sp and other indicators of postmenopausal osteoporosis and mice with a normal bone mass were detected by measuring bone density and micro-CT. The intracellular calcium ion concentration was detected using fluorescence microscopy and a full-wavelength multifunctional microplate reader, and the expression of SOCE-related genes and STIM1/ORAI1 proteins was detected using PCR and WB. Results: This study confirmed that bone density positively correlates with the melatonin level in human blood. In the animal model, melatonin supplementation reverses postmenopausal osteoporosis. We explored the internal mechanism of melatonin treatment of osteoporosis. Melatonin promotes an increase in intracellular calcium ion concentrations through the STIM1/ORAI1 pathway to induce osteoblast proliferation. Conclusions: This study provides an important theoretical basis for the clinical application of melatonin in patients with osteoporosis and helps to optimize the diagnosis and treatment of postmenopausal osteoporosis.

The endoplasmic reticulum-plasma membrane tethering protein TMEM24 is a regulator of cellular Ca2+ homeostasis

Endoplasmic reticulum (ER)–plasma membrane (PM) contacts are sites of lipid exchange and Ca²⁺ transport, and both lipid transport proteins and Ca²⁺ channels specifically accumulate at these locations. In pancreatic β-cells, both lipid and Ca²⁺ signaling are essential for insulin secretion. The recently characterized lipid transfer protein TMEM24 (also known as C2CD2L) dynamically localizes to ER–PM contact sites and provides phosphatidylinositol, a precursor of phosphatidylinositol-4-phosphate [PI(4)P] and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂], to the PM. β-cells lacking TMEM24 exhibit markedly suppressed glucose-induced Ca²⁺ oscillations and insulin secretion, but the underlying mechanism is not known. We now show that TMEM24 only weakly interacts with the PM, and dissociates in response to both diacylglycerol and nanomolar elevations of cytosolic Ca²⁺. Loss of TMEM24 results in hyper-accumulation of Ca²⁺ in the ER and in excess Ca²⁺ entry into mitochondria, with resulting impairment in glucose-stimulated ATP production.

Summary: TMEM24 reversibly localizes to ER–PM contact sites and participates in the regulation of both ER and mitochondrial Ca²⁺ homeostasis and in glucose-dependent ATP production in insulin-secreting cells.

Role of Ca2+, Calnexin and Calreticulin in Platelet from Adult Patients with Chronic Immune Thrombocytopenic Purpura

BACKGROUND

Adult chronic immune thrombocytopenia (chronic ITP) is a common autoimmune hemorrhagic disease characterized by decreased platelet production and increased platelet destruction, leading to thrombocytopenia. In this study, Ca²⁺, calnexin (CNX) and calreticulin (CRT) within platelets from adult patients with chronic ITP were investigated.

METHODS

Platelets were isolated from blood specimen collected from 20 adult patients with chronic ITP and 20 healthy volunteers. Ca²⁺, CNX and CRT were determined by flow cytometry, and the results were analyzed with EXPO32 ADC software.

RESULTS

Flow cytometry showed the expressions of Ca²⁺ (74.19±19.40% vs 22.79±10.47%) was elevated (P<0.05). However, CNX (15.10±7.32% vs 41.79±14.45%) and CRT (25.11±12.66% vs 38.58±12.02%) were decreased markedly in platelets from adult patients with chronic ITP (P<0.05 compared with healthy volunteers).

CONCLUSION

Based on enhanced expression of Ca²⁺ and attenuated expression of CNX and CRT in patients with chronic ITP, Ca²⁺ concentration and its associated down-regulated proteins may be important regulatory signals in the pathogenesis of chronic ITP.