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Calcium ions mediate the volume homeostasis of human red blood cells (RBCs) in the circulation. The mechanism by which calcium ions affect RBC hydration states always follows the same sequence. Deformation of RBCs traversing capillaries briefly activates mechanosensitive PIEZO1 channels, allowing Ca2+ influx down its steep inward gradient transiently overcoming the calcium pump and elevating [Ca2+]i. Elevated [Ca2+]i activates the Ca2+-sensitive Gardos channels, inducing KCl loss and cell dehydration, a sequence operated with infinite variations in vivo and under experimental conditions. The selected health and disease themes for this review focus on landmark experimental results that led to the development of highly constrained models of the circulatory changes in RBC homeostasis. Based on model predictions, a new perspective emerged, pointing to PIEZO1 dysfunction as the main trigger in the formation of the profoundly dehydrated irreversible sickle cells, the main pathogenic participants in vaso-occlusion, the root cause of sickle cell disease. [ABSTRACT FROM AUTHOR]

The mechanism of nacre formation in gastropods involves a vesicular system that transports organic and mineral precursors from the mantle epithelium to the mineralization chamber. Between them lies the surface membrane, a thick organic structure that covers the mineralization chamber and the forming nacre. The surface membrane is a dynamic structure that grows by the addition of vesicles on the outer side and recedes by the formation of interlamellar membranes on the inner side. By using a combination of electron microscopy imaging and spectroscopy, we have monitored the journey of the vesicles from the mantle epithelium to the mineralization chamber, focusing on the elemental composition of the organic structures at each stage. Our data reveal that transport occurs in lipid bilayer vesicles through exocytosis from the outer mantle epithelium. After release into the surface membrane, chitin undergoes a process of self-assembly and interaction with proteins, resulting in progressive changes of the internal structure of the surface membrane until the final structure of the interlamellar membranes is acquired. Finally, these detach from the inner side of the surface membrane. Elemental analysis revealed the transport of a considerable amount of calcium bound to proteins, likely forming calcium-protein complexes. The formation of nacre tablets occurs through the incorporation of organic and mineral precursors extruded from the mantle epithelium. Although much attention has been paid to the presence of amorphous phases in recent decades, the calcium transport system has not yet been elucidated. We have monitored the packaging of organic and mineral precursors in the form of vesicles from the mantle epithelium to the mineralization chamber. We have shown that the surface membrane represents the zone where chitin and protein polymerization takes place, acquiring the final structure for the formation of interlamellar membranes. Interestingly, these organic structures transport a considerable amount of organic calcium into the mineralization chamber, which support a transport system based on acidic calcium-binding proteins. [Display omitted] [ABSTRACT FROM AUTHOR]

Catfish bone collagen peptide-calcium (F3-Ca) chelatate, which had been prepared in our laboratory, was evaluated for its effect on calcium transport and absorption using a Caco-2 cell model. Its effect on the alkaline phosphatase (ALP) activity of osteoblast hFoB1.19 and the expression of the key genes and proteins involved in osteoblast differentiation was also investigated. The results indicated that the chelate increased calcium transport in Caco-2 cells to 0.31 mg/mL, and promoted the mineralization of osteoblasts. The chelate at a concentration of 100 μg/mL increased the ALP activity of osteoblasts by 53.68% compared with the control group. Reverse transcription-polymerase chain reaction (RT-PCR) and protein immunoblot analysis showed that F3-Ca chelate increased the gene and protein expression levels of osteoprotegerin (OPG), osteocalcin (OCN) and runt-related transcription factor 2 (Runx2) in osteoblasts, reduced those of receptor activator for nuclear factor-κB ligand (RANKL), and increase the ratio of OPG/RANKL, thus activating the OPG/RANKL/receptor activator for nuclear factor-κb (RANK) signaling pathway, promoting the proliferation, differentiation and mineralization of osteoblasts, and ultimately resulting in enhanced calcium absorption and anti-osteoporosis activity. This study provides a scientific basis for the high-value utilization of catfish bone and the development of new calcium supplements.

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Abstract Background Deteriorations in eggshell and bone quality are major challenges in aged laying hens. This study compared the differences of eggshell quality, bone parameters and their correlations as well as uterine physiological characteristics and the bone remodeling processes of hens laying eggs of different eggshell breaking strength to explore the mechanism of eggshell and bone quality reduction and their interaction. A total of 240 74-week-old Hy-line Brown laying hens were selected and allocated to a high (HBS, 44.83 ± 1.31 N) or low (LBS, 24.43 ± 0.57 N) eggshell breaking strength group. Results A decreased thickness, weight and weight ratio of eggshells were observed in the LBS, accompanied with ultrastructural deterioration and total Ca reduction. Bone quality was negatively correlated with eggshell quality, marked with enhanced structures and increased components in the LBS. In the LBS, the mammillary knobs and effective layer grew slowly. At the initiation stage of eggshell calcification, a total of 130 differentially expressed genes (DEGs, 122 upregulated and 8 downregulated) were identified in the uterus of hens in the LBS relative to those in the HBS. These DEGs were relevant to apoptosis due to the cellular Ca overload. Higher values of p62 protein level, caspase-8 activity, Bax protein expression and lower values of Bcl protein expression and Bcl/Bax ratio were seen in the LBS. TUNEL assay and hematoxylin-eosin staining showed a significant increase in TUNEL-positive cells and tissue damages in the uterus of the LBS. Although few DEGs were identified at the growth stage, similar uterine tissue damages were also observed in the LBS. The expressions of runt-related transcription factor 2 and osteocalcin were upregulated in humeri of the LBS. Enlarged diameter and more structural damages of endocortical bones and decreased ash were observed in femurs of the HBS. Conclusion The lower eggshell breaking strength may be attributed to a declined Ca transport due to uterine tissue damages, which could affect eggshell calcification and lead to a weak ultrastructure. Impaired uterine Ca transport may result in reduced femoral bone resorption and increased humeral bone formation to maintain a higher mineral and bone quality in the LBS. Graphical Abstract

Mitochondria shape intracellular Ca2+ signaling through the concerted activity of Ca2+ uptake via mitochondrial calcium uniporters and efflux by Na+/Ca2+ exchangers (NCLX). Here, we describe a novel relationship among NCLX, intracellular Ca2+, and autophagic activity. Conditions that stimulate autophagy in vivo and in vitro, such as caloric restriction and nutrient deprivation, upregulate NCLX expression in hepatic tissue and cells. Conversely, knockdown of NCLX impairs basal and starvation‐induced autophagy. Similarly, acute inhibition of NCLX activity by CGP 37157 affects bulk and endoplasmic reticulum autophagy (ER‐phagy) without significant impacts on mitophagy. Mechanistically, CGP 37157 inhibited the formation of FIP200 puncta and downstream autophagosome biogenesis. Inhibition of NCLX caused decreased cytosolic Ca2+ levels, and intracellular Ca2+ chelation similarly suppressed autophagy. Furthermore, chelation did not exhibit an additive effect on NCLX inhibition of autophagy, demonstrating that mitochondrial Ca2+ efflux regulates autophagy through the modulation of Ca2+ signaling. Collectively, our results show that the mitochondrial Ca2+ extrusion pathway through NCLX is an important regulatory node linking nutrient restriction and autophagy regulation. [ABSTRACT FROM AUTHOR]

Several genetic defects, including a mutation in myosin heavy chain 11 (Myh11), are reported to cause familial thoracic aortic aneurysm and dissection (FTAAD). We recently showed that mice lacking K1256 of Myh11 developed aortic dissection when stimulated with angiotensin II, despite the absence of major pathological phenotypic abnormalities prior to stimulation. In this study, we used a comprehensive, data-driven, unbiased, multi-omics approach to find underlying changes in transcription and metabolism that predispose the aorta to dissection in mice harboring the Myh11 K1256del mutation. Pathway analysis of transcriptomes showed that genes involved in membrane transport were downregulated in homozygous mutant (Myh11ΔK/ΔK) aortas. Furthermore, expanding the analysis with metabolomics showed that two mechanisms that raise the cytosolic Ca2+ concentration—multiple calcium channel expression and ADP–ribose synthesis—were attenuated in Myh11ΔK/ΔK aortas. We suggest that the impairment of the Ca2+ influx attenuates aortic contraction and that suboptimal contraction predisposes the aorta to dissection. [ABSTRACT FROM AUTHOR]

Abstract Background The high similarity in anatomical and neurophysiological processes between pigs and humans make pigs an excellent model for metabolic diseases and neurological disorders. Lipids are essential for brain structure and function, and the polyunsaturated fatty acids (PUFA) have anti-inflammatory and positive effects against cognitive dysfunction in neurodegenerative diseases. Nutrigenomics studies involving pigs and fatty acids (FA) may help us in better understanding important biological processes. In this study, the main goal was to evaluate the effect of different levels of dietary soybean oil on the lipid profile and transcriptome in pigs’ brain tissue. Results Thirty-six male Large White pigs were used in a 98-day study using two experimental diets corn-soybean meal diet containing 1.5% soybean oil (SOY1.5) and corn-soybean meal diet containing 3.0% soybean oil (SOY3.0). No differences were found for the brain total lipid content and FA profile between the different levels of soybean oil. For differential expression analysis, using the DESeq2 statistical package, a total of 34 differentially expressed genes (DEG, FDR-corrected p-value

The effect of exogenous Ca2+ on respiration, generation of membrane potential, change in volume, and proton permeability of the inner membrane of mitochondria isolated from cotyledons of etiolated seedlings of narrow-leaved lupine (Lupinus angustifolius L.) was studied. The mitochondria used in the work were characterized by a strong coupling of oxidation and phosphorylation processes. The high functional activity of mitochondria was confirmed by their ability to generate a transmembrane gradient of protons on the inner membrane (membrane potential or ∆Ψ) during the oxidation of succinate and also sustainably maintain it for a long time, both due to the operation of the electron transport chain and due to ATP hydrolysis under conditions of anaerobiosis. It was shown that the presence of 60–120 µM CaCl2 in the mitochondrial incubation medium had no significant effect on the rate of succinate oxidation and the parameters of oxidative phosphorylation; however, it induced ∆Ψ dissipation under conditions of oxygen depletion in the incubation medium. The most complete removal Ca2+ from the medium in the presence of chelators (EGTA, EDTA) prevented the membrane potential dissipation. Ca2+-dependent depolarization of the inner membrane was inhibited by dithiothreitol, suggesting involvement in this process of reactive oxygen species. The reset of the membrane potential was not accompanied by swelling of mitochondria and was not sensitive to cyclosporine A. Using metallochromic Ca2+-indicator arsenazo III, it was shown that the mitochondria of lupine cotyledons are able to actively absorb exogenous Ca2+ and store it in the matrix. Ca2+-induced dissipation of ∆Ψ under conditions of anaerobiosis was accompanied by the release of Ca2+ from mitochondria, the rate of which sharply increased in the presence of calcium ionophore A23 (A23187). It is assumed that the accumulation of Ca2+ and an increase in the level of reactive oxygen species in the matrix induces reversible permeabilization of the inner mitochondrial membrane of lupine cotyledons under conditions of anaerobiosis, which is due to the opening of a pore of nonspecific permeability in a state of low conductivity permeable to protons and, possibly, to other small cations (Na+, K+, Ca2+). [ABSTRACT FROM AUTHOR]

In this study, casein calcium-binding peptides were isolated from casein hydrolysate using calcium-peptide binding properties and their banding properties were characterized. Subsequently, the promoted calcium absorption abilities of casein calcium-binding peptides in the Caco-2 cells monolayers were investigated. Amino acid composition analysis showed that casein calcium-binding peptide-calcium chelate are rich in Glu, Ser, and Asp, with a significant increase in proportion compared to the casein hydrolysate. Molecular weight analysis showed that approximately 90 % of the casein calcium-binding peptides are oligopeptides. Thirty-seven peptide sequences were identified by mass spectrometry, and the presence, quantity, and position of some specific amino acid residues were found to correlate with calcium-binding ability. Additionally, calcium-peptide binding properties were characterized by using Ultraviolet-Visible spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy, which indicated that calcium ions were mainly chelated with the amino nitrogen atoms and oxygen atoms on the carboxyl group of casein calcium-binding peptides, thus forming chelate with porous microstructures. Compared with the control group, the casein calcium-binding peptides treatment group showed a significant increase in calcium transport at 30, 60, 120 and 180 min, respectively, by 44.25 %, 31.21 %, 20.67 % and 24.08 %. Therefore, casein calcium-binding peptides are expected to be used as dietary calcium supplements. [Display omitted] • Preparation and enrichment of casein calcium-binding peptides from milk-derived casein using calcium-peptide chelating properties. • The composition and calcium-binding properties of casein calcium-binding peptides were characterized. • Casein calcium-binding peptides can significantly enhance intestinal calcium transport in Caco-2 cell monolayers. [ABSTRACT FROM AUTHOR]

Fibroblast growth factor (FGF)-23 and calcium-sensing receptor (CaSR) have previously been postulated to be parts of a negative feedback regulation of the intestinal calcium absorption to prevent excessive calcium uptake and its toxicity. However, the underlying mechanism of this feedback regulation remained elusive, especially whether it required transcription of FGF-23. Herein, we induced calcium hyperabsorptive state (CHS) by exposing intestinal epithelium-like Caco-2 monolayer to 30 mM CaCl 2 and 1,25-dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ] after which FGF-23 mRNA levels and transepithelial calcium flux were determined. We found that CHS upregulated FGF-23 transcription, which was reverted by CaSR inhibitors (Calhex-231 and NPS2143) but without effect on CaSR transcription. Although 10 nM 1,25(OH) 2 D 3 was capable of enhancing transepithelial calcium flux, the higher-than-normal calcium inundation as in CHS led to a decrease in calcium flux, consistent with an increase in FGF-23 protein expression. Administration of inhibitors (≤10 μM CN585 and cyclosporin A) of calcineurin, a mediator of CaSR action to control transcription and production of its target proteins, was found to partially prevent FGF-23 protein production and the negative effect of CHS on calcium transport, while having no effect on FGF-23 mRNA expression. Direct exposure to FGF-23, but not FGF-23 + PD173074 (FGFR1/3 inhibitor), also completely abolished the 1,25(OH) 2 D 3 -enhanced calcium transport in Caco-2 monolayer. Nevertheless, CHS and CaSR inhibitors had no effect on the mRNA levels of calcineurin (PPP3CB) or its targets (i.e., NFATc1–4). In conclusion, exposure to CHS induced by high apical calcium and 1,25(OH) 2 D 3 triggered a negative feedback mechanism to prevent further calcium uptake. CaSR and its downstream mediator, calcineurin, possibly contributed to the regulatory process, in part by enhancing FGF-23 production to inhibit calcium transport. Our study, therefore, corroborated the physiological significance of CaSR-autocrine FGF-23 axis as a local feedback loop for prevention of excessive calcium uptake. • Vitamin D-induced Ca2+ transport was diminished by Ca2+ hyperabsorptive state (CHS). • Calcium-sensing receptor inhibitors prevented CHS-induced FGF-23 expression. • Calcineurin modulated the effects of CHS on Ca2+ transport and FGF-23 expression. • FGF-23 required FGF receptor 1/3 to abolish vitamin D-induced Ca2+ transport. [ABSTRACT FROM AUTHOR]

Intracellular Ca2+ concentrations are strictly controlled by plasma membrane transporters, the endoplasmic reticulum, and mitochondria, in which Ca2+ uptake is mediated by the mitochondrial calcium uniporter complex (MCUc), while efflux occurs mainly through the mitochondrial Na+/Ca2+ exchanger (NCLX). RNAseq database repository searches led us to identify the Nclx transcript as highly enriched in astrocytes when compared with neurons. To assess the role of NCLX in mouse primary culture astrocytes, we inhibited its function both pharmacologically or genetically. This resulted in re‐shaping of cytosolic Ca2+ signaling and a metabolic shift that increased glycolytic flux and lactate secretion in a Ca2+‐dependent manner. Interestingly, in vivo genetic deletion of NCLX in hippocampal astrocytes improved cognitive performance in behavioral tasks, whereas hippocampal neuron‐specific deletion of NCLX impaired cognitive performance. These results unveil a role for NCLX as a novel modulator of astrocytic glucose metabolism, impacting on cognition. [ABSTRACT FROM AUTHOR]

An unsolved problem of contemporary plant electrophysiology is the identity of Ca2+ channels responsible for the initiation of the action potential. We took a pharmacological approach and applied several Ca2+ channel blockers (verapamil, tetrandrine, and NED-19) on a Characean (Nitellopsis obtusa) algae model system. The impact of the selected pharmaceuticals on the parameters of excitation transients of a single cell was analysed employing the two-electrode voltage clamp technique. It was revealed that tetrandrine exerted no effect, while both verapamil and NED-19 prolonged activation and inactivation durations of the excitatory Cl− current. NED-19 also significantly depolarised the excitation threshold membrane potential and shifted Ca2+ current reversal potential. Thus, NED-19 most specifically targeted Ca2+ channels. A viability assay paired with observations of cytoplasmic streaming revealed that verapamil affected not only Ca2+ channels but also exhibited non-specific effects, which eventually lead to cell death. Since many potential Ca2+ channel blockers exert additional undesirable non-specific effects, our study underlines the necessity to search for new more specific modulators of plant Ca2+ transport systems. It is challenging to isolate transmembrane Ca2+ currents that are activated during the generation of action potentials in plants. We applied several different Ca2+ channel blockers (verapamil, tetrandrine, and NED-19). It was found that, while verapamil and NED-19 did affect Ca2+ currents, non-specific effects were also observed, compromising the usage of these blockers as selective means of distinguishing Ca2+ currents in plants. [ABSTRACT FROM AUTHOR]

Chorioallantoic membrane (CAM) is responsible for respiratory gas exchange, eggshell calcium transport, embryonic acid-base equilibrium, allantoic ion, and water reabsorption during avian embryonic development. To further understand the timing of CAM gene expression during chick embryonic development, especially the calcium absorption mechanism, transcriptome quantitative comparative analysis was conducted on chick CAM during the embryonic period (E) of 9, 13, 17, and 20 days. A total of 6378 differentially expressed genes (DEGs) were identified. Functional enrichment analysis of DEGs showed that CAM DEGs were mainly involved in biological processes such as “ion transport regulation”, “immune response” and “cell cycle”. Time series analysis of the differential genes showed that the functional cells of CAM began to proliferate and differentiate at E9 and the calcium content of egg embryo increased significantly at E13. Simultaneously, the observation of the ultrastructure of the eggshell showed that the interstice of the fiber layer was enlarged at E13, and the mastoid layer was partly exposed. Therefore, it is preliminarily inferred that CAM calcium transport starts at E13, and genes such as TRPV6, S100A10, and RANKL cooperate to regulate calcium release and transport.

Background: The high similarity in anatomical and neurophysiological processes between pigs and humans make pigs an excellent model for metabolic diseases and neurological disorders. Lipids are essential for brain structure and function, and the polyunsaturated fatty acids (PUFA) have anti-inflammatory and positive effects against cognitive dysfunction in neurodegenerative diseases. Nutrigenomics studies involving pigs and fatty acids (FA) may help us in better understanding important biological processes. In this study, the main goal was to evaluate the effect of different levels of dietary soybean oil on the lipid profile and transcriptome in pigs' brain tissue. Results: Thirty-six male Large White pigs were used in a 98-day study using two experimental diets corn-soybean meal diet containing 1.5% soybean oil (SOY1.5) and corn-soybean meal diet containing 3.0% soybean oil (SOY3.0). No differences were found for the brain total lipid content and FA profile between the different levels of soybean oil. For differential expression analysis, using the DESeq2 statistical package, a total of 34 differentially expressed genes (DEG, FDR-corrected p-value < 0.05) were identified. Of these 34 DEG, 25 are known-genes, of which 11 were up-regulated (log2 fold change ranging from + 0.25 to + 2.93) and 14 were down-regulated (log2 fold change ranging from − 3.43 to -0.36) for the SOY1.5 group compared to SOY3.0. For the functional enrichment analysis performed using MetaCore with the 34 DEG, four pathway maps were identified (p-value < 0.05), related to the ALOX15B (log2 fold change − 1.489), CALB1 (log2 fold change − 3.431) and CAST (log2 fold change + 0.421) genes. A "calcium transport" network (p-value = 2.303e-2), related to the CAST and CALB1 genes, was also identified. Conclusion: The results found in this study contribute to understanding the pathways and networks associated with processes involved in intracellular calcium, lipid metabolism, and oxidative processes in the brain tissue. Moreover, these results may help a better comprehension of the modulating effects of soybean oil and its FA composition on processes and diseases affecting the brain tissue. [ABSTRACT FROM AUTHOR]

Plant glutamate receptor-like (GLR) genes encode ion channels with demonstrated roles in electrical and calcium (Ca2+) signaling. The expansion of the GLR family along the lineage of land plants, culminating in the appearance of a multiclade system among flowering plants, has been a topic of interest since their discovery nearly 25 years ago. GLRs are involved in many physiological processes, from wound signaling to transcriptional regulation to sexual reproduction. Emerging evidence supports the notion that their fundamental functions are conserved among different groups of plants as well. In this review, we update the physiological and genetic evidence for GLRs, establishing their role in signaling and cell–cell communication. Special emphasis is given to the recent discussion of GLRs' atomic structures. Along with functional assays, a structural view of GLRs' molecular organization presents a window for novel hypotheses regarding the molecular mechanisms underpinning signaling associated with the ionic fluxes that GLRs regulate. Newly uncovered transcriptional regulations associated with GLRs—which propose the involvement of genes from all clades ofArabidopsis thaliana in ways not previously observed—are discussed in the context of the broader impacts of GLR activity. We posit that the functions of GLRs in plant biology are probably much broader than anticipated, but describing their widespread involvement will only be possible with (a) a comprehensive understanding of the channel's properties at the molecular and structural levels, including protein–protein interactions, and (b) the design of new genetic approaches to explore stress and pathogen responses where precise transcriptional control may result in more precise testable hypotheses to overcome their apparent functional redundancies. [ABSTRACT FROM AUTHOR]

As an essential structural, metabolic and signaling element, calcium shows low remobilization from old to young tissues in plants, restricting the nutrient-use efficiency and control efficacy against mosaic virus disease. Nanotechnology has been applied to prevent/minimize nutrient losses and improve the accessibility of poorly-available nutrients. Herein, the current study applied a star polycation (SPc) to prepare a calcium nutrition nanoagent. The SPc could assemble with calcium glycinate through hydrogen bond and Van der Waals force, forming stable spherical particles with nanoscale size (17.72 nm). Transcriptomic results revealed that the calcium glycinate/SPc complex could activate the expression of many transport-related genes and disease resistance genes in tomatoes, suggesting the enhanced transport and antiviral immunity of SPc-loaded calcium glycinate. Reasonably, the calcium transport was accelerated by 3.17 times into tomato leaves with the help of SPc, and the protective effect of calcium glycinate was remarkably improved to 77.40% and 67.31% toward tomato mosaic virus with the help of SPc after the third and fifth applications. Furthermore, SPc-loaded calcium glycinate could be applied to increase the leaf photosynthetic rate and control the unusual fast growth of tomatoes. The current study is the first success to apply nano-delivery system for enhanced calcium transport and antiviral immunity, which is beneficial for increasing nutrient-use efficiency and shows good prospects for field application. [ABSTRACT FROM AUTHOR]

The sarco/endoplasmic reticulum Ca-ATPase (SERCA) is a P-type ion pump that transports Ca2+ from the cytosol into the endoplasmic/sarcoplasmic reticulum (ER/SR) in most mammalian cells. It is critically important in muscle, facilitating relaxation and enabling subsequent contraction. Increasing SERCA expression or specific activity can alleviate muscle dysfunction, most notably in the heart, and we seek to develop small-molecule drug candidates that activate SERCA. Therefore, we adapted an NADH-coupled assay, measuring Ca-dependent ATPase activity of SERCA, to high-throughput screening (HTS) format, and screened a 46,000-compound library of diverse chemical scaffolds. This HTS platform yielded numerous hits that reproducibly alter SERCA Ca-ATPase activity, with few false positives. The top 19 activating hits were further tested for effects on both Ca-ATPase and Ca2+ transport, in both cardiac and skeletal SR. Nearly all hits increased Ca2+ uptake in both cardiac and skeletal SR, with some showing isoform specificity. Furthermore, dual analysis of both activities identified compounds with a range of effects on Ca2+-uptake and ATPase, which fit into distinct classifications. Further study will be needed to identify which classifications are best suited for therapeutic use. These results reinforce the need for robust secondary assays and criteria for selection of lead compounds, before undergoing HTS on a larger scale. [ABSTRACT FROM AUTHOR]

Sickle cell disease (SCD), affecting millions worldwide, is caused by the homozygous inheritance of the abnormal haemoglobin, HbS. Deoxygenation of HbS in the venous circulation permeabilizes sickle cells to calcium via PIEZO1 channels triggering a dehydration cascade driven by the outward electrochemical potassium gradient. This mechanism operates with particular intensity in a subpopulation of sickle RBCs, the irreversibly sickled cells (ISCs). The lifespan of ISCs is extremely short, about 4 to 7 days. Most of this time is spent in a profoundly dehydrated condition, the irreversibly sickled state, eliciting vaso-occlusion, which is considered the root cause of organ failure and pain crisis in SCD. There is a large experimental and clinical database on sickle cells and ISCs, but how ISCs form and evolve in the circulation remains a mystery. The present study is the first attempt to unravel the experimentally inaccessible lifecycle of ISCs in vivo applying a well-accredited model of red blood cell homeostasis and circulatory dynamics, using a vast array of validated experimental observations to tightly constrain the model parameters. The results showed that abnormally strong deoxy-PIEZO1 responses were needed for calcium to elicit a violent hyperdense collapse in ISC-destined stress reticulocytes within about a day in the circulation. The potassium-depleted ISCs remain in this maximally dehydrated but volume stable condition, the pathogenic state, sustained by vigorous pump-leak balanced sodium fluxes. Eventually, sodium pump decay initiates rapid terminal rehydration by the unbalanced net gain of NaCl and water. Analysis of the mechanisms behind this three-stage circulatory lifecycle of ISCs exposed a complex web of interactions among many components of the homeostatic fabric of RBCs. These findings point to the abnormally intense PIEZO1 response to deoxygenation in ISC-destined stress reticulocytes as a prime cause of ISC formation in vivo, a central target for future research., (Copyright © 2025 The Author(s). Published by Elsevier Inc. All rights reserved.)

Major progress has been made in defining the basis of the mitochondrial permeability transition, a Ca2+‐dependent permeability increase of the inner membrane that has puzzled mitochondrial research for almost 70 years. Initially considered an artefact of limited biological interest by most, over the years the permeability transition has raised to the status of regulator of mitochondrial ion homeostasis and of druggable effector mechanism of cell death. The permeability transition is mediated by opening of channel(s) modulated by matrix cyclophilin D, the permeability transition pore(s) (PTP). The field has received new impulse (a) from the hypothesis that the PTP may originate from a Ca2+‐dependent conformational change of F‐ATP synthase and (b) from the reevaluation of the long‐standing hypothesis that it originates from the adenine nucleotide translocator (ANT). Here, we provide a synthetic account of the structure of ANT and F‐ATP synthase to discuss potential and controversial mechanisms through which they may form high‐conductance channels; and review some intriguing findings from the wealth of early studies of PTP modulation that still await an explanation. We hope that this review will stimulate new experiments addressing the many outstanding problems, and thus contribute to the eventual solution of the puzzle of the permeability transition. [ABSTRACT FROM AUTHOR]

Background: In metabolic acidosis, a negative calcium balance is induced by decreased renal tubular calcium reabsorption. This occurs independently of the action of parathyroid hormone or vitamin D and was attributed to a direct action of metabolic acidosis on the renal tubular cells. The latter has been verified by recent studies on the molecular levels in the kidney.Summary: Whereas the regulatory role of urinary calcium excretion was traditionally assigned to the transcellular calcium transport in the distal convoluted tubule (DCT) and connecting tubule (CNT), most of the calcium reabsorption from the glomerular filtrate paracellularly occurs through the tight junctions in the proximal tubule (PT) and the thick ascending limb (TAL) of Henle's loop. Interestingly, all these nephron segments participate in producing hypercalciuria caused by metabolic acidosis. Claudin-2 is the major route of paracellular calcium transport in the PT and was downregulated in rats with 5 days' NH4Cl loading. In the TAL, the lumen-positive voltage produced by apical K+ recycling drives paracellular reabsorption of Ca2+ and Mg2+ via the claudin-16/19 complex. Activation of calcium-sensing receptor (CaSR) by extracellular calcium upregulates claudin-14, which in turn interacts with the claudin-16/19 complex and inhibits its cation permeability. This TAL CaSR-claudins axis was activated by chronic NH4Cl loading in rats. Finally, the major transcellular calcium transporters TRPV5 and 28K calcium-binding protein in the DCT-CNT were also downregulated by NH4Cl or acetazolamide administration in mice.Key Messages: Both paracellular and transcellular calcium transport pathways in the kidney are regulated by metabolic acidosis and lead to renal calcium wasting. In the PT, claudin-2 is downregulated by acidic pH. In the TAL of Henle's loop, CaSR is stimulated by the ionized calcium released from bone and upregulates claudin-14, which in turn inhibits the claudin-16/19 complex and leads to calcium and magnesium wasting. Finally, the transcellular calcium transporters, TRPV5 and calbindin-D28K, are downregulated by metabolic acidosis in the DCT and CNT. [ABSTRACT FROM AUTHOR]

Copyright of Modern Food Science & Technology is the property of Editorial Office of Modern Food Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to provide an efficient calcium transporter for the development of calcium supplement products, embryo eggs were selected for incubation. Carrying out calcium ions chelation on the embryo egg-derived egg white peptides (EED-EWPs) with high calcium binding activity produced incubation. The changes of EED-EWPs before and after chelation with calcium ions were compared, ζ-potential absolute value increased significantly, indicating that the embryo egg-derived egg white peptides calcium chelates (EED-EWPs-Ca) was successfully formed. Calcium binding activity results displayed that EED-EWPs on the 9th day of incubation had the highest calcium binding ability (6.96 μg/mg), which was 1.17 times that before incubation (5.97 μg/mg). EED-EWPs were isolated by IMAC metal chelating preloaded column, calcium binding amount was improved to 17.88 μg/mg, which was about 3 times that of those before isolation. The EED-EWPs were analyzed by mass spectrometry, six peptides with high calcium binding ability were identified. The mechanism of promoting calcium absorption of EED-EWPs produced during incubation was investigated by molecular docking with TRPV6 (a key protein for calcium transporter in the human small intestine). Results elucidated that amino and carboxyl groups in EED-EWPs were possible sites for calcium ions binding. This study would provide an efficient calcium transporter with high nutritional value for the development of calcium supplement products. [ABSTRACT FROM AUTHOR]

Extracting peptides from fish bones as calcium supplements is of great significance for patients with osteoporosis. Novel peptides were obtained from Muraenesox cinereus bone (MCBP) by enzymatic hydrolysis and membrane separation. Molecular dynamics simulation and electron microscope analysis shown MCBP could chelate with calcium ions. A Caco-2 cell monolayer model was used to investigate the effect of peptide–calcium chelates on promoting calcium transport. MC3T3-E1 osteoblasts were treated with different concentrations of MCBP (0, 0.25, 0.5, or 1 mg/mL) to analyze the effects of MCBP on calcium absorption and cell differentiation factors. The bone formation of zebrafish evaluate the therapeutic effect of MCBP on the zebrafish OP model. The results showed that there were at least 13 kinds of calcium chelation modes in the mixed peptide, and peptide–calcium chelate could significantly improve calcium transport in the Caco-2 cell monolayer. After 14 days of culture with different concentrations of MCBP, the calcium deposition in MC3T3-E1 cells increased significantly. The type I collagen (COL-I), osteocalcin (OCN) and run-related transcription factor 2 (RUNX2), and activities of alkaline phosphatase (ALP) were dose-dependent with MCBP. MCBP can increase bone mineral density in an OP model of zebrafish. After being treated with MCBP, the expression levels of ALP, OCN, osteoprotegerin (OPG) and transforming growth factor-β (TGF-β) in the model group increased, while the expression levels of tartrate-resistant acid phosphatase (TRAP) decreased. The results indicated that MCBP may act as a nutritional food and provide an effective means for dietary supplementation in OP patients.

Ca2+ signaling in trypanosomatids is an important component of energy metabolism regulation and therefore, cytosolic Ca2+ concentration is finely regulated by Ca2+ transport through the plasma membrane and Ca2+ uptake and release by intracellular organelles. To maintain intracellular Ca2+ homeostasis with different gradients of the ion within the cellular compartments, there is an energy cost and also energy dissipation in the form of heat. Using an innovative segmented fusion technique of a chip-calorimeter and CRISPR/Cas9 knockout (–KO) Trypanosoma cruzi cell lines, we evaluated the heat generation during Ca2+ uptake by digitonin-permeabilized T. cruzi epimastigotes, a system consisting of Ca2+ uptake predominantly by mitochondria and acidocalcisomes. We used three T. cruzi epimastigotes cell lines: control cells denominated scrambled, cells with the absence of the pyruvate dehydrogenase phosphatase (TcPDP-KO) and cells lacking mitochondrial Ca2+ uptake via the mitochondrial calcium uniporter (TcMCU-KO), that presented, in this respective order, decreasing rates and capacities of Ca2+ uptake. TcPDP-KO cells exhibited the lowest heat production following Ca2+ addition, which may be due to its lower mitochondrial oxidative phosphorylation capacity and lower ATP availability for acidocalcisomal Ca2+ uptake. Scrambled and TcMCU-KO cells exhibited similar Ca2+-induced heat effects, which correlates with a higher ATP-dependent acidocalcisomal Ca2+ uptake in these cells. Our results show evidences that mitochondrial Ca2+ transport via the uniporter is minimally heat dissipative, while ATPase pumps in acidocalcisomes possess a predominant contribution to the heat generated during Ca2+ uptake. [ABSTRACT FROM AUTHOR]

Calcium is a key ion involved in cardiac and skeletal muscle contractility, nerve function, and skeletal structure. Global calcium balance is affected by parathyroid hormone and vitamin D, and calcium is shuttled between the extracellular space and the bone matrix compartment dynamically. The kidney plays an important role in whole-body calcium balance. Abnormalities in the kidney transport proteins alter the renal excretion of calcium. Various hormonal and regulatory pathways have evolved that regulate the renal handling of calcium to maintain the serum calcium within defined limits despite dynamic changes in dietary calcium intake. Dysregulation of renal calcium transport can occur pharmacologically, hormonally, and via genetic mutations in key proteins in various nephron segments resulting in several disease processes. This review focuses on the regulation transport of calcium in the nephron. Genetic diseases affecting the renal handling of calcium that can potentially lead to changes in the serum calcium concentration are reviewed. [ABSTRACT FROM AUTHOR]

Calcium is a key ion involved in cardiac and skeletal muscle contractility, nerve function, and skeletal structure. Global calcium balance is affected by parathyroid hormone and vitamin D, and calcium is shuttled between the extracellular space and the bone matrix compartment dynamically. The kidney plays an important role in whole-body calcium balance. Abnormalities in the kidney transport proteins alter the renal excretion of calcium. Various hormonal and regulatory pathways have evolved that regulate the renal handling of calcium to maintain the serum calcium within defined limits despite dynamic changes in dietary calcium intake. Dysregulation of renal calcium transport can occur pharmacologically, hormonally, and via genetic mutations in key proteins in various nephron segments resulting in several disease processes. This review focuses on the regulation transport of calcium in the nephron. Genetic diseases affecting the renal handling of calcium that can potentially lead to changes in the serum calcium concentration are reviewed.

Ryanodine receptors (RyRs) are large Ca 2+ release channels residing in the endoplasmic or sarcoplasmic reticulum membrane. Three isoforms of RyRs have been identified in mammals, the disfunction of which has been associated with a series of life-threatening diseases. The need for large amounts of native tissue or eukaryotic cell cultures limits advances in structural studies of RyRs. Here, we report a method that utilizes nanobodies to purify RyRs from only 5 mg of total protein. The purification process, from isolated membranes to cryo-EM grade protein, is achieved within 4 h on the bench, yielding protein usable for cryo-EM analysis. This is demonstrated by solving the structures of rabbit RyR1, solubilized in detergent, reconstituted into lipid nanodiscs or liposomes, and bovine RyR2 reconstituted in nanodisc, and mouse RyR2 in detergent. The reported method facilitates structural studies of RyRs directed toward drug development and is useful in cases where the amount of starting material is limited., Competing Interests: Conflict of interests The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

As the genetic landscape of cardiomyopathies continues to expand, the identification of missense variants in disease-associated genes frequently leads to a classification of variant of uncertain significance (VUS). For the proper reclassification of such variants, functional characterization is an important contributor to the proper assessment of pathogenic potential. Several missense variants in the calcium transport regulatory protein phospholamban have been associated with dilated cardiomyopathy. However, >40 missense variants in this transmembrane peptide are currently known and most remain classified as VUS with little clinical information. Similarly, missense variants in cardiac myosin binding protein have been associated with hypertrophic cardiomyopathy. However, hundreds of variants are known and many have low penetrance and are often found in control populations. Herein, we focused on novel missense variants in phospholamban, an Ala15-Thr variant found in a 4-year-old female and a Pro21-Thr variant found in a 60-year-old female, both with a family history and clinical diagnosis of dilated cardiomyopathy. The patients also harbored a Val896-Met variant in cardiac myosin binding protein. The phospholamban variants caused defects in the function, phosphorylation, and dephosphorylation of this calcium transport regulatory peptide, and we classified these variants as potentially pathogenic. The variant in cardiac myosin binding protein alters the structure of the protein. While this variant has been classified as benign, it has the potential to be a low-risk susceptibility variant because of the structural change in cardiac myosin binding protein. Our studies provide new biochemical evidence for missense variants previously classified as benign or VUS. • Missense variants in phospholamban, A15T and P21T, have been previously identified in dilated cardiomyopathy patients. • The variants caused defects in the function and regulation of phospholamban and were classified as potentially pathogenic. • The patients also harbored a V896M variant in cardiac myosin binding protein. • This variant alters the structure of cardiac myosin binding protein and was classified as a low-risk susceptibility variant. [ABSTRACT FROM AUTHOR]

Phospholamban (PLB) is a transmembrane micropeptide that regulates the sarcoplasmic reticulum Ca 2+ -ATPase (SERCA) in cardiac muscle, but the physical mechanism of this regulation remains poorly understood. PLB reduces the Ca 2+ sensitivity of active SERCA, increasing the Ca 2+ concentration required for pump cycling. However, PLB does not decrease Ca 2+ binding to SERCA when ATP is absent, suggesting PLB does not inhibit SERCA Ca 2+ affinity. The prevailing explanation for these seemingly conflicting results is that PLB slows transitions in the SERCA enzymatic cycle associated with Ca 2+ binding, altering transport Ca 2+ dependence without actually affecting the equilibrium binding affinity of the Ca 2+ -coordinating sites. Here, we consider another hypothesis, that measurements of Ca 2+ binding in the absence of ATP overlook important allosteric effects of nucleotide binding that increase SERCA Ca 2+ binding affinity. We speculated that PLB inhibits SERCA by reversing this allostery. To test this, we used a fluorescent SERCA biosensor to quantify the Ca 2+ affinity of non-cycling SERCA in the presence and absence of a non-hydrolyzable ATP-analog, AMPPCP. Nucleotide activation increased SERCA Ca 2+ affinity, and this effect was reversed by co-expression of PLB. Interestingly, PLB had no effect on Ca 2+ affinity in the absence of nucleotide. These results reconcile the previous conflicting observations from ATPase assays versus Ca 2+ binding assays. Moreover, structural analysis of SERCA revealed a novel allosteric pathway connecting the ATP- and Ca 2+ -binding sites. We propose this pathway is disrupted by PLB binding. Thus, PLB reduces the equilibrium Ca 2+ affinity of SERCA by interrupting allosteric activation of the pump by ATP., Competing Interests: Conflict of interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Calcium (Ca 2+ ) is a key regulator in diverse intracellular signaling pathways and has long been implicated in metabolic control and mitochondrial function. Mitochondria can actively take up large amounts of Ca 2+ , thereby acting as important intracellular Ca 2+ buffers and affecting cytosolic Ca 2+ transients. Excessive mitochondrial matrix Ca 2+ is known to be deleterious due to opening of the mitochondrial permeability transition pore (mPTP) and consequent membrane potential dissipation, leading to mitochondrial swelling, rupture, and cell death. Moderate Ca 2+ within the organelle, on the other hand, can directly or indirectly activate mitochondrial matrix enzymes, possibly impacting on ATP production. Here, we aimed to determine in a quantitative manner if extra- or intramitochondrial Ca 2+ modulates oxidative phosphorylation in mouse liver mitochondria and intact hepatocyte cell lines. To do so, we monitored the effects of more modest versus supraphysiological increases in cytosolic and mitochondrial Ca 2+ on oxygen consumption rates. Isolated mitochondria present increased respiratory control ratios (a measure of oxidative phosphorylation efficiency) when incubated with low (2.4 ± 0.6 μM) and medium (22.0 ± 2.4 μM) Ca 2+ concentrations in the presence of complex I-linked substrates pyruvate plus malate and α-ketoglutarate, respectively, but not complex II-linked succinate. In intact cells, both low and high cytosolic Ca 2+ led to decreased respiratory rates, while ideal rates were present under physiological conditions. High Ca 2+ decreased mitochondrial respiration in a substrate-dependent manner, mediated by mPTP. Overall, our results uncover a Goldilocks effect of Ca 2+ on liver mitochondria, with specific "just right" concentrations that activate oxidative phosphorylation., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Yeast vacuoles are acidified by the v-type H + -ATPase (V-ATPase) that is comprised of the membrane embedded V O complex and the soluble cytoplasmic V 1 complex. The assembly of the V 1 -V O holoenzyme on the vacuole is stabilized in part through interactions between the V O a-subunit ortholog Vph1 and the lipid phosphatidylinositol 3,5-bisphosphate (PI(3,5)P 2 ). PI(3,5)P 2 also affects vacuolar Ca 2+ release through the channel Yvc1 and uptake through the Ca 2+ pump Pmc1. Here, we asked if H + and Ca 2+ transport activities were connected through PI(3,5)P 2 . We found that overproduction of PI(3,5)P 2 by the hyperactive fab1 T2250A mutant augmented vacuole acidification, whereas the kinase-inactive fab1 EEE mutant attenuated the formation of a H + gradient. Separately, we tested the effects of excess Ca 2+ on vacuole acidification. Adding micromolar Ca 2+ blocked vacuole acidification, whereas chelating Ca 2+ accelerated acidification. The effect of adding Ca 2+ on acidification was eliminated when the Ca 2+ /H + antiporter Vcx1 was absent, indicating that the vacuolar H + gradient can collapse during Ca 2+ stress through Vcx1 activity. This, however, was independent of PI(3,5)P 2 , suggesting that PI(3,5)P 2 plays a role in submicromolar Ca 2+ flux but not under Ca 2+ shock. To see if the link between Ca 2+ and H + transport was bidirectional, we examined Ca 2+ transport when vacuole acidification was inhibited. We found that Ca 2+ transport was inhibited by halting V-ATPase activity with Bafilomycin or neutralizing vacuolar pH with chloroquine. Together, these data show that Ca 2+ transport and V-ATPase efficacy are connected but not necessarily through PI(3,5)P 2 ., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

[Display omitted] • Novel peptides were obtained from Muraenesox cinereus bone (MCBP) by enzymatic hydrolysis and membrane separation. Molecular dynamics simulation and electron microscope analysis shown MCBP could chelate with calcium ions. • MCBP improved calcium transport in the Caco-2 cell monolayer and increased calcium deposition in MC3T3-E1 cells. • MCBP increased bone mineral density in an OP model of zebrafish. Extracting peptides from fish bones as calcium supplements is of great significance for patients with osteoporosis. Novel peptides were obtained from Muraenesox cinereus bone (MCBP) by enzymatic hydrolysis and membrane separation. Molecular dynamics simulation and electron microscope analysis shown MCBP could chelate with calcium ions. A Caco-2 cell monolayer model was used to investigate the effect of peptide–calcium chelates on promoting calcium transport. MC3T3-E1 osteoblasts were treated with different concentrations of MCBP (0, 0.25, 0.5, or 1 mg/mL) to analyze the effects of MCBP on calcium absorption and cell differentiation factors. The bone formation of zebrafish evaluate the therapeutic effect of MCBP on the zebrafish OP model. The results showed that there were at least 13 kinds of calcium chelation modes in the mixed peptide, and peptide–calcium chelate could significantly improve calcium transport in the Caco-2 cell monolayer. After 14 days of culture with different concentrations of MCBP, the calcium deposition in MC3T3-E1 cells increased significantly. The type I collagen (COL-I), osteocalcin (OCN) and run-related transcription factor 2 (RUNX2), and activities of alkaline phosphatase (ALP) were dose-dependent with MCBP. MCBP can increase bone mineral density in an OP model of zebrafish. After being treated with MCBP, the expression levels of ALP, OCN, osteoprotegerin (OPG) and transforming growth factor-β (TGF-β) in the model group increased, while the expression levels of tartrate-resistant acid phosphatase (TRAP) decreased. The results indicated that MCBP may act as a nutritional food and provide an effective means for dietary supplementation in OP patients. [ABSTRACT FROM AUTHOR]

• Acidification causes PI(4,5)P2 dissociation from TRPV5 and inhibits calcium reabsorption. • Protein kinase A structurally competes with the calmodulin binding site on TRPV5 to prevent calcium-dependent channel inhibition. TRPV5 is a highly selective calcium channel that finetunes urinary calcium excretion by reabsorbing calcium from the pro-urine. New structural findings show how PTH and pH control TRPV5 activity by altering the binding of endogenous ligands calmodulin and phosphatidylinositol 4,5-bisphosphate (PI(4,5)P 2). [Display omitted] [ABSTRACT FROM AUTHOR]

Many aquatically respiring animals acutely exposed to low pH waters suffer inhibition of ion uptake and loss of branchial (gill) epithelial integrity, culminating in a fatal loss of body Na+. Environmental calcium levels ([Ca2+]e) are pivotal in maintaining branchial junction integrity, with supplemental Ca2+ reversing the negative effects of low pH in some animals. Tolerance of some naturally acidic environments by aquatic animals is further complicated by low [Ca2+]e, yet many of these environments are surprisingly biodiverse. How animals overcome the damaging actions of low pH and low environmental Ca2+ remains unknown. We examined the effects of [Ca2+]e on the response to low pH in larvae of the highly acid-tolerant frog Limnodynastes terraereginae. Acute exposure to low pH water in the presence of low (5 μmol l-1) [Ca2+]e increased net Na+ efflux. Provision of additional [Ca2+]e reduced net Na+ efflux, but the effect was saturable. Acclimation to both low and high (250 μmol l-1) [Ca2+]e improved the resistance of larvae to Na+ efflux at low pH. Exposure to the Ca2+ channel inhibitor ruthenium red resulted in an abrupt loss of tolerance in low pH-acclimated larvae. Acclimation to acidic water increased branchial gene expression of the intracellular Ca2+ transport protein calbindin, consistent with a role for increased transcellular Ca2+ trafficking in the tolerance of acidic water. This study supports a role for [Ca2+]e in promoting branchial integrity and highlights a potential mechanism via the maintenance of transcellular Ca2+ uptake in the acid tolerance of L. terraereginae larvae., (© 2022. Published by The Company of Biologists Ltd.)

TRPV5 is a highly selective calcium channel that finetunes urinary calcium excretion by reabsorbing calcium from the pro-urine. New structural findings show how PTH and pH control TRPV5 activity by altering the binding of endogenous ligands calmodulin and phosphatidylinositol 4,5-bisphosphate (PI(4,5)P 2 )., (Copyright © 2022. Published by Elsevier Ltd.)