Increase In Ca2 Research Articles

The role of ion homeostasis imbalance due to citrate accumulation in fluoroacetic acid (FAA) toxicity in Neurospora crassa

Fluoroacetic acid (FAA) is a poison commonly used for the lethal control of invasive species in Australia and New Zealand. Despite its widespread use and long history as a pesticide, no effective treatment for accidental poisoning exists. Although it is known to inhibit the tricarboxylic acid (TCA) cycle, specific details of FAA toxicology have remained elusive, with hypocalcemia suggested to be involved in the neurological symptoms prior to death. Here, we study the effects of FAA on cell growth and mitochondrial function using the filamentous fungi Neurospora crassa as model organism. FAA toxicosis in N. crassa is characterized by an initial hyperpolarization and subsequent depolarization of the mitochondrial membranes, followed by a significant intracellular decrease in ATP and increase in Ca2+. The development of mycelium was markedly affected within 6 h, and growth impaired after 24 h of FAA exposure. Although the activity of mitochondrial complexes I, II and IV was impaired, the activity of citrate synthase was not affected. Supplementation with Ca2+ exacerbated the effects of FAA in cell growth and membrane potential. Our findings suggest that an imbalance created in the ratio of ions within the mitochondria may lead to conformational changes in ATP synthase dimers due to mitochondrial Ca2+ uptake, that ultimately result in the opening of the mitochondrial permeability transition pore (MPTP), a decrease in membrane potential, and cell death. Our findings suggest new approaches for the treatment research, as well as the possibility to use N. crassa as a high-throughput screening assay to evaluate a large number of FAA antidote candidates.

Alterations of the Ca2+ clearing mechanisms by type 2 diabetes in aortic smooth muscle cells of Zucker diabetic fatty rat.

Type 2 Diabetes Mellitus (T2DM) is a rapidly rising disease with cardiovascular complications constituting the most common cause of death among diabetic patients. Chronic hyperglycemia can induce vascular dysfunction through damage of the components of the vascular wall, such as vascular smooth muscle cells (VSMCs), which regulate vascular tone and contribute to vascular repair and remodeling. These functions are dependent on intracellular Ca2+ changes. The mechanisms by which T2DM affects Ca2+ handling in VSMCs still remain poorly understood. Therefore, the objective of this study was to determine whether and how T2DM affects Ca2+ homeostasis in VSMCs. We evaluated intracellular Ca2+ signaling in VSMCs from Zucker Diabetic Fatty rats using Ca2+ imaging with Fura-2/AM. Our results indicate that T2DM decreases Ca2+ release from the sarcoplasmic reticulum (SR) and increases the activity of store-operated channels (SOCs). Moreover, we were able to identify an enhancement of the activity of the main Ca2+ extrusion mechanisms (SERCA, PMCA and NCX) during the early stage of the decay of the ATP-induced Ca2+ transient. In addition, we found an increase in Ca2+ entry through the reverse mode of NCX and a decrease in SERCA and PMCA activity during the late stage of the signal decay. These effects were appreciated as a shortening of ATP-induced Ca2+ transient during the early stage of the decay, as well as an increase in the amplitude of the following plateau. Enhanced cytosolic Ca2+ activity in VSMCs could contribute to vascular dysfunction associated with T2DM.

SLC26A3 (DRA) is stimulated in a synergistic, intracellular Ca2+-dependent manner by cAMP and ATP in intestinal epithelial cells.

In polarized intestinal epithelial cells, downregulated in adenoma (DRA) is an apical Cl-/[Formula: see text] exchanger that is part of neutral NaCl absorption under baseline conditions, but in cyclic adenosine monophosphate (cAMP)-driven diarrheas, it is stimulated and contributes to increased anion secretion. To further understand the regulation of DRA in conditions mimicking some diarrheal diseases, Caco-2/BBE cells were exposed to forskolin (FSK) and adenosine 5'-triphosphate (ATP). FSK and ATP stimulated DRA in a concentration-dependent manner, with ATP acting via P2Y1 receptors. FSK at 1 µM and ATP at 0.25 µM had minimal to no effect on DRA given individually; however, together, they stimulated DRA to levels seen with maximum concentrations of FSK and ATP alone. In Caco-2/BBE cells expressing the Ca2+ indicator GCaMP6s, ATP increased intracellular Ca2+ (Ca2+i) in a concentration-dependent manner, whereas FSK (1 µM), which by itself did not significantly alter Ca2+i, followed by 0.25 µM ATP produced a large increase in Ca2+ that was approximately equal to the elevation caused by 1 µM ATP. 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) (BAPTA-AM) pretreatment prevented the ATP and FSK/ATP synergistically increased the DRA activity and the increase in Ca2+i caused by FSK/ATP. FSK/ATP synergistic stimulation of DRA was similarly observed in human colonoids. In Caco-2/BBE cells, subthreshold concentrations of FSK (cAMP) and ATP (Ca2+) synergistically increased Ca2+i and stimulated DRA activity with both being blocked by BAPTA-AM pretreatment. Diarrheal diseases, such as bile acid diarrhea, in which both cAMP and Ca2+ are elevated, are likely to be associated with stimulated DRA activity contributing to increased anion secretion, whereas separation of DRA from Na+/H+ exchanger isoform-3 (NHE3) contributes to reduced NaCl absorption.NEW & NOTEWORTHY The BB Cl-/[Formula: see text] exchanger DRA takes part in both neutral NaCl absorption and stimulated anion secretion. Using intestinal cell line, Caco-2/BBE high concentrations of cAMP and Ca2+ individually stimulated DRA activity, whereas low concentrations, which had no/minimal effect, synergistically stimulated DRA activity that required a synergistic increase in intracellular Ca2+. This study increases understanding of diarrheal diseases, such as bile salt diarrhea, in which both cAMP and elevated Ca2+ are involved.

A high-concentrate diet induces inflammatory injury via regulating Ca2+/CaMKKβ-mediated autophagy in mammary gland tissue of dairy cows.

Calmodulin-dependent protein kinase β (CaMKKβ) is closely related to Ca2+ concentration. An increase in Ca2+ concentration in the cytoplasm activates CaMKKβ, and activated CaMKKβ affects the activities of AMPK and mTOR and induces autophagy. A high-concentrate diet leads to Ca2+ disorder in mammary gland tissue. Therefore, this study mainly investigated the induction of mammary gland tissue autophagy by a high-concentrate diet and the specific mechanism of lipopolysaccharide (LPS)-induced autophagy in bovine mammary epithelial cells (BMECs). Twelve mid-lactation Holstein dairy cows were fed with a 40% concentrate diet (LC) and a 60% concentrate diet (HC) for 3 weeks. At the end of the trial, rumen fluid, lacteal vein blood, and mammary gland tissue were collected. The results showed that the HC diet significantly decreased rumen fluid pH, with a pH lower than 5.6 for more than 3 h, indicating successfully induction of subacute rumen acidosis (SARA). The mechanism of LPS-induced autophagy in BMECs was studied in vitro. First, the cells were divided into a Ctrl group and LPS group to study the effects of LPS on the concentration of Ca2+ and autophagy in BMECs. Then, cells were pretreated with an AMPK inhibitor (compound C) or CaMKKβ inhibitor (STO-609) to investigate whether the CaMKKβ-AMPK signaling pathway is involved in LPS-induced BMEC autophagy. The HC diet increased the concentration of Ca2+ in mammary gland tissue and pro-inflammatory factors in plasma. The HC diet also significantly increased the expression of CaMKKβ, AMPK, and autophagy-related proteins, resulting in mammary gland tissue injury. In vitro cell experiments showed that LPS increased intracellular Ca2+ concentration and upregulated protein expression of CaMKKβ, AMPK, and autophagy-related proteins. Compound C pretreatment decreased the expression of proteins related to autophagy and inflammation. In addition, STO-609 pretreatment not only reversed LPS-induced BMECs autophagy but also inhibited the protein expression of AMPK, thereby alleviating the inflammatory response in BMECs. These results suggest that inhibition of the Ca2+/CaMKKβ-AMPK signaling pathway reduces LPS-induced autophagy, thereby alleviating inflammatory injury of BMECs. Therefore, SARA may increase the expression of CaMKKβ by increasing Ca2+ levels and activate autophagy through the AMPK signaling pathway, thereby inducing inflammatory injury in mammary gland tissue of dairy cows.

PO-01-217 FUNCTIONAL CHARACTERIZATION OF CALCIUM HANDLING KINETICS IN RE-ENGINEERED CARDIOMYOCYTES FROM A PATIENT WITH TYPE 2 LONG QT SYNDROME

Type 2 long QT syndrome (LQT2) is caused by pathogenic variants in the KCNH2-encoded Kv11.1 K+ channel resulting in prolongation of the action potential duration (APD) at the cellular level and QT prolongation in the patient, predisposing LQT2 patients to potentially lethal ventricular arrhythmias. Limited evidence, namely prolonged Ca2+ transient in human induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) and enhanced Ca2+ leak in transgenic LQT2 rabbit model, suggests that KCNH2 pathogenic variants may be associated with perturbations in intracellular Ca2+ handling. To characterize the APD and Ca2+ handling properties of an iPSC-CM model of LQT2. iPSC-CMs were generated from a patient with a pathogenic KCNH2 frame-shift variant (p.Q901fs/71) and an unrelated healthy control. Confocal imaging of FluoVolt voltage dye was used to measure the APD at 90% repolarization (APD90) in iPSC-CMs. Ca2+ kinetics was characterized using Ca2+ sensing dye Fluo4-AM before and after treatment with 100 nM isoproterenol (ISO). Q901fs/71-iPSC-CMs had a significantly prolonged APD90 compared to wild-type (WT) iPSC-CMs (444 ±9 ms vs 631±8 ms, p<0.001). Q901fs/71-iPSC-CMs had a higher Ca2+ amplitude (DF/F0) before (0.423±0.043 vs 0.97±0.07, p=0.001) and after ISO treatment (0.602±0.051 vs 1.056 ±0.06, p<0.001) compared to WT. The Ca2+ transient duration (CTD90) was longer in Q901fs/71-iPSC-CMs than in WT before (1.062±0.041 s vs 1.306±0.038 s, p=0.01), but not after ISO (1.071±0.062 s vs 1.092±0.044 s, p=0.96). Peak to 90% Ca2+ decay time was increased in Q901fs/71-iPSC-CMs before (0.785±0.04 s vs 0.942±0.033 s, p=0.028), but not after ISO (0.748±0.054 s vs 0.767±0.038 s, p=0.95). Upstroke time was longer in Q901fs/71-iPSC-CMs compared to WT before (0.281±0.006 s vs 0.364±0.014 s; p=0.002) but not after ISO (0.327±0.014 s vs 0.344±0.025 s; p=0.88). Upstroke velocity (DF/F0/t) was increased in Q901fs/71-iPSC-CMs before (1.092±0.122 vs 2.278±0.278, p<0.001) and after ISO (1.310±0.117 vs 2.2±0.139, p=0.005). Ca2+ leak from sarcoplasmic reticulum was higher in Q901fs/71-iPSC-CMs before (16% vs 38%) and after ISO (16% vs 55%). We show that iPSC-CMs derived from the patient with a truncating LQT2-causative variant (yielding likely Kv11.1 channel haploinsufficiency) have prolonged APD90 and display abnormal Ca2+ handling properties such as higher amplitude, increase in Ca2+ leak, prolonged transient duration, Ca2+ decay time, and upstroke velocity compared to WT iPSC-CMs.

Studies on the Mechanism of Lactate-Induced Increase in Ca2+ Oscillations in Carotid Body Type 1 Cells

Blood lactate concentration under normal conditions is ~1 mM and increases during hypoxia and exercise due to elevated anaerobic metabolism. Recent studies suggest that lactate acts directly on carotid body Type 1 chemoreceptor (CB) cells and elevates cytosolic [Ca2+], which increases transmitter secretion from CB cells, carotid sinus afferent nerve activity and ventilation. The mechanism by which lactate increases [Ca2+] is still uncertain. Chang et al (2015) reported that lactate binds to Gs-coupled receptor (OlfR78 in rat/mice) whose signaling leads to a rise in [Ca2+]. Torres-Torrelo et al (2021) reported that lactate enters the cell via the monocarboxylate transporter and increases the ratio of NADH to NAD+, which opens cation channels to cause cell depolarization and Ca2+ influx. Another potential mechanism is that lactate itself inhibits K+ channels and/or activates non-selective cation channels to depolarize CB cells and increase Ca2+ influx. Here we studied the effects of lactate on ion channels, cell Em and Ca2+ oscillations in CB cells. Ion channel and Em studies: Sodium lactate (10 mM, pH 7.4) produced a mild depolarization (&lt;10 mV) in ~30% of CB cells. In HEK cells expressing TASK-1/3, lactate (10 mM) caused mild inhibition of the whole-cell current and cell depolarization (as detected by Fluovolt fluorescence). Lactate activated a 20-pS Ca2+-sensitive monovalent cation channel (CaMCC) in ~50% of CB cells. [Ca2+] oscillations: Lactate (1-20 mM) increased the frequency of Ca2+ oscillations in CB cells (and thus averaged [Ca2+]), and this effect was blunted by removal of extracellular Ca2+, nifedipine and 2-APB. Forskolin that elevated cytosolic [cAMP] had no effect on Ca2+ oscillations, and H-89 (PKA inhibitor) did not block lactate- and hypoxia-induced increase in Ca2+ oscillations. Summary: Our studies do not support the OlfR78-Gs-cAMP signaling pathway in lactate-induced increase in Ca2+ oscillations and [Ca2+] in CB cells. Our study supports a mechanism in which lactate activates CaMCC, possibly initiated by inhibition of TASK and/or other signals, to cause cell depolarization that increases Ca2+ influx and the frequency of Ca2+ oscillations. NIH and Rosalind Franklin University of Medicine and Science This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Sorption of Pb2+ and Zn2+ions on Zr-Ca-Mg phosphates: Kinetics and mechanism studies

The kinetics study of Pb2+ and Zn2+ ions adsorption by low-cost mixed Zr-Ca-Mg phosphates with a different Zr/(Ca + Mg) ratio was carried out, for the first time. The effect of chemical composition on adsorption characteristics of obtained adsorbents was established. It was shown that an increase of Ca2+ and Mg2+ cations content in the composition of Zr-Ca-Mg phosphate adsorbents contributed to an increase in the adsorption capacity to Pb2+ (3.82–4.76 mmol/g) and Zn2+ (2.60–4.13 mmol/g) ions. Such improvements in the adsorption capacities were due to the amelioration of the textural properties of adsorbents, so that ABET of adsorbents was in the range of 68–96 m2/g and Vdes BJH of adsorbent was in the range of 0.19–0.24 cm3/g. On the other hand, increase of Ca2+ and Mg2+ cations led to a high difference in solubility products of initial phosphates and spent adsorbents. Kinetic data of Pb2+ and Zn2+ ions adsorption revealed that the adsorption rate is controlled by film diffusion, intraparticle diffusion and chemical interaction, which was confirmed by the results of X-ray diffraction analysis of spent adsorbents and described by the pseudo-second-order model. The increase of zirconium content caused an increase in the rate constant of the pseudo-second-order of Pb2+ and Zn2+ ions adsorption. Intraparticle diffusion had a significant effect on Zn2+ ions adsorption. Due to the suitable kinetics parameters and sorption capacities of composite Zr-Ca-Mg phosphates for divalent metal ions, these sorbents can be recommended as effective materials for heavy metals removal.

The influence of Ca2+ on the growth mechanism of corrosion product film on N80 steel in CO2 corrosion environments

The influence of Ca2+ on the growth mechanism of CO2 corrosion products was investigated by weight loss, in situ electrochemical measurements and analysis of corrosion products. With the increase of Ca2+ concentration in solution, the crystallinity of product film, FexCa1−xCO3, weakened and gradually turned to amorphous structure, which provided less protectiveness and elevated the corrosion rate. The high concentration of Ca2+ resulted in the “unstable” growth of FexCa1−xCO3. At 10000 mg L−1 Ca2+, complicated FexCa1−xCO3 structures with different Ca content formed. The linear relation between Ca2+ concentration in solution and molar fraction of Ca in the film was also proposed.

Molecular modeling of ARF6 dysregulation caused by mutations in IQSEC2

IQSEC2 gene mutations are associated with epilepsy, autism, and intellectual disability. The primary function IQSEC2, mediated via its Sec 7 domain, is to act as a guanine nucleotide exchange factor for ARF6. We sought to develop a molecular model, which may explain the aberrant Sec 7 activity on ARF6 of different human IQSEC2 mutations. We integrated experimental data of IQSEC2 mutants with protein structure prediction by the RaptorX server combined with molecular modeling and molecular dynamics simulations. Normally, apocalmodulin (apoCM) binds to IQSEC2 resulting in its N-terminal fragment inhibiting access of its Sec 7 domain to ARF6. An increase in Ca2+ concentration destabilizes the interaction of IQSEC2 with apoCM and removes steric hindrance of Sec 7 binding with ARF6. Mutations at amino acid residue 350 of IQSEC2 result in loss of steric hindrance of Sec 7 binding with ARF6 leading to constitutive activation of ARF6 by Sec 7. On the other hand, a mutation at amino acid residue 359 of IQSEC2 results in constitutive hindrance of Sec 7 binding to ARF6 leading to the loss of the ability of IQSEC2 to activate ARF6. These studies provide a model for dysregulation of IQSEC2 Sec 7 activity by mutant IQSEC2 proteins. Communicated by Ramaswamy H. Sarma

Morphological and physiological adaptation characteristics of lithophytic bryophytes to karst high calcium environment

BackgroundLithophytic bryophytes grow on the rock surface, change the habitat on the rock surface through biological karstification, and provide a material basis for the growth of other plants. However, the surface calcium content of bare rock is high. The lithophytic bryophytes may have a special mechanism to adapt to the karst high calcium environment. The present study aimed to explore the physiological regulation process of karst lithophytic bryophytes under high calcium environment, and to provide scientific basis for revealing the maintenance mechanism of karst biodiversity.ResultsWith the increase of Ca2+ concentration, the contents of Pro, SP and MDA of lithophytic bryophytes showed a downward—upward—downward trend. However, when Ca2+ ≥ 400 mmol/L, the contents of Pro and SP changed significantly at 1d, 2d, 3d, 5d and 7d with the extension of culture time, and lithophytic bryophytes died after 2 months of culture. Under different Ca2+ concentrations, the maximum SOD activity of lithophytic bryophytes is 1758.00 (U/g FW), the minimum is 92.60 (U/g FW), the maximum POD activity is 120.88 (U/g FW), and the minimum is 4.80 (U/g FW). The antioxidative activity of of Hyophila involuta are higher than that of Didymodon constrictus and Eurohypnum leptothallum, and its enzyme activity changed significantly with the increase of calcium concentration and time.At the same time, the contents of TChl, Chla, and Chlb in lithophytic bryophytes decreased with the increase of Ca2+ concentration. When Ca2+ = 400 mmol/L, the contents of TChl and Chla were the lowest, but when Ca2+ > 400 mmol/L, they began to increase. In addition, ABA is negatively correlated with TChl and Chla, and positively correlated with ROS. It shows that ABA has a certain role in regulating the adaptation of lithophytic bryophytes to high calcium environment.ConclusionsLithophytic bryophytes have strong calcium tolerance, and their physiological response to high calcium stress is different from vascular bundle plants. The general stress principle is not applicable to lithophytic bryophytes. The response of lithophytic bryophytes to the change of Ca2+concentration is slow, showing passive response or inert response.

Study on the mechanism of Ca2+ and Na+ interaction during the hydration of multi-source solid waste geopolymers

As a green and new environmentally friendly material, geopolymer has been rapidly developed and applied in engineering construction and other fields. However, the interaction mechanism in the hydration process of geopolymer prepared by alkali activators containing Ca2+ and Na + respectively is not clear. Therefore, in this study, on the basis of determining the optimal amount of NaOH as an alkali activator, different contents of calcium carbide slag (CCS) were incorporated and the effect of Ca2+and Na + interaction on macroscopic properties was evaluated by compressive strength test. The mechanism of their interaction was also analyzed by XRD, FTIR, SEM-EDS and ICP to determine the microscopic morphology. The results show that when (Na + Ca)/(Si + Al) ≤ 0.6, Na+ and Ca2+ have a synergistic effect, which balances the excess negative charge generated by Al3+ and Si4+ in the four-coordinated state, which promotes the growth of crystals in the hydration products. The hydration products are mainly pin-like C–S–H and N-A-S-H gels. When 0.6 < (Na + Ca)/(Si + Al) ≤ 0.95, with the increase of Ca2+ content, the polymerization degree of Si–O-T bond and O–Si–O bond increases, Ca2+ replaces Na+ in petal-like C(N)-A-S-H gel to form large flake like C-A-S-H gel, and part of the replaced Na+ penetrates into the liquid phase through the pore structure, Al/Si ≈ 0.6, (Na + Ca)/(Si + Al) ≈ 0.95, the concentration of Na+ in the liquid phase is about 49.465 μg/ml to the equilibrium state. The hydration products were mainly C–S–H and C-A-S-H gels, and the compressive strength could reach 43.05 MPa at 28d.The results provide an experimental basis and reference for the study of the hydration mechanism of geopolymer prepared from multi-source solid waste.

Rhodojaponin VI indirectly targets Cav2.2 channels via N-ethylmaleimide-sensitive fusion protein to alleviate neuropathic pain.

Neuropathic pain is a chronic disease that severely afflicts the life and emotional status of patients, but currently available treatments are often ineffective. Novel therapeutic targets for the alleviation of neuropathic pain are urgently needed. Rhodojaponin VI, a grayanotoxin from Rhododendron molle, showed remarkable antinociceptive efficacy in models of neuropathic pain, but its biotargets and mechanisms are unknown. Given the reversible action of rhodojaponin VI and the narrow range over which its structure can be modified, we perforwmed thermal proteome profiling of the rat dorsal root ganglion to determine the protein target of rhodojaponin VI. N-Ethylmaleimide-sensitive fusion (NSF) was confirmed as the key target of rhodojaponin VI through biological and biophysical experiments. Functional validation showed for the first time that NSF facilitated trafficking of the Cav2.2 channel to induce an increase in Ca2+ current intensity, whereas rhodojaponin VI reversed the effects of NSF. In conclusion, rhodojaponin VI represents a unique class of analgesic natural products targeting Cav2.2 channels via NSF.

Spatial-Temporal Characteristics and Influencing Factors of Lake Water and Groundwater Chemistry in Hulun Lake, Northeast China

Lakes in cold and arid regions are extremely vulnerable to global climate change, and the study of seasonal spatial and temporal fluctuations of lake-groundwater chemistry is of major significance for water resource management and environmental preservation. In this study, we combined hydrogeochemical, multivariate statistical, and spatial interpolation methods to assess spatial and temporal variations of lake and groundwater chemistry in Hulun Lake during the frozen and non-frozen periods. The results show that sodium (Na+) is the most abundant cation in the Hulun Lake area. Bicarbonate (HCO3−) and sulfate (SO42−) are the most predominant anions in the lake, river, and ground water during both seasons. The higher Na+ + K+ concentrations in the frozen season were related to longer circulation time and lower renewable rate. The water chemistry of the lake was of the HCO3-SO4-Cl-Na type and that of groundwater in the east and west regions was of the SO4-Cl-Na and HCO3-Na types, respectively. The chemical compositions of groundwater in the non-frozen season were mainly affected by evaporation and concentration, while rock weathering, evaporation, and human activities jointly controlled groundwater chemical component in the frozen period. Based on hierarchical cluster analysis (HCA) and principal component analysis (PCA) methods, Ca2+, NO3−, and SO42− were identified as the main controlling indicators of the chemical characteristics of groundwater and lake water. The increase of Ca2+ concentration in the center of the lake was related to groundwater discharge along the marginal tectonic fracture zone along the lake shores, which was the potential groundwater discharge area. The unconsolidated aquifer provides recharge channels for groundwater on the eastern side, which has a certain influence on the increase of nutrient concentration (NO3−) in the lake on the eastern shore. This research adds to our rough understanding of the lake-groundwater interaction in Hulun Lake, and provides a scientific foundation for the sustainable use of water resources, as well as the eco-logical integrity preservation in cold and arid regions.

Mechanisms for the α-Adrenoceptor-Mediated Positive Inotropy in Mouse Ventricular Myocardium: Enhancing Effect of Action Potential Prolongation

Mechanisms for the α-adrenoceptor-mediated positive inotropy in neonatal mouse ventricular myocardium were studied with isolated myocardial preparations. The phenylephrine-induced positive inotropy was suppressed by prazosin, nifedipine, and chelerythrine, a protein kinase C inhibitor, but not by SEA0400, a selective Na+/Ca2+ exchanger inhibitor. Phenylephrine increased the L-type Ca2+ channel current and prolonged the action potential duration, while the voltage-dependent K+ channel current was not influenced. In the presence of cromakalim, an ATP-sensitive K+ channel opener, the phenylephrine-induced prolongation of action potential duration, as well as the positive inotropy, were smaller than in the absence of cromakalim. These results suggest that the α-adrenoceptor-mediated positive inotropy is mediated by an increase in Ca2+ influx through the L-type Ca2+ channel, and the concomitant increase in action potential duration acts as an enhancing factor.

Effects of pH, Calcium, and Phosphate on the Solubility of Arsenic in Paddy Soil Based on Surface Complexation Modeling

This study aimed to obtain a better understanding on the environmental behavior of As in paddy soil and to reveal the influence mechanisms of different environmental factors on the availability of As in the soil solution. The effects of pH, calcium, and phosphate on the solubility and speciation distribution of As in the paddy soil collected from Zhuzhou of Hunan province were studied by combining the adsorption experiments with the NOM-CD model. The results showed that the minimum concentration of soluble As in the soil was at approximately a pH of 6.0, which was mainly affected by both electrical interactions and site competition between Ca2+, PO43-, As(Ⅲ), and As(Ⅴ). The adsorption of As onto soil particles could be increased by an increase in Ca2+ in the soil system, leading to the decrease in soluble As concentration. This effect became significant at a higher pH, because adsorbed Ca2+ increased the positive charge on (hydr)oxide surfaces. With phosphate addition, the reduction in As(Ⅴ) in the soil was inhibited at pH<5.5, whereas it was promoted at pH>5.5. Moreover, the concentration of soluble As(Ⅲ) and As(Ⅴ) in the soil solution was dramatically increased with the addition of phosphate owing to the competitive adsorption between As and phosphate. At a lower background of Ca2+, there was a higher fraction of As(Ⅲ) in the soil either with or without phosphate addition. This phenomenon might be caused by the higher bioavailability of phosphorus in soil at a lower concentration of Ca2+, which favors the dissimilatory reduction of As or iron (hydr)oxides. The results indicated that the NOM-CD model could predict the influence of pH, calcium, and phosphate on the solubility and speciation distribution of As in paddy soil and reveal its main mechanisms. Therefore, the NOM-CD model would provide the quantitative and scientific method for evaluating the risk of As in soils or other solid-water systems.

Intermolecular interactions and gel properties of composite agglomerative networks based on oppositely charged polymers: Effects of pH and ionic strength

The effects of pH and ionic strength on the intermolecular interactions and gel properties—textural and mechanical properties, water holding capacity, and color— of kidney-bean-protein-isolate–sodium-alginate (KPI-SA) composite gels were investigated. According to the zeta potentials of KPI, SA, and KPI-SA in the pH range of 2.0–7.0, pH values of 3.0, 4.0, 5.0, and 7.0 were selected as the experimental conditions. Protein solubility and ATR-FTIR analysis results indicated that the forces for the formation of KPI-SA gels were different under different conditions. Specifically, under neutral conditions (pH 7.0), hydrogen bonding was the most significant force, but when the pH (5.0) approached the isoelectric point (pI), hydrophobic interactions became dominant. Furthermore, as the pH (4.0, 3.0) became lower than the pI, electrostatic association became the main force. With an increase in Ca2+ concentration (20–80 mg/mL), the hydrophobic interactions were gradually enhanced while the electrostatic association was first enhanced and then weakened. When the pH decreased or the ionic strength increased, the KPI-SA gel network gradually formed a uniform and dense honeycomb structure, and the gel texture and mechanical and water-holding properties improved accordingly. The obtained results suggest that moderate acidification and increased ionic strength are promising conditions to produce composite gels for use in the food industry and other fields.

Unraveling context-specific mechanisms governing calcium-YAP/TAZ distinct relationships through computational modeling.

Yes-associated protein (YAP) and its homolog TAZ are transducers of several biochemical and biomechanical signals, serving to integrate multiplexed inputs from the microenvironment into higher level cellular functions such as proliferation, differentiation, apoptosis, migration, and hemostasis. Emerging evidence suggests that calcium is a key second messenger that closely connects microenvironmental input signals and YAP/TAZ regulation. However, studies that directly modulate Ca2+ have reported contradictory YAP/TAZ responses: In some studies, a reduction in Ca2+ influx increases the activity of YAP/TAZ, while in others an increase in Ca2+ influx activates YAP/TAZ. Importantly, Ca2+ and YAP/TAZ exhibit distinct spatiotemporal dynamics, making it difficult to unravel their connections from a purely experimental approach. In this study, we developed a network model of Ca2+-mediated YAP/TAZ signaling to investigate how temporal dynamics and crosstalk of signaling pathways interacting with calcium can alter YAP/TAZ response. By including six signaling modules (e.g., GPCR, IP3- Ca2+, Kinases, RhoA, F-actin, and Hippo-YAP/TAZ) that interact with calcium, we investigated both transient and steady-state cell response to Angiotensin II, Thapsigargin, and ECM stiffness stimuli. The model predicts a context-dependent relationship between calcium signaling and YAP/TAZ activation primarily mediated by PKC, DAG, CaMKII, and F-actin. Model results illustrate the role of calcium dynamics and CaMKII bistable response in switching the direction of changes in Ca2+-induced YAP/TAZ activity. Frequency-dependent YAP/TAZ response revealed the competition between upstream regulators of LATS1/2, leading to the YAP/TAZ non-monotonic response to periodic GPCR stimulation. We also identified key roles of Ca2+ and CaMKII dynamics in shaping the nonlinear relationship between cell size and YAP/TAZ activity. The model predicts Ca2+-YAP/TAZ distinct relationships in different settings consistent with experiments. The model predictions provide new insights into the underlying mechanisms responsible for the controversial Ca2+-YAP/TAZ relationship observed in experiments.

Mechanistic study of mechanical stretch induced increase in Ca2+ sensitivity of troponin C.

The Frank-Starling Law of the heart is a direct consequence of myofilament length dependent activation (LDA) whereby increased sarcomere length (SL) leads to both increased myocardial Ca2+ sensitivity and maximum force. The molecular mechanisms underlying LDA remain elusive. Since troponin complex binds Ca2+ and regulates myosin-actin interaction during muscle contraction, it has been considered the key element involved LDA. This study aims to explore the molecular mechanism underlying sarcomere LDA and to investigate the functional role of each troponin protein in the LDA regulation. A mutant troponin-I, in which the SP-region was replaced with a G-linker (cTnI-ΔSP), was constructed to study the molecular interaction between troponin-I, troponin-C, and myosin during LDA regulation. The cTnI-ΔSP was used to prevent the functional effect from crossbridge (XB) on the SL-induced Ca2+ sensitivity changes of troponin complex. The SL-induced Ca2+ sensitivity change was monitored by in situ FRET which represents the Ca2+-induced cTnC structural change. Our results show that there are no significant changes of the SL-induced pCa50 shift of troponin in the absence of strong XB, suggesting that besides the XB feedback, the LDA of thin filament may have an alternative pathway involving troponin itself. To further understand the mechanism underlying LDA, recombinant cTnT and cTnI mutants carrying an enzyme cutting site at one end of the IT arm region, respectively, were used in our study. By selectively breaking T1 and T2 of cTnT or separating the C-domain of cTnI from the N-domain, we were able to examine the mechanistic pathway of SL-stretch on the Ca2+-induced structural change of cTnC. Our results provide novel information on the molecular mechanism of how troponin-Ca2+ activation senses myocardial sarcomere stretches to promote myosin-actin interactions at the diastolic level of Ca2+.

Improvement of Selectivity of RALEX-CM Membranes via Modification by Ceria with a Functionalized Surface.

Ion exchange membranes are widely used for water treatment and ion separation by electrodialysis. One of the ways to increase the efficiency of industrial membranes is their modification with various dopants. To improve the membrane permselectivity, a simple strategy of the membrane surface modification was proposed. Heterogeneous RALEX-CM membranes were surface-modified by ceria with a phosphate-functionalized surface. Despite a decrease in ionic conductivity of the prepared composite membranes, their cation transport numbers slightly increase. Moreover, the modified membranes show a threefold increase in Ca2+/Na+ permselectivity (from 2.1 to 6.1) at low current densities.

TASK inhibition by mild acidosis increases Ca2+ oscillations to mediate pH sensing in rat carotid body chemoreceptor cells.

Severe levels of acidosis (pH < 6.8) have been shown to cause a sustained rise in cytosolic Ca2+ concentration in carotid body Type 1 (glomus) cells. To understand how physiologically relevant levels of acidosis regulate Ca2+ signaling in glomus cells, we studied the effects of small changes in extracellular pH (pHo) on the kinetics of Ca2+ oscillations. A decrease in pHo from 7.4 to 7.3 (designated mild) and 7.2 (designated moderate) acidosis produced significant increases in the frequency and amplitude of Ca2+ oscillations. These effects of acidosis on Ca2+ oscillations were not blocked by NS383 and amiloride [acid-sensing ion channel (ASIC) inhibitors]. Mild and moderate levels of acidosis, however, caused a small but significant inhibition of two-pore domain acid-sensing K+ channels (TASK) (TASK-1- and TASK-3-like channels) and depolarized the cell by 6-13 mV. Acidosis-induced increase in Ca2+ oscillations was inhibited by nifedipine (1 µM; L-type Cav inhibitor) and by TTA-P2 (20 µM; T-type Cav inhibitor). Mild inhibition of TASK activity by N-[(2,4-difluorophenyl)methyl]-2'-[[[2-(4methoxyphenyl)acetyl]amino]methyl][1,1'-biphenyl]-2-carboxamide (A1899) (0.3 µM) and 1-[1-[6-[[1,1'-biphenyl]-4-ylcarbonyl)-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidine-4-yl]-4-piperidinyl]-1-butanon (PK-THPP) (0.1 µM) increased Ca2+ oscillation frequency to levels similar to those observed with mild-moderate acidosis. Mild acidosis (pHo 7.3) and mild hypoxia (∼5%O2) produced similar levels of changes in the kinetics of Ca2+ oscillations. Block of tetraethylammonium (TEA)-sensitive Kv channels did not affect acid-induced increase in Ca2+ oscillations. Our study shows that mild and moderate levels of acidosis increase the frequency and amplitude of Ca2+ oscillations primarily by inhibition of TASK without involving ASICs, and suggests a major role of TASK for signal transduction in response to a physiological change in pHo.