Thymol improves salinity tolerance of tobacco by increasing the sodium ion efflux and enhancing the content of nitric oxide and glutathione

BACKGROUND AND OBJECTIVE

Salt stress is one of the most important abiotic stresses affecting the yield and quality of tobacco (Nicotiana tabacum). Thymol (a natural medicine) has been widely used in medical research because of its antibacterial and anti-inflammatory activities. However, the influence of thymol on the root growth of tobacco is not fully elucidated. In this study, the regulatory effects of different concentrations of thymol were investigated.

METHODOLOGY

Here, histochemical staining and biochemical methods, non-invasive micro-test technology (NMT), and qPCR assay were performed to investigate the effect of thymol and mechanism of it improving salinity tolerance in tobacco seedlings.

RESULTS

In this study, our results showed that thymol rescued root growth from salt stress by ameliorating ROS accumulation, lipid peroxidation, and cell death. Furthermore, thymol enhanced contents of NO and GSH to repress ROS accumulation, further protecting the stability of the cell membrane. And, thymol improved Na+ efflux and the expression of SOS1, HKT1, and NHX1, thus protecting the stability of Na+ and K+.

CONCLUSION

Our study confirmed the protecting effect of thymol in tobacco under salt stress, and we also identified the mechanism of it, involving dynamic regulation of antioxidant system and the maintenance of Na+ homeostasis. It can be a new method to improve salinity tolerance in plants.

Intracellular phosphate sensing and regulation of phosphate transport systems in plants

Recent research on the regulation of cellular phosphate (Pi) homeostasis in eukaryotes has collectively made substantial advances in elucidating inositol pyrophosphates (PP-InsP) as Pi signaling molecules that are perceived by the SPX (Syg1, Pho81, and Xpr1) domains residing in multiple proteins involved in Pi transport and signaling. The PP-InsP-SPX signaling module is evolutionarily conserved across eukaryotes and has been elaborately adopted in plant Pi transport and signaling systems. In this review, we have integrated these advances with prior established knowledge of Pi and PP-InsP metabolism, intracellular Pi sensing, and transcriptional responses according to the dynamics of cellular Pi status in plants. Anticipated challenges and pending questions as well as prospects are also discussed.

The emerging role of GABA as a transport regulator and physiological signal

While the proposal that γ-aminobutyric acid (GABA) acts a signal in plants is decades old, a signaling mode of action for plant GABA has been unveiled only relatively recently. Here, we review the recent research that demonstrates how GABA regulates anion transport through aluminum-activated malate transporters (ALMTs) and speculation that GABA also targets other proteins. The ALMT family of anion channels modulates multiple physiological processes in plants, with many members still to be characterized, opening up the possibility that GABA has broad regulatory roles in plants. We focus on the role of GABA in regulating pollen tube growth and stomatal pore aperture, and we speculate on its role in long-distance signaling and how it might be involved in cross talk with hormonal signals. We show that in barley (Hordeum vulgare), guard cell opening is regulated by GABA, as it is in Arabidopsis (Arabidopsis thaliana), to regulate water use efficiency, which impacts drought tolerance. We also discuss the links between glutamate and GABA in generating signals in plants, particularly related to pollen tube growth, wounding, and long-distance electrical signaling, and explore potential interactions of GABA signals with hormones, such as abscisic acid, jasmonic acid, and ethylene. We conclude by postulating that GABA encodes a signal that links plant primary metabolism to physiological status to fine tune plant responses to the environment.

Transport, functions, and interaction of calcium and manganese in plant organellar compartments

Calcium (Ca2+) and manganese (Mn2+) are essential elements for plants and have similar ionic radii and binding coordination. They are assigned specific functions within organelles, but share many transport mechanisms to cross organellar membranes. Despite their points of interaction, those elements are usually investigated and reviewed separately. This review takes them out of this isolation. It highlights our current mechanistic understanding and points to open questions of their functions, their transport, and their interplay in the endoplasmic reticulum (ER), vesicular compartments (Golgi apparatus, trans-Golgi network, pre-vacuolar compartment), vacuoles, chloroplasts, mitochondria, and peroxisomes. Complex processes demanding these cations, such as Mn2+-dependent glycosylation or systemic Ca2+ signaling, are covered in some detail if they have not been reviewed recently or if recent findings add to current models. The function of Ca2+ as signaling agent released from organelles into the cytosol and within the organelles themselves is a recurrent theme of this review, again keeping the interference by Mn2+ in mind. The involvement of organellar channels [e.g. glutamate receptor-likes (GLR), cyclic nucleotide-gated channels (CNGC), mitochondrial conductivity units (MCU), and two-pore channel1 (TPC1)], transporters (e.g. natural resistance-associated macrophage proteins (NRAMP), Ca2+ exchangers (CAX), metal tolerance proteins (MTP), and bivalent cation transporters (BICAT)], and pumps [autoinhibited Ca2+-ATPases (ACA) and ER Ca2+-ATPases (ECA)] in the import and export of organellar Ca2+ and Mn2+ is scrutinized, whereby current controversial issues are pointed out. Mechanisms in animals and yeast are taken into account where they may provide a blueprint for processes in plants, in particular, with respect to tunable molecular mechanisms of Ca2+ versus Mn2+ selectivity.

The Effectiveness in Activating M-Type K+ Current Produced by Solifenacin ([(3R)-1-azabicyclo[2.2.2]octan-3-yl] (1S)-1-phenyl-3,4-dihydro-1H-isoquinoline-2-carboxylate): Independent of Its Antimuscarinic Action

Solifenacin (Vesicare^®, SOL), known to be a member of isoquinolines, is a muscarinic antagonist that has anticholinergic effect, and it has been beneficial in treating urinary incontinence and neurogenic detrusor overactivity. However, the information regarding the effects of SOL on membrane ionic currents is largely uncertain, despite its clinically wide use in patients with those disorders. In this study, the whole-cell current recordings revealed that upon membrane depolarization in pituitary GH₃ cells, the exposure to SOL concentration-dependently increased the amplitude of M-type K⁺ current (I_K(M)) with effective EC₅₀ value of 0.34 μM. The activation time constant of I_K(M) was concurrently shortened in the SOL presence, hence yielding the K_D value of 0.55 μM based on minimal reaction scheme. As cells were exposed to SOL, the steady-state activation curve of I_K(M) was shifted along the voltage axis to the left with no change in the gating charge of the current. Upon an isosceles-triangular ramp pulse, the hysteretic area of I_K(M) was increased by adding SOL. As cells were continually exposed to SOL, further application of acetylcholine (1 μM) failed to modify SOL-stimulated I_K(M); however, subsequent addition of thyrotropin releasing hormone (TRH, 1 μM) was able to counteract SOL-induced increase in I_K(M) amplitude. In cell-attached single-channel current recordings, bath addition of SOL led to an increase in the activity of M-type K⁺ (K_M) channels with no change in the single channel conductance; the mean open time of the channel became lengthened. In whole-cell current-clamp recordings, the SOL application reduced the firing of action potentials (APs) in GH₃ cells; however, either subsequent addition of TRH or linopirdine was able to reverse SOL-mediated decrease in AP firing. In hippocampal mHippoE-14 neurons, the I_K(M) was also stimulated by adding SOL. Altogether, findings from this study disclosed for the first time the effectiveness of SOL in interacting with K_M channels and hence in stimulating I_K(M) in electrically excitable cells, and this noticeable action appears to be independent of its antagonistic activity on the canonical binding to muscarinic receptors expressed in GH₃ or mHippoE-14 cells.

Hepcidin induces intestinal calcium uptake while suppressing iron uptake in Caco-2 cells

Abnormal calcium absorption and iron overload from iron hyperabsorption can contribute to osteoporosis as found in several diseases, including hemochromatosis and thalassemia. Previous studies in thalassemic mice showed the positive effects of the iron uptake suppressor, hepcidin, on calcium transport. However, whether this effect could be replicated in other conditions is not known. Therefore, this study aimed to investigate the effects of hepcidin on iron and calcium uptake ability under physiological, iron uptake stimulation and calcium uptake suppression. To investigate the potential mechanism, effects of hepcidin on the expression of iron and calcium transporter and transport-associated protein in Caco-2 cells were also determined. Our results showed that intestinal cell iron uptake was significantly increased by ascorbic acid together with ferric ammonium citrate (FAC), but this phenomenon was suppressed by hepcidin. Interestingly, hepcidin significantly increased calcium uptake under physiological condition but not under iron uptake stimulation. While hepcidin significantly suppressed the expression of iron transporter, it had no effect on calcium transporter expression. This indicated that hepcidin-induced intestinal cell calcium uptake did not occur through the stimulation of calcium transporter expression. On the other hand, 1,25(OH)₂D₃ effectively induced intestinal cell calcium uptake, but it did not affect intestinal cell iron uptake or iron transporter expression. The 1,25(OH)₂D₃-induced intestinal cell calcium uptake was abolished by 12 mM CaCl₂; however, hepcidin could not rescue intestinal cell calcium uptake suppression by CaCl₂. Taken together, our results showed that hepcidin could effectively and concurrently induce intestinal cell calcium uptake while reducing intestinal cell iron uptake under physiological and iron uptake stimulation conditions, suggesting its therapeutic potential for inactive calcium absorption, particularly in thalassemic patients or patients who did not adequately respond to 1,25(OH)₂D₃.

Resveratrol improves the iron deficiency adaptation of Malus baccata seedlings by regulating iron absorption

BACKGROUND

Resveratrol (Res), a phytoalexin, has been widely reported to participate in plant resistance to fungal infections. However, little information is available on its role in abiotic stress, especially in iron deficiency stress. Malus baccata is widely used as apple rootstock in China, but it is sensitive to iron deficiency.

RESULTS

In this study, we investigated the role of exogenous Res in M. baccata seedings under iron deficiency stress. Results showed that applying 100 μM exogenous Res could alleviate iron deficiency stress. The seedlings treated with Res had a lower etiolation rate and higher chlorophyll content and photosynthetic rate compared with the apple seedlings without Res treatment. Exogenous Res increased the iron content in the roots and leaves by inducing the expression of MbAHA genes and improving the H+-ATPase activity. As a result, the rhizosphere pH decreased, iron solubility increased, the expression of MbFRO2 and MbIRT1 was induced, and the ferric-chelated reductase activity was enhanced to absorb large amounts of Fe2+ into the root cells under iron deficiency conditions. Moreover, exogenous Res application increased the contents of IAA, ABA, and GA3 and decreased the contents of DHZR and BL for responding to iron deficiency stress indirectly. In addition, Res functioned as an antioxidant that strengthened the activities of antioxidant enzymes and thus eliminated reactive oxygen species production induced by iron deficiency stress.

CONCLUSION

Resveratrol improves the iron deficiency adaptation of M. baccata seedlings mainly by regulating iron absorption.

Na+-Coupled Respiration and Reshaping of Extracellular Polysaccharide Layer Counteract Monensin-Induced Cation Permeability in Prevotella bryantii B14

Monensin is an ionophore for monovalent cations, which is frequently used to prevent ketosis and to enhance performance in dairy cows. Studies have shown the rumen bacteria Prevotella bryantii B₁4 being less affected by monensin. The present study aimed to reveal more information about the respective molecular mechanisms in P.bryantii, as there is still a lack of knowledge about defense mechanisms against monensin. Cell growth experiments applying increasing concentrations of monensin and incubations up to 72 h were done. Harvested cells were used for label-free quantitative proteomics, enzyme activity measurements, quantification of intracellular sodium and extracellular glucose concentrations and fluorescence microscopy. Our findings confirmed an active cell growth and fermentation activity of P.bryantii B₁4 despite monensin concentrations up to 60 µM. An elevated abundance and activity of the Na⁺-translocating NADH:quinone oxidoreductase counteracted sodium influx caused by monensin. Cell membranes and extracellular polysaccharides were highly influenced by monensin indicated by a reduced number of outer membrane proteins, an increased number of certain glucoside hydrolases and an elevated concentration of extracellular glucose. Thus, a reconstruction of extracellular polysaccharides in P.bryantii in response to monensin is proposed, which is expected to have a negative impact on the substrate binding capacities of this rumen bacterium.

Effect of a chemical dispersant (Corexit 9500A) on the structure and ion transport function of blue crab (Callinectes sapidus) gills

Chemical dispersants are commercially available mixtures of surfactants and solvents that have become important tools in the remediation of spilled oil. Given the importance of oil to the world economy, the recurring nature of spills, and the prevalence of dispersant use in remediation, there is a critical need to understand potential toxic impacts of dispersants on invertebrate and vertebrate animals. Blue crabs (Callinectes sapidus) play ecologically important roles in the environments they inhabit and support economically important fisheries along the Atlantic Coast and in the Gulf of Mexico. In studies reported here, we assessed the impact of a chemical dispersant, Corexit 9500A, on the structure and ion transport function of blue crab gills. Exposure of blue crabs to Corexit 9500A for 24 h (0-300 ppm in artificial seawater under static conditions) revealed a 24-h lethal concentration 50 (LC₅₀) estimate of 210 ppm. A histological analysis of gills from crabs exposed for 24 h to a sub-lethal concentration of Corexit 9500A (125 ppm) revealed evidence of loss or disruption of cuticle, and an increase in stained amorphous material in the hemolymph spaces of gill lamellae. Quantitative image analysis of stained gill sections revealed the area/length ratio of gill lamellae in crabs exposed to Corexit 9500A (24 h, 125 ppm), was greater than that in gill lamellae from control crabs; the results are consistent with the presence of edematous swelling in gill lamellae from dispersant-exposed crabs. Quantitative PCR was used to measure the relative abundance of transcripts encoding three ion transport proteins (Na⁺/K⁺ ATPase, plasma membrane Ca²⁺ ATPase (PMCA), and sarcoplasmic reticulum/endoplasmic reticulum Ca²⁺ ATPase (SERCA)) in gills from Corexit-exposed and control crabs. In general, the abundance of transcripts encoding each ion transport protein was lower in gills from dispersant-exposed crabs than in gills from control crabs. The combined results are consistent with the hypothesis that 24-h exposure of blue crabs to a sublethal concentration of Corexit 9500A impacts both the structure and ion transport function of gills.

Ivacaftor partially corrects airway inflammation in a humanized G551D rat

Animal models have been highly informative for understanding the pathogenesis and progression of cystic fibrosis (CF) lung disease. In particular, the CF rat models recently developed have addressed mechanistic causes of the airway mucus defect characteristic of CF, and how these may change when cystic fibrosis transmembrane conductance regulator (CFTR) activity is restored using new modulator therapies. We hypothesized that inflammatory changes to the airway would develop spontaneously and progressively, and that these changes would be resolved with modulator therapy. To test this, we used a humanized-CFTR rat expressing the G551D variant that responds to the CFTR modulator ivacaftor. Markers typically found in the CF lung were assessed, including neutrophil influx, small airway histopathology, and inflammatory cytokine concentration. Young hG551D rats did not express inflammatory cytokines at baseline but did upregulate these in response to inflammatory trigger. As the hG551D rats aged, histopathology worsened, accompanied by neutrophil influx into the airway and increasing concentrations of TNF-α, IL-1α, and IL-6 in the airways. Ivacaftor administration reduced concentrations of these cytokines when administered to the rats at baseline but was less effective in the rats that had also received inflammatory stimulus. Therefore, we conclude that administration of ivacaftor resulted in an incomplete resolution of inflammation when rats received an external trigger, suggesting that CFTR activation may not be enough to resolve inflammation in the lungs of patients with CF.

Antidiabetic and Renoprotective Effects of Coffea arabica Pulp Aqueous Extract through Preserving Organic Cation Transport System Mediated Oxidative Stress Pathway in Experimental Type 2 Diabetic Rats

Coffea arabica pulp (CP) is a by-product of coffee processing. CP contains polyphenols that have exhibited beneficial effects, including antioxidant and lipid-lowering effects, as well as enhanced insulin sensitivity, in in vitro and in vivo models. How polyphenols, as found in CP aqueous extract (CPE), affect type 2 diabetes (T2D) has not been investigated. Thus, the present study examined the potential antidiabetic, antioxidant, and renoprotective effects of CPE-rich polyphenols, using an experimental model of T2D in rats induced by a high-fat diet and a single low dose of streptozotocin. The T2D rats received either 1000 mg/kg body weight (BW) of CPE, 30 mg/kg BW of metformin (Met), or a combination treatment (CPE + Met) for 3 months. Plasma parameters, kidney morphology and function, and renal organic transport were determined. Significant hyperglycemia, hypertriglyceridemia, insulin resistance, increased renal lipid content and lipid peroxidation, and morphological kidney changes related to T2D were restored by both CPE and CPE + Met treatments. Additionally, the renal uptake of organic cation, ³H-1-methyl-4-phenylpyridinium (MPP⁺), was reduced in T2D, while transport was restored by CPE and CPE + Met, through an up-regulation of antioxidant genes and protein kinase Cα deactivation. Thus, CPE has antidiabetic and antioxidant effects that potentially ameliorate kidney function in T2D by preserving renal organic cation transport through an oxidative stress pathway.

Proton Transport in Cancer Cells: The Role of Carbonic Anhydrases

Intra- and extracellular pH regulation is a pivotal function of all cells and tissues. Net outward transport of H⁺ is a prerequisite for normal physiological function, since a number of intracellular processes, such as metabolism and energy supply, produce acid. In tumor tissues, distorted pH regulation results in extracellular acidification and the formation of a hostile environment in which cancer cells can outcompete healthy local host cells. Cancer cells employ a variety of H⁺/HCO₃⁻-coupled transporters in combination with intra- and extracellular carbonic anhydrase (CA) isoforms, to alter intra- and extracellular pH to values that promote tumor progression. Many of the transporters could closely associate to CAs, to form a protein complex coined “transport metabolon”. While transport metabolons built with HCO₃⁻-coupled transporters require CA catalytic activity, transport metabolons with monocarboxylate transporters (MCTs) operate independently from CA catalytic function. In this article, we assess some of the processes and functions of CAs for tumor pH regulation and discuss the role of intra- and extracellular pH regulation for cancer pathogenesis and therapeutic intervention.

Ca2+-ATPase Molecules as a Calcium-Sensitive Membrane-Endoskeleton of Sarcoplasmic Reticulum

The Ca²⁺-transport ATPase of sarcoplasmic reticulum (SR) is an integral, transmembrane protein. It sequesters cytoplasmic calcium ions released from SR during muscle contraction, and causes muscle relaxation. Based on negative staining and transmission electron microscopy of SR vesicles isolated from rabbit skeletal muscle, we propose that the ATPase molecules might also be a calcium-sensitive membrane-endoskeleton. Under conditions when the ATPase molecules scarcely transport Ca²⁺, i.e., in the presence of ATP and ≤ 0.9 nM Ca²⁺, some of the ATPase particles on the SR vesicle surface gathered to form tetramers. The tetramers crystallized into a cylindrical helical array in some vesicles and probably resulted in the elongated protrusion that extended from some round SRs. As the Ca²⁺ concentration increased to 0.2 µM, i.e., under conditions when the transporter molecules fully carry out their activities, the ATPase crystal arrays disappeared, but the SR protrusions remained. In the absence of ATP, almost all of the SR vesicles were round and no crystal arrays were evident, independent of the calcium concentration. This suggests that ATP induced crystallization at low Ca²⁺ concentrations. From the observed morphological changes, the role of the proposed ATPase membrane-endoskeleton is discussed in the context of calcium regulation during muscle contraction.

Recording Electrical Currents across the Plasma Membrane of Mammalian Sperm Cells

Recording of the electrical activity from one of the smallest cells of a mammalian organism- a sperm cell- has been a challenging task for electrophysiologists for many decades. The method known as "spermatozoan patch clamp" was introduced in 2006. It has enabled the direct recording of ion channel activity in whole-cell and cell-attached configurations and has been instrumental in describing sperm cell physiology and the molecular identity of various calcium, potassium, sodium, chloride, and proton ion channels. However, recording from single spermatozoa requires advanced skills and training in electrophysiology. This detailed protocol summarizes the step-by-step procedure and highlights several 'tricks-of-the-trade' in order to make it available to anyone who wishes to explore the fascinating physiology of the sperm cell. Specifically, the protocol describes recording from human and murine sperm cells but can be adapted to essentially any mammalian sperm cell of any species. The protocol covers important details of the application of this technique, such as isolation of sperm cells, selection of reagents and equipment, immobilization of the highly motile cells, formation of the tight (Gigaohm) seal between a recording electrode and the plasma membrane of the sperm cells, transition into the whole-spermatozoan mode (also known as break-in), and exemplary recordings of the sperm cell calcium ion channel, CatSper, from six mammalian species. The advantages and limitations of the sperm patch clamp method, as well as the most critical steps, are discussed.

TRPM4 in Cancer-A New Potential Drug Target

Transient receptor potential melastatin 4 (TRPM4) is widely expressed in various organs and associated with cardiovascular and immune diseases. Lately, the interest in studies on TRPM4 in cancer has increased. Thus far, TRPM4 has been investigated in diffuse large B-cell lymphoma, prostate, colorectal, liver, breast, urinary bladder, cervical, and endometrial cancer. In several types of cancer TRPM4 is overexpressed and contributes to cancer hallmark functions such as increased proliferation and migration and cell cycle shift. Hence, TRPM4 is a potential prognostic cancer marker and a promising anticancer drug target candidate. Currently, the underlying mechanism by which TRPM4 contributes to cancer hallmark functions is under investigation. TRPM4 is a Ca²⁺-activated monovalent cation channel, and its ion conductivity can decrease intracellular Ca²⁺ signaling. Furthermore, TRPM4 can interact with different partner proteins. However, the lack of potent and specific TRPM4 inhibitors has delayed the investigations of TRPM4. In this review, we summarize the potential mechanisms of action and discuss new small molecule TRPM4 inhibitors, as well as the TRPM4 antibody, M4P. Additionally, we provide an overview of TRPM4 in human cancer and discuss TRPM4 as a diagnostic marker and anticancer drug target.

Exogenous Strigolactones alleviate KCl stress by regulating photosynthesis, ROS migration and ion transport in Malus hupehensis Rehd

AIMS

In recent years, the application of large amounts of potash fertilizer in apple orchards leads to worsening KCl stress. Strigolactone (SL), as a novel phytohormone, reportedly participates in plant tolerance to NaCl and drought stresses. However, the underlying mechanism and the effects of exogenous SL on the KCl stress of apple seedlings remain unclear.

METHODS

We sprayed different concentrations of exogenous SL on Malus hupehensis Rehd. under KCl stress and measured the physiological indexes like, photosynthetic parameter, content of ROS, osmolytes and mineral element. In addition, the expressions of KCl-responding genes and SL-signaling genes were also detected and analyzed.

RESULTS

Application of exogenous SL protected the chlorophyll and maintained the photosynthetic rate of apple seedlings under KCl stress. Exogenous SL strengthened the enzyme activities of peroxidase and catalase, thereby eliminating reactive oxygen species production induced by KCl stress, promoting the accumulation of proline, and maintaining osmotic balance. Exogenous SL expelled K⁺ outside of the cytoplasm and compartmentalized K⁺ into the vacuole, increased the contents of Na⁺, Mg²⁺, Fe²⁺, and Mn²⁺ in the cytoplasm to maintain the ion homeostasis under KCl stress.

CONCLUSIONS

Exogenous SL can regulate photosynthesis, ROS migration and ion transport in apple seedlings to alleviate KCl stress.

Effectiveness of Columbianadin, a Bioactive Coumarin Derivative, in Perturbing Transient and Persistent INa

Columbianadin (CBN) is a bioactive coumarin-type compound with various biological activities. However, the action of CBN on the ionic mechanism remains largely uncertain, albeit it was reported to inhibit voltage-gated Ca²⁺ current or to modulate TRP-channel activity. In this study, whole-cell patch-clamp current recordings were undertaken to explore the modifications of CBN or other related compounds on ionic currents in excitable cells (e.g., pituitary GH₃ cells and HL-1 atrial cardiomyocytes). GH₃-cell exposure to CBN differentially decreased peak or late component of voltage-gated Na⁺ current (I_Na) with effective IC₅₀ of 14.7 or 2.8 µM, respectively. The inactivation time course of I_Na activated by short depolarization became fastened in the presence of CBN with estimated K_D value of 3.15 µM. The peak I_Na diminished by 10 µM CBN was further suppressed by subsequent addition of either sesamin (10 µM), ranolazine (10 µM), or tetrodotoxin (1 µM), but it was reversed by 10 µM tefluthrin (Tef); however, further application of 10 µM nimodipine failed to alter CBN-mediated inhibition of I_Na. CBN (10 µM) shifted the midpoint of inactivation curve of I_Na to the leftward direction. The CBN-mediated inhibition of peak I_Na exhibited tonic and use-dependent characteristics. Using triangular ramp pulse, the hysteresis of persistent I_Na enhanced by Tef was noticed, and the behavior was attenuated by subsequent addition of CBN. The delayed-rectifier or erg-mediated K⁺ current was mildly inhibited by 10 µM CBN, while it also slightly inhibited the amplitude of hyperpolarization-activated cation current. In HL-1 atrial cardiomyocytes, CBN inhibited peak I_Na and raised the inactivation rate of the current; moreover, further application of 10 µM Tef attenuated CBN-mediated decrease in I_Na. Collectively, this study provides an important yet unidentified finding revealing that CBN modifies I_Na in electrically excitable cells.

Stiff-Stilbene Photoswitches: From Fundamental Studies to Emergent Applications

Stiff-stilbene, a sterically restricted fused ring analogue of stilbene, has been regularly used as a model compound in theoretical studies of stilbene photoisomerization. Lately, owing to its excellent photoswitching properties, it is increasingly being applied to reversibly control the properties and function of chemical as well as biological systems. Stiff-stilbene photoswitches possess a number of advantageous properties including a high quantum yield for photoisomerization and a high thermal stability. Furthermore, they undergo a large geometrical change upon isomerization and their synthesis is straightforward. Herein, we provide an overview of the basic properties of stiff-stilbene and of recent applications in supramolecular chemistry, catalysis, and biological systems.

Calcium Export from Neurons and Multi-Kinase Signaling Cascades Contribute to Ouabain Neuroprotection in Hyperhomocysteinemia

Pathological homocysteine (HCY) accumulation in the human plasma, known as hyperhomocysteinemia, exacerbates neurodegenerative diseases because, in the brain, this amino acid acts as a persistent N-methyl-d-aspartate receptor agonist. We studied the effects of 0.1–1 nM ouabain on intracellular Ca²⁺ signaling, mitochondrial inner membrane voltage (φ_mit), and cell viability in primary cultures of rat cortical neurons in glutamate and HCY neurotoxic insults. In addition, apoptosis-related protein expression and the involvement of some kinases in ouabain-mediated effects were evaluated. In short insults, HCY was less potent than glutamate as a neurotoxic agent and induced a 20% loss of φ_mit, whereas glutamate caused a 70% decrease of this value. Subnanomolar ouabain exhibited immediate and postponed neuroprotective effects on neurons. (1) Ouabain rapidly reduced the Ca²⁺ overload of neurons and loss of φ_mit evoked by glutamate and HCY that rescued neurons in short insults. (2) In prolonged 24 h excitotoxic insults, ouabain prevented neuronal apoptosis, triggering proteinkinase A and proteinkinase C dependent intracellular neuroprotective cascades for HCY, but not for glutamate. We, therefore, demonstrated here the role of PKC and PKA involving pathways in neuronal survival caused by ouabain in hyperhomocysteinemia, which suggests existence of different appropriate pharmacological treatment for hyperhomocysteinemia and glutamate excitotoxicity.

Quinine-Based Semisynthetic Ion Transporters with Potential Antiproliferative Activities

Synthetic ion transporters have attracted tremendous attention for their therapeutic potential against various ion-transport-related diseases, including cancer. Inspired by the structure and biological activities of natural products, we synthesized a small series of squaramide and thiourea derivatives of quinine and investigated their ion transport activities. The involvement of a quinuclidine moiety for the cooperative interactions of Cl^- and H⁺ ions with the thiourea or squaramide moiety resulted in an effectual transport of these ions across membranes. The interference of ionic equilibrium by the potent Cl^- ion carrier selectively induced cancer cell death by endorsing caspase-arbitrated apoptosis. In vivo assessment of the potent ionophore showed an efficient reduction in tumor growth with negligible immunotoxicity to other organs.

NEK7 mediated assembly and activation of NLRP3 inflammasome downstream of potassium efflux in ventilator-induced lung injury

Disordered immune regulation and persistent inflammatory damage are the key mechanisms of ventilator-induced lung injury (VILI). NLR family pyrin domain containing 3 (NLRP3) inflammasome activation causes VILI by mediating the formation of inflammatory mediators and infiltration of inflammatory cells, increasing pulmonary capillary membrane permeability, which leads to pulmonary edema and lung tissue damage. What mediates activation of NLRP3 inflammasome in VILI? In this study, we constructed an in vitro cyclic stretch (CS)-stimulated mouse lung epithelial (MLE-12) cell model that was transfected with NIMA-related kinase 7 (NEK7) small interfering RNA (siRNA) or scramble siRNA (sc siRNA) and pretreated with or without glibenclamide (glb). We also established a VILI mouse model, which was pretreated with glibenclamide or oridonin (Ori). Our goal was to investigate the regulatory effects of NEK7 on NLRP3 inflammasome activation and the anti-inflammatory effects of glibenclamide and oridonin on VILI. Mechanical stretch exaggerated the interaction between NEK7 and NLRP3, leading to assembly and activation of NLRP3 inflammasome downstream of potassium efflux. NEK7 depletion and treatment with glibenclamide or oridonin exerted anti-inflammatory effects that alleviated VILI by blocking the interaction between NEK7 and NLRP3, inhibiting NLRP3 inflammasome activation. NEK7 is a vital mediator of NLRP3 inflammasome activation, and glibenclamide or oridonin may be candidates for the development of new therapeutics against VILI driven by the interaction between NEK7 and NLRP3.

It's all about the fluxes: Temperature influences ion transport and toxicity in aquatic insects

Many freshwater ecosystems are becoming saltier and/or warmer, but our understanding of how these factors interact and affect the physiology and life history outcomes of most aquatic species remain unknown. We hypothesize that temperature modulates ion transport rates. Since ion transport is energetically expensive, increases in salinity and/or temperature may influence ion flux rates and ultimately, organismal performance. Radiotracer (²²Na⁺, ³⁵SO₄^-2, and ⁴⁵Ca²⁺) experiments with lab-reared mayflies (N. triangulifer) and other field-collected insects showed that increasing temperature generally increased ion transport rates. For example, increasing temperature from 15 °C to 25 °C, increased ²²Na⁺ uptake rates by two-fold (p < 0.0001) and ³⁵SO₄^-2 uptake rates by four-fold (p < 0.0001) in the caddisfly, Hydropsyche sparna. Smaller changes in ²²Na⁺ and ³⁵SO₄^-2 uptake rates were observed in the mayflies, Isonychia sayi and Maccaffertium sp., suggesting species-specific differences in the thermal sensitivity of ion transport. Finally, we demonstrated that the toxicity of SO₄ was influenced by temperature profoundly in a 96-h bioassay. Under the saltiest conditions (1500 mg L^-1 SO₄), mayfly survival was 78 % at 15 °C, but only 44 % at 25 °C (p < 0.0036). Conceivably, the energetic cost of osmoregulation in warmer, saltier environments may cause significant major ion toxicity in certain freshwater insects.

Inhibitory Effective Perturbations of Cilobradine (DK-AH269), A Blocker of HCN Channels, on the Amplitude and Gating of Both Hyperpolarization-Activated Cation and Delayed-Rectifier Potassium Currents

Cilobradine (CIL, DK-AH269), an inhibitor of hyperpolarization-activated cation current (I_h), has been observed to possess pro-arrhythmic properties. Whether and how CIL is capable of perturbing different types of membrane ionic currents existing in electrically excitable cells, however, is incompletely understood. In this study, we intended to examine possible modifications by it or other structurally similar compounds of ionic currents in pituitary tumor (GH₃) cells and in heart-derived H9c2 cells. The standard whole-cell voltage-clamp technique was performed to examine the effect of CIL on ionic currents. GH₃-cell exposure to CIL suppressed the density of hyperpolarization-evoked I_h in a concentration-dependent manner with an effective IC₅₀ of 3.38 μM. Apart from its increase in the activation time constant of I_h during long-lasting hyperpolarization, the presence of CIL (3 μM) distinctly shifted the steady-state activation curve of I_h triggered by a 2-s conditioning pulse to a hyperpolarizing direction by 10 mV. As the impedance-frequency relation of I_h was studied, its presence raised the impedance magnitude at the resonance frequency induced by chirp voltage. CIL also suppressed delayed-rectifier K⁺ current (I_K(DR)) followed by the accelerated inactivation time course of this current, with effective IC₅₀ (measured at late I_K(DR)) or K_D value of 3.54 or 3.77 μM, respectively. As the CIL concentration increased 1 to 3 μM, the inactivation curve of I_K(DR) elicited by 1- or 10-s conditioning pulses was shifted to a hyperpolarizing potential by approximately 10 mV, and the recovery of I_K(DR) inactivation during its presence was prolonged. The peak Na⁺ current (I_Na) during brief depolarization was resistant to being sensitive to the presence of CIL, yet to be either decreased by subsequent addition of A-803467 or enhanced by that of tefluthrin. In cardiac H9c2 cells, unlike the CIL effect, the addition of either ivabradine or zatebradine mildly led to a lowering in I_K(DR) amplitude with no conceivable change in the inactivation time course of the current. Taken together, the compound like CIL, which was tailored to block hyperpolarization-activated cation (HCN) channels effectively, was also capable of altering the amplitude and gating of I_K(DR), thereby influencing the functional activities of electrically excitable cells, such as GH₃ cells.

Differentiation of human colon tissue in culture: Effects of calcium on trans-epithelial electrical resistance and tissue cohesive properties

Background and aims

Human colonoid cultures maintained under low-calcium (0.25 mM) conditions undergo differentiation spontaneously and, concomitantly, express a high level of tight junction proteins, but not desmosomal proteins. When calcium is included to a final concentration of 1.5–3.0 mM (provided either as a single agent or as a combination of calcium and additional minerals), there is little change in tight junction protein expression but a strong up-regulation of desmosomal proteins and an increase in desmosome formation. The aim of this study was to assess the functional consequences of calcium-mediated differences in barrier protein expression.

Methods

Human colonoid-derived epithelial cells were interrogated in transwell culture under low- or high-calcium conditions for monolayer integrity and ion permeability by measuring trans-epithelial electrical resistance (TEER) across the confluent monolayer. Colonoid cohesiveness was assessed in parallel.

Results

TEER values were high in the low-calcium environment but increased in response to calcium. In addition, colonoid cohesiveness increased substantially with calcium supplementation. In both assays, the response to multi-mineral intervention was greater than the response to calcium alone. Consistent with these findings, several components of tight junctions were expressed at 0.25 mM calcium but these did not increase substantially with supplementation. Cadherin-17 and desmoglein-2, in contrast, were weakly-expressed under low calcium conditions but increased with intervention.

Conclusions

These findings indicate that low ambient calcium levels are sufficient to support the formation of a permeability barrier in the colonic epithelium. Higher calcium levels promote tissue cohesion and enhance barrier function. These findings may help explain how an adequate calcium intake contributes to colonic health by improving barrier function, even though there is little change in colonic histological features over a wide range of calcium intake levels.

Genetic Up-Regulation or Pharmacological Activation of the Na+/Ca2+ Exchanger 1 (NCX1) Enhances Hippocampal-Dependent Contextual and Spatial Learning and Memory

The Na⁺/Ca²⁺ exchanger 1 (NCX1) participates in the maintenance of neuronal Na⁺ and Ca²⁺ homeostasis, and it is highly expressed at synapse level of some brain areas involved in learning and memory processes, including the hippocampus, cortex, and amygdala. Furthermore, NCX1 increases Akt1 phosphorylation and enhances glutamate-mediated Ca²⁺ influx during depolarization in hippocampal and cortical neurons, two processes involved in learning and memory mechanisms. We investigated whether the modulation of NCX1 expression/activity might influence learning and memory processes. To this aim, we used a knock-in mouse overexpressing NCX1 in hippocampal, cortical, and amygdala neurons (ncx1.4^over) and a newly synthesized selective NCX1 stimulating compound, named CN-PYB2. Both ncx1.4^over and CN-PYB2-treated mice showed an amelioration in spatial learning performance in Barnes maze task, and in context-dependent memory consolidation after trace fear conditioning. On the other hand, these mice showed no improvement in novel object recognition task which is mainly dependent on non-spatial memory and displayed an increase in the active phosphorylated CaMKIIα levels in the hippocampus. Interestingly, both of these mice showed an increased level of context-dependent anxiety.Altogether, these results demonstrate that neuronal NCX1 participates in spatial-dependent hippocampal learning and memory processes.

Enhancing neuronal chloride extrusion rescues α2/α3 GABAA-mediated analgesia in neuropathic pain

Spinal disinhibition has been hypothesized to underlie pain hypersensitivity in neuropathic pain. Apparently contradictory mechanisms have been reported, raising questions on the best target to produce analgesia. Here, we show that nerve injury is associated with a reduction in the number of inhibitory synapses in the spinal dorsal horn. Paradoxically, this is accompanied by a BDNF-TrkB-mediated upregulation of synaptic GABAARs and by an α1-to-α2GABAAR subunit switch, providing a mechanistic rationale for the analgesic action of the α2,3GABAAR benzodiazepine-site ligand L838,417 after nerve injury. Yet, we demonstrate that impaired Cl- extrusion underlies the failure of L838,417 to induce analgesia at high doses due to a resulting collapse in Cl- gradient, dramatically limiting the benzodiazepine therapeutic window. In turn, enhancing KCC2 activity not only potentiated L838,417-induced analgesia, it rescued its analgesic potential at high doses, revealing a novel strategy for analgesia in pathological pain, by combined targeting of the appropriate GABAAR-subtypes and restoring Cl- homeostasis.

Mechanisms of transport of H+, Na+ and K+, across the distal gastric caecum of larval Aedes aegypti

Measured changes in ion fluxes, transepithelial potential (TEP) and basolateral membrane potential (V_b) in response to ion transporter inhibitors were used to assess the mechanisms of transport of H⁺, Na⁺ and K⁺, across the distal gastric caecum of larval Aedes aegypti, a vector of yellow fever. Preparations were stimulated with 5-hydroxytryptamine (5-HT, 10^-6 M) in order to maintain stable rates of H⁺, Na⁺, and K⁺ transport across the distal caecum. Transepithelial potential (TEP), basolateral membrane potential (V_b), and H⁺, Na⁺ and K⁺ fluxes all declined after the addition of a vacuolar-type H⁺-ATPase (VA) inhibitor, n-ethlymaleimide (NEM), consistent with a primary role for VA in energizing ion transport across the distal gastric caecum. Amiloride also inhibited H⁺, Na⁺, and K⁺ fluxes, consistent with an apically expressed VA that is coupled to a cation:H⁺ antiporter (AeNHE8), analogous to the coupling of apical VA and cation:nH⁺ antiporter in Malpighian tubules. A working model of transport of H⁺, Na⁺ and K⁺ across the distal gastric caecum proposes that coupling of VA and AeNHE8 in the apical membrane leads to the removal of intracellular Na⁺ or K⁺, thus creating favourable ion gradients to promote the activity of two transporters in the basal membrane, cation:H⁺ antiporter (AeNHE3) and a bumetanide-sensitive cation chloride cotransporter (CCC).

Cytosolic GABA inhibits anion transport by wheat ALMT1

Anion transport by aluminium-activated malate transporter (ALMT) proteins is negatively regulated by gamma-aminobutyric acid (GABA), which increases in concentration during stress. Here, the interaction between GABA and wheat (Triticum aestivum, Ta) TaALMT1 heterologously-expressed in Xenopus laevis oocytes was investigated. GABA inhibited anion transport by TaALMT1 in membrane patches from the cytosolic, not extracellular membrane face, via a reduction in open probability (NP_open ), not an inhibition of channel current magnitude. TaALMT1 currents in patches frequently exhibited rundown with complete removal of cytosolic factors, but were partially sustained by protein kinase C dependent phosphorylation. When applied to whole oocytes a GABA-analogue-BODIPY conjugate inhibited TaALMT1 anion currents from the cytoplasmic face only, whereas free GABA inhibited from both the inside and outside consistent with GABA traversing the TaALMT1 pore then acting from the inside. We propose GABA does not competitively inhibit ALMT conductance through the same pore but rather leads to an allosteric effect, reducing anion channel opening frequency. Across plants GABA is a conserved regulator of anion transport via ALMTs - a family with numerous physiological roles beyond Al³⁺ tolerance. Our data suggests that a GABA-ALMT interaction from the cytosolic face has the potential to form part of a novel plant signalling pathway.

Evidence for the Capability of Roxadustat (FG-4592), an Oral HIF Prolyl-Hydroxylase Inhibitor, to Perturb Membrane Ionic Currents: An Unidentified yet Important Action

Roxadustat (FG-4592), an analog of 2-oxoglutarate, is an orally-administered, heterocyclic small molecule known to be an inhibitor of hypoxia inducible factor (HIF) prolyl hydroxylase. However, none of the studies have thus far thoroughly investigated its possible perturbations on membrane ion currents in endocrine or heart cells. In our studies, the whole-cell current recordings of the patch-clamp technique showed that the presence of roxadustat effectively and differentially suppressed the peak and late components of I_K(DR) amplitude in response to membrane depolarization in pituitary tumor (GH₃) cells with an IC₅₀ value of 5.71 and 1.32 μM, respectively. The current inactivation of I_K(DR) elicited by 10-sec membrane depolarization became raised in the presence of roxadustatt. When cells were exposed to either CoCl₂ or deferoxamine (DFO), the I_K(DR) elicited by membrane depolarization was not modified; however, nonactin, a K⁺-selective ionophore, in continued presence of roxadustat, attenuated roxadustat-mediated inhibition of the amplitude. The steady-state inactivation of I_K(DR) could be constructed in the presence of roxadustat. Recovery of I_K(DR) block by roxadustat (3 and 10 μM) could be fitted by a single exponential with 382 and 523 msec, respectively. The roxadustat addition slightly suppressed erg-mediated K⁺ or hyperpolarization-activated cation currents. This drug also decreased the peak amplitude of voltage-gated Na⁺ current with a slowing in inactivation rate of the current. Likewise, in H9c2 heart-derived cells, the addition of roxadustat suppressed I_K(DR) amplitude in combination with the shortening in inactivation time course of the current. In high glucose-treated H9c2 cells, roxadustat-mediated inhibition of I_K(DR) remained unchanged. Collectively, despite its suppression of HIF prolyl hydroxylase, inhibitory actions of roxadustat on different types of ionic currents possibly in a non-genomic fashion might provide another yet unidentified mechanism through which cellular functions are seriously perturbed, if similar findings occur in vivo.

CFTR processing, trafficking and interactions

Mutations associated with cystic fibrosis (CF) have complex effects on the cystic fibrosis transmembrane conductance regulator (CFTR) protein. The most common CF mutation, F508del, disrupts the processing to and stability at the plasma membrane and function as a Cl^- channel. CFTR is surrounded by a dynamic network of interacting components, referred to as the CFTR Functional Landscape, that impact its synthesis, folding, stability, trafficking and function. CFTR interacting proteins can be manipulated by functional genomic approaches to rescue the trafficking and functional defects characteristic of CF. Here we review recent efforts to elucidate the impact of genetic variation on the ability of the nascent CFTR polypeptide to interact with the proteostatic environment. We also provide an overview of how specific components of this protein network can be modulated to rescue the trafficking and functional defects associated with the F508del variant of CFTR. The identification of novel proteins playing key roles in the processing of CFTR could pave the way for their use as novel therapeutic targets to provide synergistic correction of mutant CFTR for the greater benefit of individuals with CF.

The effects of soil phosphorus and zinc availability on plant responses to mycorrhizal fungi: a physiological and molecular assessment

The positive effects of arbuscular mycorrhizal fungi (AMF) have been demonstrated for plant biomass, and zinc (Zn) and phosphorus (P) uptake, under soil nutrient deficiency. Additionally, a number of Zn and P transporter genes are affected by mycorrhizal colonisation or implicated in the mycorrhizal pathway of uptake. However, a comprehensive study of plant physiology and gene expression simultaneously, remains to be undertaken. Medicago truncatula was grown at different soil P and Zn availabilities, with or without inoculation of Rhizophagus irregularis. Measures of biomass, shoot elemental concentrations, mycorrhizal colonisation, and expression of Zn transporter (ZIP) and phosphate transporter (PT) genes in the roots, were taken. Mycorrhizal plants had a greater tolerance of both P and Zn soil deficiency; there was also evidence of AMF protecting plants against excessive Zn accumulation at high soil Zn. The expression of all PT genes was interactive with both P availability and mycorrhizal colonisation. MtZIP5 expression was induced both by AMF and soil Zn deficiency, while MtZIP2 was down-regulated in mycorrhizal plants, and up-regulated with increasing soil Zn concentration. These findings provide the first comprehensive physiological and molecular picture of plant-mycorrhizal fungal symbiosis with regard to soil P and Zn availability. Mycorrhizal fungi conferred tolerance to soil Zn and P deficiency and this could be linked to the induction of the ZIP transporter gene MtZIP5, and the PT gene MtPT4.

Gadolinium inhibits cadmium transport by blocking non-selective cation channels in rice seedlings

Non-selective cation channels (NSCCs) play important roles in uptake of heavy metals in plants. However, little information is available concerning the contribution of NSCCs to cadmium (Cd) transport in rice seedlings. Results from the hydroponic experiment showed that the inhibition of 2.7 μM Cd on the development of rice roots was alleviated by adding 0.1 mM gadolinium (Gd) in nutrient solution, companied by reduction of Cd content by 55.3% in roots and by 45.0% in shoots. Inhibition of Gd on Cd accumulation in cytoplasm fraction (F3) was much greater than that in cell walls (F1) and organelles (F2) in roots. After increasing concentrations of Mn and Zn in nutrient solution, adding 0.1 mM Gd resulted in reductions in Cd content by 89.1%, in micronutrients by 54.9% and in macronutrients by 5.4% in roots, respectively. Cd stress resulted in significant increase of PC_2∼4 and free amino acids, but decrease of V-ATPase activity by 32.3% in roots. These results indicate that NSCCs make a great contribution to uptake of Cd in rice seedlings and opportunities for Cd to be transported by NSCCs can be efficiently reduced by blocking NSCCs and/or increasing essential microelements like Mn and Zn.

Tspan18 is a novel regulator of the Ca2+ channel Orai1 and von Willebrand factor release in endothelial cells

Ca2+ entry via Orai1 store-operated Ca2+ channels in the plasma membrane is critical to cell function, and Orai1 loss causes severe immunodeficiency and developmental defects. The tetraspanins are a superfamily of transmembrane proteins that interact with specific 'partner proteins' and regulate their trafficking and clustering. The aim of this study was to functionally characterize tetraspanin Tspan18. We show that Tspan18 is expressed by endothelial cells at several-fold higher levels than most other cell types analyzed. Tspan18-knockdown primary human umbilical vein endothelial cells have 55-70% decreased Ca2+ mobilization upon stimulation with the inflammatory mediators thrombin or histamine, similar to Orai1-knockdown. Tspan18 interacts with Orai1, and Orai1 cell surface localization is reduced by 70% in Tspan18-knockdown endothelial cells. Tspan18 overexpression in lymphocyte model cell lines induces 20-fold activation of Ca2+ -responsive nuclear factor of activated T cell (NFAT) signaling, in an Orai1-dependent manner. Tspan18-knockout mice are viable. They lose on average 6-fold more blood in a tail-bleed assay. This is due to Tspan18 deficiency in non-hematopoietic cells, as assessed using chimeric mice. Tspan18-knockout mice have 60% reduced thrombus size in a deep vein thrombosis model, and 50% reduced platelet deposition in the microcirculation following myocardial ischemia-reperfusion injury. Histamine- or thrombin-induced von Willebrand factor release from endothelial cells is reduced by 90% following Tspan18-knockdown, and histamine-induced increase of plasma von Willebrand factor is reduced by 45% in Tspan18-knockout mice. These findings identify Tspan18 as a novel regulator of endothelial cell Orai1/Ca2+ signaling and von Willebrand factor release in response to inflammatory stimuli.

Sigma-1 Receptor Agonist Amitriptyline Inhibits Store-Dependent Ca2+ Entry in Macrophages

Using Fura-2AM microfluorimetry, we have shown for the first time that sigma-1 receptor agonist-tricyclic antidepressant amitriptyline-significantly inhibits store-dependent Ca2+ entry, induced by endoplasmic Ca2+-ATPase inhibitors thapsigargin and cyclopiazonic acid, in rat peritoneal macrophages. The results suggest a possible involvement of sigma-1 receptors in the regulation of store-dependent Ca2+ entry in macrophages.

Molecular basis of PIP2-dependent regulation of the Ca2+-activated chloride channel TMEM16A

The calcium-activated chloride channel (CaCC) TMEM16A plays crucial roles in regulating neuronal excitability, smooth muscle contraction, fluid secretion and gut motility. While opening of TMEM16A requires binding of intracellular Ca2+, prolonged Ca2+-dependent activation results in channel desensitization or rundown, the mechanism of which is unclear. Here we show that phosphatidylinositol (4,5)-bisphosphate (PIP2) regulates TMEM16A channel activation and desensitization via binding to a putative binding site at the cytosolic interface of transmembrane segments (TMs) 3-5. We further demonstrate that the ion-conducting pore of TMEM16A is constituted of two functionally distinct modules: a Ca2+-binding module formed by TMs 6-8 and a PIP2-binding regulatory module formed by TMs 3-5, which mediate channel activation and desensitization, respectively. PIP2 dissociation from the regulatory module results in ion-conducting pore collapse and subsequent channel desensitization. Our findings thus provide key insights into the mechanistic understanding of TMEM16 channel gating and lipid-dependent regulation.

Molecular and electrophysiological characterization of anion transport in Arabidopsis thaliana pollen reveals regulatory roles for pH, Ca2+ and GABA

We investigated the molecular basis and physiological implications of anion transport during pollen tube (PT) growth in Arabidopsis thaliana (Col-0). Patch-clamp whole-cell configuration analysis of pollen grain protoplasts revealed three subpopulations of anionic currents differentially regulated by cytoplasmic calcium ([Ca²⁺ ]_cyt ). We investigated the pollen-expressed proteins AtSLAH3, AtALMT12, AtTMEM16 and AtCCC as the putative anion transporters responsible for these currents. AtCCC-GFP was observed at the shank and AtSLAH3-GFP at the tip and shank of the PT plasma membrane. Both are likely to carry the majority of anion current at negative potentials, as extracellular anionic fluxes measured at the tip of PTs with an anion vibrating probe were significantly lower in slah3^-/- and ccc^-/- mutants, but unaffected in almt12^-/- and tmem16^-/- . We further characterised the effect of pH and GABA by patch clamp. Strong regulation by extracellular pH was observed in the wild-type, but not in tmem16^-/- . Our results are compatible with AtTMEM16 functioning as an anion/H⁺ cotransporter and therefore, as a putative pH sensor. GABA presence: (1) inhibited the overall currents, an effect that is abrogated in the almt12^-/- and (2) reduced the current in AtALMT12 transfected COS-7 cells, strongly suggesting the direct interaction of GABA with AtALMT12. Our data show that AtSLAH3 and AtCCC activity is sufficient to explain the major component of extracellular anion fluxes, and unveils a possible regulatory system linking PT growth modulation by pH, GABA, and [Ca²⁺ ]_cyt through anionic transporters.

Thermal constraints on in vivo optogenetic manipulations

A key assumption of optogenetics is that light only affects opsin-expressing neurons. However, illumination invariably heats tissue, and many physiological processes are temperature-sensitive. Commonly used illumination protocols increased the temperature by 0.2-2 °C and suppressed spiking in multiple brain regions. In the striatum, light delivery activated an inwardly rectifying potassium conductance and biased rotational behavior. Thus, careful consideration of light-delivery parameters is required, as even modest intracranial heating can confound interpretation of optogenetic experiments.

Helicokinin alters ion transport in the secondary cell-containing region of the Malpighian tubule of the larval cabbage looper Trichoplusia ni

Excretion in insects is accomplished by the combined actions of the Malpighian tubules (MTs) and hindgut, which together form the functional kidney. MTs of many insect groups consist of principal cells (PC) and secondary cells (SC). In most insect groups SCs are reported to secrete ions from haemolymph into the tubule lumen. Paradoxically, SCs in the MTs of the lepidopteran cabbage looper T. ni are used to reabsorb Na⁺ and K⁺ back into haemolymph. The current study was designed to investigate the effects and mode of action of the lepidopteran kinin, Helicokinin (HK), on ion transport in the SC-containing region of MT of T. ni. We identified a HK receptor (HK-R) homologue in T. ni and detected its expression in the SC-containing region of the MTs. The mRNA abundance of hk-r altered in response to changes in dietary K⁺ and Na⁺ content. HK-R immunolocalized to both PCs and SCs. Ramsay assays of preparations of the isolated distal ileac plexus (DIP) indicated that [HK] = 10^-8 M: (i) decreased fluid secretion rate in unstimulated and serotonin-stimulated preparations, and (ii) increased [Na⁺]/[K⁺] ratio in the secreted fluid. Scanning ion-selective electrode technique measurements revealed that HK reduced: (i) K⁺ secretion by the PCs, and (ii) Na⁺ reabsorption by the SCs in intact tubules. In vitro incubation of the DIP with HK resulted in reduced mRNA abundance of hk-r as well as Na⁺/K⁺-ATPase subunit α (NKAα), Na⁺/K⁺/Cl^- co-transporter (nkcc), Na⁺/H⁺ exchangers (nhe) 7 and 8, and aquaporin (aqp) 1. Taken together, results of the current study suggest that HK is capable of altering fluid secretion rate and [Na⁺]/[K⁺] ratio of the fluid, and that HK targets both PCs and SCs in the DIP of T. ni.

AIMP1 regulates TCR signaling and induces differentiation of regulatory T cells by interfering with lipid raft association

In addition to a role in translation, AIMP1 is secreted to affect various immune cells, such as macrophages, dendritic cells, B cells, and natural killer cells. However, the direct effects of AIMP1 on T cells have not yet been reported. In this study, we investigated whether AIMP1 could modulate T cell responses directly. Results revealed that AIMP1 significantly inhibited T cell receptor (TCR)-dependent activation and proliferation of CD4 T cells, as well as decreased TCR stimuli-induced Ca²⁺ influx in CD4 T cells. In addition, microscopic analysis revealed that lipid raft association in response to TCR engagement was significantly reduced in the presence of AIMP1, and the phosphorylation of PLCγ and PI3K was also down-regulated in CD4 T cells by AIMP1. Furthermore, AIMP1 specifically enhanced the differentiation of regulatory T (Treg) cells, while it had no effect on T helper type 1 (Th1), type 2 (Th2), and type 17 (Th17) cell differentiation. Collectively, these results indicate that AIMP1 affects T cells directly by down-regulating TCR signaling complex formation and inducing Treg cell differentiation in CD4 T cells.

Bile acids inhibit human purinergic receptor P2X4 in a heterologous expression system

We recently demonstrated that bile acids, especially tauro-deoxycholic acid (t-DCA), modify the function of the acid-sensing ion channel ASIC1a and other members of the epithelial sodium channel (ENaC)/degenerin (DEG) ion channel family. Surprisingly, ASIC1 shares a high degree of structural similarity with the purinergic receptor P2X4, a nonselective cation channel transiently activated by ATP. P2X4 is abundantly expressed in the apical membrane of bile duct epithelial cells and is therefore exposed to bile acids under physiological conditions. Here, we hypothesize that P2X4 may also be modulated by bile acids and investigate whether t-DCA and other common bile acids affect human P2X4 heterologously expressed in Xenopus laevis oocytes. We find that application of either t-DCA or unconjugated deoxycholic acid (DCA; 250 µM) causes a strong reduction (∼70%) of ATP-activated P2X4-mediated whole-cell currents. The inhibitory effect of 250 µM tauro-chenodeoxycholic acid is less pronounced (∼30%), and 250 µM chenodeoxycholic acid, cholic acid, or tauro-cholic acid did not significantly alter P2X4-mediated currents. t-DCA inhibits P2X4 in a concentration-dependent manner by reducing the efficacy of ATP without significantly changing its affinity. Single-channel patch-clamp recordings provide evidence that t-DCA inhibits P2X4 by stabilizing the channel's closed state. Using site-directed mutagenesis, we identifiy several amino acid residues within the transmembrane domains of P2X4 that are critically involved in mediating the inhibitory effect of t-DCA on P2X4. Importantly, a W46A mutation converts the inhibitory effect of t-DCA into a stimulatory effect. We conclude that t-DCA directly interacts with P2X4 and decreases ATP-activated P2X4 currents by stabilizing the closed conformation of the channel.

Potash mining effluents and ion imbalances cause transient osmoregulatory stress, affect gill integrity and elevate chronically plasma sulfate levels in adult common roach, Rutilus rutilus

Secondary salinization is a growing global ecological issue. One cause is the discharge of effluents by the potash mining industry into surface waters such as the River Werra in Germany. Increases of major ions require various physiological responses of freshwater organisms to maintain the hydromineral balance of body fluids. However, only little is known about the acute and chronic effects of high concentrations and imbalances of ions on osmoregulation in freshwater teleosts. The present study aimed to elucidate the effects of potash mining effluents and different cation ratios on the osmoregulatory capacity and gill histopathology of a native fish species. Individuals of Rutilus rutilus were exposed to the currently allowed (HT) and intended future (LT) thresholds as well as to high concentrations of Mg²⁺ (Mg), K⁺ (K), and Mg²⁺ and K⁺ (Mg + K) for a period of 24 h, 7 d, 21 d and 8 wk. Plasma osmolarity, [Na⁺], [Mg²⁺], [K⁺], [Ca²⁺], [Cl^-] and [SO₄^2-] and branchial Na⁺/K⁺-ATPase activity were determined. Moreover, histological gill alterations after 21 d and muscle water content after 8 wk were examined. HT transiently (24 h) elevated plasma osmolarity, plasma [Na⁺] and [Ca²⁺], whereas [SO₄^2-] was chronically increased even after 8 wk. Exposure to LT, Mg and Mg + K led to increased [SO₄^2-] levels for at least 21 d. It seems that [SO₄^2-] is mainly disturbed by multiple ions at high concentrations and long-term effects are unknown. Hydromineral homeostasis was maintained as indicated by unchanged Na⁺/K⁺-ATPase activity and muscle water content. However, mild structural alterations of the gills were observed in all exposure groups suggesting adaptational responses but with the potential to affect gas exchange capacity. Hence, the current thresholds for potash mining effluents affect osmomineral regulation in roach and further investigations should address potential impacts on reproduction in native fish species and physiological effects of SO₄^2-.

Sigma-1 Receptor Antagonists Haloperidol and Chlorpromazine Modulate the Effect of Glutoxim on Na+ Transport in Frog Skin

Using voltage-clamp technique, the involvement of sigma-1 receptors in the regulation of Na+ transport in frog skin by the immunomodulatory drug glutoxim was investigated. We have shown for the first time that preincubation of the frog skin with the sigma-1 receptor antagonists haloperidol and chlorpromazine attenuates the stimulatory effect of glutoxim on the Na+ transport. The results suggest the possible involvement of the sigma-1 receptors in the regulation of Na+ transport in frog skin epithelium by glutoxim.

H+-dependent inorganic phosphate transporter in breast cancer cells: Possible functions in the tumor microenvironment

Tumor microenvironment has a high concentration of inorganic phosphate (Pi), which is actually a marker for tumor progression. Regarding Pi another class of transporter has been recently studied, an H⁺-dependent Pi transporter, that is stimulated at acidic pH in Caco2BBE human intestinal cells. In this study, we characterized the H⁺-dependent Pi transport in breast cancer cell (MDA-MB-231) and around the cancer tissue. MDA-MB-231 cell line presented higher levels of H⁺-dependent Pi transport as compared to other breast cell lines, such as MCF-10A, MCF-7 and T47-D. The Pi transport was linear as a function of time and exhibited a Michaelis-Menten kinetic of K_m = 1.387 ± 0.1674 mM Pi and V_max = 198.6 ± 10.23 Pi × h^-1 × mg protein^-1 hence reflecting a low affinity Pi transport. H⁺-dependent Pi uptake was higher at acidic pH. FCCP, Bafilomycin A1 and SCH28080, which deregulate the intracellular levels of protons, inhibited the H⁺-dependent Pi transport. No effect on pHi was observed in the absence of inorganic phosphate. PAA, an H⁺-dependent Pi transport inhibitor, reduced the Pi transport activity, cell proliferation, adhesion, and migration. Arsenate, a structural analog of Pi, inhibited the Pi transport. At high Pi conditions, the H⁺-dependent Pi transport was five-fold higher than the Na⁺-dependent Pi transport, thus reflecting a low affinity Pi transport. The occurrence of an H⁺-dependent Pi transporter in tumor cells may endow them with an alternative path for Pi uptake in situations in which Na⁺-dependent Pi transport is saturated within the tumor microenvironment, thus regulating the energetically expensive tumor processes.

Exhaustive exercise decreases renal organic anion transporter 3 function

This study aimed to investigate the effects of various types of exercise on organic anion transporter 3 (Oat3) function, a major transporter that plays a role in the secretion of a variety of drugs and endogenous compounds. Male Wistar rats were randomly allocated to non-exercise, exhaustive, acute and training exercise groups. The function of Oat3 was assessed by the uptake of [3H]-estrone sulfate ([3H]-ES) into rat renal cortical slices. Acute and training exercises had no effect on [3H]-ES uptake whereas a marked reduction in [3H]-ES uptake occurred immediately after exhaustive exercise. However, the reduction in Oat3 function was gradually recovered at 6 and 24 h after the exercise session. Importantly, the impairment of Oat3 function was associated with a decrease in renal Oat3 protein expression. Our results indicate that exhaustive exercise produces a significant impact on renal organic anion transport function, which in turn could alter the plasma level of drugs and compounds in the body.

Cloning and functional analysis of the VcCXIP4 and VcYSL6 genes as Cd-regulating genes in blueberry

Blueberries (Vaccinium ssp.) show relatively high resistance to pollution and have been reported to successfully colonize acid and heavy metal-contaminated soils. Blueberries were subjected to cadmium stress using a simulated pot-culture method. The intact CDS regions of VcCXIP4 and VcYSL6 were obtained, VcCXIP4 was located in the nucleus, while VcYSL6 was located in the chloroplast. Both genes were constructed into a modified plant expression vector pCambia1301 for tobacco transformation with agrobacterium infection methods. Results showed that VcCXIP4 did not function alone in regulating cadmium (Cd) transport. Cd content of Cd in the leaves of VcYSL6 transgenic tobacco by 15.57% under high Cd concentration. Both, VcCXIP4 and VcYSL6 genes were up-regulated under Cd stress. Blueberry primarily accumulated excess Cd in the root, but Cd content in the fruit was almost independent of Cd content in the soil. Further, the effect of soil Cd content on fruit Cd content was not significant. VcCXIP4 is likely to interact with other proteins to regulate excess Cd in blueberry, while VcYSL6 is a Cd transporter required for excess Cd detoxification in blueberry.

Lumacaftor-rescued F508del-CFTR has a modified bicarbonate permeability

Deletion of phenylalanine at position 508, F508del, the most frequent mutation among Cystic fibrosis (CF) patients, destabilizes the protein, thus causing both a folding and a trafficking defect, resulting in a dramatic reduction in expression of CFTR. In vitro treatment with lumacaftor produces an enhancement of anion transport in cells. We studied the permeability properties of the CFTR mutant F508del treated with the corrector lumacaftor, showing that the rescued protein has selectivity properties different than the wild type CFTR, showing an augmented bicarbonate permeability. This difference would indicate a diverse conformation of the rescued F508del-CFTR, that is plausibly reflected on an improper regulation of the airway surface liquid, lessening the efficacy of the corrector. Our findings rather support the idea that a combination of correctors would be required to address the CFTR-dependent bicarbonate permeability.

Mechanism of luminal ATP activated chloride secretion in a polarized epithelium

There are both secretory and absorptive pathways working in tandem to support ionic movement driving fluid secretion across epithelia. The mechanisms exerting control of fluid secretion in the oviduct is yet to be fully determined. This study explored the role of apical or luminal extracellular ATP (ATPe)-stimulated ion transport in an oviduct epithelium model, using the Ussing chamber short-circuit current (Isc) technique. Basal Isc in oviduct epithelium in response to apical ATPe comprises both chloride secretion and sodium absorption and has distinct temporal phases. A rapid transient peak followed by a sustained small increase above baseline. Both phases of the apical ATPe Isc response are sensitive to anion (HCO3-, Cl-) and cation (Na+) replacement. Additionally, the role of apical chloride channels, basolateral potassium channels and intracellular calcium in supporting the peak Isc current was confirmed. The role of ATP breakdown to adenosine resulting in the activation of P2 receptors was supported by examining the effects of non-hydrolyzable forms of ATP. A P2YR2 potency profile of ATP = UTP > ADP was generated for the apical membrane, suggesting the involvement of the P2YR2 subtype of purinoceptor. A P2X potency profile of ATP = 2MeSATP > alpha,beta-meATP > BzATP was also generated for the apical membrane. In conclusion, these results provide strong evidence that purinergic activation of apical P2YR2 promotes chloride secretion and is thus an important factor in fluid formation by the oviduct.

The inhibitory role of purinergic P2Y receptor on Mg2+ transport across intestinal epithelium-like Caco-2 monolayer

The mechanism of proton pump inhibitors (PPIs) suppressing intestinal Mg2+ uptake is unknown. The present study aimed to investigate the role of purinergic P2Y receptors in the regulation of Mg2+ absorption in normal and omeprazole-treated intestinal epithelium-like Caco-2 monolayers. Omeprazole suppressed Mg2+ transport across Caco-2 monolayers. An agonist of the P2Y2 receptor, but not the P2Y4 or P2Y6 receptor, suppressed Mg2+ transport across control and omeprazole-treated monolayers. Omeprazole enhanced P2Y2 receptor expression in Caco-2 cells. Forskolin and P2Y2 receptor agonist markedly enhanced apical HCO3- secretion by control and omeprazole-treated monolayers. The P2Y2 receptor agonist suppressed Mg2+ transport and stimulated apical HCO3- secretion through the Gq-protein coupled-phospholipase C (PLC) dependent pathway. Antagonists of cystic fibrosis transmembrane conductance regulator (CFTR) and Na+-HCO3- cotransporter-1 (NBCe1) could nullify the inhibitory effect of P2Y2 receptor agonist on Mg2+ transport across control and omeprazole-treated Caco-2 monolayers. Our results propose an inhibitory role of P2Y2 on intestinal Mg2+ absorption.

Functional Analysis of Ion Transport Properties and Salt Tolerance Mechanisms of RtHKT1 from the Recretohalophyte Reaumuria trigyna

Reaumuria trigyna is an endangered recretohalophyte and a small archaic feral shrub that is endemic to arid and semi-arid plateau regions of Inner Mongolia, China. Based on transcriptomic data, we isolated a high-affinity potassium transporter gene (RtHKT1) from R. trigyna, which encoded a plasma membrane-localized protein. RtHKT1 was rapidly up-regulated by high Na+ or low K+ and exhibited different tissue-specific expression patterns before and after stress treatment. Transgenic yeast showed tolerance to high Na+ or low K+, while transgenic Arabidopsis exhibited tolerance to high Na+ and sensitivity to high K+, or high Na+-low K+, confirming that Na+ tolerance in transgenic Arabidopsis depends on a sufficient external K+ concentration. Under external high Na+, high K+ and low K+ conditions, transgenic yeast accumulated more Na+-K+, Na+ and K+, while transgenic Arabidopsis accumulated less Na+-more K+, more Na+ and more Na+-K+, respectively, indicating that the ion transport properties of RtHKT1 depend on the external Na+-K+ environment. Salt stress induced up-regulation of some ion transporter genes (AtSOS1/AtHAK5/AtKUP5-6), as well as down-regulation of some genes (AtNHX1/AtAVP1/AtKUP9-12), revealing that multi-ion-transporter synergism maintains Na+/K+ homeostasis under salt stress in transgenic Arabidopsis. Overexpression of RtHKT1 enhanced K+ accumulation and prevented Na+ transport from roots to shoots, improved biomass accumulation and Chl content in salt-stressed transgenic Arabidopsis. The proline content and relative water content increased significantly, and some proline biosynthesis genes (AtP5CS1 and AtP5CS2) were also up-regulated in salt-stressed transgenic plants. These results suggest that RtHKT1 confers salt tolerance on transgenic Arabidopsis by maintaining Na+/K+ homeostasis and osmotic homeostasis.

Norepinephrine-Induced Stimulation of Kir4.1/Kir5.1 Is Required for the Activation of NaCl Transporter in Distal Convoluted Tubule

The stimulation of β-adrenergic receptor increases thiazide-sensitive NaCl cotransporter (NCC), an effect contributing to salt-sensitive hypertension by sympathetic stimulation. We now test whether the stimulation of β-adrenergic receptor-induced activation of NCC is achieved through activating basolateral Kir4.1 in the distal convoluted tubule (DCT). Application of norepinephrine increased the basolateral 40 pS K+ channel (Kir4.1/Kir5.1 heterotetramer) in the DCT. The stimulatory effect of norepinephrine on the K+ channel was mimicked by cAMP analogue but abolished by inhibiting PKA (protein kinase A). Also, the effect of norepinephrine on the K+ channel in the DCT was recapitulated by isoproterenol but not by α-adrenergic agonist and blocked by propranolol, suggesting that norepinephrine effect on the K+ channel was mediated by β-adrenergic receptor. The whole-cell recording shows that norepinephrine and isoproterenol increased DCT K+ currents and shifted the K+ current ( IK) reversal potential to negative range (hyperpolarization). Continuous norepinephrine perfusion (7 days) increased DCT K+ currents, hyperpolarized IK reversal potential, and increased the expression of total NCC/phosphorylated NCC, but it had no significant effect on the expression of NKCC2 (type 2 Na-Cl-K cotransporter) and ENaC-α (epithelial Na channel-α subunit). Renal clearance study demonstrated that norepinephrine perfusion augmented thiazide-induced urinary Na+ excretion only in wild-type but not in kidney-specific Kir4.1 knockout mice, suggesting that Kir4.1 is required for mediating the effect of norepinephrine on NCC. However, norepinephrine perfusion did not affect urinary K+ excretion. We conclude that the stimulation of β-adrenergic receptor activates the basolateral Kir4.1 in the DCT and that the activation of Kir4.1 is required for norepinephrine-induced stimulation of NCC.