Membrane Channels Research Articles

Reliability-based thermal-fluid-structural topological optimization of three-dimensional coolant channels in proton exchange membrane fuel cells

In order to minimize the flow resistance in designing the cooling multi-channels of proton exchange membrane fuel cells (PEMFCs) under the double constraints of target thermal reliability index and target structural performance, this work proposes a three-dimensional (3D) thermal-fluid-structural reliability-based topology optimization (RBTO) method for the first time. In the RBTO for PEMFCs’ coolant channels, the position uncertainty of the multi-heat loads on the bipolar plates caused by irregular metal foam skeleton is considered, and the multi-heat load positions are treated as the interval uncertain variables within a certain range. To solve the problem of low computational efficiency caused by the coupling of topological parameter optimization and reliability constraint analysis, the RBTO is equivalently decoupled to a sequence of cycles of deterministic topology optimization (DTO) and inverse reliability assessment, and the latter is completed by performance measure approach (PMA) based on the target reliability index. Results show that RBTO introduces more flow resistance cost than DTO, and the additional flow resistance in RBTO increases with the increase of the target reliability index. The heat concentration caused by a smaller fiber diameter of foam skeletons results in more flow resistance cost of RBTO compared to DTO. When the inlet velocity of the coolant channel varies in the region of 0.05–0.3 m/s, the flow resistance of the multi-channel obtained by RBTO is 1.29–0.96 times as that of the straight multi-channel. In addition, the uneven reactant gas concentration in PEMFC gas channels leads to the uneven distribution of heat flow, and it affects the temperature distribution on bipolar plates, which in turn affects the results of RBTO. The above method and findings can be applied to design the cooling channels of PEMFCs with irregular metal foam gas channels.

Ionophore antibiotics and hop cones as regulators of digestion and metabolism in ruminants

The general characteristics of ionophore antibiotics and the mechanisms of their antimicrobial action were analyzed. Two types of ionophore antibiotics are known: those that transport ions across the membrane, and those that form a channel in the cell membrane through which ions pass. Ionophore antibiotics used in animal husbandry belong to the former group (monensin, lasalocid, salinomycin, narasin). They are synthesized by bacteria of the Streptomyces genus. Bacterial cells and rumen fluid differ in ionic composition, which is regulated by active ion transport. As a result, the cytoplasm of bacteria contains more potassium ions, while the rumen fluid, on the contrary, has more sodium ions. Ionophores transport potassium inside the cell and remove sodium outside. The bacteria try to correct this imbalance and require ATP energy to carry out this process. Eventually, energy deficit develops in the bacterial cell and it dies. Ionophore antibiotics affect only the Gram-positive bacteria in the rumen of ruminants, because they cannot penetrate through the cell wall of Gram-negative bacteria. Thus, there is a selective destruction of some types of bacteria, the most sensitive among which are the so-called hyper-ammonia-producing bacteria (HAB). Ionophore antibiotics, which change the breakdown of protein and carbohydrates, change the ratio of volatile fatty acids by increasing the proportion of propionic acid and thus inhibit methanogenesis in the rumen. Ionophore antibiotics are an important antiketotic agent because they reduce the concentration of β-hydroxybutyrate and non-esterified fatty acids in the blood of ruminants. During the transition period, cows have metabolic disorders so they are more prone to infectious diseases due to a decrease in resistance. The use of ionophore antibiotics affects the immune function and resistance to inflammatory processes, which is caused by an indirect influence associated with a lower pathological effect of ketosis and steatosis. Ionophore antibiotics reduce the negative energy balance and its pathological impact on metabolism. The influence of ionophore antibiotics on cow’s milk productivity is mostly absent or insignificant. The study presents characteristics of biologically active substances of hop cones. Hop cones contain biologically active components similar to ionophore antibiotics by action. These are prenylated flavonoids: humulone (α-acid), lupulone (β-acid) and their derivatives. These components of hop cones can be regarded as a potential substitute for ionophoric antibiotics. In particular, lupulone and some other components of hop cones inhibit the activity of Gram-positive bacteria, causing reactions similar to ionophore antibiotics. In addition, hop cones have many other biologically active compounds: phenols, essential oils, and resins, which have antimicrobial, antioxidant, sedative, phytoestrogen, insulin stimulating, immunomodulatory, and antitumor effects.

Synergistic incorporation of Ti3C2Tx with sulfonated poly(phenylene oxide) membranes: Unravelling multifaceted advancements in physicochemical, electrochemical, and antibacterial domains for enhanced electrodialytic desalination

This study delves into the solution-phase incorporation of Ti3C2Tx nanosheets into sulfonated poly(phenylene oxide) (SPPO) to prevail the conventional challenge of distant ionic channels in membranes. A series of membranes incorporating MXene (Ti3C2Tx nanosheets) at varying weight percentages (1 wt%, 2 wt%, and 5 wt%) underwent meticulous scrutiny of their physicochemical and electrochemical attributes. Among this series, MXe-02 emerged as particularly noteworthy, showing remarkable water sorption (WS= 43.8%), ion exchange capacity (IEC: 1.65 ± 0.05 meqg−1), and ionic conductivity (IC: 2.83×10−2 S cm−1), coupled with minimal dimensional change of 8.57% compared to its pristine counterpart, SPPO-B (WS=35.70%, IEC: 1.03±0.05 meqg−1, IC: 1.98×10–2 S cm−1). Advanced analytical techniques such as atomic force microscopy (AFM) and field emission-scanning electron microscopy (FE-SEM) provided insights into hydrophilic-hydrophobic phase separation, ionic domain clustering, and membrane surface attributes pivotal for enhancing electrochemical properties. Beyond optimal concentrations (>2 wt%), a significant composite-agglomeration effect hindered further advancements in physicochemical and electrochemical aspects, as verified by zeta potential measurements. The optimized MXe-02 membrane boasted a notable transport number of 0.89 with a substantial limiting current density (Ilim = 45 mA cm−2), offering a wide window for swift electrodialytic desalination. Moreover, MXe-02 membranes demonstrated an energy consumption of 0.98 kWh kg−1 and 93.52% energy efficiency, affirming their efficacy for brackish water desalination. Antibacterial properties were evaluated against Escherichia coli and Staphylococcus aureus, revealing MXe-02 and MXe-05's distinct zones of inhibition against S. aureus, highlighting their excellent antibacterial efficacy against Gram-positive bacteria. This comprehensive study shows the intricate interplay of MXene-incorporated membranes, offering valuable insights for advancing electrochemical and antibacterial performance in water desalination.

CAMP binding to closed pacemaker ion channels is cooperative

The cooperative action of the subunits in oligomeric receptors enables fine-tuning of receptor activation, as demonstrated for the regulation of voltage-activated HCN pacemaker ion channels by relating cAMP binding to channel activation in ensemble signals. HCN channels generate electric rhythmicity in specialized brain neurons and cardiomyocytes. There is conflicting evidence on whether binding cooperativity does exist independent of channel activation or not, as recently reported for detergent-solubilized receptors positioned in zero-mode waveguides. Here, we show positive cooperativity in ligand binding to closed HCN2 channels in native cell membranes by following the binding of individual fluorescence-labeled cAMP molecules. Kinetic modeling reveals that the affinity of the still empty binding sites rises with increased degree of occupation and that the transition of the channel to a flip state is promoted accordingly. We conclude that ligand binding to the subunits in closed HCN2 channels not pre-activated by voltage is already cooperative. Hence, cooperativity is not causally linked to channel activation by voltage. Our analysis also shows that single-molecule binding measurements at equilibrium can quantify cooperativity in ligand binding to receptors in native membranes.

Milestone Papers on Signal Transduction Mechanisms of Hypertension and Its Complications.

To celebrate 100 years of American Heart Association-supported cardiovascular disease research, this review article highlights milestone papers that have significantly contributed to the current understanding of the signaling mechanisms driving hypertension and associated cardiovascular disorders. This article also includes a few of the future research directions arising from these critical findings. To accomplish this important mission, 4 principal investigators gathered their efforts to cover distinct yet intricately related areas of signaling mechanisms pertaining to the pathogenesis of hypertension. The renin-angiotensin system, canonical and novel contractile and vasodilatory pathways in the resistance vasculature, vascular smooth muscle regulation by membrane channels, and noncanonical regulation of blood pressure and vascular function will be described and discussed as major subjects.

Enhanced Mono/Divalent Ion Separation via Charged Interlayer Channels in Montmorillonite-Based Membranes.

Efficient mono- and divalent ion separation is pivotal for environmental conservation and energy utilization. Two-dimensional (2D) materials featuring interlayer nanochannels exhibit unique water and ion transport properties, rendering them highly suitable for water treatment membranes. In this work, we incorporated polydopamine/polyethylenimine (PDA/PEI) copolymers into 2D montmorillonite (MMT) nanosheet interlayer channels through electrostatic interactions and bioinspired bonding. A modified laminar structure was formed on the substrate surface via a straightforward vacuum filtration. The electrodialysis experiments reveal that these membranes could achieve monovalent permselectivity of 11.06 and Na+ flux of 2.09 × 10-8 mol cm-2 s-1. The enhanced permselectivity results from the synergistic effect of electrostatic and steric hindrance effect. In addition, the interaction between the PDA/PEI copolymer and the MMT nanosheet ensures the long-term operational stability of the membranes. Theoretical simulations reveal that Na+ has a lower migration energy barrier and higher migration rate for the modified MMT-based membrane compared to Mg2+. This work presents a novel approach for the development of monovalent permselective membranes.

Phase separation and water channels in graft-type polymer electrolyte membranes for hydrogen fuel cell

Microstructural complexity in graft-type polymer electrolyte membranes upon operating conditions is still challenging for examination. Here, the phase separation and water channels of poly(styrene sulfonic acid) (PSSA)-grafted poly(ethylene-co-tetrafluoroethylene) (ETFE) polymer electrolyte membranes (ETFE-PEMs) are characterized by a newly applying method based on electron density fluctuation, F, in the small angle X-ray scattering (SAXS) profiles. The ETFE-PEMs exhibit an increase in phase separation in the ion exchange capacity of 0–0.7 mmol/g as qualitatively determined by the increase in the SAXS invariant. The increase in the SAXS invariant is attributed to the evolution of the newly separated phase between the surfaces of crystalline ETFE backbones and the side chains of PSSA grafts. This phase separation allows the formation of water channels upon low relative humidity (RH). The ionic-domain spacing is around 1.52 nm at dry condition and then increases to 1.69 nm at low RH of 10%, reflecting the ion-water aggregation to make larger aggregate size. At 30% relative humidity, the highly ordered lamellar proton-conducting nanochannels (water channels) are formed in the membrane, which correspond to the dramatic increase in proton conductivity. It is interesting to note that these conducting nanochannels remain unchanged upon 30–70% RH. Also, in this range of RH the similar signatures in the pair distribution function suggests that the molecular packing and local structures are highly similar. Above features of phase separation and water channels can elucidate important characteristics of the ETFE-PEMs, especially the high proton conductivity at low RH.

Ion Channels in Critical Membranes: Clustering, Cooperativity, and Memory Effects

Ion Channels in Critical Membranes: Clustering, Cooperativity, and Memory Effects

Blockage of aquaporin-3 peroxiporin activity by organogold compounds affects melanoma cell adhesion, proliferation and migration.

Aquaporin-3 (AQP3) is a membrane channel with dual aquaglyceroporin/peroxiporin activity, facilitating the diffusion of water, glycerol and H2O2 across cell membranes. AQP3shows aberrant expression in melanoma and its role in cell adhesion, migration and proliferation is well described. Gold compounds were shown to modulate AQP3 activity with reduced associated toxicity, making them promising molecules for cancer therapy. In this study, we validated the phenotype resulting from AQP3-silencing of two melanoma cell lines, MNT-1 and A375, which resulted in decreased H2O2 permeability. Subsequently, the AQP3 inhibitory effect of a new series of organogold compounds derived from Auphen, a potent AQP3 inhibitor, was first evaluated in red blood cells (RBCs) that highly express AQP3, and then in HEK-293T cells with AQP3 overexpression to ascertain the compounds' specificity. The first screening in RBCs unveiled two organogold compounds as promising blockers of AQP3 permeability. Moderate reduction of glycerol permeability but drastic inhibition of H2O2 permeability was detected for some of the gold derivatives in both AQP3-overexpressing cells and human melanoma cell lines. Additionally, all compounds were effective in impairing cell adhesion, proliferation and migration, although in a cell type-dependent manner. In conclusion, our data show that AQP3 peroxiporin activity is crucial for melanoma progression and highlight organogold compounds as promising AQP3 inhibitors with implications in melanoma cell adhesion, proliferation and migration, unveiling their potential as anticancer drugs against AQP3-overexpressing tumours. KEY POINTS: AQP3 affects cellular redox balance. Gold compounds inhibit AQP3 permeability in melanoma cells. AQP3 is involved in cell adhesion, proliferation and migration of melanoma. Blockage of AQP3 peroxiporin activity impairs melanoma cell migration. Gold compounds are potential anticancer drug leads for AQP3-overexpressing cancers.

The function of mechanosensitive channels in the asymmetric lipid-protein membrane

The function of mechanosensitive channels in the asymmetric lipid-protein membrane

Boron nitride nanotube porins as a new biomimetic membrane channel for nanofluidic transport

Boron nitride nanotube porins as a new biomimetic membrane channel for nanofluidic transport

Hydrodynamic effects of the elliptical spacer filament on the flow and mass transfer in a desalination membrane channel

This study numerically investigates the impacts of an elliptical spacer on the flow and mass transfer within a desalination membrane channel. We consider the effects of the fluid Reynolds number, the elliptical spacer position yin/H, the flow attack angle θ and the aspect ratio B of spacer on the fluid flow, concentration polarization, and permeation flux. Our findings reveal that the elliptical spacers can improve both the mass transfer and permeation flux compared with the traditional circular spacers. Placing the spacer near the membrane surface effectively disrupts the concentration boundary layer, thereby amplifying the local concentration polarization surrounding the spacer. A single recirculation vortex behind the spacer induces numerous large vortices around the membrane, resulting in a significant increment in freshwater production. By changing θ and B, the system's stability can be reduced, potentially leading to a 16.0% increment in permeation flux when compared with the traditional circular spacers. Furthermore, the drag and lift coefficients acting on the elliptical spacer are greater than those of circular spacers, which is the main reason for the transition of flow condition. Our findings provide a reference for the design of the efficient structures in reverse osmosis membranes.

Na+/K+-ATPase: ion pump, signal transducer, or cytoprotective protein, and novel biological functions.

Na+/K+-ATPase is a transmembrane protein that has important roles in the maintenance of electrochemical gradients across cell membranes by transporting three Na+ out of and two K+ into cells. Additionally, Na+/K+-ATPase participates in Ca2+-signaling transduction and neurotransmitter release by coordinating the ion concentration gradient across the cell membrane. Na+/K+-ATPase works synergistically with multiple ion channels in the cell membrane to form a dynamic network of ion homeostatic regulation and affects cellular communication by regulating chemical signals and the ion balance among different types of cells. Therefore, it is not surprising that Na+/K+-ATPase dysfunction has emerged as a risk factor for a variety of neurological diseases. However, published studies have so far only elucidated the important roles of Na+/K+-ATPase dysfunction in disease development, and we are lacking detailed mechanisms to clarify how Na+/K+-ATPase affects cell function. Our recent studies revealed that membrane loss of Na+/K+-ATPase is a key mechanism in many neurological disorders, particularly stroke and Parkinson's disease. Stabilization of plasma membrane Na+/K+-ATPase with an antibody is a novel strategy to treat these diseases. For this reason, Na+/K+-ATPase acts not only as a simple ion pump but also as a sensor/regulator or cytoprotective protein, participating in signal transduction such as neuronal autophagy and apoptosis, and glial cell migration. Thus, the present review attempts to summarize the novel biological functions of Na+/K+-ATPase and Na+/K+-ATPase-related pathogenesis. The potential for novel strategies to treat Na+/K+-ATPase-related brain diseases will also be discussed.

The antiseizure medication valproate increases hemichannel activity found in brain cells, which could worsen disease outcomes.

Glial cells play relevant roles in neuroinflammation caused by epilepsy. Elevated hemichannel (HC) activity formed by connexins (Cxs) or pannexin1 (Panx1) largely explains brain dysfunctions commonly caused by neuroinflammation. Glia express HCs formed by Cxs 43, 30, or 26, while glia and neurons both express HCs formed by Panx1. Cx43 HCs allow for the influx of Ca2+, which promotes glial reactivity, enabling the release of the gliotransmitters that contribute to neuronal over-stimulation. Valproate (VPA), an antiseizure medication, has pleiotropic actions on neuronal molecular targets, and their action on glial cell HCs remains elusive. We used HeLa cells transfected with Cx43, Cx30, Cx26, or Panx1 to determine the effect of VPA on HC activity in the brain. VPA slightly increased HC activity under basal conditions, but significantly enhanced it in cells pre-exposed to conditions that promoted HC activity. Furthermore, VPA increased ATP release through Cx43 HCs. The increased HC activity caused by VPA was resistant to washout, being consistent with in silico studies, which predicted the binding site for VPA and Cx43, as well as for Panx1 HCs on the intracellular side, suggesting that VPA first enters through HCs, after which their activity increases.

Loss of activation by GABA in vertebrate delta ionotropic glutamate receptors

Ionotropic glutamate receptors (iGluRs) mediate excitatory signals between cells by binding neurotransmitters and conducting cations across the cell membrane. In the mammalian brain, most of these signals are mediated by two types of iGluRs: AMPA and NMDA (i.e. iGluRs sensitive to 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic acid and N-methyl-D-aspartic acid, respectively). Delta-type iGluRs of mammals also form neurotransmitter-binding channels in the cell membrane, but in contrast, their channel is not activated by neurotransmitter binding, raising biophysical questions about iGluR activation and biological questions about the role of delta iGluRs. We therefore investigated the divergence of delta iGluRs from their iGluR cousins using molecular phylogenetics, electrophysiology, and site-directed mutagenesis. We find that delta iGluRs are found in numerous bilaterian animals (e.g., worms, starfish, and vertebrates) and are closely related to AMPA receptors, both genetically and functionally. Surprisingly, we observe that many iGluRs of the delta family are activated by the classical inhibitory neurotransmitter, γ-aminobutyric acid (GABA). Finally, we identify nine amino acid substitutions that likely gave rise to the inactivity of today's mammalian delta iGluRs, and these mutations abolish activity when engineered into active invertebrate delta iGluRs, partly by inducing receptor desensitization. These results offer biophysical insight into iGluR activity and point to a role for GABA in excitatory signaling in invertebrates.

Facilitating Water Permeation in Graphene Oxide Membranes via Incorporating Sulfonato Calix[n]arenes.

Graphene oxide (GO) with its atomic thickness and abundant functional groups holds great potential in molecular-scale membrane separation. However, constructing high-speed and highly selective water transport channels within GO membranes remains a key challenge. Herein, sulfonato calix[n]arenes (SCn) molecules with a cavity structure, hydrophilic entrance, and hydrophobic wall were incorporated into GO interlayer channels through a layer-by-layer assembly approach to facilitate water permeation in a water/ethanol separation process. The hydrophilic entrance enables preferential access of water molecules to the cavity over ethanol molecules, while the high hydrophobicity of the cavity wall confers low resistance for water diffusion. After incorporating SCn molecules, the membrane shows a remarkable increase in the water/ethanol separation factor from 732 to 1260, while the permeate flux also increases by about 50%. In addition, the strong electrostatic interactions between the building blocks endow the membrane with excellent swelling resistance even under a high water content. This work provides an effective strategy of constructing high-efficiency water transport channels in membrane.

Somatic ion channels and action potentials in olfactory receptor cells and vomeronasal receptor cells.

Olfactory receptor cells are primary sensory neurons that catch odor molecules in the olfactory system, and vomeronasal receptor cells catch pheromones in the vomeronasal system. When odor or pheromone molecules bind to receptor proteins expressed on the membrane of the olfactory cilia or vomeronasal microvilli, receptor potentials are generated in their receptor cells. This initial excitation is transmitted to the soma via dendrites, and action potentials are generated in the soma and/or axon and transmitted to the central nervous system. Thus, olfactory and vomeronasal receptor cells play an important role in converting chemical signals into electrical signals. In this review, the electrophysiological characteristics of ion channels in the somatic membrane of olfactory receptor cells and vomeronasal receptor cells in various species are described and the differences between the action potential dynamics of olfactory receptor cells and vomeronasal receptor cells are compared.

LRRC52 is likely a functional component of human KSper†.

Completion of fertilization is orchestrated by various ion channels in sperm membrane. Hyperpolarization of membrane potential, an indispensable event during the capacitation process, is dominated by sperm potassium channel (KSper). In addition to sperm-specific SLO3, which forms the channel pore, the auxiliary subunit leucine-rich-repeat-containing protein 52 (LRRC52) is required to form mKSper to function under physiological conditions. However, in human sperm, although most evidence supports that hSLO3 is the pore-forming subunit, whether hLRRC52 contributes to hKSper conductance and modulates sperm function remains to be understood. Here, using an extracellular segment that is homologous between mice and humans as an antigen, we developed a polyclonal antibody designed as LID1 that specifically detected mLRRC52 and performed co-immunoprecipitation with mSLO3. Additionally, patch-clamp recordings of mouse sperm showed that, physiological activation of mKSper and sperm functions were dramatically attenuated after treatment with LID1, indicating that LID1 functionally disrupted the regulation of mLRRC52 on mKSper. Next, LID1 was used to investigate the significance of hLRRC52 for hKSper activation. As a result, hLRRC52 was expressed in human sperm and might be assembled with hSLO3. More importantly, LID1 inhibited hKSper currents and depolarized sperm membrane potential, supporting essential modulation of hLRRC52 in hKSper. Ca2+ signaling of human sperm was also compromised in the presence of LID1, which impaired sperm motility and acrosome reaction. Because LID1 specifically inhibited both mKSper and hKSper but not mCatSper or hCatSper, our results suggest that hLRRC52 functions as an important component of hKSper and regulates sperm physiological functions.

Side-by-side comparison of published small molecule inhibitors against thapsigargin-induced store-operated Ca2+ entry in HEK293 cells.

Calcium (Ca2+) is a key second messenger in eukaryotes, with store-operated Ca2+ entry (SOCE) being the main source of Ca2+ influx into non-excitable cells. ORAI1 is a highly Ca2+-selective plasma membrane channel that encodes SOCE. It is ubiquitously expressed in mammals and has been implicated in numerous diseases, including cardiovascular disease and cancer. A number of small molecules have been identified as inhibitors of SOCE with a variety of potential therapeutic uses proposed and validated in vitro and in vivo. These encompass both nonselective Ca2+ channel inhibitors and targeted selective inhibitors of SOCE. Inhibition of SOCE can be quantified both directly and indirectly with a variety of assay setups, making an accurate comparison of the activity of different SOCE inhibitors challenging. We have used a fluorescence based Ca2+ addback assay in native HEK293 cells to generate dose-response data for many published SOCE inhibitors. We were able to directly compare potency. Most compounds were validated with only minor and expected variations in potency, but some were not. This could be due to differences in assay setup relating to the mechanism of action of the inhibitors and highlights the value of a singular approach to compare these compounds, as well as the general need for biorthogonal validation of novel bioactive compounds. The compounds observed to be the most potent against SOCE in our study were: 7-azaindole 14d (12), JPIII (17), Synta-66 (6), Pyr 3 (5), GSK5503A (8), CM4620 (14) and RO2959 (7). These represent the most promising candidates for future development of SOCE inhibitors for therapeutic use.

2'-deoxy-ADPR activates human TRPM2 faster than ADPR and thereby induces higher currents at physiological Ca2+ concentrations.

TRPM2 is a Ca2+ permeable, non-selective cation channel in the plasma membrane that is involved in the innate immune response regulating, for example, chemotaxis in neutrophils and cytokine secretion in monocytes and macrophages. The intracellular adenine nucleotides ADP-ribose (ADPR) and 2'-deoxy-ADPR (2dADPR) activate the channel, in combination with their co-agonist Ca2+. Interestingly, activation of human TRPM2 (hsTRPM2) by 2dADPR is much more effective than activation by ADPR. However, the underlying mechanism of the nucleotides' differential effect on the channel is not yet fully understood. In this study, we performed whole-cell patch clamp experiments with HEK293 cells heterologously expressing hsTRPM2. We show that 2dADPR has an approx. 4-fold higher Ca2+ sensitivity than ADPR (EC50 = 190 and 690 nM). This allows 2dADPR to activate the channel at lower and thus physiological intracellular Ca2+ concentrations. Kinetic analysis of our data reveals that activation by 2dADPR is faster than activation by ADPR. Mutation in a calmodulin binding N-terminal IQ-like motif in hsTRPM2 completely abrogated channel activation by both agonists. However, mutation of a single amino acid residue (W1355A) in the C-terminus of hsTRPM2, at a site of extensive inter-domain interaction, resulted in slower activation by 2dADPR and neutralized the difference in rate of activation between the two agonists. Taken together, we propose a mechanism by which 2dADPR induces higher hsTRPM2 currents than ADPR by means of faster channel activation. The finding that 2dADPR has a higher Ca2+ sensitivity than ADPR may indicate that 2dADPR rather than ADPR activates hsTRPM2 in physiological contexts such as the innate immune response.