Hydrogen sulfide regulates hippocampal neuron excitability via S-sulfhydration of Kv2.1.

Hydrogen sulfide (H2S) is gaining interest as a mammalian signalling molecule with wide ranging effects. S-sulfhydration is one mechanism that is emerging as a key post translational modification through which H2S acts. Ion channels and neuronal receptors are key target proteins for S-sulfhydration and this can influence a range of neuronal functions. Voltage-gated K+ channels, including Kv2.1, are fundamental components of neuronal excitability. Here, we show that both recombinant and native rat Kv2.1 channels are inhibited by the H2S donors, NaHS and GYY4137. Biochemical investigations revealed that NaHS treatment leads to S-sulfhydration of the full length wild type Kv2.1 protein which was absent (as was functional regulation by H2S) in the C73A mutant form of the channel. Functional experiments utilising primary rat hippocampal neurons indicated that NaHS augments action potential firing and thereby increases neuronal excitability. These studies highlight an important role for H2S in shaping cellular excitability through S-sulfhydration of Kv2.1 at C73 within the central nervous system.

Bioenergetic defects in muscle fibers of RYR1 mutant knock-in mice associated with malignant hyperthermia.

Mutations in the skeletal muscle ryanodine receptor gene (RYR1) can cause susceptibility to malignant hyperthermia (MH), a potentially lethal genetic condition triggered by volatile anesthetics. MH is associated with hypermetabolism, which has directed research interest into oxidative phosphorylation and muscle bioenergetics. The most common cause of MH in the United Kingdom is the c.7300G>A RYR1 variant, which is present in ∼16% of MH families. Our study focuses on the MH susceptible G2435R-RYR1 knock-in mouse model, which is the murine equivalent of the human c.7300G>A genotype. Using a combination of transcriptomics, protein expression, and functional analysis, we investigated adult muscle fiber bioenergetics in this mouse model. RNA-Seq data showed reduced expression of genes associated with mitochondria and fatty acid oxidation in RYR1 mutants when compared with WT controls. Mitochondrial function was assessed by measuring oxygen consumption rates in permeabilized muscle fibers. Comparisons between WT and homozygous G2435R-RYR1 mitochondria showed a significant increase in complex I-facilitated oxidative phosphorylation in mutant muscle. Furthermore, we observed a gene-dose-specific increase in reactive oxygen species production in G2435R-RYR1 muscle fibers. Collectively, these findings provide evidence of metabolic defects in G2435R-RYR1 knock-in mouse muscle under basal conditions. Differences in metabolic profile could be the result of differential gene expression in metabolic pathways, in conjunction with mitochondrial damage accumulated from chronic exposure to increased oxidative stress.

Permeabilised skeletal muscle reveals mitochondrial deficiency in malignant hyperthermia-susceptible individuals.

BACKGROUND: Individuals genetically susceptible to malignant hyperthermia (MH) exhibit hypermetabolic reactions when exposed to volatile anaesthetics. Mitochondrial dysfunction has previously been associated with the MH-susceptible (MHS) phenotype in animal models, but evidence of this in human MH is limited. METHODS: We used high resolution respirometry to compare oxygen consumption rates (oxygen flux) between permeabilised human MHS and MH-negative (MHN) skeletal muscle fibres with or without prior exposure to halothane. A substrate-uncoupler-inhibitor titration protocol was used to measure the following components of the electron transport chain under conditions of oxidative phosphorylation (OXPHOS) or after uncoupling the electron transport system (ETS): complex I (CI), complex II (CII), CI+CII and, as a measure of mitochondrial mass, complex IV (CIV). RESULTS: Baseline comparisons without halothane exposure showed significantly increased mitochondrial mass (CIV, P=0.021) but lower flux control ratios in CI+CII(OXPHOS) and CII(ETS) of MHS mitochondria compared with MHN (P=0.033 and 0.005, respectively) showing that human MHS mitochondria have a functional deficiency. Exposure to halothane triggered a hypermetabolic response in MHS mitochondria, significantly increasing mass-specific oxygen flux in CI(OXPHOS), CI+CII(OXPHOS), CI+CII(ETS), and CII(ETS) (P=0.001-0.012), while the rates in MHN samples were unaltered by halothane exposure. CONCLUSIONS: We present evidence of mitochondrial dysfunction in human MHS skeletal muscle both at baseline and after halothane exposure.

Quercetin preserves redox status and stimulates mitochondrial function in metabolically-stressed HepG2 cells.

Hyperglycemia augments formation of intracellular reactive oxygen species (ROS) with associated mitochondrial damage and increased risk of insulin resistance in type 2 diabetes. We examined whether quercetin could reverse chronic high glucose-induced oxidative stress and mitochondrial dysfunction. Following long-term high glucose treatment, complex I activity was significantly decreased in isolated mitochondria from HepG2 cells. Quercetin dose-dependently recovered complex I activity and lowered cellular ROS generation under both high and normal glucose conditions. Respirometry studies showed that quercetin could counteract the detrimental increase in inner mitochondrial membrane proton leakage resulting from high glucose while it increased oxidative respiration, despite a decrease in electron transfer system (ETS) capacity, and lower non-ETS oxygen consumption. A quercetin-stimulated increase in cellular NAD+/NADH was evident within 2 h and a two-fold increase in PGC-1α mRNA within 6 h, in both normal and high glucose conditions. A similar pattern was also found for the mRNA expression of the repulsive guidance molecule b (RGMB) and its long non-coding RNA (lncRNA) RGMB-AS1 with quercetin, indicating a potential change of the glycolytic phenotype and suppression of aberrant cellular growth which is characteristic of the HepG2 cells. Direct effects of quercetin on PGC-1α activity were minimal, as quercetin only weakly enhanced PGC-1α binding to PPARα in vitro at higher concentrations. Our results suggest that quercetin may protect mitochondrial function from high glucose-induced stress by increasing cellular NAD+/NADH and activation of PGC-1α-mediated pathways. Lower ROS in combination with improved complex I activity and ETS coupling efficiency under conditions of amplified oxidative stress could reinforce mitochondrial integrity and improve redox status, beneficial in certain metabolic diseases.

Multiple mechanisms mediating carbon monoxide inhibition of the voltage-gated K+ channel Kv1.5.

The voltage-gated K+ channel has key roles in the vasculature and in atrial excitability and contributes to apoptosis in various tissues. In this study, we have explored its regulation by carbon monoxide (CO), a product of the cytoprotective heme oxygenase enzymes, and a recognized toxin. CO inhibited recombinant Kv1.5 expressed in HEK293 cells in a concentration-dependent manner that involved multiple signalling pathways. CO inhibition was partially reversed by superoxide dismutase mimetics and by suppression of mitochondrial reactive oxygen species. CO also elevated intracellular nitric oxide (NO) levels. Prevention of NO formation also partially reversed CO inhibition of Kv1.5, as did inhibition of soluble guanylyl cyclase. CO also elevated intracellular peroxynitrite levels, and a peroxynitrite scavenger markedly attenuated the ability of CO to inhibit Kv1.5. CO caused nitrosylation of Kv1.5, an effect that was also observed in C331A and C346A mutant forms of the channel, which had previously been suggested as nitrosylation sites within Kv1.5. Augmentation of Kv1.5 via exposure to hydrogen peroxide was fully reversed by CO. Native Kv1.5 recorded in HL-1 murine atrial cells was also inhibited by CO. Action potentials recorded in HL-1 cells were increased in amplitude and duration by CO, an effect mimicked and occluded by pharmacological inhibition of Kv1.5. Our data indicate that Kv1.5 is a target for modulation by CO via multiple mechanisms. This regulation has important implications for diverse cellular functions, including excitability, contractility and apoptosis.

A key role for peroxynitrite-mediated inhibition of cardiac ERG (Kv11.1) K+ channels in carbon monoxide-induced proarrhythmic early afterdepolarizations.

Exposure to CO causes early afterdepolarization arrhythmias. Previous studies in rats have indicated that arrhythmias arose as a result of augmentation of the late Na+ current. The purpose of the present study was to examine the basis for CO-induced arrhythmias in guinea pig myocytes in which action potentials (APs) more closely resemble those of human myocytes. Whole-cell current- and voltage-clamp recordings were made from isolated guinea pig myocytes as well as from human embryonic kidney 293 (HEK293) cells that express wild-type or a C723S mutant form of ether-a-go-go-related gene (ERG; Kv11.1). We also monitored the formation of peroxynitrite (ONOO-) in HEK293 cells fluorimetrically. CO-applied as the CO-releasing molecule, CORM-2-prolonged the APs and induced early afterdepolarizations in guinea pig myocytes. In HEK293 cells, CO inhibited wild-type, but not C723S mutant, Kv11.1 K+ currents. Inhibition was prevented by an antioxidant, mitochondrial inhibitors, or inhibition of NO formation. CO also raised ONOO- levels, an effect that was reversed by the ONOO- scavenger, FeTPPS [5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrinato-iron(III)], which also prevented the CO inhibition of Kv11.1 currents and abolished the effects of CO on Kv11.1 tail currents and APs in guinea pig myocytes. Our data suggest that CO induces arrhythmias in guinea pig cardiac myocytes via the ONOO--mediated inhibition of Kv11.1 K+ channels.-Al-Owais, M. M., Hettiarachchi, N. T., Kirton, H. M., Hardy, M. E., Boyle, J. P., Scragg, J. L., Steele, D. S., Peers, C. A key role for peroxynitrite-mediated inhibition of cardiac ERG (Kv11.1) K+ channels in carbon monoxide-induced proarrhythmic early afterdepolarizations.

Heme oxygenase-1 derived carbon monoxide suppresses Aß1-42 toxicity in astrocytes.

Neurodegeneration in Alzheimer's disease (AD) is extensively studied, and the involvement of astrocytes and other cell types in this process has been described. However, the responses of astrocytes themselves to amyloid ß peptides ((Aß; the widely accepted major toxic factor in AD) is less well understood. Here, we show that Aß(1-42) is toxic to primary cultures of astrocytes. Toxicity does not involve disruption of astrocyte Ca2+ homeostasis, but instead occurs via formation of the toxic reactive species, peroxynitrite. Thus, Aß(1-42) raises peroxynitrite levels in astrocytes, and Aß(1-42) toxicity can be inhibited by antioxidants, or by inhibition of nitric oxide (NO) formation (reactive oxygen species (ROS) and NO combine to form peroxynitrite), or by a scavenger of peroxynitrite. Increased ROS levels observed following Aß(1-42) application were derived from NADPH oxidase. Induction of haem oxygenase-1 (HO-1) protected astrocytes from Aß(1-42) toxicity, and this protective effect was mimicked by application of the carbon monoxide (CO) releasing molecule CORM-2, suggesting HO-1 protection was attributable to its formation of CO. CO suppressed the rise of NADPH oxidase-derived ROS caused by Aß(1-42). Under hypoxic conditions (0.5% O2, 48 h) HO-1 was induced in astrocytes and Aß(1-42) toxicity was significantly reduced, an effect which was reversed by the specific HO-1 inhibitor, QC-15. Our data suggest that Aß(1-42) is toxic to astrocytes, but that induction of HO-1 affords protection against this toxicity due to formation of CO. HO-1 induction, or CO donors, would appear to present attractive possible approaches to provide protection of both neuronal and non-neuronal cell types from the degenerative effects of AD in the central nervous system.

Regulation of the T-type Ca(2+) channel Cav3.2 by hydrogen sulfide: emerging controversies concerning the role of H2 S in nociception.

Ion channels represent a large and growing family of target proteins regulated by gasotransmitters such as nitric oxide, carbon monoxide and, as described more recently, hydrogen sulfide. Indeed, many of the biological actions of these gases can be accounted for by their ability to modulate ion channel activity. Here, we report recent evidence that H2 S is a modulator of low voltage-activated T-type Ca(2+) channels, and discriminates between the different subtypes of T-type Ca(2+) channel in that it selectively modulates Cav3.2, whilst Cav3.1 and Cav3.3 are unaffected. At high concentrations, H2 S augments Cav3.2 currents, an observation which has led to the suggestion that H2 S exerts its pro-nociceptive effects via this channel, since Cav3.2 plays a central role in sensory nerve excitability. However, at more physiological concentrations, H2 S is seen to inhibit Cav3.2. This inhibitory action requires the presence of the redox-sensitive, extracellular region of the channel which is responsible for tonic metal ion binding and which particularly distinguishes this channel isoform from Cav3.1 and 3.3. Further studies indicate that H2 S may act in a novel manner to alter channel activity by potentiating the zinc sensitivity/affinity of this binding site. This review discusses the different reports of H2 S modulation of T-type Ca(2+) channels, and how such varying effects may impact on nociception given the role of this channel in sensory activity. This subject remains controversial, and future studies are required before the impact of T-type Ca(2+) channel modulation by H2 S might be exploited as a novel approach to pain management.

The Golgi apparatus is a functionally distinct Ca2+ store regulated by the PKA and Epac branches of the ß1-adrenergic signaling pathway.

Ca(2+) release from the Golgi apparatus regulates key functions of the organelle, including vesicle trafficking. We found that the Golgi apparatus was the source of prolonged Ca(2+) release events that originated near the nuclei of primary cardiomyocytes. Golgi Ca(2+) release was unaffected by depletion of sarcoplasmic reticulum Ca(2+), and disruption of the Golgi apparatus abolished Golgi Ca(2+) release without affecting sarcoplasmic reticulum function, suggesting functional and spatial independence of Golgi and sarcoplasmic reticulum Ca(2+) stores. ß1-Adrenoceptor stimulation triggers the production of the second messenger cAMP, which activates the Epac family of Rap guanine nucleotide exchange factors and the kinase PKA (protein kinase A). Phosphodiesterases (PDEs), including those in the PDE3 and PDE4 families, degrade cAMP. Activation of ß1-adrenoceptors stimulated Golgi Ca(2+) release, an effect that required activation of Epac, PKA, and the kinase CaMKII. Inhibition of PDE3s or PDE4s potentiated ß1-adrenergic-induced Golgi Ca(2+) release, which is consistent with compartmentalization of cAMP signaling near the Golgi apparatus. Interventions that stimulated Golgi Ca(2+) release appeared to increase the trafficking of vascular endothelial growth factor receptor-1 (VEGFR-1) from the Golgi apparatus to the surface membrane of cardiomyocytes. In cardiomyocytes from rats with heart failure, decreases in the abundance of PDE3s and PDE4s were associated with increased Golgi Ca(2+) release events. These data suggest that the Golgi apparatus is a focal point for ß1-adrenergic-stimulated Ca(2+) signaling and that the Golgi Ca(2+) store functions independently from the sarcoplasmic reticulum and the global Ca(2+) transients that trigger contraction in cardiomyocytes.

T-Type Ca2+ Channel Regulation by CO: A Mechanism for Control of Cell Proliferation.

T-type Ca(2+) channels regulate proliferation in a number of tissue types, including vascular smooth muscle and various cancers. In such tissues, up-regulation of the inducible enzyme heme oxygenase-1 (HO-1) is often observed, and hypoxia is a key factor in its induction. HO-1 degrades heme to generate carbon monoxide (CO) along with Fe(2+) and biliverdin. Since CO is increasingly recognized as a regulator of ion channels (Peers et al. 2015), we have explored the possibility that it may regulate proliferation via modulation of T-type Ca(2+) channels.Whole-cell patch-clamp recordings revealed that CO (applied as the dissolved gas or via CORM donors) inhibited all 3 isoforms of T-type Ca(2+) channels (Cav3.1-3.3) when expressed in HEK293 cells with similar IC(50) values, and induction of HO-1 expression also suppressed T-type currents (Boycott et al. 2013). CO/HO-1 induction also suppressed the elevated basal [Ca(2+) ](i) in cells expressing these channels and reduced their proliferative rate to levels seen in non-transfected control cells (Duckles et al. 2015).Proliferation of vascular smooth muscle cells (both A7r5 and human saphenous vein cells) was also suppressed either by T-type Ca(2+) channel inhibitors (mibefradil and NNC 55-0396), HO-1 induction or application of CO. Effects of these blockers and CO were non additive. Although L-type Ca(2+) channels were also sensitive to CO (Scragg et al. 2008), they did not influence proliferation. Our data suggest that HO-1 acts to control proliferation via CO modulation of T-type Ca(2+) channels.

Heme Oxygenase-1 Influences Apoptosis via CO-mediated Inhibition of K+ Channels.

Hypoxic/ischemic episodes can trigger oxidative stress-mediated loss of central neurons via apoptosis, and low pO2 is also a feature of the tumor microenvironment, where cancer cells are particularly resistant to apoptosis. In the CNS, ischemic insult increases expression of the CO-generating enzyme heme oxygenase-1 (HO-1), which is commonly constitutively active in cancer cells. It has been proposed that apoptosis can be regulated by the trafficking and activity of K(+) channels, particularly Kv2.1. We have explored the idea that HO-1 may influence apoptosis via regulation of Kv2.1. Overexpression of Kv2.1 in HEK293 cells increased their vulnerability to oxidant-induced apoptosis. CO (applied as the donor CORM-2) protected cells against apoptosis and inhibited Kv2.1 channels. Similarly in hippocampal neurones, CO selectively inhibited Kv2.1 and protected neurones against oxidant-induced apoptosis. In medulloblastoma sections we identified constitutive expression of HO-1 and Kv2.1, and in the medulloblastoma-derived cell line DAOY, hypoxic HO-1 induction or exposure to CO protected cells against apoptosis, and also selectively inhibited Kv2.1 channels expressed in these cells. These studies are consistent with a central role for Kv2.1 in apoptosis in both central neurones and cancer cells. They also suggest that HO-1 expression can strongly influence apoptosis via CO-mediated regulation of Kv2.1 activity.

Inhibition of T-type Ca2+ Channels by Hydrogen Sulfide.

T-type Ca(2+) channels are a distinct family of low voltage-activated Ca(2+) channels which serve many roles in different tissues. Several studies have implicated them, for example, in the adaptive responses to chronic hypoxia in the cardiovascular and endocrine systems. Hydrogen sulfide (H(2)S) was more recently discovered as an important signalling molecule involved in many functions, including O(2) sensing. Since ion channels are emerging as an important family of target proteins for modulation by H(2)S, and both T-type Ca(2+) channels and H(2)S are involved in cellular responses to hypoxia, we have investigated whether recombinant and native T-type Ca(2+) channels are a target for modulation by H(2)S. Using patch-clamp electrophysiology, we demonstrate that the H(2)S donor, NaHS, selectively inhibits Cav3.2 T-type Ca(2+) channels heterologously expressed in HEK293 cells, whilst Cav3.1 and Cav3.3 channels were unaffected. Sensitivity of Cav3.2 channels to H2S required the presence of the redox-sensitive extracellular residue H191, which is also required for tonic binding of Zn(2+) to this channel. Chelation of Zn(2+) using TPEN prevented channel inhibition by H(2)S. H2S also selectively inhibited native T-type channels (primarily Cav3.2) in sensory dorsal root ganglion neurons. Our data demonstrate a novel target for H(2)S regulation, the T-type Ca(2+) channel Cav3.2. Results have important implications for the proposed pro-nociceptive effects of this gasotransmitter. Implications for the control of cellular responses to hypoxia await further study.

H2S does not regulate proliferation via T-type Ca2+ channels.

T-type Ca(2+) channels (Cav3.1, 3.2 and 3.3) strongly influence proliferation of various cell types, including vascular smooth muscle cells (VSMCs) and certain cancers. We have recently shown that the gasotransmitter carbon monoxide (CO) inhibits T-type Ca(2+) channels and, in so doing, attenuates proliferation of VSMC. We have also shown that the T-type Ca(2+) channel Cav3.2 is selectively inhibited by hydrogen sulfide (H2S) whilst the other channel isoforms (Cav3.1 and Cav3.3) are unaffected. Here, we explored whether inhibition of Cav3.2 by H2S could account for the anti-proliferative effects of this gasotransmitter. H2S suppressed proliferation in HEK293 cells expressing Cav3.2, as predicted by our previous observations. However, H2S was similarly effective in suppressing proliferation in wild type (non-transfected) HEK293 cells and those expressing the H2S insensitive channel, Cav3.1. Further studies demonstrated that T-type Ca(2+) channels in the smooth muscle cell line A7r5 and in human coronary VSMCs strongly influenced proliferation. In both cell types, H2S caused a concentration-dependent inhibition of proliferation, yet by far the dominant T-type Ca(2+) channel isoform was the H2S-insensitive channel, Cav3.1. Our data indicate that inhibition of T-type Ca(2+) channel-mediated proliferation by H2S is independent of the channels' sensitivity to H2S.

Protection from neurodegeneration in the 6-hydroxydopamine (6-OHDA) model of Parkinson's with novel 1-hydroxypyridin-2-one metal chelators.

Brain iron accumulation has been associated with inciting the generation of oxidative stress in a host of chronic neurological diseases, including Parkinson's disease. Using the catecholaminergic neurotoxin 6-hydroxydopamine to lesion cellular dopaminergic pathways as a model of Parkinson's disease in culture, a selection of 1-hydroxypyridin-2-one (1,2-HOPO) metal chelators were synthesized and their neuroprotective properties were compared to the 3-hydroxypyridin-4-one; deferiprone (3,4-HOPO; DFP). Protection against 6-OHDA and iron insult by the novel compounds 6 and 9 was comparable to DFP. Iron associated changes by 6-OHDA imply that the neuroprotective capacity of these compounds are due to chelation of the neuronal labile iron pool and the requirement of the iron binding moiety of compound 6 for efficacy supported this hypothesis. In conclusion, two novel 1,2-HOPO's and DFP have comparable neuroprotection against Parkinsonian-associated neurotoxins and supports the continued development of hydroxypyridinone compounds as a non-toxic therapeutic agent in the treatment of neurodegenerative disease.

Oxidative modulation of K+ channels in the central nervous system in neurodegenerative diseases and aging.

SIGNIFICANCE: Oxidative stress and damage are well-established components of neurodegenerative diseases, contributing to neuronal death during disease progression. Here, we consider key K(+) channels as target proteins that can undergo oxidative modulation, describe what is understood about how this influences disease progression, and consider regulation of these channels by gasotransmitters as a means of cellular protection. RECENT ADVANCES: Oxidative regulation of the delayed rectifier Kv2.1 and the Ca(2+)- and voltage-sensitive BK channel are established, but recent studies contest how their redox sensitivity contributes to altered excitability, progression of neurodegenerative diseases, and healthy aging. CRITICAL ISSUES: Both Kv2.1 and BK channels have recently been established as target proteins for regulation by the gasotransmitters carbon monoxide and hydrogen sulfide. Establishing the molecular basis of such regulation, and exactly how this influences excitability and vulnerability to apoptotic cell death will determine whether such regulation can be exploited for therapeutic benefit. FUTURE DIRECTIONS: Developing a more comprehensive picture of the oxidative modulation of K(+) channels (and, indeed, other ion channels) within the central nervous system in health and disease will enable us to better understand processes associated with healthy aging as well as distinct processes underlying progression of neurodegenerative diseases. Advances in the growing understanding of how gasotransmitters can regulate ion channels, including redox-sensitive K(+) channels, are a research priority for this field, and will establish their usefulness in design of future approaches for the treatment of such diseases.

Heme oxygenase-1 regulates cell proliferation via carbon monoxide-mediated inhibition of T-type Ca2+ channels.

Induction of the antioxidant enzyme heme oxygenase-1 (HO-1) affords cellular protection and suppresses proliferation of vascular smooth muscle cells (VSMCs) associated with a variety of pathological cardiovascular conditions including myocardial infarction and vascular injury. However, the underlying mechanisms are not fully understood. Over-expression of Cav3.2 T-type Ca(2+) channels in HEK293 cells raised basal [Ca(2+)]i and increased proliferation as compared with non-transfected cells. Proliferation and [Ca(2+)]i levels were reduced to levels seen in non-transfected cells either by induction of HO-1 or exposure of cells to the HO-1 product, carbon monoxide (CO) (applied as the CO releasing molecule, CORM-3). In the aortic VSMC line A7r5, proliferation was also inhibited by induction of HO-1 or by exposure of cells to CO, and patch-clamp recordings indicated that CO inhibited T-type (as well as L-type) Ca(2+) currents in these cells. Finally, in human saphenous vein smooth muscle cells, proliferation was reduced by T-type channel inhibition or by HO-1 induction or CO exposure. The effects of T-type channel blockade and HO-1 induction were non-additive. Collectively, these data indicate that HO-1 regulates proliferation via CO-mediated inhibition of T-type Ca(2+) channels. This signalling pathway provides a novel means by which proliferation of VSMCs (and other cells) may be regulated therapeutically.

Hydrogen sulfide inhibits Cav3.2 T-type Ca2+ channels.

The importance of H2S as a physiological signaling molecule continues to develop, and ion channels are emerging as a major family of target proteins through which H2S exerts many actions. The purpose of the present study was to investigate its effects on T-type Ca(2+) channels. Using patch-clamp electrophysiology, we demonstrate that the H2S donor, NaHS (10 µM-1 mM) selectively inhibits Cav3.2 T-type channels heterologously expressed in HEK293 cells, whereas Cav3.1 and Cav3.3 channels were unaffected. The sensitivity of Cav3.2 channels to H2S required the presence of the redox-sensitive extracellular residue H191, which is also required for tonic binding of Zn(2+) to this channel. Chelation of Zn(2+) with N,N,N',N'-tetra-2-picolylethylenediamine prevented channel inhibition by H2S and also reversed H2S inhibition when applied after H2S exposure, suggesting that H2S may act via increasing the affinity of the channel for extracellular Zn(2+) binding. Inhibition of native T-type channels in 3 cell lines correlated with expression of Cav3.2 and not Cav3.1 channels. Notably, H2S also inhibited native T-type (primarily Cav3.2) channels in sensory dorsal root ganglion neurons. Our data demonstrate a novel target for H2S regulation, the T-type Ca(2+) channel Cav3.2, and suggest that such modulation cannot account for the pronociceptive effects of this gasotransmitter.

Inhibition of the cardiac Na⁺ channel Nav1.5 by carbon monoxide.

Sublethal carbon monoxide (CO) exposure is frequently associated with myocardial arrhythmias, and our recent studies have demonstrated that these may be attributable to modulation of cardiac Na(+) channels, causing an increase in the late current and an inhibition of the peak current. Using a recombinant expression system, we demonstrate that CO inhibits peak human Nav1.5 current amplitude without activation of the late Na(+) current observed in native tissue. Inhibition was associated with a hyperpolarizing shift in the steady-state inactivation properties of the channels and was unaffected by modification of channel gating induced by anemone toxin (rATX-II). Systematic pharmacological assessment indicated that no recognized CO-sensitive intracellular signaling pathways appeared to mediate CO inhibition of Nav1.5. Inhibition was, however, markedly suppressed by inhibition of NO formation, but NO donors did not mimic or occlude channel inhibition by CO, indicating that NO alone did not account for the actions of CO. Exposure of cells to DTT immediately before CO exposure also dramatically reduced the magnitude of current inhibition. Similarly, l-cysteine and N-ethylmaleimide significantly attenuated the inhibition caused by CO. In the presence of DTT and the NO inhibitor N(ω)-nitro-L-arginine methyl ester hydrochloride, the ability of CO to inhibit Nav1.5 was almost fully prevented. Our data indicate that inhibition of peak Na(+) current (which can lead to Brugada syndrome-like arrhythmias) occurs via a mechanism distinct from induction of the late current, requires NO formation, and is dependent on channel redox state.

Carbon monoxide inhibition of Cav3.2 T-type Ca2+ channels reveals tonic modulation by thioredoxin.

T-type Ca(2+) channels play diverse roles in tissues such as sensory neurons, vascular smooth muscle, and cancers, where increased expression of the cytoprotective enzyme, heme oxygenase-1 (HO-1) is often found. Here, we report regulation of T-type Ca(2+) channels by carbon monoxide (CO) a HO-1 by-product. CO (applied as CORM-2) caused a concentration-dependent, poorly reversible inhibition of all T-type channel isoforms (Cav3.1-3.3, IC50 ∼3 µM) expressed in HEK293 cells, and native T-type channels in NG108-15 cells and primary rat sensory neurons. No recognized CO-sensitive signaling pathway could account for the CO inhibition of Cav3.2. Instead, CO sensitivity was mediated by an extracellular redox-sensitive site, which was also highly sensitive to thioredoxin (Trx). Trx depletion (using auranofin, 2-5 µM) reduced Cav3.2 currents and their CO sensitivity by >50% but increased sensitivity to dithiothreitol ∼3-fold. By contrast, Cav3.1 and Cav3.3 channels, and their sensitivity to CO, were unaffected in identical experiments. Our data propose a novel signaling pathway in which Trx acts as a tonic, endogenous regulator of Cav3.2 channels, while HO-1-derived CO disrupts this regulation, causing channel inhibition. CO modulation of T-type channels has widespread implications for diverse physiological and pathophysiological mechanisms, such as excitability, contractility, and proliferation.

VennPlex--a novel Venn diagram program for comparing and visualizing datasets with differentially regulated datapoints.

With the development of increasingly large and complex genomic and proteomic data sets, an enhancement in the complexity of available Venn diagram analytical programs is becoming increasingly important. Current freely available Venn diagram programs often fail to represent extra complexity among datasets, such as regulation pattern differences between different groups. Here we describe the development of VennPlex, a program that illustrates the often diverse numerical interactions among multiple, high-complexity datasets, using up to four data sets. VennPlex includes versatile output features, where grouped data points in specific regions can be easily exported into a spreadsheet. This program is able to facilitate the analysis of two to four gene sets and their corresponding expression values in a user-friendly manner. To demonstrate its unique experimental utility we applied VennPlex to a complex paradigm, i.e. a comparison of the effect of multiple oxygen tension environments (1-20% ambient oxygen) upon gene transcription of primary rat astrocytes. VennPlex accurately dissects complex data sets reliably into easily identifiable groups for straightforward analysis and data output. This program, which is an improvement over currently available Venn diagram programs, is able to rapidly extract important datasets that represent the variety of expression patterns available within the data sets, showing potential applications in fields like genomics, proteomics, and bioinformatics.