Activation of KATP channels by H2S in rat insulin-secreting cells and the underlying mechanisms

Highly selective fluorescent and colorimetric probe for live-cell monitoring of sulphide based on bioorthogonal reaction

H₂S is the third endogenously generated gaseous signaling compound and has also been known to involve a variety of physiological processes. To better understand its physiological and pathological functions, efficient methods for monitoring of H₂S are desired. Azide fluorogenic probes are popular because they can take place bioorthogonal reactions. In this work, by employing a fluorescein derivative as the fluorophore and an azide group as the recognition unit, we reported a new probe 5-azidofluorescein for H₂S with improved sensitivity and selectivety. The probe shows very low background fluorescence in the absence of H₂S. In the presence of H₂S, however, a significant enhancement for excited fluorescence were observed, resulting in a high sensitivity to H₂S in buffered (10 mmol/L HEPES, pH 7.0) aqueous acetonitrile solution (H₂O/CH₃CN = 1:3, v/v) with a detection limit of 0.035 μmol/L observed, much lower than the previously reported probes. All these features are favorable for direct monitoring of H₂S with satisfactory sensitivity, demonstrating its value of practical application.

L-cysteine reversibly inhibits glucose-induced biphasic insulin secretion and ATP production by inactivating PKM2

Increase in the concentration of plasma L-cysteine is closely associated with defective insulin secretion from pancreatic β-cells, which results in type 2 diabetes (T2D). In this study, we investigated the effects of prolonged L-cysteine treatment on glucose-stimulated insulin secretion (GSIS) from mouse insulinoma 6 (MIN6) cells and from mouse pancreatic islets, and found that the treatment reversibly inhibited glucose-induced ATP production and resulting GSIS without affecting proinsulin and insulin synthesis. Comprehensive metabolic analyses using capillary electrophoresis time-of-flight mass spectrometry showed that prolonged L-cysteine treatment decreased the levels of pyruvate and its downstream metabolites. In addition, methyl pyruvate, a membrane-permeable form of pyruvate, rescued L-cysteine-induced inhibition of GSIS. Based on these results, we found that both in vitro and in MIN6 cells, L-cysteine specifically inhibited the activity of pyruvate kinase muscle isoform 2 (PKM2), an isoform of pyruvate kinases that catalyze the conversion of phosphoenolpyruvate to pyruvate. L-cysteine also induced PKM2 subunit dissociation (tetramers to dimers/monomers) in cells, which resulted in impaired glucose-induced ATP production for GSIS. DASA-10 (NCGC00181061, a substituted N,N'-diarylsulfonamide), a specific activator for PKM2, restored the tetramer formation and the activity of PKM2, glucose-induced ATP production, and biphasic insulin secretion in L-cysteine-treated cells. Collectively, our results demonstrate that impaired insulin secretion due to exposure to L-cysteine resulted from its direct binding and inactivation of PKM2 and suggest that PKM2 is a potential therapeutic target for T2D.

Signaling molecules: hydrogen sulfide and polysulfide

SIGNIFICANCE

Hydrogen sulfide (H2S) has been recognized as a signaling molecule as well as a cytoprotectant. It modulates neurotransmission, regulates vascular tone, and protects various tissues and organs, including neurons, the heart, and kidneys, from oxidative stress and ischemia-reperfusion injury. H2S is produced from l-cysteine by cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE), and 3-mercaptopyruvate sulfurtransferase (3MST) along with cysteine aminotransferase.

RECENT ADVANCES

In addition to these enzymes, we recently identified a novel pathway to produce H2S from d-cysteine, which involves d-amino acid oxidase (DAO) along with 3MST. These enzymes are localized in the cytoplasm, mitochondria, and peroxisomes. However, some enzymes translocate to organelles under specific conditions. Moreover, H2S-derived potential signaling molecules such as polysulfides and HSNO have been identified.

CRITICAL ISSUES

The physiological stimulations, which trigger the production of H2S and its derivatives and maintain their local levels, remain unclear.

FUTURE DIRECTIONS

Understanding the regulation of the H2S production and H2S-derived signaling molecules and the specific stimuli that induce their release will provide new insights into the biology of H2S and therapeutic development in diseases involving these substances.

Hydrogen sulfide and neuronal differentiation: focus on Ca2+ channels

Hydrogen sulfide (H2S) is considered the third gasotransmitter following nitric oxide (NO) and carbon monoxide (CO) in the mammalian body including the brain, heart, blood vessels, liver, kidney, pancreas, lung, gastrointestinal tract and reproductive organs. H2S is formed endogenously from L-cysteine by multiple enzymes, such as cystathionine-γ-lyase, cystathionine-β-synthase and 3-mercaptopyruvate sulfurtransferase in combination with cysteine aminotransferase, and participates in a variety of biological events through a number of target molecules. Exogenous and/or endogenous H2S enhances the activity of T-type Ca(2+) channels in NG108-15 cells and isolated dorsal root ganglion neurons that abundantly express Cav3.2, and in Cav3.2-transfected HEK293 cells. Cav3.2 mediates not only the H2S-induced enhancement of pain signals in nociceptor neurons, but also neuronal differentiation characterized by neuritogenesis and functional upregulation of high voltage-activated Ca(2+) channels in NG108-15 cells. In this review, we focus on the functional modulation by H2S of primarily Cav3.2 T-type Ca(2+) channels and the molecular mechanisms underlying the H2S-induced neuronal differentiation.

Reaction-based epoxide fluorescent probe for in vivo visualization of hydrogen sulfide

Hydrogen sulfide (H2S) has emerged as the most important biosynthetic gasotransmitters along with nitric oxide (NO) and carbon monoxide (CO). In this study, we report the design and the synthesis of a new epoxide fluorescent probe 7-glycidyloxy-9-(2-glycidyloxycarbonylphenyl)-2-xanthone (FEPO) for use in in vivo visualization of hydrogen sulfide. The probe employs a fluorescein as a fluorophore, and is equipped with an operating epoxide unit. FEPO functions via epoxide ring opening upon nucleophilic attack of H2S. This ring opening strategy may open a new avenue for the development of various H2S fluorescent sensors. FEPO showed high selectivity and high sensitivity for H2S. FEPO's cytotoxicity was tested using MTT (2-(4,5-dimethyl-2-thiazolyl)-3,5-diphenyl-2H-tetrazolium bromide) assay. Furthermore, the use of confocal imaging of H2S and in vivo imaging in live zebra fish demonstrated FEPO's potential biological applications. We anticipate that, owing to their ideal properties, probes of this type will find great uses in exploring the role of H2S in biology.

A fluorescent probe for H2S in vivo with fast response and high sensitivity

In this work, a fluorescent probe has been designed and synthesized that could be applied for monitoring and imaging exogenous or endogenous H₂S in live MCF-7 cells and in live mice with the fastest response.

Performance comparison of two cascade reaction models in fluorescence off–on detection of hydrogen sulfide

Comparative studies on the performances of two cascade reaction based fluorescent H₂S probes are reported.

A turn-on fluorescent probe for hydrogen sulfide and its application in living cells

Herein, we described a probe for H₂S detection based on the reduction of azide to amine. This probe was highly sensitive and selective toward H₂S and successfully applied for H₂S fluorescent imaging in living cells.

A hexaphenylbenzene based AIEE active two photon probe for the detection of hydrogen sulfide with tunable self-assembly in aqueous media and application in live cell imaging

AIEE active HPB based TPE probe exhibited modulation of self-assembled architecture in presence of H₂S and was utilized for TPM imaging for detection of H₂S in HeLa cells.

Construction of a turn-on probe for fast detection of H2S in living cells based on a novel H2S trap group with an electron rich dye

A fluorescent probeANRbased on a novel H₂S trap group was synthesized for discriminating detection of H₂S in living cells.

Hydrogen sulfide mediated cascade reaction forming an iminocoumarin: applications in fluorescent probe development and live-cell imaging

The study on a fluorescent probe that undergoes a H₂S mediated cascade reaction to form an iminocoumarin fluorophore is reported.

Optical analysis of biological hydrogen sulphide: an overview of recent advancements

In this review we provide an overview of recent advancements in optical analysis of biological hydrogen sulphide, with a focus on fluorescence and non-fluorescence optical strategies for sensing and imaging subcellular hydrogen sulphide in living biosystems.

A selective and sensitive phthalimide-based fluorescent probe for hydrogen sulfide with a large Stokes shift

A phthalimide-based fluorescent probe for H₂S with a large Stokes shift has been developed. This probe displayed good selectivity and high sensitivity. Imaging intracellular H₂S by using this probe was successfully achieved in living cells.

Silicon nanowires-based fluorescent sensor for in situ detection of hydrogen sulfide in extracellular environment

Based on a Si nanowire array, a fluorescent sensor for H₂S was realized and successfully used for real time and in situ imaging of the changes in extracellular H₂S of live cells.

Hydrogen sulfide and polysulfides as signaling molecules

Hydrogen sulfide (H2S) is a familiar toxic gas that smells of rotten eggs. After the identification of endogenous H2S in the mammalian brain two decades ago, studies of this molecule uncovered physiological roles in processes such as neuromodulation, vascular tone regulation, cytoprotection against oxidative stress, angiogenesis, anti-inflammation, and oxygen sensing. Enzymes that produce H2S, such as cystathionine β-synthase, cystathionine γ-lyase, and 3-mercaptopyruvate sulfurtransferase have been studied intensively and well characterized. Polysulfides, which have a higher number of inner sulfur atoms than that in H2S, were recently identified as potential signaling molecules that can activate ion channels, transcription factors, and tumor suppressors with greater potency than that of H2S. This article focuses on our contribution to the discovery of these molecules and their metabolic pathways and mechanisms of action.

Hydrogen sulfide generated by L-cysteine desulfhydrase acts upstream of nitric oxide to modulate abscisic acid-dependent stomatal closure

Abscisic acid (ABA) is a well-studied regulator of stomatal movement. Hydrogen sulfide (H2S), a small signaling gas molecule involved in key physiological processes in mammals, has been recently reported as a new component of the ABA signaling network in stomatal guard cells. In Arabidopsis (Arabidopsis thaliana), H2S is enzymatically produced in the cytosol through the activity of l-cysteine desulfhydrase (DES1). In this work, we used DES1 knockout Arabidopsis mutant plants (des1) to study the participation of DES1 in the cross talk between H2S and nitric oxide (NO) in the ABA-dependent signaling network in guard cells. The results show that ABA did not close the stomata in isolated epidermal strips of des1 mutants, an effect that was restored by the application of exogenous H2S. Quantitative reverse transcription polymerase chain reaction analysis demonstrated that ABA induces DES1 expression in guard cell-enriched RNA extracts from wild-type Arabidopsis plants. Furthermore, stomata from isolated epidermal strips of Arabidopsis ABA receptor mutant pyrabactin-resistant1 (pyr1)/pyrabactin-like1 (pyl1)/pyl2/pyl4 close in response to exogenous H2S, suggesting that this gasotransmitter is acting downstream, although acting independently of the ABA receptor cannot be ruled out with this data. However, the Arabidopsis clade-A PROTEIN PHOSPHATASE2C mutant abscisic acid-insensitive1 (abi1-1) does not close the stomata when epidermal strips were treated with H2S, suggesting that H2S required a functional ABI1. Further studies to unravel the cross talk between H2S and NO indicate that (1) H2S promotes NO production, (2) DES1 is required for ABA-dependent NO production, and (3) NO is downstream of H2S in ABA-induced stomatal closure. Altogether, data indicate that DES1 is a unique component of ABA signaling in guard cells.

Metal-organic framework based highly selective fluorescence turn-on probe for hydrogen sulphide

Hydrogen sulphide (H₂S) is known to play a vital role in human physiology and pathology which stimulated interest in understanding complex behaviour of H₂S. Discerning the pathways of H₂S production and its mode of action is still a challenge owing to its volatile and reactive nature. Herein we report azide functionalized metal-organic framework (MOF) as a selective turn-on fluorescent probe for H₂S detection. The MOF shows highly selective and fast response towards H₂S even in presence of other relevant biomolecules. Low cytotoxicity and H₂S detection in live cells, demonstrate the potential of MOF towards monitoring H₂S chemistry in biological system. To the best of our knowledge this is the first example of MOF that exhibit fast and highly selective fluorescence turn-on response towards H₂S under physiological conditions.

Release of GLP-1 and PYY in response to the activation of G protein-coupled bile acid receptor TGR5 is mediated by Epac/PLC-ε pathway and modulated by endogenous H2S

Activation of plasma membrane TGR5 receptors in enteroendocrine cells by bile acids is known to regulate gastrointestinal secretion and motility and glucose homeostasis. The endocrine functions of the gut are modulated by microenvironment of the distal gut predominantly by sulfur-reducing bacteria of the microbiota that produce H₂S. However, the mechanisms involved in the release of peptide hormones, GLP-1 and PYY in response to TGR5 activation by bile acids and the effect of H₂S on bile acid-induced release of GLP-1 and PYY are unclear. In the present study, we have identified the signaling pathways activated by the bile acid receptor TGR5 to mediate GLP-1 and PYY release and the mechanism of inhibition of their release by H₂S in enteroendocrine cells. The TGR5 ligand oleanolic acid (OA) stimulated Gα_s and cAMP formation, and caused GLP-1 and PYY release. OA-induced cAMP formation and peptide release were blocked by TGR5 siRNA. OA also caused an increase in PI hydrolysis and intracellular Ca²⁺. Increase in PI hydrolysis was abolished in cells transfected with PLC-ε siRNA. 8-pCPT-2′-O-Me-cAMP, a selective activator of Epac, stimulated PI hydrolysis, and GLP-1 and PYY release. L-Cysteine, which activates endogenous H₂S producing enzymes cystathionine-γ-lyase and cystathionine-β-synthase, and NaHS and GYY4137, which generate H₂S, inhibited PI hydrolysis and GLP-1 and PYY release in response to OA or 8-pCPT-2′-O-Me-cAMP. Propargylglycine, an inhibitor of CSE, reversed the effect of L-cysteine on PI hydrolysis and GLP-1 and PYY release. We conclude: (i) activation of Gα_s-coupled TGR5 receptors causes stimulation of PI hydrolysis, and release of GLP-1 and PYY via a PKA-independent, cAMP-dependent mechanism involving Epac/PLC-ε/Ca²⁺ pathway, and (ii) H₂S has potent inhibitory effects on GLP-1 and PYY release in response to TGR5 activation, and the mechanism involves inhibition of PLC-ε/Ca²⁺ pathway.

A highly responsive and selective fluorescent probe for imaging physiological hydrogen sulfide

The discovery of hydrogen sulfide (H2S) as a novel gasotransmitter for cell signaling and other pathophysiological processes has spurred tremendous interest in developing analytical methods for its detection in biological systems. Herein, we report the development of a highly responsive and selective genetically encoded H2S probe, hsGFP, for the detection of H2S both in vitro and in living mammalian cells. hsGFP bestows a combination of favorable properties, including large fluorescence responses, high efficiency in folding and chromophore formation, and excellent sensitivity and selectivity toward H2S. As a genetically encoded probe, hsGFP can be readily and precisely localized to subcellular domains such as mitochondria, cell nuclei, and ion channels. hsGFP was further utilized to image H2S enzymatically produced from l-cysteine in human embryonic kidney (HEK) 293T cells.

In situ activation of CdS electrochemiluminescence film and its application in H₂S detection

Nanocrystals (NCs) usually suffer from weak electrogenerated chemiluminescence (ECL) emissions compared with conventional luminescent reagents like Ru(bpy)3(2+). In this work, we proposed a simple in situ activation approach by dipping CdS NCs film on glass carbon electrode (CdS NCs/GCE) in an activation solution containing H2O2 and citric acid, resulting in a ~58-fold enhancement of ECL intensity in the presence of coreactant H2O2. During activation, CdS NCs were oxidized by H2O2 to smaller ones which resulted in more surface S vacancies; meanwhile, citric acid played an important role in stabilizing NCs. The ECL enhancing mechanism was investigated in detail, and the coordination of H2O2 to surface excess Cd(2+) ions (S vacancies) on the CdS NCs surface formed in activation was the main factor which could stabilize the electrogenerated radicals, resulting in an enhanced ECL. ECL from the activated CdS NCs/GCE could be quenched in Na2S solution due to the bonding of S(II) to excess Cd(2+) ions on the surface of CdS NCs. On the basis of this, we then used the activated CdS NCs/GCE as an ECL probe for the detection of Na2S which showed good performance including a wide linear range of 5 nM to 20 μM and good anti-interference ability. Moreover, this ECL probe was successfully applied for hydrogen sulfide (H2S) detection in a biological system.

H2S and its role in redox signaling

Hydrogen sulfide (H2S) has emerged as an important gaseous signaling molecule that is produced endogenously by enzymes in the sulfur metabolic network. H2S exerts its effects on multiple physiological processes important under both normal and pathological conditions. These functions include neuromodulation, regulation of blood pressure and cardiac function, inflammation, cellular energetics and apoptosis. Despite the recognition of its biological importance and its beneficial effects, the mechanism of H2S action and the regulation of its tissue levels remain unclear in part owing to its chemical and physical properties that render handling and analysis challenging. Furthermore, the multitude of potential H2S effects has made it difficult to dissect its signaling mechanism and to identify specific targets. In this review, we focus on H2S metabolism and provide an overview of the recent literature that sheds some light on its mechanism of action in cellular redox signaling in health and disease. This article is part of a Special Issue entitled: Thiol-Based Redox Processes.

Development of upconversion luminescent probe for ratiometric sensing and bioimaging of hydrogen sulfide

Merocyanines adsorbed into the mesopores of mSiO2 shell of NaYF4: 20% Yb, 2% Er, 0.2% Tm nanocrystals are demonstrated as ratiometric upconversion luminescence (UCL) probe for highly selective detection of HS(-) in living cells through inhibition of energy transfer from the UCL of the nanocrystals to the absorbance of the merocyanines. The UCL probe has been used for ratiometric sensing of H2S with high sensitivity and selectivity.

Inositol 1,4,5-trisphosphate receptor-isoform diversity in cell death and survival

Cell-death and -survival decisions are critically controlled by intracellular Ca(2+) homeostasis and dynamics at the level of the endoplasmic reticulum (ER). Inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs) play a pivotal role in these processes by mediating Ca(2+) flux from the ER into the cytosol and mitochondria. Hence, it is clear that many pro-survival and pro-death signaling pathways and proteins affect Ca(2+) signaling by directly targeting IP3R channels, which can happen in an IP3R-isoform-dependent manner. In this review, we will focus on how the different IP3R isoforms (IP3R1, IP3R2 and IP3R3) control cell death and survival. First, we will present an overview of the isoform-specific regulation of IP3Rs by cellular factors like IP3, Ca(2+), Ca(2+)-binding proteins, adenosine triphosphate (ATP), thiol modification, phosphorylation and interacting proteins, and of IP3R-isoform specific expression patterns. Second, we will discuss the role of the ER as a Ca(2+) store in cell death and survival and how IP3Rs and pro-survival/pro-death proteins can modulate the basal ER Ca(2+) leak. Third, we will review the regulation of the Ca(2+)-flux properties of the IP3R isoforms by the ER-resident and by the cytoplasmic proteins involved in cell death and survival as well as by redox regulation. Hence, we aim to highlight the specific roles of the various IP3R isoforms in cell-death and -survival signaling. This article is part of a Special Issue entitled: Calcium signaling in health and disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.

H2S relaxes isolated human airway smooth muscle cells via the sarcolemmal K(ATP) channel

Here we explored the impact of hydrogen sulfide (H2S) on biophysical properties of the primary human airway smooth muscle (ASM)-the end effector of acute airway narrowing in asthma. Using magnetic twisting cytometry (MTC), we measured dynamic changes in the stiffness of isolated ASM, at the single-cell level, in response to varying doses of GYY4137 (1-10mM). GYY4137 slowly released appreciable levels of H2S in the range of 10-275 μM, and H2S released was long lived. In isolated human ASM cells, GYY4137 acutely decreased stiffness (i.e. an indicator of the single-cell relaxation) in a dose-dependent fashion, and stiffness decreases were sustained in culture for 24h. Human ASM cells showed protein expressions of cystathionine-γ-lyase (CSE; a H2S synthesizing enzyme) and ATP-sensitive potassium (KATP) channels. The KATP channel opener pinacidil effectively relaxed isolated ASM cells. In addition, pinacidil-induced ASM relaxation was completely inhibited by the treatment of cells with the KATP channel blocker glibenclamide. Glibenclamide also markedly attenuated GYY4137-mediated relaxation of isolated human ASM cells. Taken together, our findings demonstrate that H2S causes the relaxation of human ASM and implicate as well the role for sarcolemmal KATP channels. Finally, given that ASM cells express intrinsic enzymatic machinery of generating H2S, we suggest thereby this class of gasotransmitter can be further exploited for potential therapy against obstructive lung disease.

Production and physiological effects of hydrogen sulfide

SIGNIFICANCE

Hydrogen sulfide (H2S) has been recognized as a physiological mediator with a variety of functions. It regulates synaptic transmission, vascular tone, inflammation, transcription, and angiogenesis; protects cells from oxidative stress and ischemia-reperfusion injury; and promotes healing of ulcers.

RECENT ADVANCES

In addition to cystathionine β-synthase and cystathionine γ-lyase, 3-mercaptopyruvate sulfurtransferase along with cysteine aminotransferase was recently demonstrated to produce H2S. Even in bacteria, H2S produced by these enzymes functions as a defense against antibiotics, suggesting that the cytoprotective effect of H2S is a universal defense mechanism in organisms from bacteria to mammals.

CRITICAL ISSUES

The functional form of H2S-undissociated H2S gas, dissociated HS ion, or some other form of sulfur-has not been identified.

FUTURE DIRECTIONS

The regulation of H2S production by three enzymes may lead to the identification of the physiological signals that are required to release H2S. The identification of the physiological functions of other forms of sulfur may also help understand the biological significance of H2S.

A probe for ratiometric near-infrared fluorescence and colorimetric hydrogen sulfide detection and imaging in live cells

A ratiometric, near-infrared (NIR), fluorescence and colorimetric probeDNPOCyfor hydrogen sulfide (H₂S) has been developed.

A turn-on fluorescent probe for imaging lysosomal hydrogen sulfide in living cells

A 1,8-naphthalimide-derived fluorescent probe for lysosomal H₂S based on the reduction of azide is reported.

The ferrocene-pyrylium dyad as a selective colorimetric chemodosimeter for the toxic cyanide and hydrogen sulfide anions in water

A pyrylium derivative showing a remarkable ability to recognize cyanide and hydrogen sulfide anions in aqueous media through two different channels, electrochemical and chromogenic, is described.

A sensitivity tuneable tetraphenylethene-based fluorescent probe for directly indicating the concentration of hydrogen sulfide

A selective tetraphenylethene-based fluorescent H₂S probe was designed and synthesized, which exhibits tuneable sensitivity and could directly indicate the concentration of H₂S.

A water soluble FRET-based ratiometric chemosensor for Hg(ii) and S2−applicable in living cell staining

A new water soluble rhodamine-based ratiometric dual ‘off–on–off’ probe can selectively detect Hg²⁺ions in ppb level through time dependent FRET process with reversibility in presence of S²⁻anions.

Fluorescent probe for highly selective and sensitive detection of hydrogen sulfide in living cells and cardiac tissues

A coumarin-based fluorescence chemoprobe was developed and evaluated for the selective and sensitive detection of hydrogen sulfide in degassed PBS buffers and fetal bovine serum. Fluorescence detection of hydrogen sulfide in living cells was also successfully achieved using two-photon confocal fluorescence imaging. Further in situ visualization of endogenous H(2)S was realized in cardiac tissues of normal rats and atherosclerosis (AS) rats.

NBD-based colorimetric and fluorescent turn-on probes for hydrogen sulfide

Hydrogen sulfide (H2S) is an important endogenous signalling molecule and also an important environmental target for detection. New reaction-based colorimetric and fluorescent turn-on probes based on selective thiolyling of NBD (7-nitro-1,2,3-benzoxadiazole) ether were explored for sensing of H2S in aqueous buffer. The syntheses of both probes are simple and quite straightforward. The probes are highly sensitive and selective toward H2S over other biologically relevant species. Probe 1 can be used to directly visualize H2S by the naked eye and shows more than 1000-fold fluorescence increase upon reaction with H2S. Probe 2 is a near-infrared fluorescent sensor for H2S at physiological pH.

H₂S is an endothelium-derived hyperpolarizing factor

AIMS

Endothelium-dependent vasorelaxation is mediated by endothelium-derived relaxing factor and endothelium-derived hyperpolarizing factor (EDHF). However, the molecular entity of EDHF remains unclear. The present study examined whether hydrogen sulfide (H₂S) acts as EDHF and how H₂S mediates EDHF pathways from endothelial origination to downstream target of smooth muscle cells (SMCs).

RESULTS

We found that knocking-out the expression of cystathionine γ-lyase (CSE) in mice (CSE-knockout [KO]) elevated resting-membrane-potential of SMCs and eliminated methacholine-induced endothelium-dependent relaxation of mesenteric arteries, but not that of aorta. Methacholine, a cholinergic-muscarinic agonist, hyperpolarized SMC in endothelium-intact mesenteric arteries from wide-type mice. This effect was inhibited by muscarinic antagonist (atropine) or the co-application of charybdotoxin and apamin, which blocked intermediate- and small-conductance KCa (IKCa and SKCa) channels, or abolished in CSE-KO mice. Supplementation of exogenous H₂S hyperpolarized vascular SMCs and endothelial cells from wide-type and CSE-KO mice. Both methacholine and H₂S induced greater SMC hyperpolarization of female wide-type mesenteric arteries than that of male ones. H2S-induced hyperpolarization is blocked by -SH oxidants and -SSH inhibitor. The expression of SK2.3 but not IK3.1 channel in vascular tissues was increased by H₂S and decreased by CSE inhibitor or CSE gene KO.

INNOVATION AND CONCLUSIONS

Taken together, H₂S is an EDHF. The identification of H2S as an EDHF will not only solve one of the long-lasting perplexing puzzles for the mechanisms underlying endothelium-dependent vasorelaxation, but also shed light on potential therapeutic effects of H₂S on pathological abnormalities in peripheral resistance arteries.