Studies of nitric oxide over the past two decades have highlighted the fundamental importance of gaseous signaling molecules in biology and medicine. The physiological role of other gases such as carbon monoxide and hydrogen sulfide (H 2 S) is now receiving increasing attention. Here we show that H 2 S is physiologically generated by cystathionine γ-lyase (CSE) and that genetic deletion of this enzyme in mice markedly reduces H 2 S levels in the serum, heart, aorta, and other tissues. Mutant mice lacking CSE display pronounced hypertension and diminished endothelium-dependent vasorelaxation. CSE is physiologically activated by calcium-calmodulin, which is a mechanism for H 2 S formation in response to vascular activation. These findings provide direct evidence that H 2 S is a physiologic vasodilator and regulator of blood pressure.Nitric oxide (NO) and carbon monoxide (CO) are established physiologic messenger molecules, and NO has an important role as an endothelial cell-derived relaxing factor (EDRF) and regulator of blood pressure (1,2). Indirect evidence has implicated another endogenous gasotransmitter, hydrogen sulfide (H 2 S), in similar functions (3-7). H 2 S can be produced by cystathionine γ-lyase (CSE) or cystathionine β-synthase (CBS) (3,4), but definitive evidence for either of these enzymes in the physiologic formation of H 2 S is lacking.To investigate the role of H 2 S as a physiologic vasorelaxant and determinant of blood pressure, we generated mice with a targeted deletion of the gene encoding CSE (8) (fig. S1, A to C). The homozygous (CSE −/− ) and heterozygous (CSE −/+ ) mutant mice were viable, fertile, and indistinguishable from their control wild-type littermates (CSE +/+ ) in terms of growth pattern.

Hydrogen sulfide (H2S) has been shown recently to function as an important gasotransmitter. The present study investigated the vascular effects of H2S, both exogenously applied and endogenously generated, on resistance mesenteric arteries of rats and the underlying mechanisms. Both H2S and NaHS evoked concentration-dependent relaxation of in vitro perfused rat mesenteric artery beds (MAB). The sensitivity of MAB to H2S (EC50, 25.2 +/- 3.6 microM) was about fivefold higher than that of rat aortic tissues. Removal of endothelium or coapplication of charybdotoxin and apamin to endothelium-intact MAB significantly reduced the vasorelaxation effects of H2S. The H2S-induced relaxation of MAB was partially mediated by ATP-sensitive K+ (KATP) channel activity in vascular smooth muscle cells. Pinacidil (EC50, 1.7 +/- 0.1 microM, n=6) mimicked, but glibenclamide (10 microM, n=6) suppressed, the vasorelaxant effect of H2S. KATP channel currents in isolated mesenteric artery smooth muscle cells were significantly augmented by H2S. L-cysteine, a substrate of cystathionine-gamma-lyase (CSE), at 1 mM increased endogenous H2S production by sixfold in rat mesenteric artery tissues and decreased contractility of MAB. DL-propargylglycine (a blocker of CSE) at 10 microM abolished L-cysteine-dependent increase in H2S production and relaxation of MAB. Our results demonstrated a tissue-specific relaxant response of resistance arteries to H2S. The stimulation of KATP channels in vascular smooth muscle cells and charybdotoxin/apamin-sensitive K+ channels in vascular endothelium by H2S represents important cellular mechanisms for H2S effect on MAB. Our study also demonstrated that endogenous CSE can generate sufficient H2S from exogenous L-cysteine to cause vasodilation. Future studies are merited to investigate direct contribution of endogenous H2S to regulation of vascular tone.

Hydrogen sulfide (H 2 S) has been traditionally known for its toxic effects on living organisms. The role of H 2 S in the homeostatic regulation of pancreatic insulin metabolism has been unclear. The present study is aimed at elucidating the effect of endogenously produced H 2 S on pancreatic insulin release and its role in diabetes development. Diabetes development in Zucker diabetic fatty (ZDF) rats was evaluated in comparison with Zucker fatty (ZF) and Zucker lean (ZL) rats. Pancreatic H 2 S production and insulin release were also assayed. It was found that H 2 S was generated in rat pancreas islets, catalyzed predominantly by cystathionine g-lyase (CSE). Pancreatic CSE expression and H 2 S production were greater in ZDF rats than in ZF or ZL rats. ZDF rats exhibited reduced serum insulin level, hyperglycemia, and insulin resistance. Inhibition of pancreatic H 2 S production in ZDF rats by intraperitoneal injection of DL-propargylglycine (PPG) for 4 weeks increased serum insulin level, lowered hyperglycemia, and reduced hemoglobin A1c level (Po0.05). Although in ZF rats it also reduced pancreatic H 2 S production and serum H 2 S level, PPG treatment did not alter serum insulin and glucose level. Finally, H 2 S significantly increased K ATP channel activity in freshly isolated rat pancreatic b-cells. It appears that insulin release is impaired in ZDF because of abnormally high pancreatic production of H 2 S. New therapeutic approach for diabetes management can be devised based on our observation by inhibiting endogenous H 2 S production from pancreas. KEYWORDS: diabetes; hydrogen sulfide; insulin release; K ATP channel; pancreas; type 2 diabetes mellitus Known as a swamp gas or 'rotten egg' gas, hydrogen sulfide (H 2 S) has yielded a public image of air pollutant for centuries. Physiological importance of H 2 S as a gasotransmitter has been realized for less than a decade. Endogenous production of H 2 S from L-cysteine is catalyzed by cystathionine b-synthase (CBS) and/or cystathionine g-lyase (CSE) with ammonium and pyruvate as co-products. 1 This process occurs in different organs and tissues, such as neuronal, vascular, and intestinal tissues. 2 Physiological concentrations of circulating H 2 S have been reported in the range of 45-300 mM. 1 At this physiological range, exogenous H 2 S has been shown to relax different vascular tissues, including isolated rat aortae and perfused mesenteric artery bed. 3-5 Altered cell proliferation or apoptosis induced by H 2 S has also been widely reported. [6][7][8][9][10] Endogenous production and physiological function of H 2 S in pancreas have been studied with identification of both CBS and CSE in rat pancreatic tissues or cloned rat pancreatic b-cell line. 11,12 In recent years, pathophysiological implications of the CSE/H 2 S system in diabetes have been reported. 12 CSE mRNA expression and H 2 S formation in rat pancreas was significantly increased after diabetes induction by streptozotocin injection. 12 CBS expression was reported in pancreatic acinar cells. 13 Y...

Hydrogen sulfide (H(2)S) is an endogenous opener of K(ATP) channels in many different types of cells. However, the molecular mechanism for an interaction between H(2)S and K(ATP) channel proteins remains unclear. The whole-cell patch-clamp technique and mutagenesis approach were used to examine the effects of H(2)S on different K(ATP) channel subunits, rvKir6.1 and rvSUR1, heterologously expressed in HEK-293 cells. H(2)S stimulated coexpressed rvKir6.1/rvSUR1 K(ATP) channels, but had no effect on K(ATP) currents generated by rvKir6.1 expression alone. Intracellularly applied sulfhydryl alkylating agent (N-ethylmaleimide, NEM), oxidizing agent (chloramine T, CLT), and a disulfide bond-oxidizing enzyme (protein disulfide isomerase) did not alter H(2)S effects on this recombinant channels. CLT, but not NEM, inhibited basal rvKir6.1/rvSUR1 currents, and both abolished the stimulatory effects of H(2)S on K(ATP) currents, when applied extracellularly. After selective cysteine residues (C6S and C26S but not C1051S and C1057S) in the extracellular loop of rvSUR1 subunits were point-mutated, H(2)S lost its stimulatory effects on rvKir6.1/rvSUR1 currents. Our results demonstrate that H(2)S interacts with Cys6 and Cys26 residues of the extracellular N terminal of rvSUR1 subunit of K(ATP) channel complex. Direct chemical modification of rvSUR1 subunit protein constitutes a molecular mechanism for the activation of K(ATP) channels by H(2)S.

Cystathionine ␥-lyase (CSE) is a key enzyme in the trans-sulfuration pathway. CSE uses L-cysteine as a substrate to produce hydrogen sulfide (H 2 S). The CSE/H 2 S system has been shown to play an important role in regulating cellular functions in different systems. In the present study, we used CSE stably overexpressed HEK-293 cells to explore the effect of the CSE/H 2 S system on cell growth and proliferation. The overexpression of CSE resulted in increases in CSE mRNA levels, CSE proteins, and intracellular H 2 S production rates, as well as the inhibition of cell proliferation and DNA synthesis. These effects were accompanied by a sustained ERK activation and up-regulation of the cyclin-dependent kinase inhibitor p21Cip/WAK-1 . Blocking the action of ERK with U0126 inhibited the induction of p21Cip/WAK-1 , suggesting that ERK activation functions upstream of p21 Cip/WAK-1 activation to initiate the CSE overexpression-induced cell growth inhibition. The antiproliferative effect of CSE is likely mediated by endogenously produced H 2 S because the H 2 S scavenger methemoglobin (10 M) significantly decreased the H 2 S production rate and reversed the antiproliferative effect afforded by CSE. Exogenous H 2 S (100 M) also inhibited cell proliferation. However, the other CSE-catalyzed products, ammonium and pyruvate, failed to inhibit cell proliferation. Methemoglobin also abolished the inhibitory effect of exogenous H 2 S on cell proliferation. Moreover, exogenous H 2 S induced a sustained ERK and p21Cip/WAK-1 activation. These findings support the hypothesis that endogenously produced H 2 S may play a fundamental role in cell proliferation and survival.

Activation of a calcium-sensing receptor (Ca-SR) leads to increased intracellular calcium concentration and altered cellular activities. The expression of Ca-SR has been identified in both nonexcitable and excitable cells, including neurons and smooth muscle cells. Whether Ca-SR was expressed and functioning in cardiac myocytes remained unclear. In the present study, the transcripts of Ca-SR were identified in rat heart tissues using RT-PCR that was further confirmed by sequence analysis. Ca-SR proteins were detected in rat ventricular and atrial tissues as well as in isolated cardiac myocytes. Anti-(Ca-SR) Ig did not detect any specific bands after preadsorption with standard Ca-SR antigens. An immunohistochemistry study revealed the presence of Ca-SR in rat cardiac as well as other tissues.

A relatively high resistance of leaf xylem to embolism may not explain hydraulic segmentation between leaves and branches in angiosperms.

IntroductionNitric oxide (NO) is an endogenous vasorelaxant gas that is synthesized from the terminal guanidino nitrogen atoms of L-arginine by NO synthase (1). Carbon monoxide (CO) is another endogenously generated biological gas. The major route for the endogenous generation of CO involves heme oxygenase (HO), which works in concert with NADPH-cytochrome P450 reductase to cleave the heme ring in hemoproteins into biliverdin, CO, and iron (2). Results from our laboratory (3) and others (4-7) have demonstrated that endogenously generated CO can effectively relax vascular tissues. The physiological role of endogenous CO is thus indicated. NO and CO are not redundant messenger molecules. For instance, NO potently dilated hepatic artery, but only slightly dilated the portal venous vascular bed. In contrast, CO had no effect on the hepatic artery, but relaxed the portal venous vascular bed (8). In some cases, NO and CO may even have opposite effects. CO inhibited, but NO increased, the release of IL-1β from rat hypothalamus stimulated by high K + concentrations (9). NO and CO do have at least two common targets in vascular smooth muscle cells (SMCs), i.e., soluble guanylyl cyclase (sGC) and large-conductance calciumactivated K + (K Ca ) channels (10)(11)(12)(13)(14). Although the debate has not been settled on whether NO and CO directly act on K Ca channels or indirectly by altering intracellular second messengers, many single channel studies on the cell-free membrane patches have been supportive for a direct interaction of NO and CO with K Ca channel proteins. Even for these single channel studies different mechanisms for the effects of NO and CO on K Ca channels have been presented. The NO effect on K Ca channels in rabbit aortic SMCs was related to the changes in sulfhydryl groups (10). Our previous study showed that CO acted on the histidine residue of K Ca channel proteins in rat tail artery SMCs (13).Large-conductance K Ca channels are stimulated by increased intracellular calcium concentration and by membrane depolarization. These K Ca channels are composed of two noncovalently linked subunits: the poreforming α subunit and the accessory β subunit, which affects the electrophysiological and pharmacological properties of K Ca channel complexes (15). The interactions of NO and CO with α and β subunits of K Ca channels may be the determining factor for the selective modulation of K Ca channels, which has not been addressed.The interaction between NO and CO on the regulation of vascular contractility is another important but still largely uncharted issue. The activation of largeconductance K Ca channels in SMCs accounts for a significant part of the relaxation induced by NO (16) The molecular mechanisms underlying the effects of nitric oxide (NO) and carbon monoxide (CO), individually and collectively, on large-conductance calcium-activated K + (K Ca ) channels were investigated in rat vascular smooth muscle cells (SMCs). Both NO and CO increased the activity of native K Ca channels. Dehydrosoyasaponin-I, a spe...