Cardiac-specific suppression of NF-κB signaling prevents diabetic cardiomyopathy via inhibition of the renin-angiotensin system.

Activation of NF-κB signaling in the heart may be protective or deleterious depending on the pathological context. In diabetes, the role of NF-κB in cardiac dysfunction has been investigated using pharmacological approaches that have a limitation of being nonspecific. Furthermore, the specific cellular pathways by which NF-κB modulates heart function in diabetes have not been identified. To address these questions, we used a transgenic mouse line expressing mutated IκB-α in the heart (3M mice), which prevented activation of canonical NF-κB signaling. Diabetes was developed by streptozotocin injections in wild-type (WT) and 3M mice. Diabetic WT mice developed systolic and diastolic cardiac dysfunction by the 12th week, as measured by echocardiography. In contrast, cardiac function was preserved in 3M mice up to 24 wk of diabetes. Diabetes induced an elevation in cardiac oxidative stress in diabetic WT mice but not 3M mice compared with nondiabetic control mice. In diabetic WT mice, an increase in the phospholamban/sarco(endo)plasmic reticulum Ca(2+)-ATPase 2 ratio and decrease in ryanodine receptor expression were observed, whereas diabetic 3M mice showed an opposite effect on these parameters of Ca(2+) handling. Significantly, renin-angiotensin system activity was suppressed in diabetic 3M mice compared with an increase in WT animals. In conclusion, these results demonstrate that inhibition of NF-κB signaling in the heart prevents diabetes-induced cardiac dysfunction through preserved Ca(2+) handling and inhibition of the cardiac renin-angiotensin system.

Angiotensin type 1a receptor-deficient mice develop diabetes-induced cardiac dysfunction, which is prevented by renin-angiotensin system inhibitors.

BACKGROUND: Diabetes-induced organ damage is significantly associated with the activation of the renin-angiotensin system (RAS). Recently, several studies have demonstrated a change in the RAS from an extracellular to an intracellular system, in several cell types, in response to high ambient glucose levels. In cardiac myocytes, intracellular angiotensin (ANG) II synthesis and actions are ACE and AT1 independent, respectively. However, a role of this system in diabetes-induced organ damage is not clear. METHODS: To determine a role of the intracellular ANG II in diabetic cardiomyopathy, we induced diabetes using streptozotocin in AT1a receptor deficient (AT1a-KO) mice to exclude any effects of extracellular ANG II. Further, diabetic animals were treated with a renin inhibitor aliskiren, an ACE inhibitor benazeprilat, and an AT1 receptor blocker valsartan. RESULTS: AT1a-KO mice developed significant diastolic and systolic dysfunction following 10 wks of diabetes, as determined by echocardiography. All three drugs prevented the development of cardiac dysfunction in these animals, without affecting blood pressure or glucose levels. A significant down regulation of components of the kallikrein-kinin system (KKS) was observed in diabetic animals, which was largely prevented by benazeprilat and valsartan, while aliskiren normalized kininogen expression. CONCLUSIONS: These data indicated that the AT1a receptor, thus extracellular ANG II, are not required for the development of diabetic cardiomyopathy. The KKS might contribute to the beneficial effects of benazeprilat and valsartan in diabetic cardiomyopathy. A role of intracellular ANG II is suggested by the inhibitory effects of aliskiren, which needs confirmation in future studies.

Direct renin inhibition prevents cardiac dysfunction in a diabetic mouse model: comparison with an angiotensin receptor antagonist and angiotensin-converting enzyme inhibitor.

Hyperglycaemia up-regulates intracellular AngII (angiotensin II) production in cardiac myocytes, effects of which are blocked more effectively by renin inhibition than ARBs (angiotensin receptor blockers) or ACEis (angiotensin-converting enzyme inhibitors). In the present study, we determined whether renin inhibition is more effective at preventing diabetic cardiomyopathy than an ARB or ACEi. Diabetes was induced in adult mice for 10 weeks by STZ (streptozotocin). Diabetic mice were treated with insulin, aliskiren (a renin inhibitor), benazeprilat (an ACEi) or valsartan (an ARB) via subcutaneous mini-pumps. Significant impairment in diastolic and systolic cardiac functions was observed in diabetic mice, which was completely prevented by all three RAS (renin-angiotensin system) inhibitors. Hyperglycaemia significantly increased cardiac oxidative stress and circulating inflammatory cytokines, which were blocked by aliskiren and benazeprilat, whereas valsartan was partially effective. Diabetes increased cardiac PRR (prorenin receptor) expression and nuclear translocation of PLZF (promyelocytic zinc finger protein), which was completely prevented by aliskiren and valsartan, and partially by benazeprilat. Renin inhibition provided similar protection of cardiac function to ARBs and ACEis. Activation of PLZF by PRR represented a novel mechanism in diabetic cardiomyopathy. Differential effects of the three agents on oxidative stress, cytokines and PRR expression suggested subtle differences in their mechanisms of action.

Intracardiac intracellular angiotensin system in diabetes.

The renin-angiotensin system (RAS) has mainly been categorized as a circulating and a local tissue RAS. A new component of the local system, known as the intracellular RAS, has recently been described. The intracellular RAS is defined as synthesis and action of ANG II intracellularly. This RAS appears to differ from the circulating and the local RAS, in terms of components and the mechanism of action. These differences may alter treatment strategies that target the RAS in several pathological conditions. Recent work from our laboratory has demonstrated significant upregulation of the cardiac, intracellular RAS in diabetes, which is associated with cardiac dysfunction. Here, we have reviewed evidence supporting an intracellular RAS in different cell types, ANG II's actions in cardiac cells, and its mechanism of action, focusing on the intracellular cardiac RAS in diabetes. We have discussed the significance of an intracellular RAS in cardiac pathophysiology and implications for potential therapies.

The intracrine renin-angiotensin system.

The RAS (renin-angiotensin system) is one of the earliest and most extensively studied hormonal systems. The RAS is an atypical hormonal system in several ways. The major bioactive peptide of the system, AngII (angiotensin II), is neither synthesized in nor targets one specific organ. New research has identified additional peptides with important physiological and pathological roles. More peptides also mean newer enzymatic cascades that generate these peptides and more receptors that mediate their function. In addition, completely different roles of components that constitute the RAS have been uncovered, such as that for prorenin via the prorenin receptor. Complexity of the RAS is enhanced further by the presence of sub-systems in tissues, which act in an autocrine/paracrine manner independent of the endocrine system. The RAS seems relevant at the cellular level, wherein individual cells have a complete system, termed the intracellular RAS. Thus, from cells to tissues to the entire organism, the RAS exhibits continuity while maintaining independent control at different levels. The intracellular RAS is a relatively new concept for the RAS. The present review provides a synopsis of the literature on this system in different tissues.

Hydrogen sulfide regulates Na+/H+ exchanger activity via stimulation of phosphoinositide 3-kinase/Akt and protein kinase G pathways.

Intracellular pH (pH(i)) is an important endogenous modulator of cardiac function. Inhibition of Na(+)/H(+) exchanger-1 (NHE-1) protects the heart by preventing Ca(2+) overload during ischemia/reperfusion. Hydrogen sulfide (H(2)S) has been reported to produce cardioprotection. The present study was designed to investigate the pH regulatory effect of H(2)S in rat cardiac myocytes and evaluate its contribution to cardioprotection. It was found that sodium hydrosulfide (NaHS), at a concentration range of 10 to 1000 µM, produced sustained decreases in pH(i) in the rat myocytes in a concentration-dependent manner. NaHS also abolished the intracellular alkalinization caused by trans-(±)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]benzeneacetamide methane-sulfonate hydrate (U50,488H), which activates NHEs. Moreover, when measured with an NHCl(4) prepulse method, NaHS was found to significantly suppress NHE-1 activity. Both NaHS and cariporide or [5-(2-methyl-5-fluorophenyl)furan-2-ylcarbonyl]guanidine (KR-32568), two NHE inhibitors, protected the myocytes against ischemia/reperfusion injury. However, coadministration of NaHS with KR-32568 did not produce any synergistic effect. Functional study showed that perfusion with NaHS significantly improved postischemic contractile function in isolated rat hearts subjected to ischemia/reperfusion. Blockade of phosphoinositide 3-kinase (PI3K) with 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), Akt with Akt VIII, or protein kinase G (PKG) with (9S,10R,12R)-2,3,9,10,11,12-hexahydro-10-methoxy-2,9-dimethyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i][1,6]]enzodiazocine-10-carboxylic acid, methyl ester (KT5823) significantly attenuated NaHS-suppressed NHE-1 activity and/or NaHS-induced cardioprotection. Although KT5823 failed to affect NaHS-induced Akt phosphorylation, Akt inhibitor did attenuate NaHS-stimulated PKG activity. In conclusion, this work demonstrated for the first time that H(2)S produced cardioprotection via the suppression of NHE-1 activity involving a PI3K/Akt/PKG-dependent mechanism.

Hydrogen sulfide inhibits plasma renin activity.

The development of renovascular hypertension depends on the release of renin from the juxtaglomerular (JG) cells, a process regulated by intracellular cAMP. Hydrogen sulfide (H2S) downregulates cAMP production in some cell types by inhibiting adenylyl cyclase, suggesting the possibility that it may modulate renin release. Here, we investigated the effect of H2S on plasma renin activity and BP in rat models of renovascular hypertension. In the two-kidney-one-clip (2K1C) model of renovascular hypertension, the H2S donor NaHS prevented and treated hypertension. Compared with vehicle, NaHS significantly attenuated the elevation in plasma renin activity and angiotensin II levels but did not affect plasma angiotensin-converting enzyme activity. Furthermore, NaHS inhibited the upregulation of renin mRNA and protein levels in the clipped kidneys of 2K1C rats. In primary cultures of renin-rich kidney cells, NaHS markedly suppressed forskolin-stimulated renin activity in the medium and the intracellular increase in cAMP. In contrast, NaHS did not affect BP or plasma renin activity in normal or one-kidney-one-clip (1K1C) rats, both of which had normal plasma renin activity. In conclusion, these results demonstrate that H2S may inhibit renin activity by decreasing the synthesis and release of renin, suggesting its potential therapeutic value for renovascular hypertension.

Negative regulation of beta-adrenergic function by hydrogen sulphide in the rat hearts.

Beta-adrenoceptor is over-stimulated during myocardial ischemia, in which hydrogen sulphide (H2S) concentration was found to be lowered. The present study attempted to investigate if H2S modulates beta-adrenoceptor function and the underlying mechanism. We examined the effect of NaHS (a H2S donor) on myocyte contraction and electrically-induced (EI) intracellular calcium ([Ca2+](i)) transients upon beta-adrenergic stimulation in rat ventricular myocytes with a video edge tracker method and a spectrofluorometric method using fura-2/AM as a calcium indicator, respectively. We found that isoproterenol (ISO, 10(-9)-10(-6) M), a beta-adrenoceptor agonist, concentration-dependently increased the twitch amplitude of ventricular myocytes, which was attenuated by NaHS (10(-5)-10(-3) M) in a dose-dependent manner. The amplitudes and maximal velocities (+/-dl/dt) of myocyte twitch and EI-[Ca2+](i) transient amplitudes were enhanced by ISO, forskolin (an adenylyl cyclase activator), 8-bromoadenosine-3',5'-cyclic monophosphate (an activator of protein kinase A) and Bay K-8644 (a selective L-type Ca2+ channel agonist). Administration of NaHS (100 microM) only significantly attenuated the effects of ISO and forskolin. Moreover, NaHS reversed ISO-induced cAMP elevation and forskolin-stimulated adenylyl cyclase activity. In addition, stimulation of beta-adrenoceptor by ISO significantly decreased endogenous H2S production in rat ventricular myocytes. In conclusion, H2S may negatively modulate beta-adrenoceptor function via inhibiting adenylyl cyclase activity. Impairment of this negative modulation during ischemia may induce cardiac arrhythmias. Our study may provide a novel mechanism for ischemia-induced cardiac injury.

Novel mechanism of blood pressure regulation by forkhead box class O1-mediated transcriptional control of hepatic angiotensinogen.

The renin-angiotensin system is a major determinant of blood pressure regulation. It consists of a cascade of enzymatic reactions involving 3 components: angiotensinogen, renin, and angiotensin-converting enzyme, which generate angiotensin II as a biologically active product. Angiotensinogen is largely produced in the liver, acting as a major determinant of the circulating renin-angiotensin system, which exerts acute hemodynamic effects on blood pressure regulation. How the expression of angiotensinogen is regulated is not completely understood. Here, we hypothesize that angiotensinogen is regulated by forkhead transcription factor forkhead box class O1 (Foxo1), an insulin-suppressed transcription factor, and thereby controls blood pressure in mice. We generated liver-specific Foxo1 knockout mice, which exhibited a reduction in plasma angiotensinogen and angiotensin II levels and a significant decrease in blood pressure. Using hepatocyte cultures, we demonstrated that overexpression of Foxo1 increased angiotensinogen expression, whereas hepatocytes lacking Foxo1 demonstrated a reduction of angiotensinogen gene expression and partially impaired insulin inhibition on angiotensinogen gene expression. Furthermore, mouse angiotensinogen prompter analysis demonstrated that the angiotensinogen promoter region contains a functional Foxo1-binding site, which is responsible for both Foxo1 stimulation and insulin suppression on the promoter activity. Together, these data demonstrate that Foxo1 regulates hepatic angiotensinogen gene expression and controls plasma angiotensinogen and angiotensin II levels, modulating blood pressure control in mice.

Do multiple nuclear factor kappa B activation mechanisms explain its varied effects in the heart?

BACKGROUND: Multiple studies have demonstrated the important role of the nuclear factor kappa B (NF-κB) in cardiac pathology. However, these studies' conclusions differ regarding whether NF-κB is protective or detrimental for heart function. This disagreement is not surprising considering the complexity of NF-κB signaling that involves multiple components and regulation at several steps. Furthermore, NF-κB is a pleiotropic transcription factor that receives signals from multiple pathways, including the renin-angiotensin system (RAS) and cytokines, 2 important modulators of cardiac remodeling. METHODS: In this article, we review studies related to the role and mechanisms of NF-κB activation in the heart, particularly with regard to the RAS, inflammation, and diabetes. The objective of this review is to consolidate multiple, often contradictory, findings to develop a clear understanding of NF-κB signaling in the heart. CONCLUSIONS: The studies we review demonstrate that NF-κB effects in the heart are mechanism specific and that NF-κB signaling is cyclical. Consequently, the timing of NF-κB measurement is critical, and studies focused on temporal changes in the NF-κB mechanism would help clarify its multiple roles in cardiac pathophysiology.

Regulation of heart function by endogenous gaseous mediators-crosstalk between nitric oxide and hydrogen sulfide.

Both nitric oxide (NO) and hydrogen sulfide (H(2)S) are two important gaseous mediators regulating heart function. The present study examined the interaction between these two biological gases and its role in the heart. We found that l-arginine, a substrate of NO synthase, decreased the amplitudes of myocyte contraction and electrically induced calcium transients. Sodium hydrogen sulfide (an H(2)S donor), which alone had minor effect, reversed the negative inotropic effects of l-arginine. The effect of l-arginine + sodium hydrogen sulfide was abolished by three thiols (l-cysteine, N-acetyl-cysteine, and glutathione), suggesting that the effect of H(2)S + NO is thiol sensitive. The stimulatory effect on heart contractility was also induced by GYY4137, a slow-releasing H(2)S donor, when used together with sodium nitroprusside, an NO-releasing donor. More importantly, enzymatic generation of H(2)S from recombinant cystathionine-γ-lyase protein also interacted with endogenous NO generated from l-arginine to stimulate heart contraction. In summary, our data suggest that endogenous NO may interact with H(2)S to produce a new biological mediator that produces positive inotropic effect. The crosstalk between H(2)S and NO also suggests an intriguing potential for the endogenous formation of a thiol-sensitive molecule, which may be of physiological significance in the heart.

Hydrogen sulfide interacts with nitric oxide in the heart: possible involvement of nitroxyl.

AIMS: The present study aims to investigate the interaction between nitric oxide (NO) and hydrogen sulfide (H(2)S), the two important gaseous mediators in rat hearts. METHODS AND RESULTS: Intracellular calcium in isolated cardiomyocytes was measured with a spectrofluorometric method using Fura-2. Myocyte contractility was measured with a video edge system. NaHS (50 µM, an H(2)S donor) had no significant effect on the resting calcium level, electrically induced (EI) calcium transients, and cell contractility in ventricular myocytes. Stimulating endogenous NO production with l-arginine or exogenous application of NO donors [sodium nitroprusside (SNP) and 2-(N,N-diethylamino)-diazenolate-2-oxide] decreased myocyte twitch amplitudes accompanied by slower velocities of both cell contraction and relaxation. Surprisingly, NaHS reversed the negative inotropic and lusitropic effects of the above three NO-increasing agents. In addition, the mixture of SNP + NaHS increased, whereas SNP alone decreased, the resting calcium level and the amplitudes of EI calcium transients. Angeli's salt, a nitroxyl anion (HNO) donor, mimicked the effect of SNP + NaHS on calcium handling and myocyte contractility. Three thiols, N-acetyl-cysteine, l-cysteine, and glutathione, abolished the effects of HNO and SNP + NaHS on myocyte contraction. Neither Rp-cAMP [a protein kinase A (PKA) inhibitor] nor Rp-cGMP [a protein kinase G (PKG) inhibitor] affected the effects of SNP + NaHS, suggesting a cAMP/PKA- or cGMP/PKG-independent mechanism. CONCLUSION: H(2)S may interact with NO to form a thiol sensitive molecule (probably HNO) which produces positive inotropic and lusitropic effects. Our findings may shed light on the interaction of NO and H(2)S and provide new clues to treat cardiovascular diseases.

Effect of hydrogen sulfide on intracellular calcium homeostasis in neuronal cells.

Hydrogen sulfide (H(2)S) is now known as a new biological mediator. In the present study, the effects of H(2)S on intracellular calcium ([Ca(2+)](i)) in neuronal SH-SY5Y cells was investigated. In SH-SY5Y neuronal cells, NaHS, a H(2)S donor, concentration-dependently increased [Ca(2+)](i). The H(2)S-induced Ca(2+) elevation was significantly attenuated by EGTA-treated calcium-free Krebs' solution. This elevation was also reduced by antagonists of L-type (verapamil and nifedipine), T-type (mibefradil) calcium channels and N-methyl-d-aspartate receptor (MK-801, AP-5 and ifenprodil). A 90% reduction in H(2)S-induced [Ca(2+)](i) elevation was found in cells pretreated with combination of all three kinds of inhibitors. Depletion of intracellular Ca(2+) store with thapsigargin or cyclopiazonic acid or blockade of ryanodine receptor with ruthenium red significantly attenuated the effect of H(2)S on [Ca(2+)](i). Inhibition of protein kinase A (PKA), phospholipase C (PLC) and protein kinase C (PKC) suppressed the H(2)S-elevated [Ca(2+)](i), suggesting that H(2)S may regulate [Ca(2+)](i) via both PKA and PLC/PKC pathways. In conclusion, it was found in this study that H(2)S increased [Ca(2+)](i) in SH-SY5Y neuronal cells by increasing Ca(2+) influx via plasma membrane and in turn releasing calcium from intracellular calcium store. The findings in the present study provide the direct evidence that H(2)S may serve as a neuromodulator.

Cyclooxygenase-2 mediates the delayed cardioprotection induced by hydrogen sulfide preconditioning in isolated rat cardiomyocytes.

We previously reported that hydrogen sulfide (H(2)S) preconditioning (SP) produces cardioprotection in isolated rat cardiomyocytes. The present study was designed to determine the involvement of cyclooxygenase-2 (COX-2) in the SP-induced delayed cardioprotection. Isolated cardiac myocytes were treated with NaHS (100 microM, a H(2)S donor) for 30 min and then cultured for 20 h followed by ischemia/reperfusion insults. SP significantly increased cell viability, percentage of rod-shaped cells, and myocyte contractility after 10 min of reperfusion. Given 30 min before and during lethal ischemia, two selective COX-2 inhibitors, NS-398 and celebrex, abrogated SP-induced cardioprotective effects. Moreover, SP upregulated the expression of COX-2 and increased PGE(2) production in the cardiac myocytes. These effects were significantly attenuated by glibenclamide, an ATP-sensitive K(+) channel (K(ATP)) blocker, and chelerythrine, a selective protein kinase C (PKC) inhibitor, suggesting that activation of both K(ATP) and PKC is required for the stimulation of COX-2. Additionally, NG-nitro-L: -arginine methyl ester, a nitric oxide synthase inhibitor, failed to regulate COX-2 protein expression but inhibited SP-enhanced COX-2 activity and PGE(2) production. In conclusion, we provided the first evidence that SP may produce delayed cardioprotection via K(ATP)/PKC dependent induction of COX-2 expression and via nitric oxide-induced COX-2 activation.

Endogenous hydrogen sulphide mediates the cardioprotection induced by ischemic postconditioning.

The present study aimed to investigate the role of hydrogen sulphide (H2S) in the cardioprotection induced by ischemic postconditioning and to examine the underlying mechanisms. Cardiodynamics and myocardial infarction were measured in isolated rat hearts. Postconditioning with six episodes of 10-s ischemia (IPostC) significantly improved cardiodynamic function, which was attenuated by the blockade of endogenous H2S production with d-l-propargylglycine. Moreover, IPostC significantly stimulated H2S synthesis enzyme activity during the early period of reperfusion. However, d-l-propargylglycine only attenuated the IPostC-induced activation of PKC-alpha and PKC-epsilon but not that of PKC-delta, Akt, and endothelial nitric oxide synthase (eNOS). These data suggest that endogenous H2S contributes partially to the cardioprotection of IPostC via stimulating PKC-alpha and PKC-epsilon. Postconditioning with six episodes of a 10-s infusion of NaHS (SPostC) or 2 min continuous NaHS infusion (SPostC2) stimulated activities of Akt and PKC, improved the cardiodynamic performances, and reduced myocardial infarct size. The blockade of Akt with LY-294002 (15 microM) or PKC with chelerythrine (10 microM) abolished the cardioprotection induced by H2S postconditioning. SPostC2, but not SPostC, also additionally stimulated eNOS. We conclude that endogenous H2S contributes to IPostC-induced cardioprotection. H2S postconditioning confers the protective effects against ischemia-reperfusion injury through the activation of Akt, PKC, and eNOS pathways.

H2S preconditioning-induced PKC activation regulates intracellular calcium handling in rat cardiomyocytes.

The present study was aimed to investigate the regulatory effect of protein kinase C (PKC) on intracellular Ca(2+) handling in hydrogen sulfide (H(2)S)-preconditioned cardiomyocytes and its consequent effects on ischemia challenge. Immunoblot analysis was used to assess PKC isoform translocation in the rat cardiomyocytes 20 h after NaHS (an H(2)S donor, 10(-4) M) preconditioning (SP, 30 min). Intracellular Ca(2+) was measured with a spectrofluorometric method using fura-2 ratio as an indicator. Cell length was compared before and after ischemia-reperfusion insults to indicate the extent of hypercontracture. SP motivated translocation of PKCalpha, PKCepsilon, and PKCdelta to membrane fraction but only translocation of PKCepsilon and PKCdelta was abolished by an ATP-sensitive potassium channel blocker glibenclamide. It was also found that SP significantly accelerated the decay of both electrically and caffeine-induced intracellular [Ca(2+)] transients, which were reversed by a selective PKC inhibitor chelerythrine. These data suggest that SP facilitated Ca(2+) removal via both accelerating uptake of Ca(2+) into sarcoplasmic reticulum and enhancing Ca(2+) extrusion through Na(+)/Ca(2+) exchanger in a PKC-dependent manner. Furthermore, blockade of PKC also attenuated the protective effects of SP against Ca(2+) overload during ischemia and against myocyte hypercontracture at the onset of reperfusion. We demonstrate for the first time that SP activates PKCalpha, PKCepsilon, and PKCdelta in cardiomyocytes via different signaling mechanisms. Such PKC activation, in turn, protects the heart against ischemia-reperfusion insults at least partly by ameliorating intracellular Ca(2+) handling.

Role of hydrogen sulfide in the cardioprotection caused by ischemic preconditioning in the rat heart and cardiac myocytes.

Endogenous H(2)S is synthesized mainly by cystathionine gamma-lyase in the heart. The present study investigated the role of H(2)S in cardioprotection induced by ischemic preconditioning. We have examined the effect of endogenous H(2)S and exogenous application of NaHS (H(2)S donor) on cardiac rhythm in the isolated rat heart subjected to low-flow ischemia insults as well as cell viability and function in isolated myocytes exposed to simulated ischemia solution. Preconditioning with NaHS (SP) or ischemia (IP) for three cycles (3 min each cycle separated by 5 min of recovery) significantly decreased the duration and severity of ischemia/reperfusion-induced arrhythmias in the isolated heart while increasing cell viability and the amplitude of electrically induced calcium transients after ischemia/reperfusion in cardiac myocytes. Both IP and SP also significantly attenuated the decreased H(2)S production during ischemia. Moreover, decreasing endogenous H(2)S production significantly attenuated the protective effect of IP in both the isolated heart and isolated cardiac myocytes. Blockade of protein kinase C with chelerythrine or bisindolylmaleimide I as well as ATP-sensitive K(+) (K(ATP)) channel with glibenclamide (a nonselective K(ATP) blocker) and HMR-1098 (1-[[5-[2-(5-Chloro-o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl]-3-methylthiourea) (a sarcolemmal K(ATP) channel blocker) reversed the cardioprotection induced by SP or IP. However, blockade of mitochondrial K(ATP) channels with 5-hydroxydecanoic acid had no effect on the cardioprotection of SP, suggesting that, unlike the mechanism involved in IP, mitochondrial K(ATP) channels most probably do not play a major role in the cardioprotection of SP. Our findings suggest that endogenous H(2)S contributes to cardioprotection induced by IP, which effect may involve protein kinase C and sarcolemmal K(ATP) channels.