An unexpected negative inotropic effect of prostaglandin F2alpha in the rat heart

Prostanoids in Cardiac and Vascular Remodeling

Prostanoids are biologically active lipids generated from arachidonic acid by the action of the COX (cyclooxygenase) isozymes. NSAIDs, which reduce the biosynthesis of prostanoids by inhibiting COX activity, are effective anti-inflammatory, antipyretic, and analgesic drugs. However, their use is limited by cardiovascular adverse effects, including myocardial infarction, stroke, hypertension, and heart failure. While it is well established that NSAIDs increase the risk of atherothrombotic events and hypertension by suppressing vasoprotective prostanoids, less is known about the link between NSAIDs and heart failure risk. Current evidence indicates that NSAIDs may increase the risk for heart failure by promoting adverse myocardial and vascular remodeling. Indeed, prostanoids play an important role in modulating structural and functional changes occurring in the myocardium and in the vasculature in response to physiological and pathological stimuli. This review will summarize current knowledge of the role of the different prostanoids in myocardial and vascular remodeling and explore how maladaptive remodeling can be counteracted by targeting specific prostanoids.

The Link between Prostanoids and Cardiovascular Diseases

Cardiovascular diseases are the leading cause of global deaths, and many risk factors contribute to their pathogenesis. In this context, prostanoids, which derive from arachidonic acid, have attracted attention for their involvement in cardiovascular homeostasis and inflammatory processes. Prostanoids are the target of several drugs, but it has been shown that some of them increase the risk of thrombosis. Overall, many studies have shown that prostanoids are tightly associated with cardiovascular diseases and that several polymorphisms in genes involved in their synthesis and function increase the risk of developing these pathologies. In this review, we focus on molecular mechanisms linking prostanoids to cardiovascular diseases and we provide an overview of genetic polymorphisms that increase the risk for cardiovascular disease.

Confirmation of the Cardiac Safety of PGF2α Receptor Antagonist OBE022 in a First-in-Human Study in Healthy Subjects, Using Intensive ECG Assessments

OBE022, a new orally active prostaglandin F2α  receptor antagonist (OBE022) with myometrial selectivity is being developed to reduce uterine contractions during preterm labor. This first-in-human study evaluated the effect of OBE022 following multiple doses on the QT interval in 23 healthy postmenopausal women, using the effect of a meal on QTc to demonstrate assay sensitivity. We report the cardiac safety outcome performed during the multiple ascending part of this trial. OBE022 was administered after a standardized breakfast on day 1 and in the fasted state from day 3 to day 9 wth a standardized lunch 4 hours after administration. Concentration-effect modeling was used to assess the effect of prodrug OBE022 and parent OBE002 on QTc after a single dose (days 1 and 3) and multiple doses (day 9). The concentration-response analysis showed the absence of QTc prolongation at all doses tested. Two-sided 90% confidence intervals of the geometric mean Cmax  for estimated QTc effects of OBE022 and OBE002 of all dose groups were consistently below the threshold of regulatory concern. The sensitivity of this study to detect small changes in the QTc was confirmed by a significant shortening of the QTc on days 1, 3, and 9 after standardized meals. This study establishes that neither prodrug OBE022 nor parent OBE002 prolong the QTc interval. The observed food effect on the QT interval validated the assay on all assessment days. Both the change from predose, premeal and the change from premeal, postdose demonstrated the specificity of the method.

c-Jun N-terminal Kinase mediates prostaglandin-induced sympathoexcitation in rats with chronic heart failure by reducing GAD1 and GABRA1 expression

AIM

Prostaglandin E2 mediates sympathoexcitation in chronic heart failure (CHF) through EP3 receptors (PTGER3) in the paraventricular nucleus (PVN). The aim of this study was to investigate the role of c-Jun N-terminal kinase (JNK) in expressional regulation of gamma-aminobutyric acid signalling in PVN in CHF rats.

METHODS

Chronic heart failure was induced by left coronary ligation in Wistar rats. Renal sympathetic nerve discharge (RSND) and mean arterial pressure (MAP) responses to the PVN infusion were determined in anaesthetized rats. Osmotic minipumps were used for chronic PVN infusion. PTGER3 expression was examined with immunofluorescence staining, quantitative real-time PCR and Western blot.

RESULTS

Chronic heart failure rats had increased JNK activation and decreased glutamate decarboxylase 1 (GAD1) and GABA_A receptor alpha 1 subunit (GABRA1) expression in the PVN. PVN infusion of the PTGER3 agonist SC-46275 caused sympathoexcitation in sham-operated control (Sham) rats and increased it further in CHF. The PTGER3 antagonist L798106 reduced sympathoexcitation and cardiac dysfunction in CHF. PVN infusion of EP1 receptor antagonist SC-19220, EP2 receptor antagonist AH6809 or EP4 receptor antagonist L-161982 had no effect on sympathoexcitation. The JNK inhibitor SP600125 normalized sympathoexcitation and GAD1 and GABRA1 expression in PVN in CHF rats. Both the p44/42 and p38 mitogen-activated protein kinase inhibitors PD98059 and SB203580 could not prevent the downregulation of GAD1 and GABRA1 expression in PVN in CHF. PTGER3 agonist activated JNK but downregulated GAD1 and GABRA1 expression in NG108 neuronal cells.

CONCLUSION

Prostaglandin signalling through upregulated PTGER3 activates JNK which reduces GAD1 and GABRA1 expression in the PVN, and contributes to sympathoexcitation in CHF.

Positive Inotropic Effect of Prostaglandin F2α in Rat Ventricular Trabeculae

Prostaglandins are ubiquitous signaling molecules in the body that produce autocrine/paracrine effects on target cells in response to mechanical or chemical signals. In the heart, long-term exposure to prostaglandin (PG) F2α has been linked to the development of hypertrophy; however, there is no consensus on the acute effect of PGF2α. Our aim was to determine the response to exogenous PGF2α in isolated trabeculae from rat hearts. PGF2α (1 μM) increased both the Ca transients and the isometric stress in trabeculae, reaching steady state after 10-15 minutes, without altering the time course of Ca transient decay. The precursor of PGF2α, arachidonic acid, also stimulated a similar response. The positive inotropic effect of PGF2α was mediated through a protein kinase C signaling pathway that involved activation of the sarcolemmal Na/H exchanger. We also found that the slow force response to stretch was attenuated in the presence of PGF2α and by addition of indomethacin, a blocker of prostaglandin synthesis. In conclusion, PGF2α was positively inotropic when acutely applied to trabeculae and contributed to the increased Ca transients during the slow force response to stretch. Together, these data suggest that PGF2α is important in maintaining homeostasis during volume loading in healthy hearts.

Endogenous prostaglandin D2 and its metabolites protect the heart against ischemia-reperfusion injury by activating Nrf2

We recently demonstrated that glucocorticoids markedly upregulate the expression of cyclooxygenase-2 in cardiomyocytes and protect hearts from ischemia-reperfusion (I/R) injury by activating lipocalin-type prostaglandin D (PGD) synthase (L-PGDS)-derived PGD(2) biosynthesis. We examined a downstream mechanism of cardioprotection elicited by PGD(2) biosynthesis. Acute PGD(2) treatment did not protect hearts against I/R injury. We then speculated that PGD(2) and its metabolite 15-deoxy-Δ12,14-PGJ(2) activate gene expression networks to mediate the glucocorticoid-mediated cardioprotection. Using an unbiased approach, we identified that glucocorticoids induce a number of well-known erythroid-derived 2-like 2 (Nrf2) target genes in the heart in an L-PGDS-dependent manner and that the cardioprotective effect of glucocorticoids against I/R injury was not seen in Nrf2-knockout hearts. We showed relatively low expression of PGD(2) receptors (ie, DP1 and DP2) in the heart but abundant expression of PGF(2α) receptor (FP), which binds PGF(2α) and PGD(2) with equal affinity. Glucocorticoids also failed to induce the expression of L-PGDS-dependent Nrf2 target genes in FP-knockout hearts. PGD(2) acted through its metabolite 15-deoxy-Δ12,14-PGJ(2) in the heart as evidenced by the glucocorticoid-mediated activation of peroxisome proliferator-activated receptor-γ. In turn, glucocorticoids failed to induce the expression of L-PGDS-dependent Nrf2 target genes in hearts pretreated with peroxisome proliferator-activated receptor-γ antagonist GW9662, and glucocorticoid-mediated cardioprotection against I/R injury was compromised in FP-knockout mice and GW9662-treated mice. In conclusion, PGD(2) protects heart against I/R injury by activating Nrf2 predominantly via FP receptor. In addition, we propose activation of peroxisome proliferator-activated receptor-γ by the dehydrated metabolite of PGD(2) (15-deoxy-Δ12,14-PGJ(2)) as another mechanism by which glucocorticoids induce cardioprotection.

Chiral recognition of doxazosin enantiomers in 3 targets for therapy as well as adverse drug reactions in animal experiments

Doxazosin used in benign prostatic hyperplasia has the side effects of causing hypotension and the risk of heart failure. The 3 targets of α1A-adrenoceptors (in the prostate), α1D-adrenoceptors (in the aorta), and an unknown mechanism (in the heart) are involved, respectively. We hypothesized that there is a chiral recognition of doxazosin enantiomers in the 3 targets. Using isolated rat aorta (α1D-adrenoceptors) and rabbit prostate (α1A-adrenoceptors), we examined pA2 and pKB values of doxazosin enantiomers. We observed chronotropic and inotropic effects of doxazosin enantiomers in isolated rat and rabbit heart tissues. (–)Doxazosin and (+)doxazosin produced a shift to the right of concentration–contraction curves for noradrenalin (aorta) and phenylephrine (prostate smooth muscle). The pA2 value of (–)doxazosin (8.625 ± 0.053) was smaller than (+)doxazosin (9.503 ± 0.051) in rat aorta, but their pKB values in rabbit prostate were the same. In rat and rabbit heart tissues, (+)doxazosin (3–30 µmol·L−1) significantly decreased atrial rate, and produced negative inotropic effects; however, (–)doxazosin did not affect the atrial rate, and produced positive inotropic effects in the atria. Thus, the chiral carbon atom of doxazosin does not affect its activity at the therapeutic target of α1A-adrenoceptors in the prostate, but significantly changes its blocking activity against α1D-adrenoceptors in the aorta, and produces opposite inotropic effects in the atria via an α1-adrenoceptor-independent mechanism.

Putative role of prostaglandin receptor in intracerebral hemorrhage

Each year, approximately 795,000 people experience a new or recurrent stroke. Of all strokes, 84% are ischemic, 13% are intracerebral hemorrhage (ICH) strokes, and 3% are subarachnoid hemorrhage strokes. Despite the decreased incidence of ischemic stroke, there has been no change in the incidence of hemorrhagic stroke in the last decade. ICH is a devastating disease 37–38% of patients between the ages of 45 and 64 die within 30 days. In an effort to prevent ischemic and hemorrhagic strokes we and others have been studying the role of prostaglandins and their receptors. Prostaglandins are bioactive lipids derived from the metabolism of arachidonic acid. They sustain homeostatic functions and mediate pathogenic mechanisms, including the inflammatory response. Most prostaglandins are produced from specific enzymes and act upon cells via distinct G-protein coupled receptors. The presence of multiple prostaglandin receptors cross-reactivity and coupling to different signal transduction pathways allow differentiated cells to respond to prostaglandins in a unique manner. Due to the number of prostaglandin receptors, prostaglandin-dependent signaling can function either to promote neuronal survival or injury following acute excitotoxicity, hypoxia, and stress induced by ICH. To better understand the mechanisms of neuronal survival and neurotoxicity mediated by prostaglandin receptors, it is essential to understand downstream signaling. Several groups including ours have discovered unique roles for prostaglandin receptors in rodent models of ischemic stroke, excitotoxicity, and Alzheimer disease, highlighting the emerging role of prostaglandin receptor signaling in hemorrhagic stroke with a focus on cyclic-adenosine monophosphate and calcium (Ca²⁺) signaling. We review current ICH data and discuss future directions notably on prostaglandin receptors, which may lead to the development of unique therapeutic targets against hemorrhagic stroke and brain injuries alike.

Prostanoid receptors involved in regulation of the beating rate of neonatal rat cardiomyocytes

Although prostanoids are known to be involved in regulation of the spontaneous beating rate of cultured neonatal rat cardiomyocytes, the various subtypes of prostanoid receptors have not been investigated in detail. In our experiments, prostaglandin (PG)F_2α and prostanoid FP receptor agonists (fluprostenol, latanoprost and cloprostenol) produced a decrease in the beating rate. Two prostanoid IP receptor agonists (iloprost and beraprost) induced first a marked drop in the beating rate and then definitive abrogation of beating. In contrast, the prostanoid DP receptor agonists (PGD₂ and BW245C) and TP receptor agonists (U-46619) produced increases in the beating rate. Sulprostone (a prostanoid EP₁ and EP₃ receptor agonist) induced marked increases in the beating rate, which were suppressed by SC-19220 (a selective prostanoid EP₁ antagonist). Butaprost (a selective prostanoid EP₂ receptor agonist), misoprostol (a prostanoid EP₂ and EP₃ receptor agonist), 11-deoxy-PGE₁ (a prostanoid EP₂, EP₃ and EP₄ receptor agonist) did not alter the beating rate. Our results strongly suggest that prostanoid EP₁ receptors are involved in positive regulation of the beating rate. Prostanoid EP₁ receptor expression was confirmed by western blotting with a selective antibody. Hence, neonatal rat cardiomyocytes express both prostanoid IP and FP receptors (which negatively regulate the spontaneous beating rate) and prostanoid TP, DP₁ and EP₁ receptors (which positively regulate the spontaneous beating rate).

The contribution of prostaglandins versus prostacyclin in ventricular remodeling during heart failure

Although the role of Cox-2 in the heart's response to physiologic stress remains controversial (i.e. expression in myocytes versus other resident myocardial cells) the ever expanding role of prostanoids in multiple models of heart failure cannot be denied. Due to the fact that prostanoids are metabolized rather quickly (half life of seconds to minutes) it is believed these signaling mediators act in a paracrine fashion at the site of production. Evidence to date is quite convincing that these bioactive lipid derivatives are involved in physiologic homeostatic regulation as well as beneficial and maladaptive ventricular remodeling in heart failure. Thus, this review will assess the direct contribution of each PG on remodeling in the left ventricle (e.g. hypertrophy, functional effects, and fibrosis).

EP₃ receptors mediate PGE₂-induced hypothalamic paraventricular nucleus excitation and sympathetic activation

Prostaglandin E(2) (PGE(2)), an important mediator of the inflammatory response, acts centrally to elicit sympathetic excitation. PGE(2) acts on at least four E-class prostanoid (EP) receptors known as EP(1), EP(2), EP(3), and EP(4). Since PGE(2) production within the brain is ubiquitous, the different functions of PGE(2) depend on the expression of these prostanoid receptors in specific brain areas. The type(s) and location(s) of the EP receptors that mediate sympathetic responses to central PGE(2) remain unknown. We examined this question using PGE(2), the relatively selective EP receptor agonists misoprostol and sulprostone, and the available selective antagonists for EP(1), EP(3), and EP(4). In urethane-anesthetized rats, intracerebroventricular (ICV) administration of PGE(2), sulprostone or misoprostol increased renal sympathetic nerve activity, blood pressure, and heart rate. These responses were significantly reduced by ICV pretreatment with the EP(3) receptor antagonist; the EP(1) and EP(4) receptor antagonists had little or no effect. ICV PGE(2) or misoprostol increased the discharge of neurons in the hypothalamic paraventricular nucleus (PVN). ICV misoprostol increased the c-Fos immunoreactivity of PVN neurons, an effect that was substantially reduced by the EP(3) receptor antagonist. Real-time PCR detected EP(3) receptor mRNA in PVN, and immunohistochemical studies revealed sparsely distributed EP(3) receptors localized in GABAergic terminals and on a few PVN neurons. Direct bilateral PVN microinjections of PGE(2) or sulprostone elicited sympathoexcitatory responses that were significantly reduced by the EP(3) receptor antagonist. These data suggest that EP(3) receptors mediate the central excitatory effects of PGE(2) on PVN neurons and sympathetic discharge.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Prostaglandins and inflammation

Prostaglandins are lipid autacoids derived from arachidonic acid. They both sustain homeostatic functions and mediate pathogenic mechanisms, including the inflammatory response. They are generated from arachidonate by the action of cyclooxygenase isoenzymes, and their biosynthesis is blocked by nonsteroidal antiinflammatory drugs, including those selective for inhibition of cyclooxygenase-2. Despite the clinical efficacy of nonsteroidal antiinflammatory drugs, prostaglandins may function in both the promotion and resolution of inflammation. This review summarizes insights into the mechanisms of prostaglandin generation and the roles of individual mediators and their receptors in modulating the inflammatory response. Prostaglandin biology has potential clinical relevance for atherosclerosis, the response to vascular injury and aortic aneurysm.

Nicotinamide-rich diet protects the heart against ischaemia-reperfusion in mice: a crucial role for cardiac SUR2A

It is a consensus view that a strategy to increase heart resistance to ischaemia-reperfusion is a warranted. Here, based on our previous study, we have hypothesized that a nicotinamide-rich diet could increase myocardial resistance to ischaemia-reperfusion. Therefore, the purpose of this study was to determine whether nicotinamide-rich diet would increase heart resistance to ischaemia-reperfusion and what is the underlying mechanism. Experiments have been done on mice on control and nicotinamide-rich diet (mice were a week on nicotinamide-rich diet) as well as on transgenic mice overexpressing SUR2A (SUR2A mice), a regulatory subunit of cardioprotective ATP-sensitive K(+) (K(ATP)) channels and their littermate controls (WT). The levels of mRNA in heart tissue were measured by real-time RT-PCR, whole heart and single cell resistance to ischaemia-reperfusion and severe hypoxia was measured by TTC staining and laser confocal microscopy, respectively. Nicotinamide-rich diet significantly decreased the size of myocardial infarction induced by ischaemia-reperfusion (from 42.5+/-4.6% of the area at risk zone in mice on control diet to 26.8+/-1.8% in mice on nicotinamide-rich diet, n=6-12, P=0.031). The cardioprotective effect of nicotinamide-rich diet was associated with 11.46+/-1.22 times (n=6) increased mRNA levels of SUR2A in the heart. HMR1098, a selective inhibitor of the sarcolemmal K(ATP) channels opening, abolished cardioprotection afforded by nicotinamide-rich diet. Transgenic mice with a sole increase in SUR2A expression had also increased cardiac resistance to ischaemia-reperfusion. We conclude that nicotinamide-rich diet up-regulate SUR2A and increases heart resistance to ischaemia-reperfusion.

Regulation of ANP secretion from isolated atria by prostaglandins and cyclooxygenase-2

Cyclooxygenase (COX) is a key enzyme regulating the production of various prostaglandins (PGs) from arachidonic acid. Angiotensin II has been reported to be an important inflammatory mediator, which increases COX-2. The aim of this study was to determine the role of various PGs and COX-2 in the regulation of atrial natriuretic peptide (ANP) secretion. PGF2alpha and PGD2 caused dose-dependent increases in ANP release and intra-atrial pressure. The potency for the stimulation of ANP secretion by PGF2alpha was higher than that by PGD2. In contrast, PGE2, PGI2, PGJ2, and thromboxane A2 did not show any significant effects. The increases in intra-atrial pressure and ANP secretion induced by PGF2alpha and PGD2 were significantly attenuated by the pretreatment with an inhibitor of PGF2alpha receptor. By the pretreatment with an inhibitor for phospholipase C (PLC), inositol 3-phosphate (IP3) receptor, protein kinase C (PKC), or myosin light chain kinase (MLCK), PGF2alpha-mediated increase in ANP secretion and positive inotropy were attenuated. Inhibitor for COX-1 or COX-2 did not cause any significant effects on atrial parameters. In hypertrophied rat atria, PGF2alpha-induced positive inotropy and ANP secretion were markedly attenuated whereas COX-2 inhibitor stimulated ANP secretion. The expression of COX-2 increased and the expression of PGF2alpha receptor mRNA decreased in hypertrophied rat atria. These results suggest that PGF2alpha increased the ANP secretion and positive inotropy through PLC-IP3-PKC-MLCK pathway, and the modulation of ANP secretion by COX-2 inhibitor and PGF2alpha may partly relate to the development of renal hypertension.

A dual mechanism of cytoprotection afforded by M-LDH in embryonic heart H9C2 cells

Muscle form of lactate dehydrogenase (M-LDH), a minor LDH form in cardiomyocytes, physically interacts with ATP-sensitive K+ (K ATP) channel-forming subunits. Here, we have shown that expression of 193gly-M-LDH, an inactive mutant of M-LDH, inhibit regulation of the K ATP channels activity by LDH substrates in embryonic rat heart H9C2 cells. In cells expressing 193gly-M-LDH chemical hypoxia has failed to activate K ATP channels. The similar results were obtained in H9C2 cells expressing Kir6.2AFA, a mutant form of Kir6.2 with largely decreased K+ conductance. Kir6.2AFA has slightly, but significantly, reduced cellular survival under chemical hypoxia while the deleterious effect of 193gly-M-LDH was significantly more pronounced. The levels of total and subsarcolemmal ATP in H9C2 cells were not affected by Kir6.2AFA, but the expression of 193gly-M-LDH led to lower levels of subsarcolemmal ATP during chemical hypoxia. We conclude that M-LDH regulates both the channel activity and the levels of subsarcolemmal ATP and that both mechanism contribute to the M-LDH-mediated cytoprotection.

PGF(2alpha) FP receptor contributes to brain damage following transient focal brain ischemia

Although some of the COX-2 metabolites and prostaglandins have been implicated in stroke and excitotoxicity, the role of prostaglandin F(2alpha) (PGF(2alpha)) and its FP receptor have not been elucidated in the pathogenesis of ischemic-reperfusion (I/R) brain injury. Here we investigated the FP receptor's contribution in a unilateral middle cerebral artery (MCA) occlusion model of focal cerebral ischemia in mice. The MCA in wild type (WT) and FP knockout (FP(-/-)) C57BL/6 male mice was transiently occluded with a monofilament for 90 min. After 96 h of reperfusion, the FP(-/-) mice had 25.3% less neurological deficit (P < 0.05) and 34.4% smaller infarct volumes (P < 0.05) than those of the WT mice. In a separate cohort, physiological parameters were monitored before, during, and after ischemia, and the results revealed no differences between the groups. Because excitotoxicity is an acute mediator of stroke outcome, the effect of acute NMDA-induced neurotoxicity was also tested. Forty-eight hours after unilateral intrastriatal NMDA injection, excitotoxic brain damage was 20.8% less extensive in the FP(-/-) mice (P < 0.05) than in the WT counterparts, further supporting the toxic contribution of the FP receptor in I/R injury. Additionally, we investigated the effect of post-treatment with the FP agonist latanoprost in mice subjected to MCA occlusion; such treatment resulted in an increase in neurological deficit and infarct size in WT mice (P < 0.05), though no effects were observed in the latanoprost-treated FP(-/-) mice. Together, the results suggest that the PGF(2alpha) FP receptor significantly enhances cerebral ischemic and excitotoxic brain injury and that these results are of importance when planning for potential development of therapeutic drugs to treat stroke and its acute and/or long term consequences.

High-speed imaging of developing heart valves reveals interplay of morphogenesis and function

Knowing how mutations disrupt the interplay between atrioventricular valve (AVV) morphogenesis and function is crucial for understanding how congenital valve defects arise. Here, we use high-speed fluorescence microscopy to investigate AVV morphogenesis in zebrafish at cellular resolution. We find that valve leaflets form directly through a process of invagination, rather than first forming endocardial cushions. There are three phases of valve function in embryonic development. First, the atrioventricular canal (AVC) is closed by the mechanical action of the myocardium, rolls together and then relaxes. The growing valve leaflets serve to block the canal during the roll and, depending on the developmental stage, either expand or hang down as a leaflet to block the canal. These steps are disrupted by the subtle morphological changes that result from inhibiting ErbB-, TGFbeta-or Cox2 (Ptgs2)-dependent signaling. Cox2 inhibition affects valve development due to its effect on myocardial cell size and shape, which changes the morphology of the ventricle and alters valve geometry. Thus, different signaling pathways regulate distinct aspects of the behavior of individual cells during valve morphogenesis, thereby influencing specific facets of valve function.

AMP-activated protein kinase mediates preconditioning in cardiomyocytes by regulating activity and trafficking of sarcolemmal ATP-sensitive K(+) channels

Brief periods of ischemia and reperfusion that precede sustained ischemia lead to a reduction in myocardial infarct size. This phenomenon, known as ischemic preconditioning, is mediated by signaling pathway(s) that is complex and yet to be fully defined. AMP-activated kinase (AMPK) is activated in cells under conditions associated with ATP depletion and increased AMP/ATP ratio. In the present study, we have taken advantage of a cardiac phenotype overexpressing a dominant negative form of the alpha2 subunit of AMPK to analyze the role, if any, that AMPK plays in preconditioning the heart. We have found that myocardial preconditioning activates AMPK in wild type, but not transgenic mice. Cardiac cells from transgenic mice could not be preconditioned, as opposed to cells from the wild type. The cytoprotective effect of AMPK was not related to the effect that preconditioning has on mitochondrial membrane potential as revealed by JC-1, a mitochondrial membrane potential-sensitive dye, and laser confocal microscopy. In contrast, experiments with di-8-ANEPPS, a sarcolemmal-potential sensitive dye, has demonstrated that intact AMPK activity is required for preconditioning-induced shortening of the action membrane potential. The preconditioning-induced activation of sarcolemmal K(ATP) channels was observed in wild type, but not in transgenic mice. HMR 1098, a selective inhibitor of sarcolemmal K(ATP) channels opening, inhibited preconditioning-induced shortening of action membrane potential as well as cardioprotection afforded by AMPK. Immunoprecipitation followed by Western blotting has shown that AMPK is essential for preconditioning-induced recruitment of sarcolemmal K(ATP) channels. Based on the obtained results, we conclude that AMPK mediates preconditioning in cardiac cells by regulating the activity and recruitment of sarcolemmal K(ATP) channels without being a part of signaling pathway that regulates mitochondrial membrane potential.