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ABSTRACT: Prostanoid-modulatory approaches in heart failure patients have displayed effects which may seem to be mutually incompatible. Both treatment with prostanoids and inhibition of prostanoid synthesis have resulted in increased mortality in heart failure patients. Currently, it is unknown if prostanoids mediate contractile effects in failing human heart and if this can explain some of the clinical effects seen after prostanoid modulatory treatments. Therefore, the objectives of this study were to determine if prostanoids could elicit direct inotropic responses in human ventricle, and if so to determine if they are modified in failing ventricle. Contractile force was measured in left ventricular strips from non-failing or failing human and rat hearts. The ratio of phosphorylated to non-phosphorylated myosin light chain 2 (MLC-2) was measured by Western blotting in myocardial strips, and the levels of prostanoid FP receptor mRNA and protein were measured in rat by real-time RT-PCR and receptor binding assays. In non-failing human hearts, prostanoids evoked a positive inotropic effect and an increase of MLC-2 phosphorylation which was absent in failing human hearts. In failing rat heart, the prostanoid FP receptor-mediated inotropic response and prostanoid FP receptor-density was reduced by ~40-50% compared to non-failing rat heart. Prostanoids mediate a sustained positive inotropic response in non-failing heart, which appears to be down regulated in failing heart. The pathophysiological significance of changes in prostanoid-mediated inotropic support in the failing heart remains to be determined.
European journal of pharmacology 04/2012; 686(1-3):66-73. · 2.59 Impact Factor
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ABSTRACT: Whereas natriuretic peptides increase cGMP levels with beneficial cardiovascular effects through protein kinase G, we found an unexpected cardio-excitatory effect of C-type natriuretic peptide (CNP) through natriuretic peptide receptor B (NPR-B) stimulation in failing cardiac muscle and explored the mechanism.
Heart failure was induced in male Wistar rats by coronary artery ligation. Contraction studies were performed in left ventricular muscle strips. Cyclic nucleotides were measured by radio- and enzyme immunoassay. Apoptosis was determined in isolated cardiomyocytes by Annexin-V/propidium iodide staining and phosphorylation of phospholamban (PLB) and troponin I was measured by western blotting. Stimulation of NPR-B enhanced beta1-adrenoceptor (beta1-AR)-evoked contractile responses through cGMP-mediated inhibition of phosphodiesterase 3 (PDE3). CNP enhanced beta1-AR-mediated increase of cAMP levels to the same extent as the selective PDE3 inhibitor cilostamide and increased beta1-AR-stimulated protein kinase A activity, as demonstrated by increased PLB and troponin I phosphorylation. CNP promoted cardiomyocyte apoptosis similar to inhibition of PDE3 by cilostamide, indicative of adverse effects of NPR-B signalling in failing hearts.
An NPR-B-cGMP-PDE3 inhibitory pathway enhances beta(1)-AR-mediated responses and may in the long term be detrimental to the failing heart through mechanisms similar to those operating during treatment with PDE3 inhibitors or during chronic beta-adrenergic stimulation.
Cardiovascular research 11/2009; 85(4):763-72. · 5.80 Impact Factor
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ABSTRACT: The aims of this study were to determine if the prostanoid F receptor (FPR)-mediated inotropic effect in rat ventricle is mediated by increased phosphorylation of myosin light chain-2 (MLC-2) and to elucidate the signalling pathway(s) activated by FPRs to regulate MLC-2 phosphorylation.
Contractility was measured in left ventricular strips from adult male rats. Strips were also snap-frozen, and changes in the phosphorylation level of both MLC-2 and myosin phosphatase targeting subunit-2 (MYPT-2) were quantified. FPR stimulation with fluprostenol increased contractility by approximately 100% above basal and increased phosphorylation of both MLC-2 (by approximately 30%) and MYPT-2 (by approximately 50%). The FPR-mediated inotropic effect and MLC-2 phosphorylation were reduced by a similar magnitude in the presence of the myosin light chain kinase (MLCK) inhibitor ML-7 (approximately 60-70%) and an inhibitor of Ca(2+)/calmodulin, W-7 (approximately 35%). Inhibition of Rho-associated kinase by Y-27632 reduced the FPR-mediated inotropic effect and MLC-2 phosphorylation by approximately 40-45% and MYPT-2 phosphorylation by approximately 70%. ML-7 and Y-27632 together reduced contractility and MLC-2 phosphorylation by approximately 70-80%. The FPR-mediated inotropic effect was only modestly affected by high concentrations of the inositol tris-phosphate (IP(3)) receptor blocker 2-APB, but not by the protein kinase C (PKC) inhibitor bisindolylmaleimide.
The FPR-evoked inotropic effect is mediated by increasing the phosphorylation of MLC-2 through regulation of both MLCK and myosin light chain phosphatase activities. The second messenger IP(3) and PKC are unlikely to be involved in the signalling cascade of the FPR-mediated positive inotropic effect. Therefore, FPR signalling mechanism(s) regulating MLC-2 phosphorylation likely extend beyond those classically established for G(q/11)-coupled receptors.
Cardiovascular research 09/2008; 80(3):407-15. · 5.80 Impact Factor
