Cardiovascular Research Advance Access [Accepted Manuscript] published online on August 14, 2008
Cardiovascular Research, doi:10.1093/cvr/cvn216
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Prostanoid F Receptors Elicit an Inotropic Effect in Rat Left Ventricle by Enhancing Myosin Light Chain Phosphorylation
Department of Pharmacology, University of Oslo, 0316 Oslo, Norway; Center for Heart Failure Research, University of Oslo, 0407 Oslo, Norway
To whom correspondence should be addressed: Department of Pharmacology, University of Oslo, Sognsvannsvn.20, Bldg. A2/A3, P.O. Box 1057 Blindern, 0316 Oslo, Norway. Phone: +47-22840237, Fax: +47-22840202, E-mail: f.o.levy{at}medisin.uio.no
Aims: 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 signaling pathway(s) activated by FPRs to regulate MLC-2 phosphorylation.
Methods: 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.
Results: FPR stimulation with fluprostenol increased contractility by 
100% above basal and increased phosphorylation of both MLC-2 (by 30%) and MYPT-2 (by 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 inhibitor ML-7 (60-70%) and an inhibitor of Ca2+/calmodulin, W-7 (35%). Inhibition of Rho-associated kinase by Y-27632 reduced the FPR-mediated inotropic effect and MLC-2 phosphorylation by 40-45% and MYPT-2 phosphorylation by 70%. ML-7 and Y-27632 together reduced contractility and MLC-2 phosphorylation by 70-80%. The FPR-mediated inotropic effect was modestly affected by high concentrations of the inositol tris-phosphate (IP3) receptor blocker 2-APB, but not by the protein kinase C (PKC) inhibitor bisindolylmaleimide.
Conclusions: The FPR-evoked inotropic effect is mediated by increasing the phosphorylation of MLC-2 through regulation of both myosin light chain kinase and myosin light chain phosphatase activities. The second messenger IP3 and PKC are unlikely to be involved in the signaling cascade of the FPR-mediated positive inotropic effect. Therefore, FPR signaling mechanism(s) regulating MLC-2 phosphorylation likely extend beyond those classically established for Gq/11-coupled receptors.
Time for primary review: 32 Days