Prostanoid F receptors elicit an inotropic effect in rat left ventricle by enhancing myosin light chain phosphorylation.
OBJECTIVE
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.


RESULTS
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.


CONCLUSIONS
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.
Riise
Jon
J
Department of Pharmacology, University of Oslo, Sognsvannsvn. 20, Building A2/A3, PO Box 1057 Blindern, N-0316 Oslo, Norway.
Nguyen
Cam H T
CH
Qvigstad
Eirik
E
Sandnes
Dagny L
DL
Osnes
Jan-Bjørn
JB
Skomedal
Tor
T
Levy
Finn Olav
FO
Krobert
Kurt A
KA
D000818:Animals; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism; D024722:Cardiac Myosins / Q000378:metabolism*; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000037:antagonists & inhibitors / Q000378:metabolism; D006352:Heart Ventricles / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000378:metabolism; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology; D018994:Myosin Light Chains / Q000378:metabolism*; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D043263:Myosin-Light-Chain Phosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism*; D011982:Receptors, Prostaglandin / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
D002147:Calmodulin; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018994:Myosin Light Chains; D018340:Receptors, Adrenergic, alpha-1; D011982:Receptors, Prostaglandin; C107184:myosin light chain 2; C034671:prostaglandin F2alpha receptor; D054460:rho-Associated Kinases; D011493:Protein Kinase C; D009219:Myosin-Light-Chain Kinase; D043263:Myosin-Light-Chain Phosphatase; D024722:Cardiac Myosins; D043802:GTP-Binding Protein alpha Subunits, Gq-G11