title: Effects of Levosimendan, a cardiotonic agent targeted to troponin C, on cardiac function and on phosphorylation and Ca2+ sensitivity of cardiac myofibrils and sarcoplasmic reticulum in guinea pig heart.
abstract: A new cardiotonic agent, (R)-[[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)-phenyl] hydrazono]propanedinitrile (Levosimendan), has been developed and screened for its ability to bind to cardiac troponin C. In perfused hearts, low concentrations of 0.03 or 0.1 mumol/L Levosimendan increased +dP/dt, but did not affect the speed of relaxation and produced only a slight increase in spontaneous heart rate in the hearts perfused with 0.1 mumol/L of the drug. In these same hearts, perfusion with 0.03 mumol/L Levosimendan did not alter the 32P incorporation into troponin I or C protein, whereas a slight but significant increase was noted for phospholamban, with no detectable change in tissue cAMP levels. Administration of 0.1 or 0.3 mumol/L Levosimendan significantly increased myocardial cAMP levels as well as the phosphorylation of phospholamban, troponin I, and C protein. Levosimendan (0.03 to 10 mumol/L) reversibly increased force generated by detergent-extracted fiber bundles over a range of submaximally activating free Ca2+ concentrations with no significant effect on maximum force or on Ca2+ binding to myofilament troponin C. There was no direct effect of Levosimendan on Ca2+ uptake by vesicles of sarcoplasmic reticulum (SR). In contrast, under conditions optimal for cAMP-dependent phosphorylation, Levosimendan slightly but significantly lowered the concentration of Ca2+, yielding half-maximal uptake rates by the SR vesicles. Our results indicate that at low concentrations Levosimendan acts preferably as a Ca2+ sensitizer, whereas at higher concentrations its action as a phosphodiesterase inhibitor contributes to the positive inotropic effect.
authors.affiliation: Second Department of Medicine, Albert Szent-Györgyi Medical University, Szeged, Hungary.
authors.forename: I
authors.initials: I
authors.lastname: Edes
authors.forename: E
authors.initials: E
authors.lastname: Kiss
authors.forename: Y
authors.initials: Y
authors.lastname: Kitada
authors.forename: F M
authors.initials: FM
authors.lastname: Powers
authors.forename: J G
authors.initials: JG
authors.lastname: Papp
authors.forename: E G
authors.initials: EG
authors.lastname: Kranias
authors.forename: R J
authors.initials: RJ
authors.lastname: Solaro
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002316:Cardiotonic Agents / Q000494:pharmacology*; D002352:Carrier Proteins / Q000378:metabolism; D000242:Cyclic AMP / Q000032:analysis; D006152:Cyclic GMP / Q000032:analysis; D004591:Electrophoresis, Polyacrylamide Gel; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006835:Hydrazones / Q000494:pharmacology*; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D009210:Myofibrils / Q000187:drug effects* / Q000378:metabolism; D010477:Perfusion; D010766:Phosphorylation / Q000187:drug effects; D011724:Pyridazines / Q000494:pharmacology*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D000077464:Simendan; D014336:Troponin / Q000187:drug effects* / Q000378:metabolism; D019209:Troponin C; D019210:Troponin I; D016277:Ventricular Function, Left / Q000187:drug effects; D000099211:Phospholamban
chemical_list: D002118:Calcium; D002135:Calcium-Binding Proteins; D002316:Cardiotonic Agents; D002352:Carrier Proteins; D000242:Cyclic AMP; D006152:Cyclic GMP; D006835:Hydrazones; D011724:Pyridazines; D000077464:Simendan; D014336:Troponin; D019209:Troponin C; D019210:Troponin I; D000099211:Phospholamban; C020723:citrate-binding transport protein