The Carbon Monoxide Prodrug OCOm-21 Increases Ca Sensitivity of the Cardiac Myofilament

Patients undergoing cardiopulmonary bypass procedures require inotropic support to improve hemodynamic function and cardiac output. Current inotropes such as dobutamine, can promote arrhythmias, prompting a demand for improved inotropes with little effect on intracellular Ca flux. Low-dose carbon monoxide (CO) induces inotropic effects in perfused hearts. Using the CO-releasing pro-drug, oCOm-21, we investigated if this inotropic effect results from an increase in myofilament Ca sensitivity. Male Sprague Dawley rat left ventricular cardiomyocytes were permeabilized, and myofilament force was measured as a function of -log [Ca ] (pCa) in the range of 9.0-4.5 under five conditions: vehicle, oCOm-21, the oCOm-21 control BP-21, and levosimendan, (9 cells/group). Ca sensitivity was assessed by the Ca concentration at which 50% of maximal force is produced (pCa ). oCOm-21, but not BP-21 significantly increased pCa compared to vehicle, respectively (pCa 5.52 vs. 5.47 vs. 5.44; p < 0.05). No change in myofilament phosphorylation was seen after oCOm-21 treatment. Pretreatment of cardiomyocytes with the heme scavenger hemopexin, abolished the Ca sensitizing effect of oCOm-21. These results support the hypothesis that oCOm-21-derived CO increases myofilament Ca sensitivity through a heme-dependent mechanism but not by phosphorylation. Further analyses will confirm if this Ca sensitizing effect occurs in an intact heart.