USE OF 2,3-BUTANEDIONE MONOXIME TO ESTIMATE NONMECHANICAL VO2 IN RABBIT HEARTS

The purpose of the present study was to evaluate the feasibility of pa rtitioning myocardial O2 consumption (VO2) into mechanical and nonmech anical components in the whole heart preparation using a negative inot rope, 2,3-butanedione monoxime (BDM), which has been reported to have a selective effect on the contractile proteins in a low concentration range (<6 mM). In six isolated bovine red blood cell-perfused rabbit h earts, VO2 and force-time integral (FTI) were measured during infusion of varying concentrations of BDM at a constant left ventricular volum e chosen such that control left ventricular peak isovolumic pressure w as approximately 100 mmHg. The VO2-FTI relation with BDM concentration s less-than-or-equal-to 5 mM was highly linear (median r = 0.98). Its VO2-axis intercept at zero FTI had a positive value (mean 23% of contr ol, 0.014 ml O2.beat-1.100 g-1). To confirm the selective effect of BD M on the contractile proteins, the intracellular free Ca2+ transient w as measured with the fluorescent indicator indo 1 in three isolated bu ffer-perfused rabbit hearts. The amplitude of the Ca2+ transient was n ot altered by BDM at concentrations less-than-or-equal-to 10 mM, altho ugh left ventricular developed pressure was markedly depressed. This f inding indicates that BDM less-than-or-equal-to 10 mM does not affect excitation-contraction coupling. We conclude that the VO2-axis interce pt value of the VO2-FTI relation during BDM infusion in a low concentr ation range represents VO2 for nonmechanical energy utilization. The B DM method to partition VO2 into mechanical and nonmechanical component s is thus feasible in the whole rabbit heart.