Quantitative identification of superoxide anion as a negative inotropic species

Reduced oxygen intermediates have been shown to directly depress cardiac muscle function at the subcellular, tissue, and whole animal levels. The exact species of reduced oxygen intermediate [superoxide anion radical (O2-.), H2O2, hydroxyl free radical (HO.)] and the concentrations necessary to depress cardiac muscle function have not been quantified. To better understand the role of O2-. and H2O2, we have studied rabbit right ventricular papillary muscle function in the presence of these reduced oxygen intermediates generated by a xanthine-xanthine oxidase system at 37 degrees C. In the presence of xanthine (0.1 mM) and xanthine oxidase (0.02 U/ml), 57.5 +/- 0.85 nmol.l-1.s-1 O2-. and 69.25 +/- 5.3 nmol.l-1.s-1 H2O2 were produced. In the presence of superoxide dismutase (SOD), O2-. was eliminated and H2O2 concentration increased. Catalase effectively eliminated the accumulation of H2O2 without significantly changing the rate of O2-. generation. When applied to isometrically contracting right ventricular papillary muscles, this system, with or without SOD and catalase, had no effect on peak developed tension or +/- dT/dt derived either from length-tension or force-frequency studies. However, when the xanthine oxidase concentration was increased to 0.112 U/ml, the rate of O2-. generation increased to 196.67 +/- 3.26 nmol.l-1.s-1 and H2O2 production increased to 142.19 +/- 9.3 nmol.l-1.s-1 with significant depression of papillary muscle tension development. SOD virtually eliminated O2-. production, whereas H2O2 production increased to 199.48 +/- 9.8 nmol.l-1.s-1 with no effect on papillary muscle tension development.(ABSTRACT TRUNCATED AT 250 WORDS)