INVESTIGATION OF CARDIAC METABOLISM USING STABLE ISOTOPES AND MASS-SPECTROMETRY

The technique described in this communication enables detailed investi gations of cardiac metabolism using C-13-labeled substrates and mass s pectrometric measurements of (CO2)-C-13 in the coronary effluent. To v alidate this technique for further studies isolated working rat hearts were perfused with C-13-labeled substrates in a bicarbonate-free perf usion fluid. The fraction Of CO2 produced by oxidation of labeled subs trate was calculated by the (CO2)-C-13/CO2 ratio in the coronary perfu sate. The oxidation of C-13-acetate showed a linear correlation with C -13-acetate concentrations between 0.015 and 0.16 mmol/l. An inhibitor of acylcarnitine translocase, 2-(3-methylcinnamylhydrazono)-propionat e (BM42.304) decreased CO2 production from C-13-palmitate from 48 % +/ - 4 % to 31 % +/- 3 % (n = 11, SEM). Taking into account consideration s of tracer kinetic theory rapidly accessible intracellular palmitate stores were estimated to be less than 900 nmol/g ww. This technique al lows specific investigations of the oxidation of labeled substrates in the heart and may be useful for basic research and/or clinical diagno sis, thus avoiding the hazards of radiolabeled substrates.