IODINE 125-PHENYLPENTADECANOIC ACID AND ITS BETA-METHYL SUBSTITUTE METABOLISM IN CULTURED MOUSE EMBRYONAL MYOCYTES : Iodine-labelled Fatty Acids as Tracers of Myocardial High Energy Phosphate

Abstract

Iodine-labelled fatty acids have been proposed as new tracers of cardiac metabolisms. However, it is not clear how these tracers would reflect the intracellular metabolism. Therefore, we measured the uptake and release of iodine 125-labelled phenylpentadecanoic acid (IPPA), its β-methyl substitute (BMIPP) and ²⁰¹Tl in cultured myocytes of mouse embryos, and compared these values to intracellular adenosine triphosphate (ATP) content after metabolic inhibitions of oxidative phosphorylation by sodium cyanide (CN), glycolysis by 2-deoxyglucose (2-DG) or fatty acid β-oxidation by lactate. The uptake and release of BMIPP was not changed by any inhibitors suggesting BMIPP would not be metabolized in the myocytes. The uptake of IPPA was significantly reduced by 2DG and 60-80% of IPPA was metabolized to hydrophilic catabolites. The correlation of BMIPP and IPPA uptake to intracellular ATP content were high (r=0.89, p<0.05; r=0.86, p<0.1), but there was poor correlation of ²⁰¹Tl to ATP values (r=0.53, n.s.). These results suggested that iodine-labelled fatty acids could be used as better tracers of myocardial metabolism than ²⁰¹Tl.