Effects of pent-4-enoate on cellular redox state, glycolysis and fatty acid oxidation in isolated perfused rat heart

Abstract

The metabolic effects of pent-4-enoate were studied in beating and K-arrested perfused rat hearts. The addition of 0.8 mM pent-4-enoate to the fluid used to perfuse a K-arrested heart resulted in a 70% increase in the O2 consumption and a 66% decrease in the glycolytic flux as measured in terms of the de-tritiation of [3-3H]glucose, although the proportion of the O2 consumption attributable to glucose oxidation decreased from an initial 30% to 10%. The pent-4-enoate-induced increase in O2 consumption was only 15% in the beating heart. In the K-arrested heart, pent-4-enoate stimulated palmitate oxidation by more than 100% when measured in terms of the production of 14CO2 from [1-14C]palmitate, but in the beating heart palmitate oxidation was inhibited. Perfusion of the heart with pent-4-enoate had no effect on the proportion of pyruvate dehydrogenase found in the active form, in spite of large changes in the CoASH and acetyl-CoA concentrations and changes in their concentration ratios. The effects of pent-4-enoate on the cellular redox state were dependent on the ATP consumption of the heart. In the beating heart, pent-4-enoate caused a rapid mitochondrial NAD+ reduction that subsequently faded out, so that the final state was more oxidized than the initial state. The arrested heart remained in a more reduced state than initially, even after the partial re-oxidation that followed the initial rapid NAD+ reduction. The ability of pent-4-enoate to increase or decrease fatty acid oxidation can be explained by the differential effects of pent-4-enoate on the concentration of citric acid-cycle intermediates under conditions of high or low ATP consumption of the myocardial cell. The proportion of the fatty acids in the fuel consumed by the heart is probably primarily determined by the regulatory mechanisms of glycolysis. When pent-4-enoate causes an increase in the citric acid-cycle intermediates, feedback inhibition of glycolysis results in an increase in the oxidation of fatty acids.