Fatty acid metabolism in hearts containing elevated levels of CoA

Palmitate metabolism was determined in isolated perfused hearts containing elevated levels of coenzyme A (CoA). CoA levels were elevated by perfusing hearts with Krebs-Henseleit buffer containing 0.1 mM cysteine, 0.2 mM dithiothreitol, 15 microM pantothenic acid, and no energy substrate. After 45 min, CoA levels had increased from 537 +/- 14 to 818 +/- 44 nmol/g dry wt. When these hearts containing high CoA were subsequently perfused as working hearts with buffer containing 11 mM glucose and 1.2 mM palmitate, long chain acyl CoA levels increased (94 +/- 5-305 +/- 6 nmol/g dry wt). Oxidation of exogenous palmitate (as measured by 14CO2 production from [U-14C]palmitate) was significantly depressed in hearts containing elevated CoA levels. This apparent reduction in fatty acid oxidation was not due to increased glucose or glycogen utilization. When the concentration of palmitate was decreased to 0.4 mM, acyl CoA levels increased much less, and the apparent rate of [14C]palmitate oxidation was unaffected by elevated CoA. Hearts containing high CoA also incorporated [14C]palmitate into triacylglycerols to a greater extent than did control hearts. To determine whether the apparent decrease in exogenous palmitate oxidation resulted from an increased utilization of unlabeled endogenous triacylglycerol fatty acid, [14C]palmitate specific activity was measured in myocardial acylcarnitine. The specific activity of this pool of fatty acid was similar in both control hearts and hearts containing elevated CoA. Thus dilution of the total cellular [14C]acyl carnitine by triacylglycerol hydrolysis was not sufficient to account for the decrease in [U-14C]palmitate oxidation. The possibility that a small pool of rapidly turning over acyl carnitine becomes dilated is discussed.(ABSTRACT TRUNCATED AT 250 WORDS)