Demonstration of reverse fatty acid transport from rat cardiomyocytes

Fatty acids flow from adipocytes to nonadipose tissues during fasting and exercise and normally are fully ox- idized. To determine if nonadipose tissues can export unox- idized FA when FA influx exceeds oxidation, neonatal cardio- myocytes were cultured in 1 � Ci 14 C-palmitate in the presence of etomoxir to block oxidation. The cells took up and stored 25% of the radioactivity as 14 C-triacylglycerol in 12 h, but 4.5% of the label was released in 3 h and comigrated with 14 C-palmitate. Both uptake and release of radioactivity were increased by insulin and reduced by the nonspecific inhibi- tors of FA transporters phloretin and 4,4 � -diisothiocyanatos- tilbene-2,2 � -disulfonic acid (DIDS). Perfused hearts from etomoxir-treated lean rats released 221 � 59 nmol/10 min of FA. Hearts from high-fat-fed lean rats released 366 � 172 nmol/10 min ( P � 0.05). Hearts from obese rats re- leased 744 � 260 and 1,578 � 630 nmol/10 min at 8 and 12 weeks of age, respectively. Perfusion with insulin increased FA release by 32%. In vitro and ex vivo findings suggest that nonadipose tissues such as myocardium can export FA when the unoxidized lipid content is excessive. —Park, B-H., Y. Lee, M. Walton, L. Duplomb, and R. H. Unger. Demon- stration of reverse fatty acid transport from rat cardiomyo- cytes. J. Lipid Res. 2004. 45: 1992-1999.