High fatty acid availability after exercise alters the regulation of muscle lipid metabolism

We previously reported that a single exercise session protects against fatty acid (FA)-induced insulin resistance, perhaps in part through augmented intramyocellular triacylglycerol (IMTG) synthesis. The aim of this study was to examine the effect of elevated FA availability after exercise on factors regulating IMTG metabolism. After exercise (90 minutes, 65% peak oxygen uptake), 7 healthy women (body mass index, 23 ± 1 kg/m2) were infused overnight (16 hours) with either a lipid and heparin solution (LIPID, 0.11 g fat per kilogram per hour) or saline (SALINE). We measured resting FA oxidation (indirect calorimetry) and obtained a skeletal muscle biopsy sample the next morning. The 4-fold increase in overnight plasma FA concentration during LIPID increased IMTG by approximately 30% during LIPID vs SALINE. This was accompanied by an approximately 25% greater membrane-associated abundance of the FA transporter FAT/CD36 (P < .01) and an approximately 8% increase in the activity of the IMTG synthesis enzyme glycerol-3-phosphate acyltransferase (GPAT, P < .01). In contrast, resting FA oxidation was not affected. We also found no difference in the protein abundance of GPAT1 and diacylglycerol acyltransferase-1, diacylglycerol acyltransferase activity, or the abundance of the lipid droplet coat proteins (perilipins 2, 3, 4, and 5) between treatments. Our findings suggest that augmented capacity for FA flux into muscle (ie, via membrane-associated FAT/CD36), perhaps together with a slight yet significant increase in activity of a key IMTG synthesis enzyme (GPAT), may enhance IMTG storage when FA availability is high after exercise. The importance of the absence of a change in perilipin protein abundance despite increased muscle lipid storage remains to be determined.