Contraction-Induced Fatty Acid Translocase/CD36 Translocation in Rat Cardiac Myocytes Is Mediated Through AMP-Activated Protein Kinase Signaling

Abstract

Contraction of rat cardiac myocytes induces translocation of fatty acid translocase (FAT)/CD36 and GLUT4 from intracellular stores to the sarcolemma, leading to enhanced rates of long-chain fatty acid (FA) and glucose uptake, respectively. Because intracellular AMP/ ATP is elevated in contracting cardiac myocytes, we investigated whether activation of AMP-activated protein kinase (AMP kinase) is involved in contractioninducible FAT/CD36 translocation. The cell-permeable adenosine analog 5-aminoimidazole-4-carboxamide-1-␤-D-ribofuranoside (AICAR) and the mitochondrial inhibitor oligomycin, similar to 4-Hz electrostimulation, evoked a more than threefold activation of cardiomyocytic AMP kinase. Both AICAR and oligomycin stimulated FA uptake into noncontracting myocytes by 1.4-and 2.0-fold, respectively, but were ineffective in 4 Hz-contracting myocytes. These findings indicate that both agents stimulate FA uptake by a similar mechanism as electrostimulation, involving activation of AMP kinase, as evidenced from phosphorylation of acetyl-CoA carboxylase. Furthermore, the stimulating effects of both AICAR and oligomycin were antagonized by blocking FAT/CD36 with sulfo-N-succinimidylpalmitate, but not by inhibiting phosphatidylinositol 3-kinase with wortmannin, indicating the involvement of FAT/CD36, but excluding a role for insulin signaling. Subcellular fractionation showed that oligomycin was able to mobilize intracellularly stored FAT/CD36 to the sarcolemma. We conclude that AMP kinase regulates cardiac FA use through mobilization of FAT/CD36 from a contractioninducible intracellular storage compartment. Diabetes 52:1627-1634, 2003 F atty acid translocase (FAT)/CD36 is increasingly becoming recognized as a physiologically important long-chain fatty acid (FA) transport facilitator within the sarcolemma of muscle tissues (1-3). We have gathered convincing evidence that FAT/ CD36-mediated FA uptake is a rate-limiting step in FA use by heart and skeletal muscle (2). Moreover, FA uptake appears to be regulated by translocation of FAT/CD36 from intracellular, presumably endosomal, stores to the sarcolemma. Insulin and cellular contractions are two important physiological factors able to recruit FAT/CD36 to the sarcolemma (4 -7). Interestingly, the stimulation of FA uptake by contractions was additive to that of insulin, indicating that both factors operate through independent mechanisms. Furthermore, wortmannin completely blocked insulin-inducible FA uptake but had no effect on contraction-inducible FA uptake. Altogether, these findings indicate that insulin-inducible and contraction-inducible FAT/ CD36 pools are stored in two distinct intracellular sites (7). Strikingly, the effects of insulin and contractions on FA uptake by translocation of FAT/CD36 are remarkably similar to their effects on glucose uptake by translocation of the glucose transporter GLUT4 from insulin-inducible and contraction-inducible intracellular stores (7). Whereas the wortmannin sensitivity of insulin-inducible FA uptake indicates an involveme...

Enhanced Sarcolemmal FAT/CD36 Content and Triacylglycerol Storage in Cardiac Myocytes From Obese Zucker Rats

“…Previously we established that there are two signaling pathways linked to the translocation of FAT/CD36 from an intracellular compartment to the sarcolemma: insulininduced PI 3-kinaseϪdependent signaling (13)(14)(15) and contraction-induced AMPK-dependent signaling (18). Accordingly, in the present study, we found that in vitro insulin and oligomycin were effective in inducing FAT/ CD36 translocation and stimulating LCFA uptake in cardiac myocytes from lean rats.…”

“…The effect of cellular contractions on myocardial LCFA utilization was studied by means of oligomycin, a compound that inhibits F 0 /F 1 ATPase activity at relatively low concentrations. Oligomycin, at an optimal concentration (30 mol/l), increased the AMP kinase activity in cardiac myocytes by elevating the intracellular AMP/ATP ratio to approximately the same extent as that observed with cellular contractions (18). To investigate the role of FAT/CD36 in myocardial LCFA uptake and utilization in lean and obese Zucker rats, cardiac myocytes were treated with sulfo-Nsuccinimidyloleate (SSO), which inactivates FAT/CD36 by covalently binding to its LCFA binding site (24,25).…”

“…Despite the fact that both insulin and cellular contractions induce FAT/CD36Ϫmediated LCFA uptake to the same magnitude, their effects are additive and different signaling pathways are involved. Notably, insulin activates phosphatidylinositol (PI) 3-kinase (15), whereas cellular contractions activate AMP kinase (AMPK) (17,18).…”

Protein Kinase D1 Is Essential for Contraction-induced Glucose Uptake but Is Not Involved in Fatty Acid Uptake into Cardiomyocytes

“…1A). Oligomycin, an inhibitor of mitochondrial F 1 F 0 -ATPase, has been previously shown to stimulate AMPK and PKD activation in a similar manner as does contraction (3,7) and was used in these experiments as stimulus to verify whether the down-regulation of synthesis of both kinases would also reduce their activation. Silencing of PKD1 resulted in a complete loss of oligomycin-induced PKD1-Ser 916 phosphorylation, and silencing of AMPK led to a complete loss of oligomycin-induced AMPK-Thr 172 phosphorylation.…”

“…Alterations in contraction are an important denominator of cardiac substrate utilization. Increased contraction enhances the demands for glucose and LCFA, and accordingly, GLUT4 and CD36 have been found to translocate to the sarcolemma under this condition (1,3).…”