Eicosanoids and the Regulation of Cardiac Glucose Transport

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Abstract
Intact actin microfilaments are necessary for insulin‐regulated GLUT4 translocation from intracellular pools to the plasma membrane. Products of the lipoxygenase (LO) pathway were shown to be implicated in the regulation of actin cytoskeleton rearrangement. The aim of this study was to examine the role of these LO products for cardiac insulin signaling and glucose uptake, GLUT4 translocation, and actin‐based cytoskeleton structure. Exposure of cardiomyocytes to esculetin or NDGA, two structurally different LO inhibitors, induced a complete inhibition of insulin‐stimulated glucose uptake, whereas control cells showed a threefold stimulation by insulin. Addition of 12(S)‐HETE rendered the NDGA‐treated cells insulin‐sensitive. Early insulin signaling was not changed in cells exposed to LO inhibitors. Cell surface biotinylation of control cells showed a twofold increase of GLUT4 at the cell surface after insulin stimulation. In contrast, the LO inhibitors induced a complete inhibition of insulin‐stimulated GLUT4 translocation. Labeling of the F‐actin cytoskeleton revealed a prominent disassembly of actin fibers in cells exposed to the LO inhibitors. In conclusion, we show here that products of the LO reaction participate in the organization of the actin network in ventricular cardiomyocytes. Inhibition of LO blocks GLUT4 translocation without affecting insulin signaling events. These data suggest that products of the LO reaction participate in the regulation of glucose transport by contribution to a rearrangement of actin cytoskeletal elements.