Acute stimulation of glucose uptake by leptin in L6 muscle cells

The adipocyte hormone, leptin, acts via the central nervous system to modulate glucose metabolism by skeletal muscle, but the direct effects of leptin on glucose metabolism by skeletal muscle are unclear. In this study, we have examined effects of leptin on glucose uptake by cultured L6 muscle cells assessed with the non-metabolised glucose analogue 2-deoxy-D-glucose. Reverse-transcriptase polymerase chain reaction (RT-PCR) analysis of RNA showed that L6 muscle cells express a short isoform of the leptin receptor (ObRa), but not the long isoform (ObRb). In the absence of added insulin, incubation of L6 muscle cells with murine leptin (10(-11)-10(-8)M) for 10 min and 1 h increased glucose uptake by 15%-23%. This effect of leptin was lost by 4 h. Leptin (10(-10)-10(-9)M) initially (after 10 min) suppressed insulin-stimulated glucose uptake by 14 - 16 %, but had no effect in the longer term. Leptin-stimulated glucose uptake was inhibited by the phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin, but not by the janus kinase-2 (JAK-2) inhibitor tyrphostin AG490. The results suggest that leptin can act directly on L6 muscle cells via a short leptin receptor isoform to acutely stimulate basal (but not insulin-stimulated) glucose uptake via a PI3K-dependent pathway.