The aim of this study was to determine whether adiponectin elicits glucose uptake via increased GLUT4 translocation and to investigate the metabolic fate of glucose in skeletal muscle cells treated with globular adiponectin.

Basal and insulin-stimulated 2-deoxy-d-[³H]glucose uptake, cell surface myc-tagged GLUT4 content, production of ¹⁴CO₂ by oxidation of d-[U-¹⁴C]glucose and [1-¹⁴C]oleate, and incorporation of d-[U-¹⁴C]glucose into glycogen and lactate were measured in the presence and absence of globular adiponectin.

RT-PCR and Western blot analysis revealed that L6 cells and rat skeletal muscle cells express AdipoR1 mRNA and protein. Globular adiponectin increased both GLUT4 translocation and glucose uptake by increasing the transport V _max of glucose without altering the K _m. Interestingly, the incorporation of d-[U-¹⁴C]glucose into glycogen under basal and insulin-stimulated conditions was significantly decreased by globular adiponectin, whereas lactate production was increased. Furthermore, globular adiponectin did not affect glucose oxidation, but enhanced phosphorylation of AMP kinase and acetyl-CoA carboxylase, and fatty acid oxidation.

The present study is the first to show that globular adiponectin increases glucose uptake in skeletal muscle cells via GLUT4 translocation and subsequently reduces the rate of glycogen synthesis and shifts glucose metabolism toward lactate production. These effects are consistent with the increased phosphorylation of AMP kinase and acetyl-CoA carboxylase and oxidation of fatty acids induced by globular adiponectin.