Our results show that the CB1R system may play a role in the development of insulin resistance in human SkM. The results obtained with CM support the notion that adipocytes may secrete factors which are able to activate the CB1R. Furthermore, we identified two stress kinases in the signalling pathway of AEA and enhanced IRS-1(Ser307) phosphorylation, potentially underlying the development of insulin resistance.

Aims/hypothesis Obesity is closely associated with muscle insulin resistance and is a major risk factor for the pathogenesis of type 2 diabetes. Regular physical activity not only prevents obesity, but also considerably improves insulin sensitivity and skeletal muscle metabolism. We sought to establish and characterise an in vitro model of human skeletal muscle contraction, with a view to directly studying the signalling pathways and mechanisms that are involved in the beneficial effects of muscle activity. Methods Contracting human skeletal muscle cell cultures were established by applying electrical pulse stimulation. To induce insulin resistance, skeletal muscle cells were incubated with human adipocyte-derived conditioned medium, monocyte chemotactic protein (MCP)-1 and chemerin. Results Similarly to in exercising skeletal muscle in vivo, electrical pulse stimulation induced contractile activity in human skeletal muscle cells, combined with the formation of sarcomeres, activation of AMP-activated protein kinase (AMPK) and increased IL-6 secretion. Insulin-stimulated glucose uptake was substantially elevated in contracting cells compared with control. The incubation of skeletal muscle cells with adipocyte-conditioned media, chemerin and MCP-1 significantly reduced the insulin-stimulated phosphorylation of Akt. This effect was abrogated by concomitant pulse stimulation of the cells. Additionally, proinflammatory signalling by adipocyte-derived factors was completely prevented by electrical pulse stimulation of the myotubes. Conclusions/interpretation We showed that the effects of electrical pulse stimulation on skeletal muscle cells were similar to the effect of exercise on skeletal muscle in vivo in terms of enhanced AMPK activation and IL-6 secretion. In our model, muscle contractile activity eliminates insulin resistance by blocking pro-inflammatory signalling pathways. This novel model therefore provides a unique tool for investigating the molecular mechanisms that mediate the beneficial effects of muscle contraction.

These results show that ZAG leads to phosphorylation of AMPKα and ACC, thereby activating a pathway central to the regulation of energy metabolism. This mechanism may be involved in mediating the effects of ZAG in relation to increased energy utilization.