Normal increases in insulin-stimulated glucose uptake after ex vivo contraction in neuronal nitric oxide synthase mu (nNOSμ) knockout mice

Nitric oxide (NO) is involved in skeletal muscle glucose uptake during exercise and also in the increase in insulin sensitivity after exercise. Given that neuronal nitric oxide synthase (NOS) isoform mu (nNOSμ) is a major isoform of NOS in skeletal muscle, we examined if the increase in skeletal muscle insulin-stimulated glucose uptake 3.5 h following ex vivo contraction of extensor digitorum longus (EDL) is reduced in muscles from nNOSμ+/− and nNOSμ−/− mice compared with nNOSμ+/+ mice. 3.5 h post-contraction/basal, muscles were exposed to saline or insulin (120μU/ml) with or without the presence of the NOS inhibitor NG-monomethyl-L-arginine (L-NMMA) during the last 30 min and glucose uptake was determined by radioactive tracers. Skeletal muscle insulin-stimulated glucose uptake from nNOSμ+/+, nNOSμ+/−, and nNOSμ−/− mice increased approximately twofold 3.5 h following ex vivo contraction when compared to rest. L-NMMA significantly attenuated this increase in muscle insulin-stimulated glucose uptake by around 50%, irrespective of genotype. Low levels of NOS activity were detected in muscles from nNOSμ−/− mice. In conclusion, NO mediates increases in mouse skeletal muscle insulin response following ex vivo contraction independently of nNOSμ.