Witczak CA, Jessen N, Warro DM, Toyoda T, Fujii N, Anderson ME, Hirshman MF, Goodyear LJ. CaMKII regulates contraction- but not insulin-induced glucose uptake in mouse skeletal muscle. Am J Physiol Endocrinol Metab 298: E1150-E1160, 2010. First published March 9, 2010; doi:10.1152/ajpendo.00659.2009.-Studies using chemical inhibitors have suggested that the Ca2+-sensitive serine/threonine kinase Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a key regulator of both insulin-and contraction-stimulated glucose uptake in skeletal muscle. However, due to nonspecificity of these inhibitors, the specific role that CaMKII may play in the regulation of glucose uptake is not known. We sought to determine whether specific inhibition of CaMKII impairs insulin- and/or contraction- induced glucose uptake in mouse skeletal muscle. Expression vectors containing green fluorescent protein conjugated to a CaMKII inhibitory (KKALHRQEAVDCL) or control (KKALHAQERVDCL) peptide were transfected into tibialis anterior muscles by in vivo electroporation. After 1 wk, muscles were assessed for peptide expression, CaMK activity, insulin-and contraction-induced 2-[H-3]deoxyglucose uptake, glycogen concentrations, and changes in intracellular signaling proteins. Expression of the CaMKII inhibitory peptide decreased muscle CaMK activity similar to 35% compared with control peptide. Insulin-induced glucose uptake was not changed in muscles expressing the inhibitory peptide. In contrast, expression of the inhibitory peptide significantly decreased contraction-induced muscle glucose uptake (similar to 30%). Contraction-induced decreases in muscle glycogen were not altered by the inhibitory peptide. The CaMKII inhibitory peptide did not alter expression of the glucose transporter GLUT4 and did not impair contraction-induced increases in the phosphorylation of AMP-activated protein kinase (Thr(172)) or TBC1D1/TBC1D4 on phospho-Akt substrate sites. These results demonstrate that CaMKII does not regulate insulin-stimulated glucose uptake in skeletal muscle. However, CaMKII plays a critical role in the regulation of contraction-induced glucose uptake in mouse skeletal muscle.