An intrinsic role of CaMKIIα in insulin‐induced glucose uptake by L6 myotubes

In skeletal muscle, the molecular mechanisms by which insulin interacts with other parallel glucose transport pathways or vice versa remain poorly understood. Our study investigated the role of Ca 2+ /calmodulin‐dependent protein kinase II α (CaMKIIα) in insulin‐mediated glucose transport using L6 myotubes. Cells were treated without or with insulin [100 nM] for 15 minutes and subsequently monitored for both glucose uptake using isotope‐labelled 2‐deoxyglucose (I‐2DOG) and intracellular Ca 2+ (Ca i 2+ ) release using Fluo‐4 AM as well as protein phosphorylation events using Western blotting. Acute exposure of myotubes to insulin activated the various insulin‐dependent signals, including Akt substrate‐160 kDa (AS160) and stimulated I‐2DOG uptake. Under identical conditions, insulin concurrently activated both Ca i 2+ release and CaMKIIα. Exposing myotubes to BAPTA‐AM or KN93 did not affect insulin‐mediated glucose transport. However, blocking either calmodulin or the autoregulatory domain of CaMKIIα blocked the effect of insulin on both AS160 phosphorylation and glucose transport. Likewise, genetic knock down of CaMKIIα in myotubes using siRNA completely abolished insulin‐mediated glucose uptake. These results indicate that insulin‐dependent signals do not require Ca i 2+ ‐CaMKIIα to mediate glucose uptake. However impairment in the autoregulatory domain or genetic disruption of CaMKIIα is sufficient to negatively influence insulin‐dependent glucose transport by L6 myotubes.