ATP-sensitive K⁺ channel-mediated glucose uptake is independent of IRS-1/phosphatidylinositol 3-kinase signaling

Abstract

We previously found that disruption of Kir6.2-containing ATP-sensitive K+ (KATP) channels increases glucose uptake in skeletal muscle, but the mechanism is not clear. In the present study, we generated knockout mice lacking both Kir6.2 and insulin receptor substrate-1 (IRS-1). Because IRS-1 is the major substrate of insulin receptor kinase, we expected disruption of the IRS-1 gene to reduce glucose uptake in Kir6.2 knockout mice. However, the double-knockout mice do not develop insulin resistance or glucose intolerance. An insulin tolerance test reveals the glucose-lowering effect of exogenous insulin in double-knockout mice and in Kir6.2 knockout mice to be similarly enhanced compared with wild-type mice. The basal 2-deoxyglucose uptake rate in skeletal muscle of double-knockout mice is increased similarly to the rate in Kir6.2 knockout mice. Accordingly, disruption of the IRS-1 gene affects neither systemic insulin sensitivity nor glucose uptake in skeletal muscles of Kir6.2-deficient mice. In addition, no significant changes were observed in phosphatidylinositol 3-kinase (PI3K) activity and its downstream signal in skeletal muscle due to lack of the Kir6.2 gene. Disruption of Kir6.2-containing Katp channels clearly protects against IRS-1-associated insulin resistance by increasing glucose uptake in skeletal muscles by a mechanism separate from the IRS-1/PI3K pathway.