Stimulation of AMP-activated protein kinase (AMPK) is associated with enhancement of Glut1-mediated glucose transport

In cells expressing only the Glut1 isoform of glucose transporters, we have shown that glucose transport is markedly stimulated in response to hypoxia or inhibition of oxidative phosphorylation, conditions that would be expec ted to cause a stimulation of AMP-activated protein kinase (AMPK) activity. In the present study we tested the hypothesis that the stimulation of AMPK activity might be accompanied by an enhancement of Glut1-mediated glucose transport. Exposure of Clone 9 cells, 3T3-L1 preadipocytes, and C2C12 myobl asts (cells that express only the Glut1 isoform) to 5-aminoimidazole-4-carb oxamide ribonucleoside (AICAR), an adenosine analog that stimulates AMPK ac tivity, resulted in a marked increase in the rate of glucose transport (ran ging from four- to sixfold) that was accompanied by activation of AMPK. Thi s stimulation of AMPK activity was associated with an increase in the phosp horylation of threonine 172 on the activation loop of its alpha subunit, wi th the predominant change being in the alpha-a isoform. Exposure of Clone 9 cells to 5-iodotubercidin, an inhibitor of adenosine kinase, abolished the accumulation of AICAR-5'-monophosphate (ZMP), stimulation of AMPK, and the enhancement of glucose transport in response to AICAR. There was no signif icant increase in the content of Glut1 in plasma membranes of Clone 9 cells exposed to AICAR, We conclude that stimulation of AMPK activity is associa ted with enhancement of Glut1-mediated glucose transport, and that the gluc ose! transport response is mediated by activation of Glut1 transporters pre existing in the plasma membrane. (C) 2000 Academic Press.