DISSECTION OF STRESS-ACTIVATED GLUCOSE-TRANSPORT FROM INSULIN-INDUCEDGLUCOSE-TRANSPORT IN MAMMALIAN-CELLS USING WORTMANNIN AND ML-9

The signalling pathways responsible for the activation of glucose tran sport by insulin and by metabolic stress in mammalian cells were studi ed in Clone 9 cells and 3T3-L1 adipocytes. Exposure of both cell types to azide or insulin markedly increased their glucose uptake capacity (V-max) without affecting their apparent affinity for glucose (K-m). T he effects of azide and insulin were not additive. Wortmannin, a selec tive inhibitor of phosphatidylinositol (PI) 3-kinase, did not affect s timulation of transport by azide but inhibited insulin-induced glucose transport with a K-i of < 10 nM. ML-9, a putative mitogen-activated p rotein kinase inhibitor, was equipotent in its inhibition of azide- an d insulin-stimulated glucose transport. These findings suggest that mu ltiple signalling cascades are involved in the stimulation of glucose transport in mammalian cells and that PI 3-kinase, an essential link i n the pathway by which insulin stimulates glucose transport, is not ne cessary for the activation of glucose uptake by metabolic stress.