ADP-ribosylation factor 6 delineates separate pathways used by endothelin 1 and insulin for stimulating glucose uptake in 3T3-L1 adipocytes

In 3T3-L1 adipocytes, both insulin and endothelin 1 stimulate glucose trans port via translocation of the GLUT4 glucose carrier from an intracellular c ompartment to the cell surface, Yet it remains uncertain as to whether both hormones utilize identical pathways and to what extent each depends on the heterotrimeric G protein G alphaq as an intermediary signaling molecule. I n this study, we used a novel inducible system to rapidly and synchronously activate expression of a dominant inhibitory form of ADP-ribosylation fact or 6, ARF6 T27N, in 3T3-L1 adipocytes and assessed its effects on insulin- and endothelin-stimulated hexose uptake. Expression of ARF6(T27N) in 3T3-L1 adipocytes was without effect on the ability of insulin to stimulate eithe r 2-deoxyglucose uptake of the translocation of GLUT4 or GLUT1 to the plasm a membrane. However, the same ARF6 inhibitory mutant blocked the stimulatio n of hexose uptake and GLUT4 translocation in response to either endothelin 1 or an activated form of G alphaq, G alphaq(Q209L), These results suggest that endothelin stimulates glucose transport through a pathway that is dis tinct from that utilized by insulin but is likely to depend on both a heter otrimeric G protein from the Gq family and the small G protein ARF6. These data are consistent with the interpretation that endothelin and insulin sti mulate functionally different pools of glucose transporters to be redistrib uted to the plasma membrane.