Multiple sites of vanadate and peroxovanadate action in Xenopus oocytes

In Xenopus laevis oocytes, the insulin mimics, vanadate and peroxovanadates (PV), stimulated the uptake of 3H-2-deoxyglucose and incorporation of 35S-methionine into protein. For both hexose transport and protein synthesis, peroxovanadates (produced by reacting vanadate and H2O2) were at least as potent as vanadate. Microinjection of peroxovanadates into the oocytes stimulated 2-deoxyglucose uptake. However, methionine incorporation was not stimulated by microinjection of peroxovanadate or vanadate solutions. Consistent with these results and with the possibility that vanadate and peroxovanadates enter the cell on a phosphate transporter, raising the medium phosphate concentration from 1 mM to 10 mM blocked vanadate-stimulated hexose transport and partially reduced peroxovanadates stimulation of hexose transport. Increased medium phosphate did not reduce stimulation of protein synthesis by either effector. Taken together, these data indicate that vanadate/peroxovanadates act at both intracellular and extracellular sites. Action at the former stimulates hexose uptake and action at the latter, protein synthesis.