GTP ANALOGS SUPPRESS UPTAKE BUT NOT TRANSPORT OF D-GLUCOSE ANALOGS INGLUT1 GLUCOSE TRANSPORTER-EXPRESSING XENOPUS-OOCYTES

A Xenopus oocyte expression-co-injection system was used to study the influence of guanine nucleotides on D-glucose uptake. GTP analogs like GTPgammaS and GppNHp had no effect on 3-O-methylglucose transport det ermined by zero-trans uptake or equilibrium exchange, but suppressed 2 -deoxyglucose uptake into Glut1 glucose transporter-expressing oocytes by up to 86%. Both GTP analogs showed concentration dependence of the ir effectiveness, with GTPgammaS being more potent than GppNHp. No sta tistically significant differences were observed between groups of ooc ytes co-injected with water or GDPbetaS (250 and 500 muM intracellular concentration). Glut1 transporter expression in plasma membrane was n ot different between water or GTPgammaS-co-injected oocytes. Thus, inh ibition of hexokinase catalytic activity is the most likely causative factor for down-regulation of 2-deoxyglucose uptake.