Effects of thiol reagents on glucose transport in thymocytes

Rat thymocytes were incubated with 3-O-[14C]methyl D-glucose for 1 h and diluted 100X and the efflux was followed for 1 h. In control cells, about half of the methyl glucose efflux was rapid (t 1/2 approximately 3 min) and about half was slow (t 1/2 congruent to 40 min). The fast and slow compartments represent active and quiescent cells, respectively. A physiological mixture of amino acids present during the loading period dramatically increased the amount of methyl glucose exiting rapidly at the expense of that exiting slowly. Further studies revealed that cysteine was entirely responsible for the action. Cysteine (0.06 mM), glutathione (0.5 mM) and dithiothreitol (0.02 mM) added after completion of fast-phase exit, stimulated subsequent exit about 3-4-fold with no detectable delay. This action was inhibited by catalase and mimicked by 0.04 mM H2O2 and by 0.03 mM N-ethylmaleimide. It did not require extracellular or intracellular Ca2+. These effects are analogous to those seen in adipocytes, implicating sulfhydryl groups in glucose transport regulation [12]. Sulfhydryl oxidation may be a late event in the chain of events leading to glucose transport stimulation by physiological agents.