Multiple effects of mercuric chloride on hexose transport in Xenopus oocytes

HgCl2 had both stimulatory and inhibitory effects on [H-3]2-deoxyglucose (DG) uptake in Xenopus laevis oocytes. The Hg dose response was complex, with 0.1-10 mu M Hg increasing total DG uptake, 30-50 mu M Hg inhibiting, and concentrations > 100 mu M increasing uptake. Analyses of the effects of Hg on DG transport kinetics and cell membrane permeability indicated that low concentrations of Hg stimulated mediated uptake, intermediate concentrations inhibited mediated uptake, but high Hg concentrations increased non-mediated uptake. 10 mu M Hg increased the apparent V-max for DG uptake, but caused little or no change in apparent K-m. Phenylarsine oxide prevented the increase in DG uptake by 10 mu M Hg, suggesting that the increase was due to transporter recruitment. Microinjecting low doses of HgCl2 into the cell increased mediated DG uptake. Higher intracellular doses of Hg increased both mediated and non-mediated DG uptake. Both insulin and Hg cause cell swelling in isotonic media and, for insulin, this swelling has been linked to the mechanism of hormone action. Osmotically swelling Xenopus oocytes stimulated DG transport 2-5-fold and this increase was due to an increased apparent V-max. Exposing cells to 10 mu M Hg or 140 nM insulin both increased cellular water content by 18% and increased hexose transport 2-4-fold. These data indicate that low concentrations of Hg and insulin affect hexose transport in a similar manner and that for both an increase cellular water content could be an early event in signaling the increase in hexose transport. (C) 1999 Published by Elsevier Science B.V. All rights reserved.