Multiple effects of mercuric chloride on hexose transport in Xenopus oocytes

HgCl2 had both stimulatory and inhibitory effects on [H-3]2-deoxyglucose (D G) 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 c oncentrations > 100 mu M increasing uptake. Analyses of the effects of Hg o n DG transport kinetics and cell membrane permeability indicated that low c oncentrations of Hg stimulated mediated uptake, intermediate concentrations inhibited mediated uptake, but high Hg concentrations increased non-mediat ed uptake. 10 mu M Hg increased the apparent V-max for DG uptake, but cause d little or no change in apparent K-m. Phenylarsine oxide prevented the inc rease in DG uptake by 10 mu M Hg, suggesting that the increase was due to t ransporter recruitment. Microinjecting low doses of HgCl2 into the cell inc reased mediated DG uptake. Higher intracellular doses of Hg increased both mediated and non-mediated DG uptake. Both insulin and Hg cause cell swellin g in isotonic media and, for insulin, this swelling has been linked to the mechanism of hormone action. Osmotically swelling Xenopus oocytes stimulate d 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 cellul ar 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 c ould be an early event in signaling the increase in hexose transport. (C) 1 999 Published by Elsevier Science B.V. All rights reserved.