Intravesicular glucose modulates magnesium2+ transport in liver plasma membrane from streptozotocin-treated rats

Plasma membrane vesicles purified from livers of 4-week-old streptozotocin-injected diabetic rats present an increased basal and cation-stimulated magnesium (Mg)(2+) transport as compared with vesicles purified from age-matched nondiabetic animals. Furthermore, diabetic basolateral membranes are unable to accumulate extravesicular Mg2+ in exchange for intravesicular sodium (Na)(+). Loading diabetic vesicles with varying concentrations of D-glucose, in addition to Mg2+, renormalizes basal and Na+- or calcium (Ca)(2+)- induced Mg2+ extrusion in a dose-dependent manner, but does not restore Na+/Mg2+ exchanger reversibility. A similar effect on Mg2+ extrusion is observed when D-glucose is replaced with 2-deoxyglucose, amylopectin, or glycogen. The loading with 3-methyl-O-glucose or L-glucose, instead, affects basal and Na+-dependent Mg2+ extrusion, but not Ca2+-dependent Mg2+ fluxes. In contrast, loading the vesicles with hexoses other than glucose or varying extravesicular glucose concentration from 5 to 20 mmol/L does not modify basal or cation-stimulated Mg2+ fluxes. Taken together, these data indicate that basal and cation-stimulated Mg2+ transport across the hepatocyte plasma membrane is altered under diabetic conditions as a result of a decrease in intravesicular (intracellular) glucose. (C) 2003 Elsevier Inc. All rights reserved.