Permeability of liver microsomal membranes to glucose

The permeability of rat liver microsomes to glucose has been studied by using 14C-labelled D-glucose and a light-scattering technique. 1) The microsomal intravesicular apparent isotope space for D-glucose (1 mM; after 5 min incubation at 22°C) was 2.34 μl/mg protein, i.e., approximately 72% of the apparent water space. 2) Efflux of [14C]D-glucose from microsomal vesicles pre-loaded as in 1) and measured by rapid Millipore filtration after dilution (100 fold) in a glucose-free medium revealed that 15 sec after dilution only 15% of intravesicular glucose was still retained by microsomes. 3) Osmotic behaviour of microsomes upon addition of D-glucose measured by a light-scattering technique revealed a glucose influx, saturable at [D-glucose] ≥ 100 mM, and (partially) inhibited by pentamidine and cytochalasin B. Ascorbic acid, L-glucose and other monosaccharides and related compounds also permeated liver microsomes in a fashion similar to D-glucose. These data indicate the existence of a facilitative transport system(s) for glucose in the membrane of liver endoplasmic reticulum vesicles.