PERMEABILITY OF LIVER MICROSOMAL-MEMBRANES TO GLUCOSE

The permeability of rat liver microsomes to glucose has been studied b y using C-14-labelled D-glucose and a light-scattering technique. 1) T he microsomal intravesicular apparent isotope space for D-glucose (1mM ; after 5min incubation at 22 degrees C was 2.34 mu l/mg protein, i.e. , approximately 72% of the apparent water space. 2) Efflux of [C-14]D- glucose from microsomal vesicles pre-loaded as in 1) and measured by r apid 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 micr osomes upon addition of D-glucose measured by a light-scattering techn ique revealed a glucose influx, saturable at [D-glucose] greater than or equal to 100 mM, and (partially) inhibited by pentamidine and cytoc halasin B. Ascorbic acid, L-glucose and other monosaccharides and rela ted compounds also permeated liver microsomes in a fashion similar to D-glucose. These data indicate the existence of a facilitative transpo rt system(s) for glucose in the membrane of liver endoplasmic reticulu m vesicles. (C) 1996 Academic Press, Inc.