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Permeability of liver microsomal membranes to glucose
P Marcolongo1, R Fulceri, R Giunti
1Istituto di Patologia Generale, University of Siena, Italy.
Abstract:
The permeability of rat liver microsomes to glucose has been studied by using (14)C-labelled D-glucose and a light-scattering technique. 1) The microsomal intravesicular apparent isotope space for D-glucose (1mM; after 5 min incubation at 22 degrees C) was 2.34 microl/mg protein, i.e., approximately 72% of the apparent water space. 2) Efflux of [(14)C]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.
Insights
Rat liver microsomes exhibit facilitated glucose transport across their membranes, indicated by rapid glucose influx and efflux studies. This suggests specific transport systems are present in the endoplasmic reticulum vesicles.
Area of Science:
- Biochemistry
- Cell Biology
- Membrane Transport
Background:
- Liver microsomes are crucial for metabolic processes.
- Understanding glucose transport is vital for liver function and metabolic disease research.
Purpose of the Study:
- To investigate the permeability of rat liver microsomes to D-glucose.
- To characterize the mechanism and kinetics of glucose transport in liver endoplasmic reticulum vesicles.
Main Methods:
- Utilized (14)C-labelled D-glucose to quantify intravesicular space and efflux.
- Employed a light-scattering technique to monitor osmotic changes indicative of glucose influx.
- Investigated the effects of inhibitors (pentamidine, cytochalasin B) and various substrates on glucose transport.
Main Results:
- Determined a significant intravesicular D-glucose space (72% of water space) in microsomes.
- Observed rapid efflux of D-glucose from pre-loaded vesicles, with only 15% retained after 15 seconds.
- Demonstrated saturable glucose influx (>100 mM), partially inhibited by pentamidine and cytochalasin B, and similar transport for other monosaccharides.
Conclusions:
- Rat liver microsomes possess facilitative transport systems for glucose.
- These systems are located in the membrane of liver endoplasmic reticulum vesicles.
- The transport mechanism exhibits saturation kinetics and sensitivity to specific inhibitors.