Ontogeny of Na+/D-glucose cotransport in guinea-pig jejunal vesicles: only one system is involved at both 20 degrees C and 35 degrees C.
The kinetic parameters of Na+/D-glucose cotransport were examined in fetal, newborn and adult guinea-pig jejunal brush-border membrane vesicles using a displacement curve and non-linear regression procedure. Our data indicated the presence of a single system with a Km of 0.34 +/- 0.04 mM at both 20 degrees C and 35 degrees C. Vmax was increased by about 4-fold when the kinetic experiments were performed at 35 degrees C. Since our results were not in agreement with the findings of Brot-Laroche et al. (J. Biol. Chem. (1986) 261, 6168-6176) which indicated the existence of a distinct D-glucose transport system in the adult guinea-pig jejunum at 35 degrees C, we verified the influence of their experimental conditions on initial rate uptake measurements. In the presence of D-sorbitol instead of D-mannitol in the transport media, 70% inhibition of D-glucose uptake was observed, an effect which was attributable to contamination of sorbitol preparations by D-glucose. After removal of glucose contamination D-sorbitol did not significantly reduce the initial rate of D-glucose transport. These results led us to conclude the existence of a single D-glucose transport system in the guinea-pig small intestine and to stress the choice of experimental conditions as being crucial for an accurate estimation of kinetic parameters.
Malo
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Department of Physiology, Faculty of Medicine, Université de Montréal, Canada.
D000375:Aging / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D001693:Biological Transport, Active / Q000187:drug effects; D002021:Buffers; D005260:Female; D005333:Fetus; D006168:Guinea Pigs; D007413:Intestinal Mucosa / Q000254:growth & development / Q000378:metabolism*; D007583:Jejunum / Q000254:growth & development / Q000378:metabolism*; D007700:Kinetics; D008353:Mannitol / Q000494:pharmacology; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D011247:Pregnancy; D013012:Sorbitol / Q000494:pharmacology; D013816:Thermodynamics
D002021:Buffers; D009004:Monosaccharide Transport Proteins; D008353:Mannitol; D013012:Sorbitol