Kinetics of D-glucose transport across the intestinal brush-border membrane of the cat.
1. D-glucose transport across the intestinal brush-border membrane of the cat, a carnivorous animal, was investigated using isolated brush-border membrane vesicles (BBMV). Kinetic experiments were performed under zero-trans conditions (initial [Na+]in and [Gluc]in = O) with the transmembrane electrical potential difference clamped to zero. 2. D-glucose uptake by the BBMV was strongly stimulated by an inwardly directed Na+-gradient. Uptake under Na+-free conditions seemed to occur by simple diffusion. 3. The apparent kinetic constants (Vmax, Km) of Na+-dependent D-glucose transport were computed by forcing initial uptake rates at 0.002-10.0 mmol/l D-glucose to either a Michaelis-Menten type equation with a single or with two carrier-mediated components. 4. Best fit of the experimental data was obtained with the two-component model indicating the existence of two Na+-dependent carrier-mediated mechanisms. System 1 and system 2 differ with respect to the transport velocity as well as the substrate affinity constants with Vmax being 2.5-fold and Km being 5-fold higher for system 1 compared with system 2.
Wolffram
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S
Institut für Veterinär-Physiologie, Veterinär-Medizinische Fakultät, Universität Zürich, Switzerland.
Eggenberger
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E
Scharrer
E
E
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002415:Cats; D005260:Female; D005947:Glucose / Q000378:metabolism*; D007422:Intestines / Q000648:ultrastructure*; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology
D012964:Sodium; D005947:Glucose