Kinetic evidence for heterogeneity in Na+-D-glucose cotransport systems in the normal human fetal small intestine.
Zero-trans kinetic studies of Na+-D-glucose cotransport have been performed under voltage-clamped conditions in brush-border membrane vesicles isolated from both jejunum and ileum of 17-20-week-old normal human fetuses. Varying glucose concentrations in the incubation medium led to curvilinear Eadie-Hofstee plots in the jejunum only, thus suggesting the presence of both high-affinity, low-capacity (Km 0.37 mM; Vmax 8.3 nmol/min per mg protein) and low-affinity, high-capacity (Km 4.2 mM; Vmax 30.9 nmol/min per mg protein) systems in the proximal small intestine, and of a single carrier (Km 1.2 mM; Vmax 4.9 nmol/min per mg protein) in the distal small intestine. Sodium activation curves provide further evidence for heterogeneity in glucose transport systems in the fetal small intestine: Hill coefficients of 2 and 1 were found for the jejunal high-affinity and ileal systems, and for the jejunal low-affinity system, respectively. It is concluded that there is early differentiation of a functional heterogeneity in glucose transport capacity along the human fetal small intestine.
Malo
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Department of Physiology, Faculty of Medicine, University of Montreal, Quebec, Canada.
D005333:Fetus / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007082:Ileum / Q000196:embryology / Q000378:metabolism*; D007583:Jejunum / Q000196:embryology / Q000378:metabolism*; D007700:Kinetics; D008871:Microvilli / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D012016:Reference Values
D009004:Monosaccharide Transport Proteins; D005947:Glucose