Proximo-distal gradient of Na+-dependent D-glucose transport activity in the brush border membrane vesicles from the human fetal small intestine.

Brush-border membrane vesicles were isolated from the jejunum and ileum of 17-20-week-old normal human fetuses and found to be highly enriched in sucrase activity with less than 5% contamination by basolateral membranes. Time course studies of D-glucose uptake clearly showed a transient, phlorizin-sensitive, and Na+-dependent accumulation of sugar into these vesicles. Higher maximum overshoot values and initial rates of D-glucose uptake were recorded in jejunal as compared to ileal vesicles while low substrate binding to the membranes, identical intravesicular volumes and equivalent dissipation of the Na+-gradient were found in the two preparations. It was concluded that a fully functional Na+-D-glucose cotransport system is present with a proximo-distal gradient of activity during the early gestation period.