Gradient ford-glucose and linoleic acid uptake along the crypt-villus axis of rabbit jejunal brush border membrane vesicles

Glucose uptake into jejunal brush border membrane (BBM) varies along the crypt-villus axis (CVA). In the present study, the question was addressed whether uptake of the essential long-chain fatty acid linoleic acid also varies along the CVA. Using agitation techniques, five jejunal enterocyte fractions were sequentially isolated from female New Zealand white rabbits. A sixth and final fraction of lower-villus/crypt cells was obtained by the scraping of the remaining jejunal mucosa. Cell fraction along the CVA was proven histologically, by noting decreasing alkaline phosphatase activities in sequentially isolated fractions, and by demonstrating [³H-methyl]thymidine uptake mainly in the final fraction of the lower villus/crypt cells. BBM vesicles were prepared from the upper-, mid- and lower-villus/crypt enterocyte fractions, using differential centrifugation and divalent ion precipitation.d-Glucose uptake into each fraction showed an Na⁺-gradient dependent time-course “overshoot” with linear uptake to 15 s and a subsequent decline to a steady-state plateau. Varying D-glucose concentrations from 50–1000 μM demonstrated saturation kinetics of uptake, with maximal transport rates (V_max) and Michaelis affinity constants (K_m) varying between fractions; the K_m and V_max were both lowest in the upper-villus fraction. A linear relationship existed between linoleic acid concentration (25–200 μM) and uptake in each fraction. Linoleic acid uptake was equivalent in all fractions when expressed per mg protein, but when expressed in terms of the estimated minimal BBM, vesicle surface area uptake was greater in the upper- than in the lower-villus/crypt fractions. Thus, BBM vesicle uptake of both linoleic acid and glucose vary along the crypt-villus axis of the rabbit jejunum.