| Abstract: | Differentiation and maturation of enterocytes occur with migration from the crypt to villus compartments. To investigate the effect of epithelial cell differentiation on sodium-dependent D-glucose transport, brush-border membrane vesicles were prepared from small intestinal epithelial cell suspensions selectively isolated from villus and crypt populations. Enterocytes were isolated with a morphologically monitored sequential cell dissociation method. Thymidine kinase, sucrase, and alkaline phosphatase activities were measured as differentiation markers of specific cell populations. Brush-border membrane vesicles were purified and their kinetic characteristics defined with a rapid filtration method under conditions of a zero-trans, 100 mM cis-NaSCN gradient. Typical "overshoot" phenomena characteristic of sodium D-glucose cotransport were observed for both villus (five- to eight-fold equilibrium values) and crypt brush-border membrane vesicles (two- to four-fold equilibrium values). Kinetics analyses of the initial D-glucose flux in brush-border membrane vesicles suggested the presence of at least two sodium-dependent D-glucose carriers in the villus and only a single carrier in the crypt compartments. These data indicate that sodium D-glucose cotransport occurs in brush-border membranes of both villus and crypt populations. Moreover, quantitative and qualitative differences between these two membrane populations suggest that epithelial D-glucose transport processes are differentiation dependent and reflect the degree of enterocyte development. |
