Diabetes mellitus: changes in the transport properties of isolated intestinal microvillous membranes.

Isolated, small intestinal microvillous membranes from normal and acutely diabetic rats were compared with respect to D-glucose transport. D-Glucose was accumulated to a greater extent by diabetic membrane vesicles when supplied with energy in the form of a NaC1 or a NaSCN gradient across the vesicle membrane. The difference appeared to be caused by an ability of the diabetic membranes to maintain a higher driving force for active D-glucose transport and not by changes in the glucose "carrier." Increasing the glucose-independent Na-+-conductance of the membrane with monactin or gramicidin D reduced the active accumulation of D-glucose by membrane preparations from both control and diabetic groups. Concentrations of monactin and gramicidin D in the incubation medium of membrane vesicles from diabetic animals could be adjusted so that their D-glucose transport became indistinguishable from that of membranes from normal animals not treated with ionophores. These observatins suggest the microvillous membranes as one site where changes occur in acute diabetes. In addition, the change in the transport properties of the isolated membranes offer a rational explanation for the simultaneous elevation of active intestinal sugar, amino acid, and bile salt transport observed for intact intestinal tissue.