Effect of Medium-Chain Glycerides on the Membrane Transport of D-Glucose and Sulfanilic Acid in the Intestinal Brush-Border Membrane Vesicles

To clarify the influence of medium-chain glycerides (MCG) on a biological membrane, we investigated the membrane transport of D-glucose and sulfanilic acid in the brush-border membrane (BBM) vesicles pretreated with MCG. The size distribution of the BBM vesicles determined by electron microscopic observation was not significantly different between the vesicles incorporated with MCG and those of the control. However, the amount of D-glucose taken up by the vesicles at an equilibrated stage (30 min) was significantly decreased in the MCG-treated ones based on unit content of protein. Based on these results we estimated the membrane transport of D-glucose and sulfanilic acid in consideration of vesiculation or filter-capturing efficiency in MCG-treated vesicles. The rates of Na⁺ gradient-independent D-glucose transport and sulfanilic acid transport were significantly greater in MCG-treated vesicles than in the control. On the other hand, the magnitude of overshooting effect in Na⁺ gradient-dependent uptake of D-glucose in MCG-treated vesicles was maintained similar to the control. Comparison of kinetic parameters for active D-glucose transport at different concentrations indicated that K_m and F_max were not significantly different between MCG-treated and the control vesicles. These results indicated that passive diffusion of D-glucose and sulfanilic acid was significantly increased but Na⁺-glucose cotransporter was not significantly changed by the incorporation of MCG in the intestinal BBM vesicles.