alpha-Methylglucoside satisfies only Na+-dependent transport system of intestinal epithelium

Abstract

The unidirectional influx of alpha-methylglucoside (alpha-MG) by isolated chicken intestinal epithelial cells is 98% inhibited by phlorizin. The remaining 2% of the total influx occurs in the absence of Na+, is not sensitive to phloretin, and is equal to the diffusional entry rate for 2-deoxyglucose. The glucoside is much more strongly accumulated (75-fold) than 3-O-methylglucose (3-OMG) (10-fold). Inhibitors of the serosal sugar carrier (phloretin, cytochalasin B, theophylline, and flavanoids) do not enhance alpha-MG accumulation. It is concluded that the glycoside is not a substrate for the intestinal serosal transport system. Steady-state gradients of the sugar can be represented accurately by a concentrative, phlorizin-sensitive system that is opposed by a diffusional efflux process.