Electrical properties and active solute transport in rat small intestine. I. Potential profile changes associated with sugar and amino acid transports.

Addition of D-glucose to the mucosal fluid resulted in a significant depolarization of the mucosal membrane potential (V-m) in rat duodenum, jejunum, and ileum accompanied by an increase in the transepithelial potential difference (PDt). On the other hand, L-glucose did not induce PDt and Vm changes. Glycine applied from the mucosal side also induced Vm-depolarization and PDt-increment in the ileum. Phlorizin added to the mucosal fluid or ouabain added to the serosal fluid inhibited the sugar-dependent changes in PDt and Vm. According to the analysis with an equivalent circuit model for the epithelium, it was concluded that an actively transported solute induced not only a depolarization of the mucosal (brush border) membrane but also a hyperpolarization of the serosal (baso-lateral) membrane of an epithelial cell, so that the origin of solute-induced PDt changes should be attributed to changes in emf's at both membranes. The hyperpolarization of the serosal membrane in the presence of an actively transported solute was attributed to a mechanism of serosal electrogenic sodium pump stimulated by the increase in the extrusion rate of Na+ co-transported into the cell with sugar or amino acid.