Electrical properties and active solute transport in rat small intestine

Abstract

Summary Addition ofd-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 (PD _t). On the other hand,l-glucose did not inducePD _t andV _m changes. Glycine applied from the mucosal side also inducedV _m-depolarization andPD _t-increment in the ileum. Phlorizin added to the mucosal fluid or ouabain added to the serosal fluid inhibited the sugar-dependent changes inPD _t andV _m. 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-inducedPD _t 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.