Role of Hydrogen Bonding in Organic Cation Discrimination by Gallbladder Epithelium

Abstract

THE main route of ion permeation across some epithelia, including that of the gallbladder, is by the so-called ‘tight’ junctions between adjacent cells¹. In the case of the gallbladder, this pathway is much more permeable to cations than to anions, and it also discriminates markedly among different inorganic cations^2,3. We have extended selective permeability measurements to a series of small amines in the form with one positive charge (compare ref. 4). The rationale behind these experiments is that permeability differences among cationic amines may help to identify the chemical nature and arrangement of ion-selective sites, as well as the possible existence of steric restraints in the permeation channel. The results indicate that gallbladder ‘tight’ junctions contain proton-acceptor sites which distinguish more markedly among cationic proton donors than does water.