The selective permeability of the pancreatic duct of the cat to monovalent ions.

In the anaethetised cat the electrical potential difference between the lumen of the main collecting duct of the pancreas and blood in the jugular vein was measured. The duct was perfused with isotonic solutions of monovalent ions and the recorded potential corrected for the liquid junction potentials. The data were fitted to the Shinagawa extension of the Goldman constant field equation and the relative permeabilities of the duct epithelium to the ions were determined. The duct showed negligible selectivity between the monovalent cations Li:Na:K:Rb:Cs = 1.08:1.10:1.09:1.12 in contrast to the definite selectivity sequence for the anions F:Br:Cl:I:HCO3 = 0.44:1.38:1.08:2.05:0.60. This halide selectivity sequence is the Eisenman sequence I and is indicative of the selectivity being due to weak positive charges on membrane bound sites surrounding a highly hydrated channel. It is argued that these highly hydrated channels may be identified with the "tight junctions" between cells and the selectivity properties of the pancreatic duct are determined by flow of ions through these areas rather than flow through the epithelial cells.