Effects of choline and other quaternary ammonium compounds on Na movements in frog skin

Abstract

Effects of choline on short-circuit current and radioactive sodium flux were measured in isolated frog skins. Replacement of control ions (K or Mg) by choline in the outside solution increased the short-circuit current and inward Na flux. When K was the control ion, the average increase in short-circuit current was 52%; with Mg, it was 36%. In both cases, the increase in inward Na flux accounted for about 75% of the short-circuit current increase, while passive choline movement possibly accounted for the remainder. Similar results were obtained using tetramethylammonium and tetraethylammonium in place of choline. One implication of these results is that studies in which choline is used as an inert substitute for Na must be interpreted with caution.