The Journal of Membrane Biology

, Volume 67, Issue 1, pp 91–98 | Cite as

Ion selectivity of the apical membrane Na channel in the toad urinary bladder

  • Lawrence G. Palmer


The ion selectivity of the apical membrane Na channel in the toad urinary bladder was investigated. The electrical potential difference and resistance across the basal-lateral membrane were reduced using high concentrations of KCl in the serosal bathing medium, and gradients for various ions were imposed across the apical membrane by altering the composition of the mucosal bathing medium. Ion fluxes through the channel were measured as the transepithelial current inhibited by amiloride, a specific blocker of the channel's Na conductance. The selectivity sequence for alkali metal cations was H>Li>Na≫K. K, permeability was barely detectable; the selectivity for Na over K was about 1000:1. Ammonium, hydroxyl ammonium and hydrazinium ions were, like K, virtually impermeant. The results suggest that the size of the unhydrated ion is an important factor in determining permeability in this channel.

Key words

epithelial Na transport toad urinary bladder apical membrane ion selectivity Na channels 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Al-Awqati, Q., Norby, L.H., Mueller, A., Steinmetz, P.R. 1976. Characteristics of stimulation of H+ transport by aldosterone in turtle urinary bladder.J. Clin. Invest. 58:351–358PubMedGoogle Scholar
  2. Balaban, R.S., Mandel, L.J., Benos, D.J. 1979. On the cross-reactivity of amiloride and 2,4,6-triaminopyrimidine (TAP) for cellular entry and tight junctional cation permeation pathways in epithelia.J. Membrane Biol. 49:363–390Google Scholar
  3. Benos, D.J., Mandel, L.J., Simon, S.A. 1980. Cation selectivity and competition at the sodium entry site in frog skin.J. Gen. Physiol. 76:223–247Google Scholar
  4. Bentley, P.J. 1968. Amiloride: A potent inhibitor of sodium transport across the toad bladder.J. Physiol. (London) 195:317–330Google Scholar
  5. Biber, T.U.L., Mullen, T.L. 1980. Effect of external cation and anion substitutions of sodium transport in isolated frog skin.J. Membrane Biol. 52:121–132Google Scholar
  6. DeLong, J., Civan, M.M. 1978. Dissociation of cellular K+ accumulation from net Na+ transport by toad urinary bladder.J. Membrane Biol. 42:19–43Google Scholar
  7. DiBona, D.R., Civan, M.M. 1973. Pathways for movement of ions and water across toad urinary bladder. I. Anatomic site of transepithelial shunt pathways.J. Membrane Biol. 12:101–128Google Scholar
  8. Ehrlich, E.N., Crabbé, J. 1968. The mechanism of action of amipramizide.Pfluegers Arch. 302:79–96Google Scholar
  9. Eisenman, G. 1962. Cation selective glass electrodes and their mode of operation.Biophys. J. 2 (2, pt. 2):259–323PubMedGoogle Scholar
  10. Fuchs, W., Hviid Larsen, E., Lindemann, B. 1977. Current-voltage curve of sodium channels and concentration dependence of sodium permeability in frog skin.J. Physiol. (London) 267:137–166Google Scholar
  11. Herrera, F.C., Egea, R., Herrera, A.M., 1971. Movement of lithium across the toad urinary bladder.Am. J. Physiol. 220:1501–1508PubMedGoogle Scholar
  12. Higgins, J.T., Jr., Gebler, B., Frömter, E. 1977. Electrical properties of amphibian urinary bladder epithelia. II. The cell potential profile inNecturus maculosus.Pfluegers Arch. 371:87–97Google Scholar
  13. Hille, B. 1971. The permeability of the sodium channel to organic cations in myelinated nerve.J. Gen. Physiol. 58:599–619PubMedGoogle Scholar
  14. Hille, B. 1972. The permeability of the sodium channel to metal cations in myelinated nerve.J. Gen. Physiol. 59:637–658PubMedGoogle Scholar
  15. Koefoed-Johnsen, V., Ussing, H.H. 1958. The nature of the frog skin potential.Acta Physiol. Scand. 42:298–308PubMedGoogle Scholar
  16. Leaf, A., Keller, A., Dempsey, E.F. 1964. Stimulation of sodium transport in toad bladder by acidification of the mucosal medium.Am. J. Physiol. 207:547–552PubMedGoogle Scholar
  17. Lewis, S.A., Wills, N.K. 1980. Interaction between apical and basolateral membranes during Na transport across tight epithelia.J. Gen. Physiol. F6:3aGoogle Scholar
  18. Li, J.H.-Y., Palmer, L.G., Edelman I.S., Lindemann, B. 1979. Effect of ADH on Na-channel parameters in toad urinary bladder.Pfluegers Arch. 382:R13Google Scholar
  19. Lindemann, B., Van Driessche, W. 1977. Sodium specific membrane channels of frog skin are pores: Current fluctuations reveal high turnover.Science 195:292–294PubMedGoogle Scholar
  20. Lindley, B.D., Hoshiko, T. 1964. The effects of alkali metal cations and common anions on the frog skin potential.J. Gen. Physiol. 47:749–771PubMedGoogle Scholar
  21. Macknight, A.D.C., Hughes, P.M. 1981. Transepithelial lithium transport and cellular lithium in toad bladder epithelial cells.In: Epithelial Ion and Water Transport. A.D.C. Macknight and J.P. Leader, editors. pp. 147–153. Raven Press, New YorkGoogle Scholar
  22. Narvarte, J., Finn, A.L. 1980. Anion-sensitive sodium conductance in the apical membrane of toad urinary bladder.J. Gen. Physiol. 76:69–81PubMedGoogle Scholar
  23. Palmer, L.G., Edelman, I.S., Lindemann, B. 1980. Current-voltage analysis of apical Na transport in the toad urinary bladder: Effects of inhibitors of transport and metabolism.J. Membrane Biol. 57:59–71Google Scholar
  24. Rick, R., Dörge, A., Macknight, A.D.C., Leaf, A., Thurau, K. 1978. Electron microprobe analysis of the different epithelial cells of toad urinary bladder.J. Membrane Biol. 39:257–271Google Scholar
  25. Rossier, B.C., Wilce, P.A., Edelman, I.S. 1974. Kinetics of RNA labeling in toad bladder epithelium: Effects of aldosterone and other steroids.Proc. Natl. Acad. Sci. USA 71:3101–3105PubMedGoogle Scholar
  26. Sarracino, S.M., Dawson, D.C. 1979. Cation selectivity in active transport: Properties of the turtle colon in the presence of mucosal lithium.J. Membrane Biol. 46:295–313Google Scholar
  27. Steinmetz, P.R. 1974. Cellular mechanisms of urinary acidification.Physiol. Rev. 54:890–956PubMedGoogle Scholar
  28. Ussing, H.H., Windhager, E.E. 1964. Nature of shunt path and active sodium transport through frog skin epithelium.Acta Physiol. Scand. 61:484–504PubMedGoogle Scholar
  29. Warncke, J., Lindemann, B. 1981. Effect of ADH on the capacitance of apical epithelial membranes.Adv. Physiol. Sci. 3:129–133Google Scholar

Copyright information

© Springer-Verlag New York Inc. 1982

Authors and Affiliations

  • Lawrence G. Palmer
    • 1
    • 2
  1. 1.Department of BiochemistryColumbia University College of Physicians and SurgeonsNew York
  2. 2.Department of PhysiologyCornell University Medical CollegeNew York

Personalised recommendations