Demonstration of an apical chloride conductive pathway in granular cells of toad urinary bladder

Miner Electrolyte Metab. 1993;19(1):39-46.


Chloride electrodiffusion across the apical membrane of granular cells from toad urinary bladder, an analogue of mammalian principal cells, was examined using the patch clamp technique. A chloride conductance was demonstrated in cell-attached membrane patches exposed to barium chloride pipette solutions. A change in the pipette chloride concentration from 30 to 100 mM caused a shift in the current voltage curve which demonstrated chloride selectivity. The chloride conductance was also examined in excised, inside out membrane patches using choline chloride solutions (chloride:choline selectivity ratio was 18:1). A closed and two open chloride conductive states were found (states A and B, 10.1 +/- 1.0 and 17.2 +/- 5.5 pS, respectively, p < 0.01). Incubation of the preparation with arginine vasopressin, dibutyryl-cAMP, or 8-bromo-cAMP approximately doubled chloride conductance to 16.6 +/- 1.7 pS (p < 0.01). The enhanced electrodiffusion was accounted for by a shift in the channel kinetics from the closed state C to the high conductance state B (p < 0.05, n = 9). 4,4'-Diisothio-cyanatostilbene- 2,2'-disulfonic acid (DIDS) and 9-anthracene-carboxylic acid (9-AC) failed to block the chloride currents. In conclusion, the regulated apical chloride conductance described would balance the sodium and potassium electrodiffusive pathways and maintain a stable membrane potential, facilitating overall conductive transport by these cells.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Arginine Vasopressin / pharmacology
  • Bufo marinus
  • Cell Membrane Permeability
  • Chloride Channels
  • Chlorides / metabolism
  • Choline / metabolism
  • Cyclic AMP / pharmacology
  • Diffusion
  • Electric Conductivity
  • Ion Channel Gating / physiology
  • Membrane Potentials
  • Membrane Proteins / drug effects
  • Membrane Proteins / physiology*
  • Urinary Bladder / physiology*


  • Chloride Channels
  • Chlorides
  • Membrane Proteins
  • Arginine Vasopressin
  • Cyclic AMP
  • Choline