Na+ channel activity in cultured renal (A6) epithelium: regulation by solution osmolarity

J Membr Biol. 1991 Apr;121(1):79-90. doi: 10.1007/BF01870653.


Solution osmolarity is known to affect Na+ transport rates across tight epithelia but this variable has been relatively ignored in studies of cultured renal epithelia. Using electrophysiological methods to study A6 epithelial monolayers, we observed a marked effect of solution tonicity on amiloride-sensitive Na+ currents (I(sc)). I(sc) for tissues bathed in symmetrical hyposmotic (170 mOsm), isosmotic (200 mOsm), and hyperosmotic (230 or 290 mOsm) NaCl Ringer's solutions averaged 25 +/- 2, 9 +/- 2, 3 +/- 0.4, and 0.6 +/- 0.5 microA/cm2, respectively. Similar results were obtained following changes in the serosal tonicity: mucosal changes did not significantly affect I(sc). The changes in I(sc) were slow and reached steady-state within 30 min. Current fluctuation analysis measurements indicated that single-channel currents and Na+ channel blocker kinetics were similar for isosmotic and hyposmotic conditions. However, the number of conducting Na+ channels was approximately threefold higher for tissues bathed in hyposmotic solutions. No channel activity was detected during hyperosmotic conditions. The results suggest that Na+ channels in A6 epithelia are highly sensitive to relatively small changes in serosal solution tonicity. Consequently, osmotic effects may partly account for the large variability in Na+ transport rates for A6 epithelia reported in the literature.

Publication types

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

MeSH terms

  • Amiloride / analogs & derivatives
  • Amiloride / pharmacology
  • Animals
  • Cell Line
  • Electric Conductivity
  • Epithelium / drug effects
  • Epithelium / metabolism
  • Kidney / cytology
  • Kidney / metabolism*
  • Kinetics
  • Membrane Potentials
  • Osmolar Concentration
  • Potassium / metabolism
  • Sodium / metabolism
  • Sodium Channels / drug effects
  • Sodium Channels / metabolism*
  • Xenopus laevis


  • Sodium Channels
  • 6-chloro-3,5-diaminopyrazine-3-carboxamide
  • Amiloride
  • Sodium
  • Potassium