Na+ channel activity in cultured renal (A6) epithelium: regulation by solution osmolarity.
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.
Wills
N K
NK
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77550.
Millinoff
L P
LP
Crowe
W E
WE
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D004553:Electric Conductivity; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D014982:Xenopus laevis
D015222:Sodium Channels; C058206:6-chloro-3,5-diaminopyrazine-3-carboxamide; D000584:Amiloride; D012964:Sodium; D011188:Potassium