Basolateral K+ conductance in principal cells of rat CCD

Am J Physiol Renal Physiol. 2005 Mar;288(3):F493-504. doi: 10.1152/ajprenal.00301.2004. Epub 2004 Nov 16.

Abstract

Whole cell K+ current was measured by forming seals on the luminal membrane of principal cells in split-open rat cortical collecting ducts. The mean inward, Ba2+-sensitive conductance, with 40 mM extracellular K+, was 76 +/- 12 and 141 +/- 22 nS/cell for animals on control and high-K+ diets, respectively. The apical contribution to this was estimated to be 3 and 16 nS/cell on control and high-K+ diets, respectively. To isolate the basolateral component of whole cell current, we blocked ROMK channels with either tertiapin-Q or intracellular acidification to pH 6.6. The current was weakly inward rectifying when bath K+ was > or =40 mM but became more strongly rectified when bath K+ was lowered into the physiological range. Including 1 mM spermine in the pipette moderately increased rectification, but most of the outward current remained. The K+ current did not require intracellular Ca2+ and was not inhibited by 3 mM ATP in the pipette. The negative log of the acidic dissociation constant (pKa) was approximately 6.5. Block by extracellular Ba2+ was voltage dependent with apparent Ki at -40 and -80 mV of approximately 160 and approximately 80 microM, respectively. The conductance was TEA insensitive. Substitution of Rb+ or NH4+ for K+ led to permeability ratios of 0.65 +/- 0.07 and 0.15 +/- 0.02 and inward conductance ratios of 0.17 +/- 0.03 and 0.57 +/- 0.09, respectively. Analysis of Ba2+-induced noise, with 40 mM extracellular K+, yielded single-channel currents of 0.39 +/- 0.04 and -0.28 +/- 0.04 pA at voltages of 0 and -40 mV, respectively, and a single-channel conductance of 17 +/- 1 pS.

Publication types

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

MeSH terms

  • Algorithms
  • Animals
  • Barium / pharmacology
  • Bee Venoms / pharmacology
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Diet
  • Hydrogen-Ion Concentration
  • In Vitro Techniques
  • Kidney Cortex / metabolism*
  • Kidney Tubules, Collecting / metabolism*
  • Membrane Potentials
  • Oocytes / metabolism
  • Patch-Clamp Techniques
  • Potassium Channel Blockers / pharmacology
  • Potassium Channels / metabolism*
  • Potassium Channels, Inwardly Rectifying / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Solutions
  • Spermine / pharmacology
  • Tetraethylammonium / pharmacology
  • Xenopus laevis

Substances

  • Bee Venoms
  • Kcnj1 protein, rat
  • Potassium Channel Blockers
  • Potassium Channels
  • Potassium Channels, Inwardly Rectifying
  • Solutions
  • Barium
  • Spermine
  • tertiapin
  • Tetraethylammonium