title: Basolateral K+ conductance in principal cells of rat CCD.
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.
authors.affiliation: Dept. of Physiology and Biophysics, Weill Medical College of Cornell Univ., 1300 York Ave., New York, NY 10021, USA. dag2007@med.cornell.edu
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Gray
authors.forename: Gustavo
authors.initials: G
authors.lastname: Frindt
authors.forename: Yu-Yang
authors.initials: YY
authors.lastname: Zhang
authors.forename: Lawrence G
authors.initials: LG
authors.lastname: Palmer
mesh_terms: D000465:Algorithms; D000818:Animals; D001464:Barium / Q000494:pharmacology; D001514:Bee Venoms / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004032:Diet; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008564:Membrane Potentials; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012996:Solutions; D013096:Spermine / Q000494:pharmacology; D019789:Tetraethylammonium / Q000494:pharmacology; D014982:Xenopus laevis
chemical_list: D001514:Bee Venoms; C510692:Kcnj1 protein, rat; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D012996:Solutions; D001464:Barium; D013096:Spermine; C029738:tertiapin; D019789:Tetraethylammonium