title: Apical membrane of native OMCD(i) cells has nonselective cation channels.
abstract: The purpose of this study was to examine cation channel activity in the apical membrane of the outer medullary collecting duct of the inner stripe (OMCD(i)) using the patch-clamp technique. In freshly isolated and lumen-opened rabbit OMCD(i), we have observed a single channel conductance of 23.3 +/- 0.6 pS (n = 17) in cell-attached (c/a) patches with high KCl in the bath and in the pipette at room temperature. Channel open probability varied among patches from 0.06 +/- 0.01 at -60 mV (n = 5) to 0.31 +/- 0.04 at 60 mV (n = 6) and consistently increased upon membrane depolarization. In inside-out (i/o) patches with symmetrical KCl solutions, the channel conductance (22.8 +/- 0.8 pS; n = 10) was similar as in the c/a configuration. Substitution of the majority of Cl- with gluconate from KCl solution in the pipette and bath did not significantly alter reversal potential (E(rev)) or the channel conductance (19.7 +/- 1.1 pS in asymmetrical potassium gluconate, n = 4; 21.4 +/- 0.5 pS in symmetrical potassium gluconate, n = 3). Experiments with 10-fold lower KCl concentration in bath solution in i/o patches shifted E(rev) to near the E(rev) of K+. The estimated permeability of K+ vs. Cl- was over 10, and the conductance was 13.4 +/- 0.1 pS (n = 3). The channel did not discriminate between K+ and Na+, as evidenced by a lack of a shift in the E(rev) with different K+ and Na+ concentration solutions in i/o patches (n = 3). The current studies demonstrate the presence of cation channels in the apical membrane of native OMCD(i) cells that could participate in K+ secretion or Na+ absorption.
authors.affiliation: Department of Medicine, University of Florida, Gainsville 32610-0224, USA. xiasl@ufl.edu
authors.forename: S L
authors.initials: SL
authors.lastname: Xia
authors.forename: S H
authors.initials: SH
authors.lastname: Noh
authors.forename: J W
authors.initials: JW
authors.lastname: Verlander
authors.forename: C H
authors.initials: CH
authors.lastname: Gelband
authors.forename: C S
authors.initials: CS
authors.lastname: Wingo
mesh_terms: D000818:Animals; D002412:Cations; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D005260:Female; D007473:Ion Channels / Q000032:analysis*; D007679:Kidney Medulla / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D010539:Permeability; D011189:Potassium Chloride; D011817:Rabbits; D012965:Sodium Chloride
chemical_list: D002412:Cations; D007473:Ion Channels; D012965:Sodium Chloride; D011189:Potassium Chloride