title: Single-channel recordings of apical membrane chloride conductance in A6 epithelial cells.
abstract: The apical membrane of epithelial cells from the A6 cell line grown on impermeable substrata was studied using the patch-clamp technique. We defined the apical membrane as that membrane in contact with the growth medium. In about 50% of the patches, channels with single-unit conductances of 360 +/- 45 pS in symmetrical 105 mM NaCl solutions, and characteristic voltage-dependent inactivation were observed. Using excised membrane patches and varying the ionic composition of the bathing medium, we determined that the channels were anion selective, with a permeability ratio for Cl- over Na+ of about 9:1, calculated from the reversal potential using the constant-field equation. The channel was most active at membrane potentials between +/- 20 mV and inactivated, usually within a few seconds, at higher potentials of either polarity. Reactivation from this inactivation was slow, sometimes requiring minutes. In addition to its fully open state, the channel could also enter a flickering state, which appeared to involve rapid transitions to one or more submaximal conductance levels. The channel was inhibited by the disulfonic stilbene SITS in a manner characteristic of reversible open-channel blockers.
mesh_terms: D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D002712:Chlorides / Q000378:metabolism*; D004848:Epithelium / Q000502:physiology; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007668:Kidney; D008564:Membrane Potentials; D014981:Xenopus
chemical_list: D002712:Chlorides; D007473:Ion Channels; D003994:Bucladesine