title: Apical nonspecific cation channels in everted collecting tubules of potassium-adapted ambystoma.
abstract: We observed intermediate conductance channels in approximately 20% of successful patch-clamp seals made on collecting tubules dissected from Ambystoma adapted to 50 mm potassium. These channels were rarely observed in collecting tubules taken from animals which were maintained in tap water. Potassium-adaptation either leads to an increase in the number of channels present or activates quiescent channels. In cell-attached patches the conductance averaged 30.3 +/- 2.4 (9) pS. Since replacement of the chloride in the patch pipette with gluconate did not change the conductance, the channel carries cations, not anions. Notably, channel activity was observed at both positive and negative pipette voltages. When the pipette was voltage clamped at 0 mV or positive voltages, the current was directed inward, consistent with the movement of sodium into the cell. The pipette voltage at which the polarity of the current reversed (movement of potassium into the pipette) was -29.6 +/- 6.5(9) mV. Open probability at 0 mV pipette voltage was 0.08 +/- 0.03 and was unaffected when the apical membrane was exposed to either 2 x 10(-6) or 2 x 10(-5) m of amiloride. Exposure of the basolateral surface of the tubule to a saline containing 15 mm potassium caused a significant increase (P less than 0.001) in the open probability of these channels to 0.139 +/- 0.002 without affecting the conductance of the apical channel. These data illustrate the presence of an intermediate conductance, poorly selective, amiloride-insensitive cation channel in native vertebrate collecting tubule. We postulate that, at least in amphibia, this channel may be used to secrete potassium.
authors.affiliation: Department of Neuroscience and Physiology, State University of New York, Health Science Center, 766 Irving Avenue, Syracuse, New York, 13210, USA.
authors.forename: L C
authors.initials: LC
authors.lastname: Stoner
authors.forename: S C
authors.initials: SC
authors.lastname: Viggiano
mesh_terms: D000557:Ambystoma; D000818:Animals; D000831:Animals, Newborn; D002462:Cell Membrane / Q000502:physiology; D053503:Epithelial Sodium Channels; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D007473:Ion Channels / Q000502:physiology; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000502:physiology*; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D024681:Potassium Channels, Calcium-Activated; D011189:Potassium Chloride / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*
chemical_list: D053503:Epithelial Sodium Channels; D007473:Ion Channels; D051036:Large-Conductance Calcium-Activated Potassium Channels; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D015222:Sodium Channels; D011189:Potassium Chloride