title: Unidirectional K+ fluxes through recombinant Shaker potassium channels expressed in single Xenopus oocytes.
abstract: We describe a method to evaluate the ratio of ionic fluxes through recombinant channels expressed in a single Xenopus oocyte. A potassium channel encoded by the Drosophila Shaker gene tested by this method exhibited flux ratios far from those expected for independent ion movement. At a fixed extracellular concentration of 25 mM K+, this channel showed single-file diffusion with an Ussing flux-ratio exponent, n', of 3.4 at a membrane potential of -30 mV. There was an apparent, small voltage dependence of this parameter with n' values of 2.4 at -15 and -5 mV. These results indicate that the pore in these channels can simultaneously accommodate at least four K+ ions. If each of these K+ ions is in contact with two water molecules, the minimum length of the pore is 24 A.
authors.affiliation: Department of Pharmacology and Physiology, University of Rochester Medical Center, NY 14642, USA.
authors.forename: P
authors.initials: P
authors.lastname: Stampe
authors.forename: T
authors.initials: T
authors.lastname: Begenisich
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D017136:Ion Transport / Q000502:physiology*; D009865:Oocytes; D018408:Patch-Clamp Techniques / Q000379:methods*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D014981:Xenopus
chemical_list: D015221:Potassium Channels; D015761:4-Aminopyridine