Unidirectional K+ fluxes through recombinant Shaker potassium channels expressed in single Xenopus oocytes.
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.
Stampe
P
P
Department of Pharmacology and Physiology, University of Rochester Medical Center, NY 14642, USA.
Begenisich
T
T
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
D015221:Potassium Channels; D015761:4-Aminopyridine