title: A Shaker homologue encodes an A-type current in Xenopus laevis.
abstract: In Xenopus laevis, several distinct K(+)-channels (xKv1.1, xKv1.2, xKv2,1, xKv2.2, xKv3.1) have been cloned, sequenced, and electrophysiologically characterized. K(+)-channels significantly shape neuronal excitability by setting the membrane potential, and latency and duration of action potentials. We identified a further Shaker homologue, xKv1.4, in X. laevis. The open reading frame encodes a K(+)-channel that shares 72% of its 698 amino acids with the human Shaker homologue, hKv1.4. Northern blot analysis revealed xKv1.4 in the brain, muscle, and spleen but not in the ovary, intestine, heart, liver, kidney, lung, and skin. Whole-cell patch clamp recording from rat basophilic leukaemia (RBL) cells transfected with xKv1.4 revealed a voltage-gated, outward rectifying, transient A-type, K(+) selective current. xKv1.4 was strongly dependent on extracellular K(+). Exposure of cells to K(+) free bath solution almost completely abolished the current, whereas in the presence of high K(+), inactivation in response to a maintained depolarizing step and the frequency-dependent cumulative inactivation decreased. Ion channels encoded by xKv1.4 are sensitive to 4-aminopyridine and quinidine but insensitive to tetraethylammonium and the peptide toxins, charybdotoxin, margatoxin, and dendrotoxin. In conclusion, our results indicate that the biophysical and pharmacological signature of xKv1.4 closely resemble those of the A-current described in Xenopus embryonic neurons and is similar to the human Shaker homologue, hKv1.4.
authors.affiliation: Department of Molecular Neurobiology and Cellular Physiology, Institute of Zoology, University of Salzburg, Hellbrunnerstr. 34, 5020 Salzburg, Austria. hubert.kirschbaum@sbg.ac.at
authors.forename: Hubert H
authors.initials: HH
authors.lastname: Kerschbaum
authors.forename: Stephan
authors.initials: S
authors.lastname: Grissmer
authors.forename: Edwin
authors.initials: E
authors.lastname: Engel
authors.forename: Klaus
authors.initials: K
authors.lastname: Richter
authors.forename: Christine
authors.initials: C
authors.lastname: Lehner
authors.forename: Heike
authors.initials: H
authors.lastname: Jäger
mesh_terms: D000818:Animals; D001483:Base Sequence; D001923:Brain Chemistry / Q000502:physiology; D002478:Cells, Cultured; D005260:Female; D015870:Gene Expression / Q000502:physiology; D015640:Ion Channel Gating / Q000502:physiology; D051665:Kv1.4 Potassium Channel; D015471:Leukemia, Basophilic, Acute; D008564:Membrane Potentials / Q000502:physiology; D008969:Molecular Sequence Data; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated; D051381:Rats; D017386:Sequence Homology, Amino Acid; D051637:Shaker Superfamily of Potassium Channels; D014162:Transfection; D014407:Tumor Cells, Cultured; D029867:Xenopus Proteins; D014982:Xenopus laevis
chemical_list: C496979:Kcna4 protein, rat; D051665:Kv1.4 Potassium Channel; C496980:Kv1.4 potassium channel, Xenopus; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D051637:Shaker Superfamily of Potassium Channels; D029867:Xenopus Proteins