PMID:9184204

Citation	Czempinski, K, Zimmermann, S, Ehrhardt, T and Müller-Röber, B (1997) New structure and function in plant K+ channels: KCO1, an outward rectifier with a steep Ca2+ dependency. EMBO J. 16:2565-75
Abstract	Potassium (K+) channels mediating important physiological functions are characterized by a common pore-forming (P) domain. We report the cloning and functional analysis of the first higher plant outward rectifying K+ channel (KCO1) from Arabidopsis thaliana. KCO1 belongs to a new class of 'two-pore' K+ channels recently described in human and yeast. KCO1 has four putative transmembrane segments and tandem calcium-binding EF-hand motifs. Heterologous expression of KCO1 in baculovirus-infected insect (Spodoptera frugiperda) cells resulted in outwardly rectifying, K+-selective currents elicited by depolarizing voltage pulses in whole-cell measurements. Activation of KCO1 was strongly dependent on the presence of nanomolar concentrations of cytosolic free Ca2+ [Ca2+]cyt. No K+ currents were detected when [Ca2+]cyt was adjusted to <150 nM. However, KCO1 strongly activated at increasing [Ca2+]cyt, with a saturating activity observed at approximately 300 nM [Ca2+]cyt. KCO1 single channel analysis on excised membrane patches, resulting in a single channel conductance of 64 pS, confirmed outward rectification as well as Ca2+-dependent activation. These data suggest a direct link between calcium-mediated signaling processes and K+ ion transport in higher plants. The identification of KCO1 as the first plant K+ outward channel opens a new field of structure-function studies in plant ion channels.
Links	PubMed PMC1169868 Online version:10.1093/emboj/16.10.2565
Keywords	Amino Acid Sequence; Animals; Arabidopsis/genetics; Arabidopsis Proteins; Baculoviridae/genetics; Biological Transport; Calcium/pharmacology; Cloning, Molecular; Genes, Plant; Ion Channel Gating; Models, Molecular; Molecular Sequence Data; Patch-Clamp Techniques; Plant Proteins/physiology; Potassium/metabolism; Potassium Channels/classification; Potassium Channels/drug effects; Potassium Channels/physiology; Potassium Channels, Tandem Pore Domain; Protein Conformation; RNA, Messenger/biosynthesis; RNA, Plant/biosynthesis; Recombinant Proteins/metabolism; Sequence Analysis, DNA; Sequence Homology, Amino Acid; Spodoptera/cytology
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