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New structure and function in plant K+ channels: KCO1, an outward rectifier with a steep Ca2+ dependency
K Czempinski1, S Zimmermann, T Ehrhardt
1Max-Planck-Institut für Molekulare Pflanzenphysiologie, Golm, Germany.
The EMBO Journal
|May 15, 1997
Summary
Researchers identified the first higher plant outward rectifying potassium (K+) channel, KCO1, from Arabidopsis thaliana. This channel
Area of Science:
- Plant molecular biology
- Ion channel physiology
- Biophysics
Background:
- Potassium (K+) channels are crucial for physiological functions and share a common pore-forming (P) domain.
- Outward rectifying K+ channels play significant roles in cellular processes.
- Understanding plant K+ channels is vital for agricultural and biological research.
Purpose of the Study:
- To clone and functionally characterize the first higher plant outward rectifying K+ channel (KCO1) from Arabidopsis thaliana.
- To investigate the properties and regulation of KCO1, particularly its dependence on calcium.
- To establish a link between calcium signaling and K+ transport in plants.
Main Methods:
- Cloning of the KCO1 gene from Arabidopsis thaliana.
- Heterologous expression of KCO1 in insect cells (Spodoptera frugiperda) using a baculovirus system.
- Electrophysiological recordings, including whole-cell and single-channel patch-clamp analysis, to measure K+ currents.
- Manipulation of cytosolic free Ca2+ ([Ca2+]cyt) concentrations to assess channel activation.
Main Results:
- KCO1 was identified as a novel two-pore K+ channel with four transmembrane segments and EF-hand motifs.
- Heterologous expression yielded outwardly rectifying, K+-selective currents activated by depolarizing voltage pulses.
- KCO1 activation was highly dependent on cytosolic free Ca2+ ([Ca2+]cyt), with significant activation observed at nanomolar concentrations (around 300 nM).
- Single-channel analysis confirmed outward rectification and Ca2+-dependent gating, with a conductance of 64 pS.
Conclusions:
- KCO1 represents the first identified plant outward rectifying K+ channel, belonging to a new class of two-pore channels.
- The study demonstrates a direct functional link between calcium-mediated signaling and K+ ion transport in higher plants.
- The discovery of KCO1 opens new avenues for structure-function studies of plant ion channels and their physiological roles.
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