Extracellular Mg2+ regulates activation of rat eag potassium channel

  • Terlau H
  • Ludwig J
  • Steffan R
 et al. 
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The rat homologue of Drosophila ether à gogo cDNA (rat eag) encodes voltage-activated potassium (K) channels with distinct activation properties. Using the Xenopus expression system, we examined the importance of extracellular Mg2+ on the activation of rat eag. Extracellular Mg2+ at physiological concentrations dramatically slowed the activation in a dose- and voltage-dependent manner. Other divalent cations exerted similar effects on the activation kinetics that correlated with their enthalpy of hydration. Lowering the external pH also resulted in a slowing of the activation. Protons competed with Mg2+ as the effect of Mg2+ was abolished at low pH. A kinetic model for rat eag activation was derived from the data indicating that all four channel subunits undergo a Mg2+-dependent conformational transition prior to final channel activation. The strong dependence of rat eag activation on both the resting potential and the extracellular Mg2+ concentration constitutes a system for fine-tuning K channel availability in neuronal cells.

Author-supplied keywords

  • Activation kinetics
  • Kinetic model
  • Magnesium pH
  • Oocyte expression system
  • Potassium (K) channels
  • Rat eag

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  • Heinrich Terlau

  • Jost Ludwig

  • Rüdiger Steffan

  • Olaf Pongs

  • Walter Stühmer

  • Stefan H. Heinemann

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