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Pflugers Arch. 1996 Jun;432(2):301-12.

Extracellular Mg2+ regulates activation of rat eag potassium channel.

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Max-Planck-Institut für experimentelle Medizin, Abteilung Molekulare Biologie neuronaler Signale, Hermann-Rein-Strasse 3, D-37075 Göttingen, Germany.


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.

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