= Potassium channel
A <potassium channel> is an <ion channel> that preferentially conducts <potassium> ions. Its selectivity filter can compensate for the energetic cost of removing water from an ion, while discriminating between ions of different geometry. A crystal structure of a bacterial <potassium channel> revealed how repeated backbone oxygen atoms line the narrow filter. <The structure of the potassium channel: molecular basis of K+ conduction and selectivity by Declan A. Doyle and others>[1998, abstract and selectivity-filter structure]{ref}
Different <potassium channels> open under different conditions. Leak channels contribute to resting <membrane potential>, whereas voltage-dependent channels can support <repolarization> after an <action potential>. The direction of current depends on voltage relative to the potassium reversal potential, not simply on the channel's name. Selectivity and gating describe different aspects of its function.
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