TWIK-1 two-pore domain potassium channels change ion selectivity and conduct inward leak sodium currents in hypokalemia

Liqun Ma, Xuexin Zhang, Haijun Chen

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Abstract

Background potassium (K+) channels, which are normally selectively permeable to K+, maintain the cardiac resting membrane potential at around -80 mV. In subphysiological extracellular K+ concentrations ([K+]o), which occur in pathological hypokalemia, the resting membrane potential of human cardiomyocytes can depolarize to around -50 mV, whereas rat and mouse cardiomyocytes become hyperpolarized, consistent with the Nernst equation for K+. This paradoxical depolarization of cardiomyocytes in subphysiological [K +]o, which may contribute to cardiac arrhythmias, is thought to involve an inward leak sodium (Na+) current. Here, we show that human cardiac TWIK-1 (also known as K2P1) two-pore domain K+ channels change ion selectivity, becoming permeable to external Na+, and conduct inward leak Na+ currents in subphysiological [K +]o. A specific threonine residue (Thr118) within the pore selectivity sequence TxGYG was required for this altered ion selectivity. Mouse cardiomyocyte-derived HL-1 cells exhibited paradoxical depolarization with ectopic expression of TWIK-1 channels, whereas TWIK-1 knockdown in human spherical primary cardiac myocytes eliminated paradoxical depolarization. These findings indicate that ion selectivity of TWIK-1 K + channels changes during pathological hypokalemia, elucidate a molecular basis for inward leak Na+ currents that could trigger or contribute to cardiac paradoxical depolarization in lowered [K+] o, and identify a mechanism for regulating cardiac excitability.

Original languageEnglish (US)
Article numberra37
JournalScience Signaling
Volume4
Issue number176
DOIs
StatePublished - Jun 7 2011

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All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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