The Effect of TWIK-1 Two Pore Potassium Channels on Cardiomyocytes in Low Extracellular Potassium Conditions.

Backgroound: At low extracellular potassium ([K+]e) conditions, human cardiomyocytes can depolarize to -40 mV. This is closely related to hypokalemia-induced fatal cardiac arrhythmia. The underlying mechanism, however, is still not well understood. TWIK-1 channels are background K+ channels that are highly expressed in human cardiomyocytes. We previously reported that TWIK-1 channels changed ion selectivity and conducted leak Na+ currents at low [K+]e. Moreover, a specific threonine residue (Thr118) within the ion selectivity filter was responsible for this altered ion selectivity.

Methods: Patch clamp were used to investigate the effects of TWIK-1 channels on the membrane potentials of cardiomyocytes in response to low [K+]e.

Results: At 2.7 mM [K+]e and 1 mM [K+]e, both Chinese hamster ovary (CHO) cells and HL-1 cells ectopically expressed human TWIK-1 channels displayed inward leak Na+ currents and reconstitute depolarization of membrane potential. In contrast, cells ectopically expressed human TWIK-1-T118I mutant channels that remain high selectivity to K+ exhibited hyperpolarization of membrane potential. Furthermore, human iPSC-derived cardiomyocytes showed depolarization of membrane potential in response to 1 mM [K+]e, while the knockdown of TWIK-1 expression eliminated this phenomenon.

Conclusions: These results demonstrate that leak Na+ currents conducted by TWIK-1 channels contribute to the depolarization of membrane potential induced by low [K+]e in human cardiomyocytes.