Optical measurement of gating pore currents in hypokalemic periodic paralysis model cells

Hypokalemic periodic paralysis (HypoPP) is a rare genetic disease associated with mutations in CACNA1S or SCN4A, encoding Cav1.1 or Nav1.4, respectively. Most HypoPP-associated missense changes occur at the arginine residues within the voltage-sensing domain (VSD) of these channels. It is established that such mutations destroy the hydrophobic seal separating the external water and the internal cytosolic crevices, resulting in the generation of aberrant leak currents called gating pore currents. Presently, the gating pore currents are thought to underlie HypoPP. Here, we generated HEK293T-based HypoPP-model cell lines with the Sleeping Beauty transposon system that co-express mouse inward-rectifier potassium channel (mKir2.1) and HypoPP2-associated Nav1.4 variants. Whole cell patch-clamp measurements confirmed that mKir2.1 successfully hyperpolarized the membrane potential to comparable levels to myofibers, and that some Nav1.4 variants induced notable proton-based gating pore currents. Importantly, we succeeded in fluorometrically measuring the gating pore currents in these variants using a ratiometric pH indicator, SNARF-4F. Our optical method provides a potential in vitro platform for high-throughput drug screen, not only for HypoPP but also for other channelopathies caused by VSD mutations.