K ir 2.1 potassium channels (encoded by KCNJ2) contribute to the inward rectifier K + current that provides ventricular myocytes a stable resting potential and participates in terminal cardiac action potential repolarization. Loss of function K ir 2.1 variants underlie Anderson-Tawil syndrome (ATS). Previously, it has been suggested that K ir 2.1 form functional complexes with another cardiac channel, Na v 1.5. This existence of a so-called “channelosome” has profound implications in cardiac physiology and, indeed, pathology. In this study, we utilized both trafficking and gating-defective ATS-associated KCNJ2 variants to interrogate possible interactions between K ir 2.1 and Na v 1.5. Introduction of ATS-associated KCNJ2 variants abolished whole-cell I Kir2.1 , in transfected HEK-293 cells. Co-expression of variant and wild-type (WT) channels partially recovered current, without changes in conductance or activation kinetics. Under ventricular action potential clamp, the Ba 2+ -sensitive current (300 μM) was significantly reduced, consistent with impaired repolarizing capacity. A western In-Cell/On-Cell LI-COR® assay was used to distinguish K ir 2.1 variants that resulted from perturbed membrane localization (Δ314-315) from gating/conduction (E138V). Co-expression of these variants with WT-Na v 1.5 did not significantly change the membrane expression of trafficking competent or incompetent K ir 2.1, nor was the total channel synthesis altered. Notably, trafficking-defective K ir 2.1 (Δ314-315) significantly reduced whole-cell I Nav1.5 , whereas gating-defective K ir 2.1 (E138V) had no effect; WT-Na v 1.5 did not recover I Kir2.1 for either trafficking or gating-defective channels. To determine whether there was any direct Na v 1.5-dependent modulation of K ir 2.1, as has previously been suggested, cell-attached single-channel recording was used. This revealed no change in K ir 2.1 unitary conductance or opening probability when alone or co-expressed with WT-Na v 1.5. Taken together, our data support a role for trafficking defective K ir 2.1 in modulating Na v 1.5. This has significant implications for the characterization and classification of future arrhythmia-associated KCNJ2 variants. This work was supported by a British Heart Foundation PhD Studentship for JC (FS/4yPhD/F/22/34173).
Carr et al. (Sun,) studied this question.