FIGURE 10.

Calpain-1 decreases hERG through targeting the extracellular S5-pore linker. A, calpain-1 decreases hERG but not hERG-EAGS5P current. 24 h after transfection of pcDNA3- (control) or CAPN-1 into HEK cells, transfected cell medium (Ctrl-m or CAPN-1-m) was collected and applied to hERG-HEK cells for 12 h before patch clamp analyses. Topologies of a single subunit of hERG and hERG-EAGS5P are shown at the top. Representative currents of hERG or hERG-EAGS5P channels with Ctrl-m or CAPN-1-m are shown in the middle. The current of hERG or hERG-EAGS5P from each cell under all conditions is normalized to its mean value from cells cultured with Ctrl-m and summarized below the current traces. B and C, BeKm-1 (1 μm) abolishes CAPN-1-m-mediated reduction in mature hERG protein expression (B) and I_hERG (C). Ctrl-m or CAPN-1-m were applied to hERG-HEK cells cultured in the absence or presence of BeKm-1 (1 μm) for 12 h. For Western blotting analysis, intensities of the 155-kDa hERG band from cells cultured with CAPN-1-m in the absence or presence of BeKm-1 (1 μm) were normalized to the control (Ctrl-m) in each gel and then summarized (n = 4). Actin was used as a loading control. For patch clamp analysis, summarized tail current amplitudes from each group of cells are shown below the representative current traces. The numbers above the bar graphs indicate the number of cells examined from three independent treatments. **, p < 0.01 versus control. Error bars, S.E.