Figure 3. The [K⁺]_o controls HERG membrane expression.

(A and B) Concentration-dependent effects of K⁺_o, after overnight exposure, on (A) HERG channel expression levels and (B) relative intensity of the 155-kDa band. (B) The intensity of the 155-kDa band at each [K⁺]_o was normalized to the value at 5 mM K⁺ and plotted against [K⁺]_o. (C) Effects of [K⁺]_o on cell surface HERG expression. Surface proteins from HERG-HEK cells cultured in 0 or 5 mM K⁺ for 12 hours were isolated and analyzed by Western blot using an anti-HERG antibody. For statistical analysis (see Results), the intensity of the 155-kDa band in 0 mM K⁺ was normalized to its pair in 5 mM K⁺ for each set of 3 experiments. Na/K-ATPase (100 kDa), detected using an anti–Na/K-ATPase antibody, was used as a loading control for isolated cell surface proteins. (D and E) Time-dependent effects of exposure to 0 or 5 mM K⁺ MEM on I_HERG (D) or on HERG protein expression levels (E). The HERG currents were recorded using the protocol shown in Figure 1A. (E) Intensities of the 155-kDa bands in 0 or 5 mM K⁺ at each time point were normalized to their initial values and plotted as a function of time. Numbers in parentheses denote n from at least 3 independent experiments.