Extracellular K+ concentration controls cell surface density of IKr in rabbit hearts and of the HERG channel in human cell lines
Jun Guo, … , Nasrin Mesaeli, Shetuan Zhang
Jun Guo, … , Nasrin Mesaeli, Shetuan Zhang
Published August 24, 2009
Citation Information: J Clin Invest. 2009;119(9):2745-2757. https://doi.org/10.1172/JCI39027.
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Research Article

Extracellular K+ concentration controls cell surface density of IKr in rabbit hearts and of the HERG channel in human cell lines

Abstract

Although the modulation of ion channel gating by hormones and drugs has been extensively studied, much less is known about how cell surface ion channel expression levels are regulated. Here, we demonstrate that the cell surface density of both the heterologously expressed K+ channel encoded by the human ether-a-go-go–related gene (HERG) and its native counterpart, the rapidly activating delayed rectifier K+ channel (IKr), in rabbit hearts in vivo is precisely controlled by extracellular K+ concentration ([K+]o) within a physiologically relevant range. Reduction of [K+]o led to accelerated internalization and degradation of HERG channels within hours. Confocal analysis revealed colocalization between HERG and ubiquitin during the process of HERG internalization, and overexpression of ubiquitin facilitated HERG degradation under low [K+]o. The HERG channels colocalized with a marker of multivesicular bodies during internalization, and the internalized HERG channels were targeted to lysosomes. Our results provide the first evidence to our knowledge that the cell surface density of a voltage-gated K+ channel, HERG, is regulated by a biological factor, extracellular K+. Because hypokalemia is known to exacerbate long QT syndrome (LQTS) and Torsades de pointes tachyarrhythmias, our findings provide a potential mechanistic link between hypokalemia and LQTS.

Authors

Jun Guo, Hamid Massaeli, Jianmin Xu, Zongchao Jia, Jeffrey T. Wigle, Nasrin Mesaeli, Shetuan Zhang

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Figure 3

The [K+]o controls HERG membrane expression.

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The [K+]o controls HERG membrane expression. (A and B) Concentration...
(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 IHERG (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.