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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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 4

Accelerated internalization and degradation of cell surface HERG protein is responsible for 0 mM K+o–induced IHERG reduction.

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Accelerated internalization and degradation of cell surface HERG protein...
(A and B) Time-dependent effects of incubating HERG-HEK cells with BFA (10 μM) in 0 or 5 mM K+ MEM on HERG protein expression level (A) or IHERG amplitude (B). (A) The 155-kDa band intensities in 0 or 5 mM K+ MEM at each time point were normalized to their initial values and plotted against time (n = 5). (B) HERG tail current upon repolarization to –50 mV after a 50-mV depolarization was measured and normalized to control value (time 0). The HERG currents shown in the inset were recorded using the protocol shown in Figure 1A. (C) Pulse-chase analysis of HERG trafficking in 0 or 5 mM K+ MEM. (D) Pulse-chase analysis of HERG trafficking in 0 or 5 mM K+ MEM with or without 20 μM lactacystin (Lact). The mature 155-kDa HERG channel protein is denoted by an arrow. (E) Time-dependent internalization of the surface HERG channels (green) labeled using an anti-HERG antibody. The cells were shown using DIC images. Similar results were observed in each set of 8 independent experiments. Scale bar: 10 μm. Numbers in parentheses denote n from at least 3 independent experiments.