Dynamic Partnership between KCNQ1 and KCNE1 and Influence on Cardiac IKs Current Amplitude by KCNE2

Abstract

Cardiac slow delayed rectifier (I Ks ) channel is composed of KCNQ1 (pore-forming) and KCNE1 (auxiliary) subunits. Although KCNE1 is an obligate I Ks component that confers the uniquely slow gating kinetics, KCNE2 is also expressed in human heart. In vitro experiments suggest that KCNE2 can associate with the KCNQ1-KCNE1 complex to suppress the current amplitude without altering the slow gating kinetics. Our goal here is to test the role of KCNE2 in cardiac I Ks channel function. Pulse-chase experiments in COS-7 cells show that there is a KCNE1 turnover in the KCNQ1-KCNE1 complex, supporting the possibility that KCNE1 in the I Ks channel complex can be substituted by KCNE2 when the latter is available. Biotinylation experiments in COS-7 cells show that although KCNE1 relies on KCNQ1 coassembly for more efficient cell surface expression, KCNE2 can independently traffic to the cell surface, thus becoming available for substituting KCNE1 in the I Ks channel complex. Injecting vesicles carrying KCNE1 or KCNE2 into KCNQ1-expressing oocytes leads to KCNQ1 modulation in the same manner as KCNQ1؉KCNEx (where x ‫؍‬ 1 or 2) cRNA coinjection. Thus, free KCNEx peptides delivered to the cell membrane can associate with existing KCNQ1 channels to modulate their function. Finally, adenovirus-mediated KCNE2 expression in adult guinea pig ventricular myocytes exhibited colocalization with native KCNQ1 protein and reduces the native I Ks current density. We propose that in cardiac myocytes the I Ks current amplitude is under dynamic control by the availability of KCNE2 subunits in the cell membrane.The slow delayed rectifier (I Ks ) channel functions as a "repolarization reserve" in the heart (1). It provides needed outward currents to prevent excessive action potential prolongation when the ␤-adrenergic tone is high or when there is a blockade of the rapid delayed rectifier channel as in acquired long QT syndrome (1). The I Ks channel is composed of a pore-forming component (the KCNQ1 channel, also known as Kv7.1 or KvLQT1) and an auxiliary regulatory component (the KCNE1 subunit, also known as minK or IsK) (2, 3). KCNE1 association with KCNQ1 produces the unique I Ks channel phenotype: very slow activation and deactivation rates and a positive voltage range of activation. There has been a strong interest in understanding how KCNQ1 and KCNE1 interact with each other (4 -12). Such knowledge is important for understanding why the I Ks channel malfunctions under pathological conditions (13,14) or when congenital mutations occur to . This information is also useful for the design of antiarrhythmic agents targeting malfunctioning I Ks channels (18).More KCNE subunits (KCNE2-KCNE5) have been cloned and characterized (19). In heterologous expression systems, each of these new members of the KCNE subfamily can associate with the KCNQ1 channel and confer distinct channel phenotypes (20). KCNE3, like KCNE1, increases KCNQ1 current amplitude, whereas KCNE2, KCNE4, and KCNE5 decrease or abolish KCNQ1 current. KCNE5, like KCNE1, shifts the v...

Decreased KCNE2 Expression Participates in the Development of Cardiac Hypertrophy by Regulation of Calcineurin–NFAT (Nuclear Factor of Activated T Cells) and Mitogen-Activated Protein Kinase Pathways

“…[11][12][13][14][15] It is well established that KCNE2 plays an important role in maintaining the cardiac electric stability. Downregulation in KCNE2 expression has been observed in HF and linked to cardiac arrhythmia.…”

Stoichiometry of the KCNQ1 - KCNE1 ion channel complex

“…Our results indicate that addition of the other KCNE subunits, such as KCNE3, to a complex of KCNQ1 with fewer than four KCNE1 subunits, could substantially inhibit the current. Not only could modulatory subunit addition take place during channel assembly in endoplasmic reticulum or Golgi (40,41) to create stable stoichiometries that last for the lifetime of the channel, but it may also occur on the cell surface (42,43). Our results indicate that KCNE1 subunits can be transported to the plasma membrane by themselves and that, at high expression levels, they can be found on their own, not colocalized with KCNQ1 ( Fig.…”

[Ca2+] Elevation and Oxidative Stress Induce KCNQ1 Protein Translocation from the Cytosol to the Cell Surface and Increase Slow Delayed Rectifier (IKs) in Cardiac Myocytes

“…After being cultured for 3 days, cells were incubated with adenoviruses harboring Q1-GFP and E1-dsR (0.25 ϫ 10 7 plaque-forming units/ml each) overnight. After removing the viruses, culture continued for the specified amounts of time (1,3,6, and 12 h). At the end of the culture, cells were used for patch clamp experiments or live-or fixed-cell confocal imaging.…”

“…Myocyte Isolation, Culture, and Adenoviral Infection-Guinea pig atrial and ventricular (GPA 2 and GPV) myocytes were isolated from 2-to 3-month-old adult animals using enzymatic (collagenase, type II, Worthington) digestion, followed by mechanical trituration as described previously (6). Isolated myocytes were used in three types of experiments.…”