The cardiac I
            <sub>Ks</sub>
            channel, complex indeed

Osteen, Jeremiah D.; Sampson, Kevin J.; Kass, Robert S.

doi:10.1073/pnas.1014150107

Cited by 33 publications

(26 citation statements)

References 19 publications

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“…This finding refutes the single-particle studies of Nakajo et al (25) in oocytes and macroscopic studies (21)(22)(23)(24)(30)(31)(32), arguing that forcing cells to express excess E1 produces I Ks channels containing more than two E1 subunits and that low levels of E1 yields I Ks channels with less than two E1 subunits. Not once did we observe an I Ks channel with three or four E1 subunits.…”

contrasting

confidence: 54%

mentioning

confidence: 99%

“…Nakajo et al (25) reported a variable number of E1 subunits, from one to four, in I Ks channels studied in Xenopus laevis oocytes. The impact of this result has been striking because it has engendered new models of cardiac physiology, altered models of I Ks channel biosynthesis and function, stimulated the use of transgenic animals artificially enforced to express I Ks channels with four E1 subunits (by expression of a fused E1-Q1 subunit), and prompted cardiac drug design based on the assumption that I Ks channels can form with one E1 subunit (23,(30)(31)(32).We were concerned that the conclusions of Nakajo et al (25) were in error because they appraised only a limited fraction of particles that were immobile in the oocyte membrane; counted E1 and Q1 asynchronously rather than simultaneously (increasing the risk that particles moved into or out of the field of view); and studied Q1 and E1 appended not only with the fluorescent proteins (FP) required to count subunits by photobleaching but also with a common trafficking motif that suppressed channel mobility by interacting with an overexpressed anchoring protein, thereby risking nonnatural aggregation of subunits.Here, to resolve mobility problems and obviate the need for modification of subunits with targeting motifs, we describe and perform single-fluorescent-particle photobleaching at the surface of live mammalian cells, demonstrating three spectroscopic counting approaches: standard, asynchronous subunit counting; simultaneous, two-color subunit counting; and toxin-directed, simultaneous, two-color photobleaching. To analyze the data, we use two Significance I Kslow (I Ks ) channels allow heartbeats and hearing.…”

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confidence: 99%

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Individual I _Ks channels at the surface of mammalian cells contain two KCNE1 accessory subunits

Plant

Xiong

Dai

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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KCNE1 (E1) β-subunits assemble with KCNQ1 (Q1) voltage-gated K + channel α-subunits to form I Kslow (I Ks ) channels in the heart and ear. The number of E1 subunits in I Ks channels has been an issue of ongoing debate. Here, we use single-molecule spectroscopy to demonstrate that surface I Ks channels with human subunits contain two E1 and four Q1 subunits. This stoichiometry does not vary. Thus, I Ks channels in cells with elevated levels of E1 carry no more than two E1 subunits. Cells with low levels of E1 produce I Ks channels with two E1 subunits and Q1 channels with no E1 subunits-channels with one E1 do not appear to form or are restricted from surface expression. The plethora of models of cardiac function, transgenic animals, and drug screens based on variable E1 stoichiometry do not reflect physiology.V oltage-gated potassium (K V ) channels include four α-subunits that form a single, central ion conduction pathway with four peripheral voltage sensors (1-3). Incorporation of accessory β-subunits modifies the function of K V channels to suit the diverse requirements of different tissues. KCNE genes encode minK-related peptides (MiRPs) (4-6), β-subunits with a single transmembrane span that assemble with a wide array of K V α-subunits (7, 8) to control surface expression, voltage dependence, and kinetics of gating transitions, unitary conductance, ion selectivity, and pharmacology of the resultant channel complexes (4, 9-15). I Kslow (I Ks ) channels in the heart and inner ear are formed by the α-subunit encoded by KCNQ1 (called Q1, K V LQT1, K V 7.1, or KCNQ1) and the β-subunit encoded by KCNE1 (called E1, mink, or KCNE1) (16,17). Inherited mutations in Q1 and E1 are associated with cardiac arrhythmia and deafness.The number of E1 subunits in I Ks channels has been a longstanding matter of disagreement. We first argued for two E1 subunits per channel based on the suppression of current by an E1 mutant (18). Subsequently, we reached the same conclusion by determining the total number of channels using radiolabeled charybdotoxin (CTX), a scorpion toxin that blocks channels when one molecule binds in the external conduction pore vestibule, and an antibody-based luminescence assay to tally E1 subunits (19). Morin and Kobertz (20) used iterative chemical linkage between CTX in the pore and E1, and they also assigned two accessory subunits to >95% of I Ks channels without gathering evidence for variation in subunit valence. Furthermore, when we formed I Ks channels from separate E1 and Q1 subunits and compared them with channels enforced via genetic encoding to contain two or four E1 subunits (19), we observed the natural I Ks channels to have the same gating attributes, small-molecule pharmacology, and CTX on and off rates (a reflection of pore vestibule structure) as channels encoded with two E1 subunits but not those with four. These findings support the conclusion that two E1 subunits are necessary, sufficient, and the normal number in I Ks channels.In contrast, others have argued that I Ks channels have va...

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confidence: 54%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Individual I _Ks channels at the surface of mammalian cells contain two KCNE1 accessory subunits

Plant

Xiong

Dai

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…Several studies have suggested that KCNQ1 exhibits flexible stoichiometry with KCNE1 varying from one to four subunits per KCNQ1 tetramer, depending on the relative expression levels of the two genes (13)(14)(15)(16)(17)(18). More recent experiments with cardiomyocytes differentiated from human stem cells or from induced pluripotent stem cells have shown that the voltage-dependence properties of I Ks fall between KCNQ1 homomultimers and heteromultimeric complexes with saturated KCNE1 levels, further suggesting that I Ks results from coassembled channels with KCNQ1/KCNE1 stoichiometry other than a uniform 4:4 (19,20).…”

mentioning

confidence: 99%

Dynamic subunit stoichiometry confers a progressive continuum of pharmacological sensitivity by KCNQ potassium channels

Lin

Mattmann

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Voltage-gated KCNQ1 (Kv7.1) potassium channels are expressed abundantly in heart but they are also found in multiple other tissues. Differential coassembly with single transmembrane KCNE beta subunits in different cell types gives rise to a variety of biophysical properties, hence endowing distinct physiological roles for KCNQ1-KCNEx complexes. Mutations in either KCNQ1 or KCNE1 genes result in diseases in brain, heart, and the respiratory system. In addition to complexities arising from existence of five KCNE subunits, KCNE1 to KCNE5, recent studies in heterologous systems suggest unorthodox stoichiometric dynamics in subunit assembly is dependent on KCNE expression levels. The resultant KCNQ1-KCNE channel complexes may have a range of zero to two or even up to four KCNE subunits coassembling per KCNQ1 tetramer. These findings underscore the need to assess the selectivity of small-molecule KCNQ1 modulators on these different assemblies. Here we report a unique small-molecule gating modulator, ML277, that potentiates both homomultimeric KCNQ1 channels and unsaturated heteromultimeric (KCNQ1) 4 (KCNE1) n (n < 4) channels. Progressive increase of KCNE1 or KCNE3 expression reduces efficacy of ML277 and eventually abolishes ML277-mediated augmentation. In cardiomyocytes, the slowly activating delayed rectifier potassium current, or I Ks , is believed to be a heteromultimeric combination of KCNQ1 and KCNE1, but it is not entirely clear whether I Ks is mediated by KCNE-saturated KCNQ1 channels or by channels with intermediate stoichiometries. We found ML277 effectively augments I Ks current of cultured human cardiomyocytes and shortens action potential duration. These data indicate that unsaturated heteromultimeric (KCNQ1) 4 (KCNE1) n channels are present as components of I Ks and are pharmacologically distinct from KCNE-saturated KCNQ1-KCNE1 channels.cardiac physiology | drug | long QT | pharmacology

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“…The underlying channel is a macromolecular complex composed of a-(Kv7.1) and modulatory b-(KCNE1) subunits. Mutations in either of them can give rise to congenital long QT syndrome and, hence, this channel was originally named KvLQT1 (59,93). Structurally, Kv7 channels are different from other channels of the Kv family with respect to a short cytoplasmic N terminus (*100 residues) and lack of a tetramerization (T1) domain.…”

Section: Kcnq Channelsmentioning

confidence: 99%

Oxidative Modulation of Voltage-Gated Potassium Channels

Sahoo

Hoshi

Heinemann

2014

Antioxidants & Redox Signaling

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Significance: Voltage-gated K + channels are a large family of K + -selective ion channel protein complexes that open on membrane depolarization. These K + channels are expressed in diverse tissues and their function is vital for numerous physiological processes, in particular of neurons and muscle cells. Potentially reversible oxidative regulation of voltage-gated K + channels by reactive species such as reactive oxygen species (ROS) represents a contributing mechanism of normal cellular plasticity and may play important roles in diverse pathologies including neurodegenerative diseases. Recent Advances: Studies using various protocols of oxidative modification, site-directed mutagenesis, and structural and kinetic modeling provide a broader phenomenology and emerging mechanistic insights. Critical Issues: Physicochemical mechanisms of the functional consequences of oxidative modifications of voltage-gated K + channels are only beginning to be revealed. In vivo documentation of oxidative modifications of specific amino-acid residues of various voltage-gated K + channel proteins, including the target specificity issue, is largely absent. Future Directions: High-resolution chemical and proteomic analysis of ion channel proteins with respect to oxidative modification combined with ongoing studies on channel structure and function will provide a better understanding of how the function of voltage-gated K + channels is tuned by ROS and the corresponding reducing enzymes to meet cellular needs. Antioxid. Redox Signal. 21, 933-952.

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The cardiac I _Ks channel, complex indeed

Cited by 33 publications

References 19 publications

Individual I _Ks channels at the surface of mammalian cells contain two KCNE1 accessory subunits

Individual I _Ks channels at the surface of mammalian cells contain two KCNE1 accessory subunits

Dynamic subunit stoichiometry confers a progressive continuum of pharmacological sensitivity by KCNQ potassium channels

Oxidative Modulation of Voltage-Gated Potassium Channels

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The cardiac I Ks channel, complex indeed

Cited by 33 publications

References 19 publications

Individual I Ks channels at the surface of mammalian cells contain two KCNE1 accessory subunits

Individual I Ks channels at the surface of mammalian cells contain two KCNE1 accessory subunits

Dynamic subunit stoichiometry confers a progressive continuum of pharmacological sensitivity by KCNQ potassium channels

Oxidative Modulation of Voltage-Gated Potassium Channels

Contact Info

Product

Resources

About

The cardiac I _Ks channel, complex indeed

Individual I _Ks channels at the surface of mammalian cells contain two KCNE1 accessory subunits

Individual I _Ks channels at the surface of mammalian cells contain two KCNE1 accessory subunits