Molecular mechanisms underlying KVS-1-MPS-1 complex assembly

Formation of heteromeric complexes between voltage-gated K(+) (Kv) channels and accessory (beta) subunits is a widespread means to generate heterogeneity of K(+) current in the nervous system. Here we investigate the principles that determine the interactions of Caenorhabditis elegans MPS-1, a bifunctional beta-subunit that possesses kinase activity, with Kv channels. MPS-1 belongs to the evolutionarily conserved family of KCNE beta-subunits that modulate the functional properties of a variety of Kv channels and that, when defective, can cause congenital and acquired disease in Homo sapiens. In Chinese hamster ovary cells, MPS-1 forms stable complexes with different alpha-subunits. The transmembrane domain of MPS-1 is necessary and sufficient for MPS-1 complex formation. The hydropathicity of the transmembrane domain is an important factor controlling MPS-1 assembly. A highly hydrophobic MPS-1 mutant fails to interact with its endogenous channel partners when transgenically expressed in living worms. The hydropathic mechanism does not require specific points of contact between interacting proteins. This may allow MPS-1 to assemble with various Kv channels, presumably modifying the electrical properties of each.     

The KCNE2 potassium channel ancillary subunit is essential for gastric acid secretion

Genes in the KCNE family encode single transmembrane domain ancillary subunits that co-assemble with voltage-gated potassium (Kv) channel alpha subunits to alter their function. KCNE2 (also known as MiRP1) is expressed in the heart, is associated with human cardiac arrhythmia, and modulates cardiac Kv alpha subunits hERG and KCNQ1 in vitro. KCNE2 and KCNQ1 are also expressed in parietal cells, leading to speculation they form a native channel complex there. Here, we disrupted the murine kcne2 gene and found that kcne2 (-/-) mice have a severe gastric phenotype with profoundly reduced parietal cell proton secretion, abnormal parietal cell morphology, achlorhydria, hypergastrinemia, and striking gastric glandular hyperplasia arising from an increase in the number of non-acid secretory cells. KCNQ1 exhibited abnormal distribution in gastric glands from kcne2 (-/-) mice, with increased expression in non-acid secretory cells. Parietal cells from kcne2 (+/-) mice exhibited normal architecture but reduced proton secretion, and kcne2 (+/-) mice were hypochlorhydric, indicating a gene-dose effect and a primary defect in gastric acid secretion. These data demonstrate that KCNE2 is essential for gastric acid secretion, the first genetic evidence that a member of the KCNE gene family is required for normal gastrointestinal function.     

Disruption of the K+ Channel β-Subunit KCNE3 Reveals an Important Role in Intestinal and Tracheal Cl? Transport

The KCNE3 β-subunit constitutively opens outwardly rectifying KCNQ1 (Kv7.1) K⁺ channels by abolishing their voltage-dependent gating. The resulting KCNQ1/KCNE3 heteromers display enhanced sensitivity to K⁺ channel inhibitors like chromanol 293B. KCNE3 was also suggested to modify biophysical properties of several other K⁺ channels, and a mutation in KCNE3 was proposed to underlie forms of human periodic paralysis. To investigate physiological roles of KCNE3, we now disrupted its gene in mice. kcne3^−/− mice were viable and fertile and displayed neither periodic paralysis nor other obvious skeletal muscle abnormalities. KCNQ1/KCNE3 heteromers are present in basolateral membranes of intestinal and tracheal epithelial cells where they might facilitate transepithelial Cl⁻ secretion through basolateral recycling of K⁺ ions and by increasing the electrochemical driving force for apical Cl⁻ exit. Indeed, cAMP-stimulated electrogenic Cl⁻ secretion across tracheal and intestinal epithelia was drastically reduced in kcne3^−/− mice. Because the abundance and subcellular localization of KCNQ1 was unchanged in kcne3^−/− mice, the modification of biophysical properties of KCNQ1 by KCNE3 is essential for its role in intestinal and tracheal transport. Further, these results suggest KCNE3 as a potential modifier gene in cystic fibrosis.     

An evolutionarily conserved family of accessory subunits of K+ channels

Accessory subunits are an essential feature of voltage-gated potassium (Kv) channels. They determine trafficking to the plasma membrane, surface expression, gating, permeation, and pharmacology. At least three distinct classes of accessory subunits including the KCNE family can regulate Kv channel function. KCNE genes encode integral membrane proteins with a single transmembrane domain. KCNE genes span the eukaryotic kingdom and, in mutated form, can cause acquired and congenital disease. Here we review genetic, physiological, and biophysical aspects of KCNE proteins with particular emphasis on the Caenorhabditis elegans subfamily.     

KCNE gene expression is dependent on the proliferation and mode of activation of leukocytes

Voltage-dependent K⁺ (Kv) channels are tightly regulated during the immune system response. Leukocytes have a limited repertoire of Kv channels, whose physiological role is under intense investigation. A functional Kv channel is an oligomeric complex composed of pore-forming and ancillary subunits. The KCNE gene family is a novel group of modulatory Kv channel elements in leukocytes. Here, we characterized the gene expression of KCNEs (1–5) in leukocytes and investigated their regulation during leukocyte proliferation and mode of activation. Murine bone-marrow-derived macrophages, human Jurkat T-lymphocytes and human Raji B-cells were analyzed. KCNEs (1–5) are expressed in all leukocytes lineages. Most KCNE mRNAs show cell cycle-dependent regulation and are differentially regulated under specific insults. Our results further suggest a new and yet undefined physiological role for KCNE subunits in the immune system. Putative associations of these ancillary proteins with Kv channels would yield a wide variety of biophysically and pharmacologically distinct channels that fine-tune the immunological response.     

KCNE1 and KCNE3 β-Subunits Regulate Membrane Surface Expression of Kv12.2 K+ Channels In Vitro and Form a Tripartite Complex In Vivo

Voltage-gated potassium channels that activate near the neuronal resting membrane potential are important regulators of excitation in the nervous system, but their functional diversity is still not well understood. For instance, Kv12.2 (ELK2, KCNH3) channels are highly expressed in the cerebral cortex and hippocampus, and although they are most likely to contribute to resting potassium conductance, surprisingly little is known about their function or regulation. Here we demonstrate that the auxiliary MinK (KCNE1) and MiRP2 (KCNE3) proteins are important regulators of Kv12.2 channel function. Reduction of endogenous KCNE1 or KCNE3 expression by siRNA silencing, significantly increased macroscopic Kv12.2 currents in Xenopus oocytes by around 4-fold. Interestingly, an almost 9-fold increase in Kv12.2 currents was observed with the dual injection of KCNE1 and KCNE3 siRNA, suggesting an additive effect. Consistent with these findings, over-expression of KCNE1 and/or KCNE3 suppressed Kv12.2 currents. Membrane surface biotinylation assays showed that surface expression of Kv12.2 was significantly increased by KCNE1 and KCNE3 siRNA, whereas total protein expression of Kv12.2 was not affected. KCNE1 and KCNE3 siRNA shifted the voltages for half-maximal activation to more hyperpolarized voltages, indicating that KCNE1 and KCNE3 may also inhibit activation gating of Kv12.2. Native co-immunoprecipitation assays from mouse brain membranes imply that KCNE1 and KCNE3 interact with Kv12.2 simultaneously in vivo, suggesting the existence of novel KCNE1-KCNE3-Kv12.2 channel tripartite complexes. Together these data indicate that KCNE1 and KCNE3 interact directly with Kv12.2 channels to regulate channel membrane trafficking.     

KCNE4 is an inhibitory subunit to Kv1.1 and Kv1.3 potassium channels

Kv1 potassium channels are widely distributed in mammalian tissues and are involved in a variety of functions from controlling the firing rate of neurons to maturation of T-lymphocytes. Here we show that the newly described KCNE4 beta-subunit has a drastic inhibitory effect on currents generated by Kv1.1 and Kv1.3 potassium channels. The inhibition is found on channels expressed heterologously in both Xenopus oocytes and mammalian HEK293 cells. mKCNE4 does not inhibit Kv1.2, Kv1.4, Kv1.5, or Kv4.3 homomeric complexes, but it does significantly reduce current through Kv1.1/Kv1.2 and Kv1.2/Kv1.3 heteromeric complexes. Confocal microscopy and Western blotting reveal that Kv1.1 is present at the cell surface together with KCNE4. Real-time RT-PCR shows a relatively high presence of mKCNE4 mRNA in several organs, including uterus, kidney, lung, intestine, and in embryo, whereas a much lower mRNA level is detected in the heart and in five different parts of the brain. Having the broad distribution of Kv1 channels in mind, the demonstrated inhibitory property of KCNE4-subunits could locally and/or transiently have a dramatic influence on cellular excitability and on setting resting membrane potentials.     

KCNE1 remodels the voltage sensor of Kv7.1 to modulate channel function

The KCNE1 auxiliary subunit coassembles with the Kv7.1 channel and modulates its properties to generate the cardiac I_Ks current. Recent biophysical evidence suggests that KCNE1 interacts with the voltage-sensing domain (VSD) of Kv7.1. To investigate the mechanism of how KCNE1 affects the VSD to alter the voltage dependence of channel activation, we perturbed the VSD of Kv7.1 by mutagenesis and chemical modification in the absence and presence of KCNE1. Mutagenesis of S4 in Kv7.1 indicates that basic residues in the N-terminal half (S4-N) and C-terminal half (S4-C) of S4 are important for stabilizing the resting and activated states of the channel, respectively. KCNE1 disrupts electrostatic interactions involving S4-C, specifically with the lower conserved glutamate in S2 (Glu¹⁷⁰ or E2). Likewise, Trp scanning of S4 shows that mutations to a cluster of residues in S4-C eliminate current in the presence of KCNE1. In addition, KCNE1 affects S4-N by enhancing MTS accessibility to the top of the VSD. Consistent with the structure of Kv channels and previous studies on the KCNE1-Kv7.1 interaction, these results suggest that KCNE1 alters the interactions of S4 residues with the surrounding protein environment, possibly by changing the protein packing around S4, thereby affecting the voltage dependence of Kv7.1.     

KCNE3 is an inhibitory subunit of the Kv4.3 potassium channel

The mammalian Kv4.3 potassium channel is a fast activating and inactivating K+ channel widely distributed in mammalian tissues. Kv4.3 is the major component of various physiologically important currents ranging from A-type currents in the CNS to the transient outward potassium conductance in the heart (I(to)). Here we show that the KCNE3 beta-subunit has a strong inhibitory effect on current conducted by heterologously expressed Kv4.3 channels. KCNE3 reduces the Kv4.3 current amplitude, and it slows down the channel activation and inactivation as well as the recovery from inactivation. KCNE3 also inhibits currents generated by Kv4.3 in complex with the accessory subunit KChIP2. We find the inhibitory effect of KCNE3 to be specific for Kv4.3 within the Kv4 channel family. Kv4.3 has previously been shown to interact with a number of beta-subunits, but none of the described subunit-interactions exert an inhibitory effect on the Kv4.3 current.     

KCNE1 constrains the voltage sensor of Kv7.1 K+ channels

Kv7 potassium channels whose mutations cause cardiovascular and neurological disorders are members of the superfamily of voltage-gated K(+) channels, comprising a central pore enclosed by four voltage-sensing domains (VSDs) and sharing a homologous S4 sensor sequence. The Kv7.1 pore-forming subunit can interact with various KCNE auxiliary subunits to form K(+) channels with very different gating behaviors. In an attempt to characterize the nature of the promiscuous gating of Kv7.1 channels, we performed a tryptophan-scanning mutagenesis of the S4 sensor and analyzed the mutation-induced perturbations in gating free energy. Perturbing the gating energetics of Kv7.1 bias most of the mutant channels towards the closed state, while fewer mutations stabilize the open state or the inactivated state. In the absence of auxiliary subunits, mutations of specific S4 residues mimic the gating phenotypes produced by co-assembly of Kv7.1 with either KCNE1 or KCNE3. Many S4 perturbations compromise the ability of KCNE1 to properly regulate Kv7.1 channel gating. The tryptophan-induced packing perturbations and cysteine engineering studies in S4 suggest that KCNE1 lodges at the inter-VSD S4-S1 interface between two adjacent subunits, a strategic location to exert its striking action on Kv7.1 gating functions.     

KCNE2 protein is more abundant in ventricles than in atria and can accelerate hERG protein degradation in a phosphorylation-dependent manner

KCNE2 functions as an auxiliary subunit in voltage-gated K and HCN channels in the heart. Genetic variations in KCNE2 have been linked to long QT syndrome. The underlying mechanisms are not entirely clear. One of the issues is whether KCNE2 protein is expressed in ventricles. We use adenovirus-mediated genetic manipulations of adult cardiac myocytes to validate two antibodies (termed Ab1 and Ab2) for their ability to detect native KCNE2 in the heart. Ab1 faithfully detects native KCNE2 proteins in spontaneously hypertensive rat and guinea pig hearts. In both cases, KCNE2 protein is more abundant in ventricles than in atria. In both ventricular and atrial myocytes, KCNE2 protein is preferentially distributed on the cell surface. Ab1 can detect a prominent KCNE2 band in human ventricular muscle from nonfailing hearts. The band intensity is much fainter in atria and in failing ventricles. Ab2 specifically detects S98 phosphorylated KCNE2. Through exploring the functional significance of S98 phosphorylation, we uncover a novel mechanism by which KCNE2 modulates the human ether-a-go-go related gene (hERG) current amplitude: by accelerating hERG protein degradation and thus reducing the hERG protein level on the cell surface. S98 phosphorylation appears to be required for this modulation, so that S98 dephosphorylation leads to an increase in hERG/rapid delayed rectifier current amplitude. Our data confirm that KCNE2 protein is expressed in the ventricles of human and animal models. Furthermore, KCNE2 can modulate its partner channel function not only by altering channel conductance and/or gating kinetics, but also by affecting protein stability.     

The role of voltage-gated potassium channels in the regulation of mouse uterine contractility

Background  

Uterine smooth muscle cells exhibit ionic currents that appear to be important in the control of uterine contractility, but how these currents might produce the changes in contractile activity seen in pregnant myometrium has not been established. There are conflicting reports concerning the role of voltage-gated potassium (Kv) channels and large-conductance, calcium-activated potassium (BK) channels in the regulation of uterine contractility. In this study we provide molecular and functional evidence for a role for Kv channels in the regulation of spontaneous contractile activity in mouse myometrium, and also demonstrate a change in Kv channel regulation of contractility in pregnant mouse myometrium.     

Endogenous KCNE subunits govern Kv2.1 K+ channel activation kinetics in Xenopus oocyte studies

Kv2.1 is a voltage-gated potassium (Kv) channel that generates delayed rectifier currents in mammalian heart and brain. The biophysical properties of Kv2.1 and other ion channels have been characterized by functional expression in heterologous systems, and most commonly in Xenopus laevis oocytes. A number of previous oocyte-based studies of mammalian potassium channels have revealed expression-level-dependent changes in channel properties, leading to the suggestion that endogenous oocyte factors regulate channel gating. Here, we show that endogenous oocyte potassium channel KCNE ancillary subunits xMinK and xMiRP2 slow the activation of oocyte-expressed mammalian Kv2.1 channels two-to-fourfold. This produces a sigmoidal relationship between Kv2.1 current density and activation rate in oocyte-based two-electrode voltage clamp studies. The effect of endogenous xMiRP2 and xMinK on Kv2.1 activation is diluted at high Kv2.1 expression levels, or by RNAi knockdown of either endogenous subunit. RNAi knockdown of both xMiRP2 and xMinK eliminates the correlation between Kv2.1 expression level and activation kinetics. The data demonstrate a molecular basis for expression-level-dependent changes in Kv channel gating observed in heterologous expression studies.     

KCNE4 can co-associate with the I(Ks) (KCNQ1-KCNE1) channel complex

Voltage-gated potassium (K(V)) channels can form heteromultimeric complexes with a variety of accessory subunits, including KCNE proteins. Heterologous expression studies have demonstrated diverse functional effects of KCNE subunits on several K(V) channels, including KCNQ1 (K(V)7.1) that, together with KCNE1, generates the slow-delayed rectifier current (I(Ks)) important for cardiac repolarization. In particular, KCNE4 exerts a strong inhibitory effect on KCNQ1 and other K(V) channels, raising the possibility that this accessory subunit is an important potassium current modulator. A polyclonal KCNE4 antibody was developed to determine the human tissue expression pattern and to investigate the biochemical associations of this protein with KCNQ1. We found that KCNE4 is widely and variably expressed in several human tissues, with greatest abundance in brain, liver and testis. In heterologous expression experiments, immunoprecipitation followed by immunoblotting was used to establish that KCNE4 directly associates with KCNQ1, and can co-associate together with KCNE1 in the same KCNQ1 complex to form a 'triple subunit' complex (KCNE1-KCNQ1-KCNE4). We also used cell surface biotinylation to demonstrate that KCNE4 does not impair plasma membrane expression of either KCNQ1 or the triple subunit complex, indicating that biophysical mechanisms probably underlie the inhibitory effects of KCNE4. The observation that multiple KCNE proteins can co-associate with and modulate KCNQ1 channels to produce biochemically diverse channel complexes has important implications for understanding K(V) channel regulation in human physiology.     

Intracellular domains interactions and gated motions of IKS potassium channel subunits

Voltage‐gated K⁺ channels co‐assemble with auxiliary β subunits to form macromolecular complexes. In heart, assembly of Kv7.1 pore‐forming subunits with KCNE1 β subunits generates the repolarizing K⁺ current I_KS. However, the detailed nature of their interface remains unknown. Mutations in either Kv7.1 or KCNE1 produce the life‐threatening long or short QT syndromes. Here, we studied the interactions and voltage‐dependent motions of I_KS channel intracellular domains, using fluorescence resonance energy transfer combined with voltage‐clamp recording and in vitro binding of purified proteins. The results indicate that the KCNE1 distal C‐terminus interacts with the coiled‐coil helix C of the Kv7.1 tetramerization domain. This association is important for I_KS channel assembly rules as underscored by Kv7.1 current inhibition produced by a dominant‐negative C‐terminal domain. On channel opening, the C‐termini of Kv7.1 and KCNE1 come close together. Co‐expression of Kv7.1 with the KCNE1 long QT mutant D76N abolished the K⁺ currents and gated motions. Thus, during channel gating KCNE1 is not static. Instead, the C‐termini of both subunits experience molecular motions, which are disrupted by the D76N causing disease mutation.     

Differential modulation of cardiac potassium channels by Grb adaptor proteins

Scaffolding growth factor receptor-bound (Grb) adaptor proteins are components of macromolecular signaling complexes at the plasma membrane and thus are putative regulators of ion channel activity. The present study aimed to define the impact of Grb adaptor proteins on the function of cardiac K⁺ channels. To this end channel proteins were coinjected with the adaptor proteins in Xenopus oocytes and channel activity analyzed with two-electrode voltage-clamp. It is shown that coexpression of Grb adaptor proteins can reduce current amplitudes of coexpressed channels. Grb7 and 10 significantly inhibited functional currents generated by hERG, Kv1.5 and Kv4.3 channels. Only Grb10 significantly inhibited KCNQ1/KCNE1 K⁺ channels, and only Grb7 reduced Kir2.3 activity, whereas neither Grb protein significantly affected the closely related Kir2.1 and Kir2.2 channels. The present observations for the first time provide evidence for a selective and modulatory role of Grb adaptor proteins in the functional expression of cardiac K⁺ channels.     

KCNQ1 subdomains involved in KCNE modulation revealed by an invertebrate KCNQ1 orthologue

KCNQ1 channels are voltage-gated potassium channels that are widely expressed in various non-neuronal tissues, such as the heart, pancreas, and intestine. KCNE proteins are known as the auxiliary subunits for KCNQ1 channels. The effects and functions of the different KCNE proteins on KCNQ1 modulation are various; the KCNQ1-KCNE1 ion channel complex produces a slowly activating potassium channel that is crucial for heartbeat regulation, while the KCNE3 protein makes KCNQ1 channels constitutively active, which is important for K(+) and Cl(-) transport in the intestine. The mechanisms by which KCNE proteins modulate KCNQ1 channels have long been studied and discussed; however, it is not well understood how different KCNE proteins exert considerably different effects on KCNQ1 channels. Here, we approached this point by taking advantage of the recently isolated Ci-KCNQ1, a KCNQ1 homologue from marine invertebrate Ciona intestinalis. We found that Ci-KCNQ1 alone could be expressed in Xenopus laevis oocytes and produced a voltage-dependent potassium current, but that Ci-KCNQ1 was not properly modulated by KCNE1 and totally unaffected by coexpression of KCNE3. By making chimeras of Ci-KCNQ1 and human KCNQ1, we determined several amino acid residues located in the pore region of human KCNQ1 involved in KCNE1 modulation. Interestingly, though, these amino acid residues of the pore region are not important for KCNE3 modulation, and we subsequently found that the S1 segment plays an important role in making KCNQ1 channels constitutively active by KCNE3. Our findings indicate that different KCNE proteins use different domains of KCNQ1 channels, and that may explain why different KCNE proteins give quite different outcomes by forming a complex with KCNQ1 channels.     

Conserved Kv4 N-terminal domain critical for effects of Kv channel-interacting protein 2.2 on channel expression and gating

Association of Kv channel-interacting proteins (KChIPs) with Kv4 channels leads to modulation of these A-type potassium channels (An, W. F., Bowlby, M. R., Betty, M., Cao, J., Ling, H. P., Mendoza, G., Hinson, J. W., Mattsson, K. I., Strassle, B. W., Trimmer, J. S., and Rhodes, K. J. (2000) Nature 403, 553-556). We cloned a KChIP2 splice variant (KChIP2.2) from human ventricle. In comparison with KChIP2.1, coexpression of KChIP2.2 with human Kv4 channels in mammalian cells slowed the onset of Kv4 current inactivation (2-3-fold), accelerated the recovery from inactivation (5-7-fold), and shifted Kv4 steady-state inactivation curves by 8-29 mV to more positive potentials. The features of Kv4.2/KChIP2.2 currents closely resemble those of cardiac rapidly inactivating transient outward currents. KChIP2.2 stimulated the Kv4 current density in Chinese hamster ovary cells by approximately 55-fold. This correlated with a redistribution of immunoreactivity from perinuclear areas to the plasma membrane. Increased Kv4 cell-surface expression and current density were also obtained in the absence of KChIP2.2 when the highly conserved proximal Kv4 N terminus was deleted. The same domain is required for association of KChIP2.2 with Kv4 alpha-subunits. We propose that an efficient transport of Kv4 channels to the cell surface depends on KChIP binding to the Kv4 N-terminal domain. Our data suggest that the binding is necessary, but not sufficient, for the functional activity of KChIPs.     

Ca2+-Calmodulin and PIP2 interactions at the proximal C-terminus of Kv7 channels

In the heart, co-assembly of Kv7.1 with KCNE1 produces the slow I_KS potassium current, which repolarizes the cardiac action potential and mutations in human Kv7.1 and KCNE1 genes cause cardiac arrhythmias. The proximal Kv7.1 C-terminus binds calmodulin (CaM) and phosphatidylinositol-4,5-bisphosphate (PIP₂) and recently we revealed the competition of PIP₂ with the calcified CaM N-lobe to a previously unidentified site in Kv7.1 helix B, also known to harbor a LQT mutation. Data indicated that PIP₂ and Ca²⁺-CaM perform the same function on I_KS channel gating to stabilize the channel open state. Here we show that similar features were observed for Kv7.1 currents expressed alone. We also find that conservation of homologous residues in helix B of other Kv7 subtypes confer similar competition of Ca²⁺-CaM with PIP2 binding to their proximal C-termini and suggest that PIP2-CaM interactions converge to Kv7 helix B to modulates channel activity in a Kv7 subtype-dependent manner.     

Extracellular potassium inhibits Kv7.1 potassium channels by stabilizing an inactivated state

Kv7.1 (KCNQ1) channels are regulators of several physiological processes including vasodilatation, repolarization of cardiomyocytes, and control of secretory processes. A number of Kv7.1 pore mutants are sensitive to extracellular potassium. We hypothesized that extracellular potassium also modulates wild-type Kv7.1 channels. The Kv7.1 currents were measured in Xenopus laevis oocytes at different concentrations of extracellular potassium (1–50 mM). As extracellular potassium was elevated, Kv7.1 currents were reduced significantly more than expected from theoretical calculations based on the Goldman-Hodgkin-Katz flux equation. Potassium inhibited the steady-state current with an IC₅₀ of 6.0 ± 0.2 mM. Analysis of tail-currents showed that potassium increased the fraction of channels in the inactivated state. Similarly, the recovery from inactivation was slowed by potassium, suggesting that extracellular potassium stabilizes an inactivated state in Kv7.1 channels. The effect of extracellular potassium was absent in noninactivating Kv7.1/KCNE1 and Kv7.1/KCNE3 channels, further supporting a stabilized inactivated state as the underlying mechanism. Interestingly, coexpression of Kv7.1 with KCNE2 did not attenuate the inhibition by potassium. In a number of other Kv channels, including Kv1.5, Kv4.3, and Kv7.2–5 channels, currents were only minimally reduced by an increase in extracellular potassium as expected. These results show that extracellular potassium modulates Kv7.1 channels and suggests that physiological changes in potassium concentrations may directly control the function of Kv7.1 channels. This may represent a novel regulatory mechanism of excitability and of potassium transport in tissues expressing Kv7.1 channels.