Identification and characterisation of a novel KCNQ1 mutation in a family with Romano-Ward syndrome

Romano-Ward syndrome (RWS), the autosomal dominant form of the congenital long QT syndrome, is characterised by prolongation of the cardiac repolarisation process associated with ventricular tachyarrhythmias of the torsades de pointes type. Genetic studies have identified mutations in six ion channel genes, KCNQ1, KCNH2, SCN5A, KCNE1 and KCNE2 and the accessory protein Ankyrin-B gene, to be responsible for this disorder. Single-strand conformation polymorphism (SSCP) analysis and subsequent DNA sequence analysis have identified a KCNQ1 mutation in a family that were clinically conspicuous due to several syncopes and prolonged QTc intervals in the ECG. The mutant subunit was expressed and functionally characterised in the Xenopus oocyte expression system. A novel heterozygous missense mutation with a C to T transition at the first position of codon 343 (CCA) of the KCNQ1 gene was identified in three concerned family members (QTc intervals: 500, 510 and 530 ms, respectively). As a result, proline 343 localised within the highly conserved transmembrane segment S6 of the KCNQ1 channel is replaced by a serine. Co-expression of mutant (KCNQ1-P343S) and wild-type (KCNQ1) cRNA in Xenopus oocytes produced potassium currents reduced by approximately 92%, while IKs reconstitution experiments with a combination of KCNQ1 mutant, wild-type and KCNE1 subunits yielded currents reduced by approximately 60%. A novel mutation (P343S) identified in the KCNQ1 subunit gene of three members of a RWS family showed a dominant-negative effect on native IKs currents leading to prolongation of the heart repolarisation and possibly increases the risk of malign arrhythmias with sudden cardiac death.     

Mutations in a dominant-negative isoform correlate with phenotype in inherited cardiac arrhythmias

The long QT syndrome is characterized by prolonged cardiac repolarization and a high risk of sudden death. Mutations in the KCNQ1 gene, which encodes the cardiac KvLQT1 potassium ion (K+) channel, cause both the autosomal dominant Romano-Ward (RW) syndrome and the recessive Jervell and Lange-Nielsen (JLN) syndrome. JLN presents with cardiac arrhythmias and congenital deafness, and heterozygous carriers of JLN mutations exhibit a very mild cardiac phenotype. Despite the phenotypic differences between heterozygotes with RW and those with JLN mutations, both classes of variant protein fail to produce K+ currents in cultured cells. We have shown that an N-terminus-truncated KvLQT1 isoform endogenously expressed in the human heart exerts strong dominant-negative effects on the full-length KvLQT1 protein. Because RW and JLN mutations concern both truncated and full-length KvLQT1 isoforms, we investigated whether RW or JLN mutations would have different impacts on the dominant-negative properties of the truncated KvLQT1 splice variant. In a mammalian expression system, we found that JLN, but not RW, mutations suppress the dominant-negative effects of the truncated KvLQT1. Thus, in JLN heterozygous carriers, the full-length KvLQT1 protein encoded by the unaffected allele should not be subject to the negative influence of the mutated truncated isoform, leaving some cardiac K+ current available for repolarization. This is the first report of a genetic disease in which the impact of a mutation on a dominant-negative isoform correlates with the phenotype.     

Structural models for the KCNQ1 voltage-gated potassium channel

Mutations in the human voltage-gated potassium channel KCNQ1 are associated with predisposition to deafness and various cardiac arrhythmia syndromes including congenital long QT syndrome, familial atrial fibrillation, and sudden infant death syndrome. In this work 3-D structural models were developed for both the open and closed states of human KCNQ1 to facilitate structurally based hypotheses regarding mutation-phenotype relationships. The KCNQ1 open state was modeled using Rosetta in conjunction with Molecular Operating Environment software, and is based primarily on the recently determined open state structure of rat Kv1.2 (Long, S. B., et al. (2005) Science 309, 897-903). The closed state model for KCNQ1 was developed based on the crystal structures of bacterial potassium channels and the closed state model for Kv1.2 of Yarov-Yarovoy et al. ((2006) Proc. Natl. Acad. Sci. U.S.A. 103, 7292-7207). Using the new models for KCNQ1, we generated a database for the location and predicted residue-residue interactions for more than 85 disease-linked sites in both open and closed states. These data can be used to generate structure-based hypotheses for disease phenotypes associated with each mutation. The potential utility of these models and the database is exemplified by the surprising observation that four of the five known mutations in KCNQ1 that are associated with gain-of-function KCNQ1 defects are predicted to share a common interface in the open state structure between the S1 segment of the voltage sensor in one subunit and both the S5 segment and top of the pore helix from another subunit. This interface evidently plays an important role in channel gating.     

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.     

Nano-environmental changes by KCNE proteins modify KCNQ channel function

The KCNQ1 channel is a voltage-dependent potassium channel, which is widely expressed in various tissues of the human body including heart, inner ear, intestine, kidney and pancreas. The ion channel properties of KCNQ1 change remarkably when auxiliary subunit KCNE proteins co-exist. The mechanisms of KCNQ1 channel regulation by KCNE proteins are of longstanding interest but are still far from being fully understood. The pore region (S5-S6 segments) of KCNQ1 is thought to be the main interaction site for KCNE proteins. However, some recent reports showed that the voltage-sensing domain (S1-S4 segments) is critically involved in the regulation of KCNQ1 by KCNE proteins. In addition, we recently re-examined the stoichiometry of the KCNQ1-KCNE1 complex and found that the stoichiometry is not fixed but rather flexible and the KCNQ1 channel can have up to four associated KCNE1 proteins. We will review these recent findings concerning the mechanisms of KCNQ1 regulation by KCNE proteins.     

Nano-environmental changes by KCNE proteins modify KCNQ channel function

The KCNQ1 channel is a voltage-dependent potassium channel, which is widely expressed in various tissues of the human body including heart, inner ear, intestine, kidney and pancreas. The ion channel properties of KCNQ1 change remarkably when auxiliary subunit KCNE proteins co-exist. The mechanisms of KCNQ1 channel regulation by KCNE proteins are of longstanding interest but are still far from being fully understood. The pore region (S5-S6 segments) of KCNQ1 is thought to be the main interaction site for KCNE proteins. However, some recent reports showed that the voltage-sensing domain (S1-S4 segments) is critically involved in the regulation of KCNQ1 by KCNE proteins. In addition, we recently re-examined the stoichiometry of the KCNQ1-KCNE1 complex and found that the stoichiometry is not fixed but rather flexible and the KCNQ1 channel can have up to four associated KCNE1 proteins. We will review these recent findings concerning the mechanisms of KCNQ1 regulation by KCNE proteins.     

Characterization of a novel mutant KCNQ1 channel subunit lacking a large part of the C-terminal domain

A mutation of KCNQ1 gene encoding the alpha subunit of the channel mediating the slow delayed rectifier K⁺ current in cardiomyocytes may cause severe arrhythmic disorders. We identified KCNQ1(Y461X), a novel mutant gene encoding KCNQ1 subunit whose C-terminal domain is truncated at tyrosine 461 from a man with a mild QT interval prolongation. We made whole-cell voltage-clamp recordings from HEK-293T cells transfected with either of wild-type KCNQ1 [KCNQ1(WT)], KCNQ1(Y461X), or their mixture plus KCNE1 auxiliary subunit gene. The KCNQ1(Y461X)-transfected cells showed no delayed rectifying current. The cells transfected with both KCNQ1(WT) and KCNQ1(Y461X) showed the delayed rectifying current that is thought to be mediated largely by homomeric channel consisting of KCNQ1(WT) subunit because its voltage-dependence of activation, activation rate, and deactivation rate were similar to the current in the KCNQ1(WT)-transfected cells. The immunoblots of HEK-293T cell-derived lysates showed that KCNQ1(Y461X) subunit cannot form channel tetramers by itself or with KCNQ1(WT) subunit. Moreover, immunocytochemical analysis in HEK-293T cells showed that the surface expression level of KCNQ1(Y461X) subunit was very low with or without KCNQ1(WT) subunit. These findings suggest that the massive loss of the C-terminal domain of KCNQ1 subunit impairs the assembly, trafficking, and function of the mutant subunit-containing channels, whereas the mutant subunit does not interfere with the functional expression of the homomeric wild-type channel. Therefore, the homozygous but not heterozygous inheritance of KCNQ1(Y461X) might cause major arrhythmic disorders. This study provides a new insight into the structure–function relation of KCNQ1 channel and treatments of cardiac channelopathies.     

Interaction between the cardiac rapidly (IKr) and slowly (IKs) activating delayed rectifier potassium channels revealed by low K+-induced hERG endocytic degradation

Cardiac repolarization is controlled by the rapidly (I(Kr)) and slowly (I(Ks)) activating delayed rectifier potassium channels. The human ether-a-go-go-related gene (hERG) encodes I(Kr), whereas KCNQ1 and KCNE1 together encode I(Ks). Decreases in I(Kr) or I(Ks) cause long QT syndrome (LQTS), a cardiac disorder with a high risk of sudden death. A reduction in extracellular K(+) concentration ([K(+)](o)) induces LQTS and selectively causes endocytic degradation of mature hERG channels from the plasma membrane. In the present study, we investigated whether I(Ks) compensates for the reduced I(Kr) under low K(+) conditions. Our data show that when hERG and KCNQ1 were expressed separately in human embryonic kidney (HEK) cells, exposure to 0 mM K(+) for 6 h completely eliminated the mature hERG channel expression but had no effect on KCNQ1. When hERG and KCNQ1 were co-expressed, KCNQ1 significantly delayed 0 mM K(+)-induced hERG reduction. Also, hERG degradation led to a significant reduction in KCNQ1 in 0 mM K(+) conditions. An interaction between hERG and KCNQ1 was identified in hERG+KCNQ1-expressing HEK cells. Furthermore, KCNQ1 preferentially co-immunoprecipitated with mature hERG channels that are localized in the plasma membrane. Biophysical and pharmacological analyses indicate that although hERG and KCNQ1 closely interact with each other, they form distinct hERG and KCNQ1 channels. These data extend our understanding of delayed rectifier potassium channel trafficking and regulation, as well as the pathology of LQTS.     

Purification and membrane interactions of human KCNQ1100–370 potassium ion channel

KCNQ1 (Kv7.1 or KvLQT1) is a voltage-gated potassium ion channel that is involved in the ventricular repolarization following an action potential in the heart. It forms a complex with KCNE1 in the heart and is the pore forming subunit of slow delayed rectifier potassium current (I_ks). Mutations in KCNQ1, leading to a dysfunctional channel or loss of activity have been implicated in a cardiac disorder, long QT syndrome. In this study, we report the overexpression, purification, biochemical characterization of human KCNQ1_100–370, and lipid bilayer dynamics upon interaction with KCNQ1_100–370. The recombinant human KCNQ1 was expressed in Escherichia coli and purified into n-dodecylphosphocholine (DPC) micelles. The purified KCNQ1_100–370 was biochemically characterized by SDS-PAGE electrophoresis, western blot and nano-LC-MS/MS to confirm the identity of the protein. Circular dichroism (CD) spectroscopy was utilized to confirm the secondary structure of purified protein in vesicles. Furthermore, ³¹P and ²H solid-state NMR spectroscopy in DPPC/POPC/POPG vesicles (MLVs) indicated a direct interaction between KCNQ_100–370 and the phospholipid head groups. Finally, a visual inspection of KCNQ1_100–370 incorporated into MLVs was confirmed by transmission electron microscopy (TEM). The findings of this study provide avenues for future structural studies of the human KCNQ1 ion channel to have an in depth understanding of its structure-function relationship.     

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.     

Contribution of KCNQ1 to the regulatory volume decrease in the human mammary epithelial cell line MCF-7

Using the human mammary epithelial cell line MCF-7, we have investigated volume-activated changes in response to hyposmotic stress. Switching MCF-7 cells from an isosmotic to a hyposmotic solution resulted in an initial cell swelling response, followed by a regulatory volume decrease (RVD). This RVD response was inhibited by the nonselective K⁺ channel inhibitors Ba²⁺, quinine, and tetraethylammonium chloride, implicating K⁺ channel activity in this volume-regulatory mechanism. Additional studies using chromonol 293B and XE991 as inhibitors of the KCNQ1 K⁺ channel, and also a dominant-negative NH₂-terminal truncated KCNQ1 isoform, showed complete abolition of the RVD response, suggesting that KCNQ1 plays an important role in regulation of cell volume in MCF-7 cells. We additionally confirmed that KCNQ1 mRNA and protein is expressed in MCF-7 cells, and that, when these cells are cultured as a polarized monolayer, KCNQ1 is located exclusively at the apical membrane. Whole cell patch-clamp recordings from MCF-7 cells revealed a small 293B-sensitive current under hyposmotic, but not isosmotic conditions, while recordings from mammalian cells heterologously expressing KCNQ1 alone or KCNQ1 with the accessory subunit KCNE3 reveal a volume-sensitive K⁺ current, inhibited by 293B. These data suggest that KCNQ1 may play important physiological roles in the mammary epithelium, regulating cell volume and potentially mediating transepithelial K⁺ secretion. potassium channel; volume regulation; mammary gland     

Biophysical characteristics of a new mutation on the KCNQ1 potassium channel (L251P) causing long QT syndrome

The congenital long QT syndrome (LQTS) is a hereditary cardiac disease characterized by prolonged ventricular repolarization, syncope, and sudden death. Mutations causing LQTS have been identified in various genes that encode for ionic channels or their regulatory subunits. Several of these mutations have been reported on the KCNQ1 gene encoding for a potassium channel or its regulatory subunit (KCNE1). In this study, we report the biophysical characteristics of a new mutation (L251P) in the transmembrane segment 5 (S5) of the KCNQ1 potassium channel. Potassium currents were recorded from CHO cells transfected with either wild type or mutant KCNQ1 in the presence or in the absence of its regulatory subunit (KCNE1), using the whole-cell configuration of the patch clamp technique. Wild-type KCNQ1 current amplitudes are increased particularly by KCNE1 co-expression but no current is observed with the KCNQ1 (L251P) mutant either in the presence or in the absence of KCNE1. Coexpressing KCNE1 with equal amount of cDNAs encoding wild type and mutant KCNQ1 results in an 11-fold reduction in the amplitude of potassium currents. The kinetics of activation and inactivation and the activation curve are minimally affected by this mutation. Our results suggest that the dominant negative effect of the P251L mutation on KCNQ1 channel explains the prolonged repolarization in patients carrying this mutation.     

Molecular cloning and functional expression of KCNQ5, a potassium channel subunit that may contribute to neuronal M-current diversity

We have isolated KCNQ5, a novel human member of the KCNQ potassium channel gene family that is differentially expressed in subregions of the brain and in skeletal muscle. When expressed in Xenopus oocytes, KCNQ5 generated voltage-dependent, slowly activating K(+)-selective currents that displayed a marked inward rectification at positive membrane voltages. KCNQ5 currents were insensitive to the K(+) channel blocker tetraethylammonium but were strongly inhibited by the selective M-current blocker linopirdine. Upon coexpression with the structurally related KCNQ3 channel subunit, current amplitudes increased 4-5-fold. Compared with homomeric KCNQ5 currents, KCNQ3/KCNQ5 currents also displayed slower activation kinetics and less inward rectification, indicating that KCNQ5 combined with KCNQ3 to form functional heteromeric channel proteins. This functional interaction between KCNQ5 and KCNQ3, a component of the M-channel, suggests that KCNQ5 may contribute to a diversity of heteromeric channels underlying native neuronal M-currents.     

The KVLQT1 gene is not a common target for mutations in patients with various heart pathologies

The long QT syndrome (LQTS) is a disorder of ventricular repolarization that exposes affected individuals to cardiac arrhythmias and sudden death. The first gene for LQTS has been mapped to chromosome 11 p.15.5 by genome-wide linkage analysis. This gene, originally named KVLQT1 (and later KCNQ1), is a novel potassium channel gene. Mutations in the human KVLQT1 gene, encoding the alpha-subunit of the KVLQT1 channel, cause the long QT syndrome. In this work, we analysed the sequence of six KVLQT1 exons in patients with various heart pathologies. We describe 6 different mSSCP patterns with no disease-related SSCP conformers in any sample. Direct sequencing of exons 2 to 7 confirmed the absence of mutations. This suggests that the analysed region of the KVLQT1 gene is not commonly involved in pathogenesis of the long QT syndrome.     

Expression profile and characterisation of a truncated KCNQ5 splice variant

Ion channels encoded by KCNQ genes (1-5) are key regulators of membrane properties in many cell types. The KCNQ5 gene was the last to be identified and has three splice variants that are expressed in human brain and skeletal muscle. The KCNQ5 encoded channel possesses M-current properties and so far no channelopathy has been associated with any of the three variants. We now show that only the shortest KCNQ5 variant, which has exon 9 deleted, was expressed in a variety of murine vascular smooth muscle. In Xenopus oocytes, this variant generated currents with amplitudes, activation kinetics and biophysical properties similar to the full-length variant normally expressed in neuronal tissue. Furthermore sensitivity to block by XE991 and activation by retigabine were also similar between both variants. These data represent an exhaustive characterisation of a truncated KCNQ5 splice variant that may contribute to the native XE991-sensitive channel in murine vasculature.     

KCNQ1/KCNE1 assembly,co-translation not required

Voltage-gated potassium channels are often assembled with accessory proteins which increases their functional diversity. KCNE proteins are small accessory proteins that modulate voltage-gated potassium (K_V) channels. Although the functional effects of various KCNE proteins have been described, many questions remain regarding their assembly with the pore-forming subunits. For example, while previous experiments with some K_V channels suggest that the association of the pore-subunit with the accessory subunits occurs co-translationally in the endoplasmic reticulum, it is not known whether KCNQ1 assembly with KCNE1 occurs in a similar manner to generate the medically important cardiac slow delayed rectifier current (IKs). In this study we used a novel approach to demonstrate that purified recombinant human KCNE1 protein (prKCNE1) modulates KCNQ1 channels heterologously expressed in Xenopus oocytes resulting in generation of IKs. Incubation of KCNQ1-expressing oocytes with cycloheximide did not prevent IKs expression following prKCNE1 injection. By contrast, incubation with brefeldin A prevented KCNQ1 modulation by prKCNE1. Moreover, injection of the trafficking-deficient KCNE1-L51H reduced KCNQ1 currents. Together, these observations indicate that while assembly of KCNE1 with KCNQ1 does not require co-translation, functional KCNQ1-prKCNE1 channels assemble early in the secretory pathway and reach the plasma membrane via vesicular trafficking.     

Identification of specific pore residues mediating KCNQ1 inactivation. A novel mechanism for long QT syndrome

KCNQ1 inactivation bears electrophysiological characteristics different from classical N- and C-type inactivation in Shaker-like potassium channels. However, the molecular site of KCNQ1 inactivation has not yet been determined. KCNQ2 channels do not exert a fast inactivation in contrast to KCNQ1 channels. By expressing functional chimeras between KCNQ1 and KCNQ2 in Xenopus oocytes, we mapped the region of this inactivation to transmembrane domain S5 and the pore loop H5 and finally narrowed down the site to positions Gly(272) and Val(307) in KCNQ1. Exchanging these two amino acids individually with the analogous KCNQ2 residue abolished inactivation. Furthermore, a KCNQ1-like inactivation was introduced into KCNQ2 by mutagenesis in the corresponding region, confirming its relevance for the inactivation process. As KCNQ1 inactivation involves the regions S5 and H5, it exhibits a geography distinct from N- or C-type inactivation. Native cardiac I(Ks) channels comprising KCNQ1 and accessory MinK subunits do not inactivate because of the functional interaction of KCNQ1 with MinK. Mutations in KCNQ1 can lead to long QT1 syndrome, an inherited form of arrhythmia. The long QT1 mutant KCNQ1(L273F) displays a pronounced KCNQ1 inactivation. Here we show that when expressing mutant I(Ks) channels formed from KCNQ1(L273F) and MinK, MinK association no longer eliminates KCNQ1 inactivation. This results in smaller repolarizing currents in the heart and therefore represents a novel mechanism leading to long QT syndrome.     

KCNE5 induces time- and voltage-dependent modulation of the KCNQ1 current

The function of the KCNE5 (KCNE1-like) protein has not previously been described. Here we show that KCNE5 induces both a time- and voltage-dependent modulation of the KCNQ1 current. Interaction of the KCNQ1 channel with KCNE5 shifted the voltage activation curve of KCNQ1 by more than 140 mV in the positive direction. The activation threshold of the KCNQ1+KCNE5 complex was +40 mV and the midpoint of activation was +116 mV. The KCNQ1+KCNE5 current activated slowly and deactivated rapidly as compared to the KCNQ1+KCNE1 at 22 degrees C; however, at physiological temperature, the activation time constant of the KCNQ1+KCNE5 current decreased fivefold, thus exceeding the activation rate of the KCNQ1+KCNE1 current. The KCNE5 subunit is specific for the KCNQ1 channel, as none of other members of the KCNQ-family or the human ether a-go-go related channel (hERG1) was affected by KCNE5. Four residues in the transmembrane domain of the KCNE5 protein were found to be important for the control of the voltage-dependent activation of the KCNQ1 current. We speculate that since KCNE5 is expressed in cardiac tissue it may here along with the KCNE1 beta-subunit regulate KCNQ1 channels. It is possible that KCNE5 shapes the I(Ks) current in certain parts of the mammalian heart.     

Regulation and Properties of KCNQ1 (KVLQT1) and Impact of the Cystic Fibrosis Transmembrane Conductance Regulator

The K⁺ channel KCNQ1 (K_VLQT1) is a voltage-gated K⁺ channel, coexpressed with regulatory subunits such as KCNE1 (IsK, mink) or KCNE3, depending on the tissue examined. Here, we investigate regulation and properties of human and rat KCNQ1 and the impact of regulators such as KCNE1 and KCNE3. Because the cystic fibrosis transmembrane conductance regulator (CFTR) has also been suggested to regulate KCNQ1 channels we studied the effects of CFTR on KCNQ1 in Xenopus oocytes. Expression of both human and rat KCNQ1 induced time dependent K⁺ currents that were sensitive to Ba²⁺ and 293B. Coexpression with KCNE1 delayed voltage activation, while coexpression with KCNE3 accelerated current activation. KCNQ1 currents were activated by an increase in intracellular cAMP, independent of coexpression with KCNE1 or KCNE3. cAMP dependent activation was abolished in N-terminal truncated hKCNQ1 but was still detectable after deletion of a single PKA phosphorylation motif. In the presence but not in the absence of KCNE1 or KCNE3, K⁺ currents were activated by the Ca²⁺ ionophore ionomycin. Coexpression of CFTR with either human or rat KCNQ1 had no impact on regulation of KCNQ1 K⁺ currents by cAMP but slightly shifted the concentration response curve for 293B. Thus, KCNQ1 expressed in Xenopus oocytes is regulated by cAMP and Ca²⁺ but is not affected by CFTR. Received: 13 December 2000/Revised: 30 March 2001