KCNE1 Expression Research Articles

Dynamic changes in HCN2, HCN4, KCNE1, and KCNE2 expression in ventricular cells from acute myocardial infarction rat hearts

Aims: To investigate dynamic changes in the expression of HCN2, HCN4, as well as KCNE1, and KCNE2 mRNA and protein levels in ventricular cells from acute myocardial infarction (AMI) rat hearts. Main methods: An AMI model was induced by ligating the left anterior descending coronary artery (LAD) of Sprague–Dawley rats. The rats were randomly divided into four experimental groups: 24-hour (24 h) post-AMI, 1-week (1w) post-AMI, 2-week (2w) post-AMI, and 4-week (4w) post-AMI; sham-operated control rat groups were established in parallel for each time point. HCN2, HCN4, KCNE1, and KCNE2 mRNA and protein levels were measured by reverse transcription-polymerase chain reaction (RT-PCR) and by immunohistochemistry and Western blot, respectively. Key findings: Ventricular arrhythmias occurred in all the post-AMI groups, particularly in the 1w and 2w post-AMI groups. Although HCN2, HCN4, KCNE1, and KCNE2 genes were expressed in the left ventricular myocardium of sham-operated control rats, their expression increased in rat ischemic left ventricular myocardium, with dynamic changes in expression observed 4 weeks after AMI. HCN2, HCN4, and KCNE2 protein levels were highest at 1w and KCNE2 protein levels peaked at 2w post-AMI. Significance: The expression of the HCN2, HCN4, as well as KCNE1, and KCNE2 genes in ventricular cells from AMI rat hearts underwent dynamic changes, reaching peak levels at 1 or 2 weeks post-AMI. The increased expression maybe related to ventricular arrhythmogenesis after AMI.

Thyroid hormone receptor α can control action potential duration in mouse ventricular myocytes through the KCNE1 ion channel subunit

The reduced heart rate and prolonged QT(end) duration in mice deficient in thyroid hormone receptor (TR) alpha1 may involve aberrant expression of the K(+) channel alpha-subunit KCNQ1 and its regulatory beta-subunit KCNE1. Here we focus on KCNE1 and study whether increased KCNE1 expression can explain changes in cardiac function observed in TRalpha1-deficient mice. TR-deficient, KCNE1-overexpressing and their respective wildtype (wt) mice were used. mRNA and protein expression were assessed with Northern and Western blot respectively. Telemetry was used to record electrocardiogram and temperature in freely moving mice. Patch-clamp was used to measure action potentials (APs) in isolated cardiomyocytes and ion currents in Chinese hamster ovary (CHO) cells. KCNE1 was four to 10-fold overexpressed in mice deficient in TRalpha1. Overexpression of KCNE1 with a heart-specific promoter in transgenic mice resulted in a cardiac phenotype similar to that in TRalpha1-deficient mice, including a lower heart rate and prolonged QT(end) time. Cardiomyocytes from KCNE1-overexpressing mice displayed increased AP duration. CHO cells transfected with expression plasmids for KCNQ1 and KCNE1 showed an outward rectifying current that was maximal at equimolar plasmids for KCNQ1-KCNE1 and decreased at higher KCNE1 levels. The bradycardia and prolonged QT(end) time in hypothyroid states can be explained by altered K(+) channel function due to decreased TRalpha1-dependent repression of KCNE1 expression.

Stoichiometry of KCNQ1-KCNE1 Ion Channel Complex is Flexible and Density-Dependent

Many membrane proteins including ion channels form multi-molecular complexes. Because the composition of a molecular complex may define its functional properties, it is important to know its stoichiometry. KCNQ1 encodes a voltage-gated potassium channel alpha subunit, and four KCNQ1 subunits form one ion channel. KCNQ1 channel forms a molecular complex with auxiliary subunit KCNE proteins. In the heart the KCNQ1-KCNE1 complex underlies slowly-activating IKs current, which plays a significant role in regulation of the cardiac action potential. Assuming a fixed KCNQ1-KCNE1 stoichiometry macroscopic current measurements led earlier investigators to the conclusion that each 4-subunit channel is associated with two KCNE1 subunits (4:2 subunit stoichiometry). We asked whether the KCNQ1-KCNE1 stoichiometry is indeed fixed by counting subunits in many individual complexes using TIRF microscopy (Ulbrich and Isacoff, 2007, 2008). We expressed GFP-tagged KCNQ1 or KCNE1 in Xenopus oocytes at low density and counted bleaching steps in many fluorescent spots corresponding to single channel complexes. First, we confirmed that KCNQ1 forms a tetramer. Next we counted GFP-tagged KCNE1 subunits co-expressed with mCherry-tagged KCNQ1. We observed up to four bleaching steps from GFP-KCNE1 co-localized with mCherry, indicating that up to four KCNE1 subunits can bind to one KCNQ1 tetrameric channel. We find that the number of KCNE1 subunits per complex increases as the expression of KCNE1 is raised relative to that of KCNQ1. Our results suggest that modulation of KCNQ channels may be regulated by the level of expression of KCNE subunits.

Kcne2 Expression is Regulated both by Estrogen and Cardiac Stress in the Adult Male Mouse Heart

KCNE2 is a single transmembrane modulatory β subunit that can modulate a variety of K+ channel pore-forming α subunits in heterologous systems; recently we have shown KCNE2 to be an estrogen-responsive gene. KCNE2 is linked to LQTs and fatal arrhythmia. Pathological heart hypertrophy is associated with abnormal electrical activity leading to a considerable propensity to arrhythmias. We hypothesized KCNE2 expression might be modulated by pathological heart hypertrophy and by estrogen. The trans-aortic constriction (TAC) procedure was used to induce pressure overload and eventually heart failure (TAC-HF) in male mice. Once the ejection fraction reached ∼30%, the mice were treated with estrogen for 10 days. Real-time PCR showed that transcript levels of KCNE2 were similar between TAC-HF and control (CTRL), while strikingly upregulated ∼3 fold by estrogen treatment. To gain insight into the KCNE2 cell biology in heart failure and after treatment with estrogen, isolated cardiomyocytes were labeled with anti-KCNE2 antibody. In healthy hearts, KCNE2 was distributed both at the surface membrane as well as in the T-tubules, while in failing hearts KCNE2 completely disappeared from the T-tubules but its surface plasma membrane labeling increased. The disappearance of KCNE2 from the T-tubules in TAC-HF was not due to the disruption of their structure, since their integrity was maintained as evident by a similar α-actinin labeling in control and TAC-HF. E2 treatment of TAC-HF significantly increased overall KCNE2 labeling; KCNE2 was distributed both at the surface membrane as well as in the T-tubules. We speculate higher KCNE2 transcript levels, as well as reappearance of KCNE2 in the T-tubules by estrogen treatment of TAC-HF, would increase the association of KCNE2 with Kv4.3 and/or Kv4.2, therefore potentiating Ito,f currents thus resulting in a better cardiac repolarization.

The stoichiometric relationship between KCNH-2 and KCNE-2 in IKr channel formation

KCNH-2 and KCNE-2 may encode the channel-forming alpha- and regulatory beta-subunits, respectively, of I(Kr) channels, which are involved in inherited or acquired long QT syndrome. However, in contrast to other multimeric channels, the stoichiometry of KCNH-2 and KCNE-2, which should be reasonably maintained if they are to be accepted as the components of a multi-molecular complex, has not been established, yet. In this study, we found that the protein expression of KCNE-2 was adequate to support the formation of a complex with KCNH-2; however, the level of transcription was not. This finding, together with previous data from electrophysiological and molecular biological studies, supports that KCNH-2 and KCNE-2 are molecular components of I(Kr) channels.

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

Cardiac slow delayed rectifier (IKs) channel is composed of KCNQ1 (pore-forming) and KCNE1 (auxiliary) subunits. Although KCNE1 is an obligate IKs 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 IKs 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 IKs 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 IKs 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 IKs current density. We propose that in cardiac myocytes the IKs current amplitude is under dynamic control by the availability of KCNE2 subunits in the cell membrane.

Cardiac Kv4.3 and KCNE2 Are Differentially Regulated by E2 and Have Different Sensitivities to Local Heart E2 Concentrations

Recently we reported that the KCNE2 gene is an estrogen-responsive gene and its transcripts are upregulated 6 fold by estrogen (E2) in ovariectomized (ovx) mice1. We have also shown that cardiac Kv4.3 transcripts were downregulated ∼2 fold by E22. As the effect of E2 treatment was more powerful on KCNE2 upregulation than Kv4.3 downregulation, we hypothesized that cardiac Kv4.3 and KCNE2 have different sensitivities to heart E2 concentrations [E2]. We measured heart [E2] together with KCNE2 and Kv4.3 transcript levels in 4 estrogenic conditions: i) E2-depleted (anastrozole treated mice, [E2]=4.2±0.4 pg/ml n=4; ii) low E2 (ovx sham, [E2]=16±1.4 pg/ml n=3 and diestrus [E2]=20.2±1.5 n=4), iii) intermediate E2 (male [E2]=35±3 pg/ml, n=6) and iv) high E2 (ovx mice treated with E2, [E2]=62.7±2.9 pg/ml, n=3). Kv4.3 transcript levels were not affected by heart [E2] lower than 35 pg/ml whereas KCNE2 transcript levels were very sensitive to this range of heart [E2], reaching a ∼10 fold increase from low to intermediate heart [E2], saturating at 35 pg/ml. The fact that Kv4.3 levels were unaffected by anastrozole treatment, whereas KCNE2 levels were dramatically reduced by ∼8 fold by anastrozole, further supports the finding that KCNE2 upregulation can take place at very low E2 levels. The downregulation of Kv4.3 transcripts were only evident at high estrogenic conditions, whereas KCNE2 remains at its maximum. As Kv4.3 is one of the molecular correlate of Ito,f and it has also been shown that KCNE2 can potentiate Kv4.3 currents in the expression system, we speculate that the relative expression of KCNE2 and Kv4.3 as defined by heart [E2] will determine Ito,f amplitude.1. Kundu et al., Mol Cell Endocrinol 2008;292:50-62.2. Eghbali et al., Circ Res 2005;96:1208-16.

Hormonal regulation of cardiac KCNE2 gene expression.

The KCNE2 gene encodes a single transmembrane domain protein that modulates a variety of K+ channel functions in various tissues. Here we show that cardiac KCNE2 transcript levels are approximately 10-fold upregulated at the end of pregnancy. This upregulation was mimicked by 17-beta estradiol but not by 5alpha-dihydrotestosterone treatments in ovariectomized mice. To investigate the mechanism of KCNE2 transcriptional regulation by estrogen, we experimentally identified KCNE2 transcription start sites, delineated its gene structure and characterized its promoter region. Estrogen treatment stimulated KCNE2 promoter activity in a dose-dependent manner and ICI 182,780 blocked estrogen stimulation. A direct genomic mechanism was demonstrated by (i) the loss of estrogen responsiveness in the presence of a DNA-binding domain mutant estrogen receptor alpha or mutant KCNE2 ERE and (ii) binding of ERalpha to the KCNE2 ERE. These findings show that a genomic mechanism of estrogen action alters KCNE2 expression, which may have important physiological implications.

KCNE2 is colocalized with KCNQ1 and KCNE1 in cardiac myocytes and may function as a negative modulator of I Ks current amplitude in the heart

In heterologous expression systems, KCNE1 and KCNE2 each can associate with KCNQ1 and exert apparently opposite effects on its channel function. KCNQ1 and KCNE1 associate to form the slow delayed rectifier I(Ks) channels in the heart. Whether KCNE2 plays any role in I(Ks) function is not clear. The purpose of this study was to study whether KCNE2 can associate with KCNQ1 in the presence of KCNE1 and modulate its function. Voltage clamp methods were used to study channel function in cardiomyocytes and in oocytes or COS-7 cells and immunocytochemistry/coimmunoprecipitation was used to study protein colocalization/association. Adult rat ventricular myocytes express functional I(Ks), and KCNE2 is colocalized with KCNQ1 and KCNE1 at surface membrane and t-tubules. A detailed study of KCNQ1 modulation by KCNE2 at different KCNE2 expression levels reveals that, surprisingly, KCNE2 and KCNE1 share the major features in modulating KCNQ1 gating kinetics: slowing of activation, positive shift in the voltage range of activation, and suppression of inactivation. However, KCNE2 reduces KCNQ1 current amplitude whereas KCNE1 increases it, and KCNE2 induces a constitutively active KCNQ1 component whereas KCNE1 does not. Coimmunoprecipitation suggests that KCNQ1, KCNE1, and KCNE2 can form a tripartite complex, indicating that KCNE2 can bind to KCNQ1 in the presence of KCNE1. Coexpressing KCNE2 with KCNQ1 and KCNE1 leads to a decrease in the I(Ks) current amplitude without altering the gating kinetics. Our data suggest that KCNE2 is in close proximity to KCNQ1 and KCNE1 in cardiomyocytes and may participate in dynamic regulation of I(Ks) current amplitude in the heart.

KCNE2, a down-regulated gene identified by in silico analysis, suppressed proliferation of gastric cancer cells

It is important to identify the differentially expressed gene in gastric cancer for elucidating the molecular mechanisms of tumorigenesis of stomach. Here, 38 genes differentially expressed genes between gastric cancer and normal gastric mucosa by in silico approaches. A potassium channel protein KCNE2, identified as a down-regulated gene in gastric cancer, was chosen for further study. We investigated the expression of KCNE2 in gastric cancer tissues and cell lines and examined the effect of KCNE2 on proliferation of gastric cancer. The expression of KCNE2 was markedly down-regulated in gastric cancer tissues and cell lines. Forced overexpression of KCNE2 suppressed the growth of SGC7901 cells and cell cycle progression significantly, which might be related to the down-regulation of Cyclin D1. KCNE2 also inhibited SGC7901 cell growth in soft agar and its tumorigenicity in nude mice. Taken together, our work showed that in silico analysis approaches could be used to identify cancer-related genes effectively. KCNE2, as a novel down-regulated gene in gastric cancer, suppressed cell proliferation and tumorigenesis of stomach.

Expression of multiple KCNE genes in human heart may enable variable modulation of IKs

Voltage-gated potassium (K V) channels are modulated by at least three distinct classes of proteins including the KCNE family of single transmembrane accessory subunits. In the human genome, KCNE proteins are encoded by five genes designated KCNE1 through KCNE5. KCNE1 associates with KCNQ1 in vitro to generate a potassium current closely resembling the slowly activating delayed rectifier ( I Ks). Other KCNE proteins also affect the activity of heterologously expressed KCNQ1. To investigate the potential physiological relevance of this gene family in human heart, we examined the relative expression of KCNQ1 and all five KCNE genes in samples derived from normal tissues representing major regions of human heart by real-time, quantitative RT-PCR. KCNE genes are expressed in human heart with a relative abundance ranking of KCNE1 > KCNE4 > KCNE5 ~ KCNE3 >> KCNE2. In situ hybridization revealed prominent expression of KCNE1 and KCNE3–5 in human atrial myocytes. In cardiomyopathic hearts, expression of KCNE1, KCNE3, KCNE4, and KCNQ1 was significantly increased, while KCNE2 and KCNE5 exhibited reduced expression. In a cell line stably expressing KCNQ1 and KCNE1, transient expression of KCNE3, KCNE4, or KCNE5 significantly altered I Ks current profiles. Even in the presence of additional KCNE1, KCNE4 and KCNE5 exert dominant effects on I Ks. Although KCNE1 is the predominant KCNE family member expressed in human heart, the abundance of other KCNE transcripts including potential KCNQ1 suppressors (KCNE4 and KCNE5) and their altered expression patterns in disease lead us to speculate that a balance of KCNE accessory subunits may be important for cardiac K V channel function.

Analysis of QT Interval Prolongation With Heart Failure by Simulation of Repolarization Process.

It has been postulated that action potential duration (APD) is prolonged and I<inf>Ks</inf>, a slow component of delayed rectifier potassium current, decreases in heart failure. We have reported that QT interval is prolonged and expression weight of KCNE1, coding I<inf>Ks</inf>channel, increases in patients with heart failure. Since it is known that increase in KCNE1 increases the maximum conductance of I<inf>Ks</inf>channel, the mechanism of APD prolongation is not explained by over expression of KCNE1. In this study, we construct a cardiac membrane action potential simulation model based on the experimental data from Xenopus oocytes expressed KCNQ1 and KCNE1 to investigate the relationship between increase in KCNE1 and APD. In addition, we investigated effect of reduction in Ca2+-independent transient outward potassium current (I<inf>to</inf>) on APD in heart failure. In simulation, APD at 5ng KCNE1 was 180.96ms, which was 4.63% longer than that at 1ng KCNE1 (APD=172.96ms) and 55.9% longer than that at 0.2ng KCNE1 (APD=110.96ms. In the cases of KCNQ1 alone and 0.2ng KCNE1 coinjected, APD shortened as density of I<inf>to</inf>decreased, and APD prolonged as density of I<inf>to</inf>decreased in other cases. This study shows that increase in KCNE1 expression level makes maximum conductance of I<inf>Ks</inf>channel increase and I<inf>Ks</inf>channel open slowly and conductance of I<inf>Ks</inf>channel decrease according to the APD time scale. Therefore increasing the KCNE1 expression level may prolong APD with this mechanism. This method of constructing a simulation model based on experiments helps to explain the relationship between potassium currents and QT interval prolongation.

Volume regulation is defective in renal proximal tubule cells isolated from KCNE1 knockout mice.

The membrane protein KCNE1 has been implicated in cell volume regulation. Using a knockout mouse model, this study examined the role of KCNE1 in regulatory volume decrease (RVD) in freshly isolated renal proximal tubule cells. Cell diameter was measured using an optical technique in response to hypotonic shock and stimulation of Na(+)-alanine cotransport in cells isolated from wild-type and KCNE1 knockout mice. In HEPES buffered solutions 64% of wild-type and 56% of knockout cells demonstrated RVD. In HCO3- buffered solutions 100% of the wild-type cells showed RVD, while in the knockout cells the proportion of cells displaying RVD remained unchanged. RVD in the knockout cells was rescued by valinomycin, a K+ ionophore. In wild-type HCO3- dependent cells the K+ channel inhibitors barium and clofilium inhibited RVD. These data suggest that mouse renal proximal tubule is comprised of two cell populations. One cell population is capable of RVD in the absence of HCO3-, whereas RVD in the other cell population has an absolute requirement for HCO3-. The HCO3- dependent RVD requires the normal expression of KCNE1.

Canine ventricular KCNE2 expression resides predominantly in Purkinje fibers.

Mutations in minK-related peptide 1 (MiRP1), the product of the KCNE2 gene, have been associated with malignant ventricular arrhythmia syndromes related to impaired repolarization. MiRP1 interacts with a variety of ion-channel alpha-subunits, dysfunction of which could account for arrhythmia syndromes; however, the observation of very low-level expression of MiRP1 in ventricular tissue has led to doubts about its relevance. The specialized His-Purkinje system plays a key role in cardiac electrophysiology and is an important contributor to ventricular arrhythmias related to abnormal repolarization. We examined the relative abundance of MiRP1 in canine Purkinje versus ventricular tissue and found much greater expression at both mRNA and protein levels in Purkinje tissue. Thus, the cardiac Purkinje system is a strong candidate to play a role in arrhythmic syndromes due to MiRP1 abnormalities.

Coordinated down-regulation of KCNQ1 and KCNE1 expression contributes to reduction of IKs in canine hypertrophied hearts

In animal models of hypertrophy, electrical remodeling giving rise to QT prolongation occurs rapidly and is associated with the development of torsade de pointes (TdP) arrhythmias and sudden death. Chronic AV block (CAVB)-induced hypertrophy in dogs has been associated with a reduction in the slow component (I(Ks)) of the delayed rectifier potassium current (I(K)), which contributes to a prolongation of ventricular repolarization, the development of an acquired form of long QT, and the substrate for triggered activity and TdP. The present study was designed to probe the molecular basis for the decrease in I(Ks) by studying the characteristics of KCNE1 and KCNQ1, the putative genes responsible for formation of the channel. Using a combination of Northern blot, competitive multiplex PCR and immunoblot assays, we found that CAVB reduces KCNE1 and KCNQ1 RNA in the canine ventricles by 70 and 80%, respectively. Protein levels of KCNE1 and KCNQ1 were reduced by 60 and 50%, respectively. We also demonstrate at the molecular level the basis for inter-ventricular difference in I(Ks) density previously reported in hearts of normal dogs and show the basis for reduction of this difference in the CAVB dog. Our results indicate that the CAVB-induced reduction in I(Ks) is due to a down-regulation of KCNE1 and KCNQ1 transcription. The data suggest that electrical remodeling of the cardiac ventricle during hypertrophy involves regulation of the gene expression through modulation of transcriptional and translational regulatory pathways. The reduction in KCNE1 and KCNQ1 expression increases the dependence of ventricular repolarization on the rapid component of I(K) and may potentiate the action of Class III antiarrhythmic agents.

Microarray analysis reveals complex remodeling of cardiac ion channel expression with altered thyroid status: relation to cellular and integrated electrophysiology.

Although electrophysiological remodeling occurs in various myocardial diseases, the underlying molecular mechanisms are poorly understood. cDNA microarrays containing probes for a large population of mouse genes encoding ion channel subunits ("IonChips") were developed and exploited to investigate remodeling of ion channel transcripts associated with altered thyroid status in adult mouse ventricle. Functional consequences of hypo- and hyperthyroidism were evaluated with patch-clamp and ECG recordings. Hypothyroidism decreased heart rate and prolonged QTc duration. Opposite changes were observed in hyperthyroidism. Microarray analysis revealed that hypothyroidism induces significant reductions in KCNA5, KCNB1, KCND2, and KCNK2 transcripts, whereas KCNQ1 and KCNE1 expression is increased. In hyperthyroidism, in contrast, KCNA5 and KCNB1 expression is increased and KCNQ1 and KCNE1 expression is decreased. Real-time RT-PCR validated these results. Consistent with microarray analysis, Western blot experiments confirmed those modifications at the protein level. Patch-clamp recordings revealed significant reductions in I(to,f) and I(K,slow) densities, and increased I(Ks) density in hypothyroid myocytes. In addition to effects on K+ channel transcripts, transcripts for the pacemaker channel HCN2 were decreased and those encoding the alpha1C Ca2+ channel (CaCNA1C) were increased in hypothyroid animals. The expression of Na+, Cl-, and inwardly rectifying K+ channel subunits, in contrast, were unaffected by thyroid hormone status. Taken together, these data demonstrate that thyroid hormone levels selectively and differentially regulate transcript expression for at least nine ion channel alpha- and beta-subunits. Our results also document the potential of cDNA microarray analysis for the simultaneous examination of ion channel transcript expression levels in the diseased/remodeled myocardium.

Divergent expression of delayed rectifier K(+) channel subunits during mouse heart development.

The repolarization phase of the cardiac action potential is dependent on transmembrane K(+) currents. The slow (I(Ks)) and fast (I(Kr)) components of the delayed-rectifier cardiac K(+) current are generated by pore-forming alpha subunits KCNQ1 and KCNH2, respectively, in association with regulatory beta-subunit KCNE1, KCNE2 and perphaps KCNE3. In the present study we have investigated the distribution of transcripts encoding these five potassium channel-forming subunits during mouse heart development as well as the protein distribution of KCNQ1 and KCNH2. KCNQ1 and KCNH2 mRNAs (and protein) are first expressed at embryonic day (E) 9.5, showing comparable levels of expression within the atrial and ventricular myocardium during the embryonic and fetal stages. In contrast, the beta-subunits display a more dynamic pattern of expression during development. KCNE1 expression is first observed at E9.5 throughout the entire myocardium and progressively is confined to the ventricular myocardium. With further development (E16.5), KCNE1 expression is mainly confined to the compact ventricular myocardium. KCNE2 is first expressed at E9.5 and it is restricted already to the atrial myocardium. KCNE3 is first expressed at E8.5 throughout the myocardium and with further development, it becomes restricted to the atrial myocardium. The fact that alpha subunits are homogeneously distributed within the myocardium, whereas the beta subunits display a regionalized expression profile during cardiac development, suggest that differences in the slow and fast component of the delayed-rectifier cardiac K(+) currents between the atrial and the ventricular cardiomyocytes are mainly determined by differential beta-subunit distribution.

M-type KCNQ2–KCNQ3 potassium channels are modulated by the KCNE2 subunit

KCNQ2 and KCNQ3 subunits belong to the six transmembrane domain K + channel family and loss of function mutations are associated with benign familial neonatal convulsions. KCNE2 (MirP1) is a single transmembrane domain subunit first described to be a modulator of the HERG potassium channel in the heart. Here, we show that KCNE2 is present in brain, in areas which also express KCNQ2 and KCNQ3 channels. We demonstrate that KCNE2 associates with KCNQ2 and/or KCNQ3 subunits. In transiently transfected COS cells, KCNE2 expression produces an acceleration of deactivation kinetics of KCNQ2 and of the KCNQ2–KCNQ3 complex. Effects of two previously identified arrhythmogenic mutations of KCNE2 have also been analyzed.