Ultrasensitive detection of hERG potassium channel in single-cell with photocleavable and entropy-driven reactions by using an electrochemical biosensor.

Ion channel is a pore-forming membrane protein that allows ions to pass through the cell membrane, which is essential for the continuation of life. Analysis of ion channel characteristics at the single cell level will help to study the role of cellular heterogeneity in disease progression and cellular signaling processes. In this study, we fabricate a photocleavable and entropy-driven reaction based electrochemical biosensor for ultrasensitive detection of human ether-a-go-go related gene (hERG) potassium channel activity on HEK293 cell. We employed an antibody-DNA1 to conjugate the hERG channel in the cell membrane via antibody-antigen reaction. The release of the DNA1 by photocleavable reaction will trigger an amplification reaction by using the Exonuclease III (Exo III) to generate intermediate DNA. In addition, two hairpin DNA (DNA3 and DNA4) was employed for the signal amplification. We well designed a toehold on DNA3 for intermediate DNA hybridization to form double-strand DNA that opens the DNA3 hairpin. The free DNA3 exposed the relocked toehold domain to open the DNA4. After the entropy-driven toehold-mediated displacement amplification reaction by using intermediate DNA, DNA4 hybridized with DNA3 effectively, making the ferrocene labeled on the 5'-termini DNA4 close to the Au electrode surface to produce the electrochemical response. Then, the displaced intermediate DNA was released from the cell surface into solution for the next entropy-driven reaction. After two steps amplification reaction, one ion channel triggered thousands of DNA3/DNA4 duplex on the biosensor surface. By using this biosensor, electrochemical curve of hERG ion channels on a single cell was obtained.

In Situ Visualization of hERG Potassium Channel via Dual Signal Amplification.

Dysfunction of the human ether-a-go-go related gene (hERG)-encoded potassium channel is identified as a major cause of the long QT syndrome, a marker for lethal cardiac arrhythmia. Furthermore, recent studies revealed that hERG K+ channel is a regulator of tumor cell apoptosis and proliferation. Herein, an ultrasensitive fluorescence assay combining DNA-functionalized gold nanoparticles and rolling circle amplification (RCA) was attempted for the first time to visualize hERG channels in living cells. The spherical nucleic acid gold nanoparticles, which can anchor on hERG channels in the cell membrane, not only act as the primary amplification elements but also trigger the subsequent RCA reaction to achieve the secondary amplification. Within 30 min, the ratio of reporter to target can reach up to 104, realizing the detection of hERG channels in cells with low-level expression. Therefore, the strategy provides a valuable tool for hERG-related studies. More importantly, it opens a new horizon for imaging various membrane proteins which possess specific aptamers or antibodies.

The poor prognosis of the primary gastric epithelioid angiosarcoma: A case report.

RATIONALE: Primary gastric epithelioid angiosarcoma is a highly aggressive endothelial cell malignancy and may pose a great diagnostic challenge. PATIENT CONCERNS: Here we describe the case of a 56-year-old man presented with melena and epigastric dull pain for 2 weeks. DIAGNOSIS: Primary gastric epithelioid angiosarcomas: the definitive diagnosis was provided by immunohistochemical analysis with endothelial markers such as cluster of differentiation 31 (CD31), ether-a-go-go-related gene (ERG), and Freund leukemia integration (FLI-1). INTERVENTIONS: After gastroscopic biopsy was performed at the bleeding fundus and the results suggested malignant tumor, radical gastrectomy was performed. OUTCOMES: Unfortunately, regional lymph node enlargement and distant metastases occurred about 1 month later. The patient did not have the opportunity to undergo chemotherapy or other treatment and died from multiple organ dysfunction syndrome. LESSONS: Primary gastric epithelioid angiosarcomas are rare tumors with a high rate of lymph nodes and peripheral organs metastasis. The strong cytokeratin expression in epithelioid angiosarcomas represents a diagnostic pitfall for pathologists. Their clinical behaviors are unpredictable and results with surgical excision alone have been disappointing. Thus, the prognosis is generally considered poor and patients seldom can survive over 1 year after diagnosis.

Environment-Sensitive Fluorescent Probe for the Human Ether-a-go-go-Related Gene Potassium Channel.

A novel environment-sensitive probe S2 with turn-on switch for Human Ether-a-go-go-Related Gene (hERG) potassium channel was developed herein. After careful evaluation, this fluorescent probe showed high binding affinity with hERG potassium channel with an IC50 value of 41.65 nM and can be well applied to hERG channel imaging or cellular distribution study for hERG channel blockers. Compared with other imaging techniques, such as immunofluorescence and fluorescent protein-based approaches, this method is convenient and affordable, especially since a washing procedure is not needed. Meanwhile, this environment-sensitive turn-on design strategy may provide a good example for the probe development for these targets that have no reactive or catalytic activity.

Role for myosin-V motor proteins in the selective delivery of Kv channel isoforms to the membrane surface of cardiac myocytes.

RATIONALE: Kv1.5 (KCNA5) mediates the ultra-rapid delayed rectifier current that controls atrial action potential duration. Given its atrial-specific expression and alterations in human atrial fibrillation, Kv1.5 has emerged as a promising target for the treatment of atrial fibrillation. A necessary step in the development of novel agents that selectively modulate trafficking pathways is the identification of the cellular machinery controlling Kv1.5 surface density, of which little is yet known. OBJECTIVE: To investigate the role of the unconventional myosin-V (MYO5A and MYO5B) motors in determining the cell surface density of Kv1.5. METHODS AND RESULTS: Western blot analysis showed MYO5A and MYO5B expression in the heart, whereas disruption of endogenous motors selectively reduced IKur current in adult rat cardiomyocytes. Dominant negative constructs and short hairpin RNA silencing demonstrated a role for MYO5A and MYO5B in the surface trafficking of Kv1.5 and connexin-43 but not potassium voltage-gated channel, subfamily H (eag-related), member 2 (KCNH2). Live-cell imaging of Kv1.5-GFP and retrospective labeling of phalloidin demonstrated motility of Kv1.5 vesicles on actin tracts. MYO5A participated in anterograde trafficking, whereas MYO5B regulated postendocytic recycling. Overexpression of mutant motors revealed a selective role for Rab11 in coupling MYO5B to Kv1.5 recycling. CONCLUSIONS: MYO5A and MYO5B control functionally distinct steps in the surface trafficking of Kv1.5. These isoform-specific trafficking pathways determine Kv1.5-encoded IKur in myocytes to regulate repolarizing current and, consequently, cardiac excitability. Therapeutic strategies that manipulate Kv1.5 selective trafficking pathways may prove useful in the treatment of arrhythmias.

Generation of an antibody toolbox to characterize hERG.

The human ether-a-go-go related gene (hERG) potassium channel plays a major role in the repolarization of the cardiac action potential. Inhibition of the hERG function by mutations or a wide variety of pharmaceutical compounds cause long QT syndrome and lead to potentially lethal arrhythmias. For detailed insights into the structural and biochemical background of hERG function and drug binding, the purification of recombinant protein is essential. Because the hERG channel is a challenging protein to purify, fast and easy techniques to evaluate different expression, solubilization and purification conditions are of primary importance. Here, we describe the generation of a set of 12 monoclonal antibodies against hERG. Beside their suitability in western blot, immunoprecipitation and immunostaining, these antibodies were used to establish a sandwich ELISA for the detection and relative quantification of hERG in different expression systems. Furthermore, a Fab fragment was used in fluorescence size exclusion chromatography to determine the oligomeric state of hERG after solubilization. These new tools can be used for a fast and efficient screening of expression, solubilization and purification conditions.

Eag1 channels as potential cancer biomarkers.

Cancer is a leading cause of death worldwide. New early tumor markers are needed to treat the disease at curable stages. In addition, new therapeutic targets are required to treat patients not responding to available treatments. Ion channels play major roles in health and disease, including cancer. Actually, several ion channels have been suggested as potential tumor markers and therapeutic targets for different types of malignancies. One of most studied ion channels in cancer is the voltage-gated potassium channel Eag1 (ether à go-go 1), which has a high potential to be used as a cancer biomarker. Eag1 is expressed in most human tumors, in contrast to its restricted distribution in healthy tissues. Several findings suggest Eag1 as a potential early marker for cervical, colon, and breast cancer. In addition, because Eag1 amplification/expression is associated with poor survival in leukemia, colon and ovarian cancer patients, it has also been proposed as a prognosis marker. Moreover, inhibition of either expression or activity of Eag1 leads to reduced proliferation of cancer cells, making Eag1 a potential anticancer target. Using Eag1 in cancer detection programs could help to reduce mortality from this disease.

A generic bioanalytical method development strategy and fit-for-purpose qualification to support hERG in vitro sample analysis.

BACKGROUND: The amount of method development and assay validation required to support analysis of solutions from in vitro systems is a consideration of analytical laboratories performing this type of analysis. As there is little information from regulatory bodies as to how much assay development and validation is required, analytical laboratories need to decide on the best approach for this type of work. In this paper, we describe an efficient 'fit-for-purpose' approach that has been developed to support buffer sample analysis from Safety Pharmacology hERG studies. RESULTS: Method development has been minimized with the aid of compound modeling software and generic HPLC-MS/MS analytical systems. The assay is evaluated prior to sample analysis using simple qualification procedures to support 'one-off' analyses. CONCLUSION: The result is an efficient process that allows speedy and confident analysis of in vitro samples to successfully support regulatory hERG in vitro studies without the additional workload of a full validation procedure.

Abundant expression of KCNE1 in the left ventricle of the miniature pig.

Delayed rectifier potassium currents such as I (Kr) and I (Ks) play an important role in the repolarization phase of the action potential in cardiac myocytes. Electrophysiological studies have shown that the pig is a useful animal not only for clinical use as a good candidate for humans, but also for basic research in heart function or arrhythmia. However, no studies concerning the potassium channels on a molecular level have been done. To elucidate the expression level and distribution of delayed rectifier potassium channels in pigs, we quantitatively investigated the I (Kr) and I (Ks) channel subunits using the real-time polymerase chain reaction (PCR) method. The hearts from Clawn miniature pigs were separated into the apical and basal regions, and subsequently excised into transmural trisections within each of the left ventricular walls, epicardium, midcardium, and endocardium. After RNA extraction from these sites, real-time PCR was executed with reverse transcriptional products for quantitative analysis. The expression level of KCNE1 was significantly higher than those of KCNQ1, KCNH2, and KCNE2, which were comparable in all sites. Transmural heterogeneity of these potassium channel subunits was not detected on the mRNA level. These results indicate that KCNE1 is a dominant subunit on the post-transcriptional level in the miniature pig.

Drug-induced hERG block and long QT syndrome.

Drug-induced long QT syndrome is a cardiac safety issue that all drugs seeking approval must currently address, in part via in vitro electrophysiological testing of the drug's effects on the function of the human Ether-à-go-go Related Gene (hERG) potassium channel. This regulatory strategy has also been scientifically successful, in that these in vitro assays are cheaper and faster than are many other surrogates for arrhythmogenic risk, including QT prolongation in humans and action potential prolongation in cardiomyocytes. In some ways hERG assays are also more sensitive to the underlying repolarization anomalies that lead to the risk of the Torsades de pointes arrhythmia. In addition, the higher throughput of hERG assays combined with advances in our understanding of the molecular structures underlying this pathophysiology have led to new approaches in the medicinal chemistry of "designing out" hERG liability from lead compounds. While generally effectual, hERG screening produces some false positives: drugs with an apparent liability that are known not to be clinically arrhythmogenic. New technologies continue to be developed to improve hERG screening, while further insights into the molecular pharmacology of hERG and cardiac repolarization are providing avenues to mitigate and make sense of the lack of torsadogenic specificity in extant hERG assays.

HERG1 gene expression as a specific tumor marker in colorectal tissues.

INTRODUCTION: Colorectal carcinomas exhibit a frequent recurrence after curative surgery, which may partially be due to histopathologically inconspicuous minimal residual disease. Reliable markers for tumor cells in colorectal tissue are still missing. Therefore, in this study we compared the predictive value of the putative tumor markers carcinoembryonic antigen (CEA), cytokeratin-19 (CK19) and cytokeratin-20 (CK20) to that of a novel marker, the human ether-a-go-go-related gene (HERG1) K(+) channel, a suggested regulator of tumor cell proliferation. MATERIALS AND METHODS: Using RT-PCR we studied HERG, CEA, CK19 and CK20 expression in colorectal carcinomas and non-carcinoma controls. HERG1 immunhistochemistry was performed in a total of 66 specimens, in colorectal carcinoma (n = 23), in matched histopathologically negative samples (n = 23) taken near the excision site from the same tumor patients and in healthy control biopsies (n = 20). In order to verify the relevance of HERG1 for tumor proliferation we studied the effect of HERG1 inhibition in the Colo-205 colon cancer carcinoma cell line using the MTT-assay. RESULTS: HERG1 was expressed in all tumor samples regardless of their stage and in adenomas larger than 0.4 cm, but absent in small adenomas, sigmadiverticulitis specimen and healthy histopathologically negative samples, except for one which developed a tumor recurrence. In contrast, CEA, CK19 and CK20 were absent in some tumors. The selective HERG1 inhibitor E-4031 dose-dependently impaired tumor growth in the proliferation assays. DISCUSSION: Our data indicate that HERG1, but not CEA, CK19 or CK20, is a highly sensitive and reliable tumor biomarker that may constitute a novel molecular target for tumor treatment.

Test article concentrations in the hERG assay: losses through the perfusion, solubility and stability.

INTRODUCTION: Drug-induced prolongation of the electrocardiographic QT interval (long QT syndrome) has been associated with increased risk of a serious ventricular arrhythmia, torsade de pointes. Inhibition of hERG, a cardiac potassium channel that controls action potential repolarization, is the most common cause of QT prolongation by non-cardiac drugs. The ICH S7B describes preclinical safety testing required for new drugs, including the determination of the hERG IC(50). Actual and target concentrations may differ due to solubility, stability, or loss of compound. Significant differences will invalidate quantitative concentration-response curves which may be critical to interpretation of drug safety. To examine the frequency and significance of these differences, we conducted an analysis of studies where both the electrophysiology and the dose solution analysis were conducted in-house. We have investigated the actual concentrations of test article in vehicle solution as compared to the target concentrations in an attempt to determine the reasons behind differences between the two values. METHODS: Studies that involved both electrophysiology and dose solution analysis performed at ChanTest Corporation were evaluated. The effects of stability, solubility and loss through the perfusion apparatus on actual dosing concentrations were investigated. RESULTS: There was a large range in the loss of the test article attributed to the perfusion apparatus (range from 0 to 74% loss). For 12 of the 22 studies evaluated, the IC(50) was>2-fold more potent when using actual values as determined by HPLC versus the target concentrations. Twenty-two percent of the test articles were not stable 24 h after room temperature storage; 16% after 24 h frozen conditions. DISCUSSION: The best practices when considering dose solution concentration verification of test article solutions are to: determine the solubility of the compound in a physiological buffer, analyze samples collected from the perfusion chamber, and analyze samples the same day as sample collection (e.g., same day as hERG assay).

[Analysis and analyzing mechanisms of HERG channel kinetics].

We have investigated the methods and mechanisms for analysis of the channel kinetics parameters of voltage-gated potassium channels, HERG (Human ether-à-go-go related gene) channels, in the process of electrophysiological recording. The current of HERG K+ channels expressed in Xenopus oocytes was studied using a two-electrode voltage clamp technique, and the channel kinetics parameters were analyzed through compiling different pulse protocol and recording the current. Results showed: (1) The HERG K+ channels, under conditions of being activated with depolarized pulse, expressed an inward-rectified property attributing to rapid inactivation. The activation curve could be obtained through fitting the depolarized potential and the following peak amplitude of tail current, while the parameters of time-dependent activation was obtained through fitting different depolarized duration and the corresponding peak amplitude of tail current. (2) The I-V relationship still exhibit marked inward rectification. Tail current decay traces were fitted with a bi-exponential function to determine the time constants of the fast and slow components of current decay. (3) The inactivation of HERG channels is voltage-dependent. The inactivation process was isolated with two different three-pulse protocols, with which the inactivation curve and nearly linear I-V relationship were obtained, respectively. Thus, altough the kinetics properties of HERG channels were complicated, the channels kinetics could be indirectly analyzed through differently designed pulse protocols, which provided the basis for investigation on Alanine-scanning mutagenesis and agent action.

The four and a half LIM domain protein 2 interacts with and regulates the HERG channel.

Protein-protein interactions are critical for protein trafficking, localization and the regulation of ion channels. The human ether-a-go-go-related gene (herg) encodes the alpha-subunit of the potassium channel underlying the rapid component of the cardiac delayed rectifier current. To identify the cellular proteins involved in the regulation of the HERG channel, a human heart cDNA library was screened using a yeast two-hybrid system, with the N-terminus of HERG as bait. The four and a half LIM domain protein 2 (FHL2) was identified as a potential HERG partner. The interaction between these two proteins was confirmed by co-immunoprecipitation and glutathione transferase pull-down assays and immunocytochemical analysis. The physiological implication of HERG-FHL2 interaction, assessed by whole-cell, patch-clamp electrophysiology experiments, showed a significant increase in the HERG current amplitude and a faster deactivation of the tail current in human embryonic kidney 293 cells co-expressing HERG and FHL2. These data indicate that FHL2 interacts with and regulates the HERG channel. Our findings may aid in the further understanding of the molecular basis of HERG channel diversity and arrhythmogenesis in the long-QT syndrome.

HERG K+ channel expression in CD34+/CD38-/CD123(high) cells and primary leukemia cells and analysis of its regulation in leukemia cells.

The human ether-a-go-go-related (herg) gene encoding K+ channels (HERG) belongs to an evolutionarily conserved multigene family of voltage activated K+ channels. The functional properties of HERG K+ channels are complex and their contribution to the repolarization of the cardiac action potential are well understood. Recent studies revealed that HERG K+ channels are preferentially expressed in different histogenesis of tumor cells. Leukemia is a cancer that originates in the bone marrow hematopoietic stem cells (HSCs). Leukemia stem cells (LSCs) are critical in the perpetuation of the disease. A better understanding of LSCs and molecular biology will allow the design of more effective therapies. We report in this study that herg was expressed in CD34+/CD38-/ CD123(high) LSCs but not expressed in normal bone marrow CD34+/CD38- HSCs. In addtion, herg is also expressed in leukemia cell lines K562 and HL-60 and almost all the primary leukemia cells whereas not in the normal bone marrow cells. In addition, the expression of herg mRNA was not associated with the clinical and cytogenetic feature of leukemia. Moreover, HERG K+ channels can regulate leukemia cells proliferation and cell cycle. These data provide evidence for the oncogenic potential of HERG K+ channels and it may be a novel, potential pharmacological target for leukemia therapy in the future.

Expression and prognostic roles of Eag1 in resected esophageal squamous cell carcinomas.

Expression of Eag1 was detected in resected esophageal squamous cell carcinomas tissues and matched tissues by immunohistochemistry and RT-PCR. Positive expression of Eag1 protein was 75% (51/68), and mRNA was 73% (8/11) in primary cancer tissues. Eag1 protein positively stained in all 10 metastatic lymph nodes. Eag1 protein and mRNA were negatively expressed in all non-cancerous matched tissues. Eag1 protein was associated with depth of penetration (P = 0.023), but not associated with other clinicopathological factors. Eag1 protein positive group had a significantly shorter survival time than the negative group (P = 0.005). Survival rates at each time-point for the positive group were lower than that for the negative group (P = 0.006), and Eag1 was identified as an independent prognostic factor of long-term survival (P = 0.016). In conclusion, Eag1 was aberrantly expressed in ESCC and correlated with poor prognosis after surgery.

Expression and significance of HERG protein in gastric cancer.

OBJECTIVES: Our previous studies showed that delayed rectifier potassium currents existed in human gastric cancer cells and the currents were related to the growth of gastric cancer cells. Human ether-a-go-go-related gene (herg) encoding alpha subunit of delayed rectifier potassium channel has been indicated with involvement in tumor cell growth and death. The purpose of the present study is to investigate the expression of HERG protein in gastric cancer tissue and cells; analyze the relationship between the expression of HERG protein and the clinicopathological characteristics of patients with gastric cancer; explore the effects of HERG protein on biological behaviours of gastric cancer cells. METHODS: The expression of HERG protein in gastric cancer tissues and cells was measured by immunohistochemistry and Western blot, respectively. Reduction of HERG protein was carried out by siRNA technology. The proliferation, ability of clone formation, cell cycle, apoptosis and invasive ability of gastric cancer cells were evaluated by MTT assay, clone formation assay, flow cytometry and cell invasion assay. Tumor growth in nude mice was to be used to access the tumorigenicity of gastric cancer cells and HERG currents were recorded by patch-clamp. RESULTS: HERG protein was exclusively expressed in gastric cancer cells. The expression of HERG protein was associated with tumor differentiation, TNM stage and lymph node involvement of gastric cancer. Silencing HERG protein could eliminate the HERG currents and inhibit proliferation, clone formation, invasiveness and tumorigenicity of gastric cancer cells. Reducing HERG protein could also inhibit gastric cancer cells entering S phase from G(1) phase and induce apoptosis of gastric cancer cells. CONCLUSION: HERG protein is involved in carcinogenesis of gastric cancer and is a potential therapeutic target of gastric cancer.

Mutation screening in KCNQ1, HERG, KCNE1, KCNE2 and SCN5A genes in a long QT syndrome family.

INTRODUCTION: Long QT syndrome (LQTS), an inherited cardiac arrhythmia, is a disorder of ventricular repolarisation characterised by electrocardiographic abnormalities and the onset of torsades de pointes leading to syncope and sudden death. Genetic polymorphisms in 5 well-characterised cardiac ion channel genes have been identified to be responsible for the disorder. The aim of this study is to identify disease-causing mutations in these candidate genes in a LQTS family. MATERIALS AND METHODS: The present study systematically screens the coding region of the LQTS-associated genes (KCNQ1, HERG, KCNE1, KCNE2 and SCN5A) for mutations using DNA sequencing analysis. RESULTS: The mutational analysis revealed 7 synonymous and 2 non-synonymous polymorphisms in the 5 ion channel genes screened. CONCLUSION: We did not identify any clear identifiable genetic marker causative of LQTS, suggesting the existence of LQTS-associated genes awaiting discovery.

Electrical alternans and hemodynamics in the anesthetized guinea pig can discriminate the cardiac safety of antidepressants.

INTRODUCTION: The arrhythmogenic risk of fluoxetine, citalopram, and venlafaxine were evaluated through preclinical assays measuring hERG, blood pressure and electrical alternans over their respective clinical unbound concentration ranges. METHODS: Anesthetized guinea pigs were instrumented with jugular and carotid cannulae for drug infusion and blood pressure monitoring respectively; a thoracotomy was performed for placement of a monophasic action potential probe on the left ventricle and for placement of pacing wires on the left ventricular apex. Drugs were infused as a 5-min loading dose immediately followed by a 10-min maintenance dose to achieve clinically relevant plasma concentrations; blood samples were taken at the end of each maintenance dose. Ventricular pacing was performed twice at baseline and at each dose level as follows: 50 preconditioning-beats at S1=220 (or 240) ms immediately followed by 30 test-beats at S2=200 ms. This S1-S2 protocol was repeated for S2=190 to 140 ms. HERG and calcium current measurements were recorded in HEK-293 cells stably expressing hERG potassium currents and freshly isolated guinea pig cardiac myocytes using the whole-cell configuration of the patch clamp technique. RESULTS: Physiologically relevant inhibition (IC(20)) of hERG occurred at concentrations 22-fold (fluoxetine), 9-fold (citalopram), and 11-fold (venlafaxine) beyond their respective clinically effective concentration (C(eff)). At the highest achievable levels, fluoxetine (20-fold C(eff)) and citalopram (28-fold C(eff)) significantly decreased heart rate and/or blood pressure as well as increasing electrical alternans by 5 and 18 ms respectively. Venlafaxine increased blood pressure at only 1.3-fold C(eff), but did not increase electrical alternans at the highest achievable dose (3.1-fold C(eff)). DISCUSSION: These data suggest that evaluating other dose limiting side effects in relation to a drug's therapeutic range may be crucial for accurate assessment of arrhythmia liability.

Upregulation of HERG channels by the serum and glucocorticoid inducible kinase isoform SGK3.

Human ether-a-go-go (HERG) channels participate in the repolarization of the cardiac action potential. Loss of function mutations of HERG lead to delayed cardiac repolarization reflected by prolonged QT interval. HERG channels are regulated through a signaling cascade involving phosphatidylinositol 3 (PI3) kinase. Downstream targets of PI3 kinase include the serum and glucocorticoid inducible kinase (SGK) and protein kinase B (PKB) isoforms. The present study has been performed to explore whether SGK1 and SGK3 participate in the regulation of HERG channel activity. HERG was expressed in Xenopus oocytes with or without additional expression of SGK1 or SGK3. Chemiluminescence was employed to determine HERG plasma membrane protein abundance. Coexpression of SGK3 but not of SGK1 in Xenopus oocytes resulted in an increase of steady state current (I(HERG)) and enhanced cell membrane protein abundance without affecting gating kinetics of the channel. Replacement of serine by alanine at the two SGK consensus sites decreased I(HERG) but neither mutation abolished the stimulating effect of SGK3. In conclusion, SGK3 participates in the regulation of HERG by increasing HERG protein abundance in the plasma membrane and may thus modify the duration of the cardiac action potential.