High-throughput, accurate Monte Carlo simulation on CPU hardware for PET applications.

Monte Carlo simulations (MCS) represent a fundamental approach to modelling the photon interactions in positron emission tomography (PET). A variety of PET-dedicated MCS tools are available to assist and improve PET imaging applications. Of these, GATE has evolved into one of the most popular software for PET MCS because of its accuracy and flexibility. However, simulations are extremely time-consuming. The use of graphics processing units (GPU) has been proposed as a solution to this, with reported acceleration factors about 400-800. These factors refer to GATE benchmarks performed on a single CPU core. Consequently, CPU-based MCS can also be easily accelerated by one order of magnitude or beyond when exploiting multi-threading on powerful CPUs. Thus, CPU-based implementations become competitive when further optimisations can be achieved. In this context, we have developed a novel, CPU-based software called the PET physics simulator (PPS), which combines several efficient methods to significantly boost the performance. PPS flexibly applies GEANT4 cross-sections as a pre-calculated database, thus obtaining results equivalent to GATE. This is demonstrated for an elaborated PET scanner with 3-layer block detectors. All code optimisations yield an acceleration factor of ≈20 (single core). Multi-threading on a high-end CPU workstation (96 cores) further accelerates the PPS by a factor of 80. This results in a total speed-up factor of ≈1600, which outperforms comparable GPU-based MCS by a factor of ≳2. Optionally, the proposed method of coincidence multiplexing can further enhance the throughput by an additional factor of ≈15. The combination of all optimisations corresponds to an acceleration factor of ≈24 000. In this way, the PPS can simulate complex PET detector systems with an effective throughput of 106photon pairs in less than 10 milliseconds.

Improving antibiotic treatment of bacterial biofilm by hyperbaric oxygen therapy: Not just hot air.

Bacteria and fungi show substantial increased recalcitrance when growing as infectious biofilms. Chronic infections caused by biofilm growing microorganisms is considered a major problem of modern medicine. New strategies are needed to improve antibiotic treatment of biofilms. We have improved antibiotic treatment of bacterial biofilms by reviving the dormant bacteria and thereby make them susceptible to antibiotics by means of reoxygenation. Here we review the rationale for associating lack of oxygen with low susceptibility in infectious biofilm, and how hyperbaric oxygen therapy may result in reoxygenation leading to enhanced bactericidal activity of antibiotics. We address issues of feasibility and potential adverse effects regarding patient safety and development of resistance. Finally, we propose means for supplying reoxygenation to antibiotic treatment of infectious biofilm with the potential to benefit large groups of patients.

Multimodal Fingerprints of Resting State Networks as assessed by Simultaneous Trimodal MR-PET-EEG Imaging.

Simultaneous MR-PET-EEG (magnetic resonance imaging - positron emission tomography - electroencephalography), a new tool for the investigation of neuronal networks in the human brain, is presented here for the first time. It enables the assessment of molecular metabolic information with high spatial and temporal resolution in a given brain simultaneously. Here, we characterize the brain's default mode network (DMN) in healthy male subjects using multimodal fingerprinting by quantifying energy metabolism via 2- [18F]fluoro-2-desoxy-D-glucose PET (FDG-PET), the inhibition - excitation balance of neuronal activation via magnetic resonance spectroscopy (MRS), its functional connectivity via fMRI and its electrophysiological signature via EEG. The trimodal approach reveals a complementary fingerprint. Neuronal activation within the DMN as assessed with fMRI is positively correlated with the mean standard uptake value of FDG. Electrical source localization of EEG signals shows a significant difference between the dorsal DMN and sensorimotor network in the frequency range of δ, θ, α and ß-1, but not with ß-2 and ß-3. In addition to basic neuroscience questions addressing neurovascular-metabolic coupling, this new methodology lays the foundation for individual physiological and pathological fingerprints for a wide research field addressing healthy aging, gender effects, plasticity and different psychiatric and neurological diseases.

Hyperbaric oxygen therapy augments tobramycin efficacy in experimental Staphylococcus aureus endocarditis.

Staphylococcus aureus infective endocarditis (IE) is a serious disease with an in-hospital mortality of up to 40%. Improvements in the effects of antibiotics and host responses could potentially benefit outcomes. Hyperbaric oxygen therapy (HBOT) represents an adjunctive therapeutic option. In this study, the efficacy of HBOT in combination with tobramycin in S. aureus IE was evaluated. A rat model of S. aureus IE mimicking the bacterial load in humans was used. Infected rats treated subcutaneously with tobramycin were randomised into two groups: (i) HBOT twice daily (n = 13); or (ii) normobaric air breathing (non-HBOT) (n = 17). Quantitative bacteriology, cytokine expression, valve vegetation size and clinical status were assessed 4 days post-infection. Adjunctive HBOT reduced the bacterial load in the aortic valves, myocardium and spleen compared with the non-HBOT group (P = 0.004, <0.001 and 0.01, respectively) and improved the clinical score (P <0.0001). Photoplanimetric analysis and weight of valve vegetations showed significantly reduced vegetations in the HBOT group (P <0.001). Key pro-inflammatory cytokines [IL-1ß, IL-6, keratinocyte-derived chemokine (KC) and vascular endothelial growth factor (VEGF)] were significantly reduced in valves from the HBOT group compared with the non-HBOT group. In conclusion, HBOT augmented tobramycin efficacy as assessed by several parameters. These findings suggest the potential use of adjunctive therapy in severe S. aureus IE.

UVR: sun, lamps, pigmentation and vitamin D.

Exposure to ultraviolet radiation (UVR) has important and significant consequences on human health. Recently, there has been renewed interest in the beneficial effects of UVR. This perspective gives an introduction to the solar spectrum, UV lamps, UV dosimetry, skin pigment and vitamin D. The health benefits of UVR exposure through vitamin D production or non-vitamin D pathways will be discussed in this themed issue in the following articles.

Fractional laser-assisted drug delivery: Laser channel depth influences biodistribution and skin deposition of methotrexate.

BACKGROUND AND OBJECTIVE: Ablative fractional laser (AFXL) facilitates delivery of topical methotrexate (MTX). This study investigates impact of laser-channel depth on topical MTX-delivery. MATERIALS AND METHODS: MTX (1% [w/v]) diffused for 21 hours through AFXL-exposed porcine skin in in vitro Franz Cells (n = 120). A 2,940 nm AFXL generated microscopic ablation zones (MAZs) into epidermis (11 mJ/channel, MAZ-E), superficial-dermis (26 mJ/channel, MAZ-DS), and mid-dermis (256 mJ/channel, MAZ-DM). High performance liquid chromatography (HPLC) was used to quantify MTX deposition in full-thickness skin, biodistribution profiles at specific skin levels, and transdermal permeation. Fluorescence microscopy was used to visualize UVC-activated MTX-fluorescence (254 nm) and semi-quantify MTX distribution in skin. RESULTS: AFXL increased topical MTX-delivery (P < 0.001). Without laser exposure, MTX-concentration in full-thickness skin was 0.07 mg/cm(2) , increasing sixfold (MAZ-E), ninefold (MAZ-DS), and 11-fold (MAZ-DM) after AFXL (P < 0.001). Deeper MAZs increased MTX-concentrations in all skin layers (P < 0.038) and favored maximum accumulation in deeper skin layers (MAZ-E: 1.85 mg/cm(3) at 500 µm skin-level vs. MAZ-DM: 3.75 mg/cm(3) at 800 µm, P = 0.002). Ratio of skin deposition versus transdermal permeation remained constant, regardless of MAZ depth (P = 0.172). Fluorescence intensities confirmed MTX biodistribution through coagulation zones and into surrounding skin, regardless of thickness of coagulation zones (6-47 µm, P ≥ 0.438). CONCLUSION: AFXL greatly increases topical MTX-delivery. Deeper MAZs deliver higher MTX-concentrations than superficial MAZs, which indicates that laser channel depth may be important for topical delivery of hydrophilic molecules. Lasers Surg. Med. 48:519-529, 2016. © 2016 Wiley Periodicals, Inc.

Low efficacy of tobramycin in experimental Staphylococcus aureus endocarditis.

The empiric treatment of infective endocarditis (IE) varies widely and, in some places, a regimen of penicillin in combination with an aminoglycoside is administered. The increasing incidence of Staphylococcus aureus IE, poor tissue penetration by aminoglycosides and low frequency of penicillin-susceptible S. aureus may potentially lead to functional tobramycin monotherapy. Therefore, this study aimed to evaluate tobramycin monotherapy in an experimental S. aureus IE rat model. Catheter-induced IE at the aortic valves were established with S. aureus (NCTC 8325-4) and rats were randomised into untreated (n = 22) or tobramycin-treated (n = 13) groups. The treatment group received tobramycin once-daily. Animals were evaluated at 1 day post infection (DPI), 2 DPI or 3 DPI. Quantitative bacteriology and cytokine expression were measured for valves, myocardium and serum. A decrease of bacterial load was observed in valves and the spleens of the treated (n = 6) compared to the untreated group at 2 DPI (n = 8) (p ≤ 0.02 and p ≤ 0.01, respectively), but not at 3 DPI (n = 7). Quantitative bacteriology in the myocardium was not different between the groups. Keratinocyte-derived chemokine (KC) in the aortic valves was significantly reduced at 2 DPI in the tobramycin-treated group (p ≤ 0.03). However, the expression of interleukin (IL)-1b, IL-6 and granulocyte-colony stimulating factor (G-CSF) in the valves was not different between the two groups. In the myocardium, a significant reduction in IL-1b was observed at 2 DPI (p ≤ 0.001) but not at 3 DPI. Tobramycin as functional monotherapy only reduced bacterial load and inflammation transiently, and was insufficient in most cases of S. aureus IE.

One versus two-step Roux-en-Y gastric bypass after gastric banding­data analysis of the German Bariatric Surgery Registry.

BACKGROUND: Bariatric surgery outcomes have been examined in Germany since January 1, 2005. All data were registered prospectively in cooperation with the Institute of Quality Assurance in Surgery at the Otto-von-Guericke University Magdeburg. METHODS: The data were collected from an online data bank. Data collection began in 2005 for gastric banding (GB) and Roux-en-Y gastric bypass (RYGB) results. In addition to primary bariatric operations, data regarding the complications of revision procedures and redo operations were analyzed. Participation in the quality assurance study was required for all certified centers in Germany. RESULTS: RYGBs are a popular redo operation after failed gastric banding. In the German Bariatric Surgery Registry (GBSR), we analyzed data from 263 RYGB operations that used a one-step approach after GB and 116 operations that used a two-step approach. The leakage rates for primary RYGB decreased to 1.8%. The incidence of leakage after a one-step RYGB after GB was lower (1.9%) than after the two-step procedure (2.6%). CONCLUSION: RYGBs are popular procedures after failed GB in Germany. The multivariable analysis for overall intraoperative complications revealed a significant difference between the two-step and the one-step procedure. In an unadjusted and multivariate assessment, the one-step procedure had statistically lower general postoperative complications than the two-step approach. Therefore, we suggest performing band removal and RYGB as a one-step procedure. Further analysis is necessary to evaluate the risk factors for the one-step procedure. Follow-up investigations must be performed to determine whether RYGB is an effective and safe option after GB.

Validation of self-reported erythema: comparison of self-reports, researcher assessment and objective measurements in sun worshippers and skiers.

BACKGROUND: Most epidemiological data of sunburn related to skin cancer have come from self-reporting in diaries and questionnaires. We thought it important to validate the reliability of such data. OBJECTIVE: To validate the quality of self-reported erythema by sun worshippers and skiers, and to validate the ability to determine erythema visually compared with objectively measured erythema. METHODS: The skin in a group of sun worshippers in Tenerife and of skiers in Austria was closely monitored over a week. The participants used a diary to record any erythema assessed on different skin sites and underwent a twice daily skin examination by researchers who assessed erythema on the same sites. Lastly, the erythema assessment was validated by objective measurements. RESULTS: We found that the participants' agreed with researchers' assessment of erythema in only 57-61% of cases, and that the researchers detected up to 28% more of the objectively measured erythema than the participants did. We also found that, even for the trained eye (researchers), it was difficult to detect an increase in erythema as only 71-91% of those cases with an increase >15 in measured erythema percentage were detected in the evening. Possibly, detection was impeded by a simultaneous increase in pigmentation. CONCLUSION: Self-assessment of erythema from diaries is unreliable. Erythema is considerably underestimated and possibly neglected. Even for the trained eye, it can be difficult to detect erythema.

Performance tests of two portable mini gamma cameras for medical applications.

We have developed two prototypes of portable gamma cameras for medical applications based on a previous prototype designed and tested by our group. These cameras use a CsI(Na) continuous scintillation crystal coupled to the new flat-panel-type multianode position-sensitive photomultiplier tube, H8500 from Hamamatsu Photonics. One of the prototypes, mainly intended for intrasurgical use, has a field of view of 44 x 44 mm2, and weighs 1.2 kg. Its intrinsic resolution is better than 1.5 mm and its energy resolution is about 13% at 140 keV. The second prototype, mainly intended for osteological, renal, mammary, and endocrine (thyroid, parathyroid, and suprarenal) scintigraphies, weighs a total of 2 kg. Its average spatial resolution is 2 mm; it has a field of view of 95 x 95 mm2, with an energy resolution of about 15% at 140 keV. The main advantages of these gamma camera prototypes with respect to those previously reported in the literature are high portability and low weight, with no significant loss of sensitivity and spatial resolution. All the electronic components are packed inside the mini gamma cameras, and no external electronic devices are required. The cameras are only connected through the universal serial bus port to a portable PC. In this paper, we present the design of the cameras and describe the procedures that have led us to choose their configuration together with the most important performance features of the cameras. For one of the prototypes, clinical tests on melanoma patients are presented and images are compared with those obtained with a conventional camera.

Carcinogenesis related to intense pulsed light and UV exposure: an experimental animal study.

This study examines whether intense pulsed light (IPL) treatment has a carcinogenic potential itself or may influence ultraviolet (UV)-induced carcinogenesis. Secondly, it evaluates whether UV exposure may influence IPL-induced side effects. Hairless, lightly pigmented mice (n=144) received three IPL treatments at 2-week intervals. Simulated solar radiation was administered preoperatively [six standard erythema doses (SED) four times weekly for 11 weeks] as well as pre- and postoperatively (six SED four times weekly up to 26 weeks). Skin tumors were assessed weekly during a 12-month observation period. Side effects were evaluated clinically. No tumors appeared in untreated control mice or in just IPL-treated mice. Skin tumors developed in UV-exposed mice independently of IPL treatments. The time it took for 50% of the mice to first develop skin tumor ranged from 47 to 49 weeks in preoperative UV-exposed mice (p=0.94) and from 22 to 23 weeks in pre- and postoperative UV-exposed mice (p=0.11). IPL rejuvenation of lightly pigmented skin did not induce pigmentary changes (p=1.00). IPL rejuvenation of UV-pigmented skin resulted in an immediate increased skin pigmentation and a subsequent short-term reduced skin pigmentation (p<0.002). Postoperative UV radiation resulted in re-pigmentation of IPL-induced pigment reduction (p=0.12). No texture changes were observed. Postoperative edema and erythema were increased by preoperative UV exposure (p<0.002). IPL rejuvenation has no carcinogenic potential itself and does not influence UV-induced carcinogenesis. UV exposure influences the occurrence of side effects after IPL rejuvenation in an animal model.

A kinetic study on the stereospecific inhibition of KCNQ1 and I(Ks) by the chromanol 293B.

1. Recently we and others have demonstrated a stereoselective inhibition of slowly activating human I(Ks) (KCNQ1/MinK) and homomeric KCNQ1 potassium channels by the enantiomers of the chromanol 293B. Here, we further characterized the mechanism of the 293B block and studied the influence of the 293B enantiomers on the gating kinetics of both channels after their heterologous expression in Xenopus oocytes. 2. Kinetic analysis of currents partially blocked with 10 microM of each 293B enantiomer revealed that only 3R,4S-293B but not 3S,4R-293B exhibited a time-dependent block of I(Ks) and KCNQ1 currents, indicating preferential open channel block activity. 3. Inhibition of both KCNQ1 and I(Ks) channels by 3R,4S-293B but not by 3S,4R-293B increased during a 2 Hz train of stimuli. 4. At high extracellular potassium concentrations the inhibition of KCNQ1 by 3R,4S-293B and 3S,4R-293B was unaffected. Drug inhibition of KCNQ1 and I(Ks) by both enantiomers also did not display a significant voltage-dependence, indicating that 293B does not strongly interact with permeant ions in the pore. 5. The inhibitory properties of 3R,4S-293B on I(Ks)-channels but not those of 3S,4R-293B fulfill the theoretical requirements for a novel class III antiarrhythmic drug, i.e. positive use-dependency. This enantiomer therefore represents a valuable pharmacological tool to evaluate the therapeutic efficiency of I(Ks)blockade.

Dependence of I(Ks) biophysical properties on the expression system.

The delayed rectifier potassium current I(Ks) is important for repolarization of the cardiac action potential. In heart I(Ks) is a heteromeric channel composed of KCNQ1 (KvLQT1) and minK (KCNE1, IsK). Here we show that the KCNQ1/minK interaction is influenced by the expression system. Co-expression of KCNQ1 and minK in Xenopus oocytes resulted in potassium currents comparable to endogenous guinea pig cardiac I(Ks) in terms of temperature dependency and activation kinetics. In contrast, heterologous expression of I(Ks) in CHO cells revealed currents with a markedly different biophysical behavior. The sensitivity to the extracellular potassium concentration, temperature dependency and kinetics differ qualitatively. Potentially there is an endogenous component that affects I(Ks) which does not appear in all expression systems.

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.

Frequency of triggering bacteria in patients with reactive arthritis and undifferentiated oligoarthritis and the relative importance of the tests used for diagnosis.

OBJECTIVE: Reactive arthritis (ReA) triggered by Chlamydia trachomatis or enteric bacteria such as yersinia, salmonella, Campylobacter jejuni, or shigella is an important differential diagnosis in patients presenting with the clinical picture of an undifferentiated oligoarthritis (UOA). This study was undertaken to evaluate the best diagnostic approach. PATIENTS AND METHODS: 52 patients with ReA, defined by arthritis and a symptomatic preceding infection of the gut or the urogenital tract, and 74 patients with possible ReA, defined by oligoarthritis without a preceding symptomatic infection and after exclusion of other diagnoses (UOA), were studied. The following diagnostic tests were applied for the identification of the triggering bacterium: for yersinia induced ReA-stool culture, enzyme immunoassay (EIA), and Widal's agglutination test for detection of antibodies to yersinia; for salmonella or campylobacter induced ReA-stool culture, EIA for the detection of antibodies to salmonella and Campylobacter jejuni; for infections with shigella-stool culture; for infections with Chlamydia trachomatis-culture of the urogenital tract, microimmunofluorescence and immunoperoxidase assay for the detection of antibodies to Chlamydia trachomatis. RESULTS: A causative pathogen was identified in 29/52 (56%) of all patients with ReA. In 17 (52%) of the patients with enteric ReA one of the enteric bacteria was identified: salmonella in 11/33 (33%) and yersinia in 6/33 (18%). Chlamydia trachomatis was the causative pathogen in 12/19 (63%) of the patients with urogenic ReA. In patients with the clinical picture of UOA a specific triggering bacterium was also identified in 35/74 (47%) patients: yersinia in 14/74 (19%), salmonella in 9/74 (12%), and Chlamydia trachomatis in 12/74 (16%). CONCLUSIONS: Chlamydia trachomatis, yersinia, and salmonella can be identified as the causative pathogen in about 50% of patients with probable or possible ReA if the appropriate tests are used.

The induction of the human hepatic CYP2E1 gene by interleukin 4 is transcriptional and regulated by protein kinase C.

Cytochrome P4502E1 (CYP2E1) plays a key role in the metabolism of numerous drug substrates, mostly in mammalian liver. Both the apoprotein and mRNA levels are increased in response to interleukin 4 (IL-4) in primary human hepatocyte cultures. We developed a human hepatoma cell model that faithfully reproduces the responsiveness of the CYP2E1 gene to IL-4 at least in part through transcriptional activation, upon treatment with 150 U/ml of IL-4. As expected, IL-4 induced tyrosine phosphorylation of the STAT6 transcription factor, an effect prevented by the tyrosine kinase inhibitor tyrphostin A25. However, this inhibitor as well as genistein (another inhibitor of tyrosine kinases) had no effect on the IL-4 induction of CYP2E1. Similarly, protein kinase A activators (forskolin and dibutyryl-cAMP) and inhibitor (H89) did not influence the response to IL-4. However, PKC inhibitors (H7 and calphostin C) strongly blocked any induction of the gene, as well as the IL-4-dependent translocation of PKCS. Taken together, our results show that IL-4 coordinately induces CYP2E1 transcription, mRNA and apoprotein levels in human hepatoma cells in a PKC-dependent manner, potentially through the activity of the PKCzeta isoform.

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.

Construction of urease-negative mutants of Yersinia enterocolitica serotypes O:3 and o:8: role of urease in virulence and arthritogenicity.

Yersinia enterocolitica serotype O:3 and O:8 urease-negative mutants unable to express the 19-kDa beta subunit of urease were constructed and tested for virulence and arthritogenicity. Our results indicate that urease is needed for full virulence in oral infections and that it is not an arthritogenic factor in the rat model.

Molecular impact of MinK on the enantiospecific block of I(Ks) by chromanols.

Slowly activating I:(Ks) (KCNQ1/MinK) channels were expressed in Xenopous: oocytes and their sensitivity to chromanols was compared to homomeric KCNQ1 channels. To elucidate the contribution of the ss-subunit MinK on chromanol block, a formerly described chromanol HMR 1556 and its enantiomer S5557 were tested for enantio-specificity in blocking I:(Ks) and KCNQ1 as shown for the single enantiomers of chromanol 293B. Both enantiomers blocked homomeric KCNQ1 channels to a lesser extent than heteromeric I:(Ks) channels. Furthermore, we expressed both WT and mutant MinK subunits to examine the involvement of particular MinK protein regions in channel block by chromanols. Through a broad variety of MinK deletion and point mutants, we could not identify amino acids or regions where sensitivity was abolished or strikingly diminished (>2.5 fold). This could indicate that MinK does not directly take part in chromanol binding but acts allosterically to facilitate drug binding to the principal subunit KCNQ1.

Stilbenes and fenamates rescue the loss of I(KS) channel function induced by an LQT5 mutation and other IsK mutants.

Genetic and physiological studies have established a link between potassium channel dysfunction and a number of neurological and muscular disorders. Many 'channelopathies' are accounted for by a dominant-lethal suppression of potassium channel function. In the cardiac I(KS) channel complex comprising the alpha and beta subunits, KvLQT1 and IsK, respectively, several mutations lead to a dominant-negative loss of channel function. These defects are responsible for a human cardiovascular disease called long QT (LQT) syndrome. Here we show that binding of I(KS) channel activators, such as stilbenes and fenamates, to an extracellular domain flanking the human IsK transmembrane segment, restores normal I(KS) channel gating in otherwise inactive IsK C-terminal mutants, including the naturally occurring LQT5 mutant, D76N. Our data support a model in which allosteric interactions exist between the extracellular and intracellular boundaries of the IsK transmembrane segment as well as between domains of the alpha and beta subunits. Disruption of this allosteric interplay impedes slow activation gating, decreases current amplitude and restores channel inactivation. Owing to allosteric interactions, stilbene and fenamate compounds can rescue the dominant-negative suppression of I(KS) produced by IsK mutations and thus, may have important therapeutic relevance for LQT syndrome.