Optimized J to T peak and T peak to T end measurements in nonclinical species administered moxifloxacin and amiodarone.

INTRODUCTION: Cardiovascular safety and the risk of developing the potentially fatal ventricular tachyarrhythmia, Torsades de Pointes (TdP), have long been major concerns of drug development. TdP is associated with a delayed ventricular repolarization represented by QT interval prolongation in the electrocardiogram (ECG), typically due to block of the potassium channel encoded by the human ether-a-go-go related gene (hERG). Importantly however, not all drugs that prolong the QT interval are torsadagenic and not all hERG blockers prolong the QT interval. Recent clinical reports suggest that partitioning the QT interval into early (J to T peak; JTp) and late repolarization (T peak to T end; TpTe) components may be valuable for distinguishing low-risk mixed ion channel blockers (hERG plus calcium and/or late sodium currents) from high-risk pure hERG channel blockers. This strategy, if true for nonclinical animal models, could be used to de-risk QT prolonging compounds earlier in the drug development process. METHODS: To explore this, we investigated JTp and TpTe in ECG data collected from telemetered dogs and/or monkeys administered moxifloxacin or amiodarone at doses targeting relevant clinical exposures. An optimized placement of the Tpeak fiducial mark was utilized, and all intervals were corrected for heart rate (QTc, JTpc, TpTec). RESULTS: Increases in QTc and JTpc intervals with administration of the pure hERG blocker moxifloxacin and an initial QTc and JTpc shortening followed by prolongation with the mixed ion channel blocker amiodarone were detected as expected, aligning with clinical data. However, anticipated increases in TpTec by both standard agents were not detected. DISCUSSION: The inability to detect changes in TpTec reduces the utility of these subintervals for prediction of arrhythmias using continuous single­lead ECGs collected from freely moving dogs and monkeys.

Thallium-sensitive fluorescent assay reveals loperamide as a new inhibitor of the potassium channel Kv10.1.

BACKGROUND: Ion channels have been proposed as therapeutic targets for different types of malignancies. One of the most studied ion channels in cancer is the voltage-gated potassium channel ether-à-go-go 1 or Kv10.1. Various studies have shown that Kv10.1 expression induces the proliferation of several cancer cell lines and in vivo tumor models, while blocking or silencing inhibits proliferation. Kv10.1 is a promising target for drug discovery modulators that could be used in cancer treatment. This work aimed to screen for new Kv10.1 channel modulators using a thallium influx-based assay. METHODS: Pharmacological effects of small molecules on Kv10.1 channel activity were studied using a thallium-based fluorescent assay and patch-clamp electrophysiological recordings, both performed in HEK293 stably expressing the human Kv10.1 potassium channel. RESULTS: In thallium-sensitive fluorescent assays, we found that the small molecules loperamide and amitriptyline exert a potent inhibition on the activity of the oncogenic potassium channel Kv10.1. These results were confirmed by electrophysiological recordings, which showed that loperamide and amitriptyline decreased the amplitude of Kv10.1 currents in a dose-dependent manner. Both drugs could be promising tools for further studies. CONCLUSIONS: Thallium-sensitive fluorescent assay represents a reliable methodological tool for the primary screening of different molecules with potential activity on Kv10.1 channels or other K+ channels.

Latest Insights into the Pathophysiology of Migraine: the ATP-Sensitive Potassium Channels.

PURPOSE OF REVIEW: Migraine remains a challenging condition to treat, thus highlighting the need for a better understanding of its molecular mechanisms. This review intends to unravel a new emerging target in migraine pathophysiology, the adenosine 5'-triphosphate-sensitive K+ (KATP) channel. RECENT FINDINGS: KATP channel is a common denominator in the cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) mediated intracellular cascades, both of which are involved in migraine. Intravenous infusion of KATP channel opener, levcromakalim, provoked migraine attack associated with dilation of extracerebral arteries in all persons with migraine. Preclinical and clinical studies implicate KATP channels in migraine initiation. KATP channel is a novel therapeutic target for the acute and preventive treatment of migraine. Future studies are warranted to provide a better understanding of the role of KATP channel subgroups in migraine.

ASP2905, a specific inhibitor of the potassium channel Kv12.2 encoded by the Kcnh3 gene, is psychoactive in mice.

Schizophrenia is a major psychiatric disorder associated with positive and negative symptoms and cognitive impairments. In this study, we used animal models of behavior to evaluate the antipsychotic activity of ASP2905, a potent and selective inhibitor of the potassium channel Kv12.2 encoded by the Kcnh3/BEC1 gene. ASP2905 inhibited hyperlocomotion induced by methamphetamine and by phencyclidine. In contrast, ASP2905 did not affect spontaneous locomotion, suggesting that ASP2905 selectively inhibits abnormal behaviors induced by stimulants. Chronic infusion of ASP2905 significantly ameliorated phencyclidine-induced prolongation of immobility time in mice subjected to the forced swimming test. These findings suggest that ASP2905 potentially mitigates symptoms of schizophrenia, such as apathy. The antipsychotic clozapine also reversed phencyclidine-induced prolonged immobility, while risperidone and haloperidol had no effect. Assessment of the effects of ASP2905 on latent learning deficits in mice treated with phencyclidine as neonates subjected to the water-finding task showed that ASP2905 significantly ameliorated phencyclidine-induced prolongation of finding latency, which reflects latent learning performance. These findings suggest that ASP2905 potentially mitigates cognitive impairments caused by schizophrenia, such as attention deficits. In contrast, administration of clozapine did not ameliorate phencyclidine-induced prolongation of finding latency. Therefore, ASP2905 may alleviate the broad spectrum of symptoms of schizophrenia, including positive and negative symptoms and cognitive impairments, which is in contrast to currently available antipsychotics, which are generally only partially effective for ameliorating these symptoms.

Amifampridine tablets for the treatment of Lambert-Eaton myasthenic syndrome.

Introduction: Lambert-Eaton myasthenic syndrome is an autoimmune disease of the neuromuscular junction characterized by a presynaptic defect of neuromuscular transmission resulting in muscle weakness and fatigability. Diagnostic features are specific neurophysiological alterations and autoantibody detection. The present review is focused on the use of Amifampridine Phosphate to treat LEMS patients.Areas covered: Medline search from 1990 to 2019 was examined using the free subject terms: Lambert-Eaton myasthenic syndrome, LEMS, Amifampridine, 3,4-diaminopyridine, which were then combined with Treatment, Therapy, Clinical Trial, Controlled Clinical Trial, Randomized Clinical Trial and Cochrane Review. The author has done a supervised analysis of the retrieved articles and focused on those subjectively evaluated as most relevant.Expert commentary: Data from randomized clinical trials and case series have demonstrated that Lambert-Eaton myasthenic syndrome symptoms were successfully treated by Amifampridine Phosphate. Hence, the drug represents a substantial step forward in the symptomatic treatment of the disease due to its efficacy, safety and reliable GMP formulation. As Amifampridine Phosphate works by enhancing the release of acetylcholine at the neuromuscular junction by blocking K+ efflux at the pre-synaptic membrane, it is also conceivable to use it for other diseases of the neuromuscular junction in which such an effect is searched for.

Classification of drug-induced hERG potassium-channel block from electrocardiographic T-wave features using artificial neural networks.

BACKGROUND: Human ether-à-go-go-related gene (hERG) potassium-channel block represents a harmful side effect of drug therapy that may cause torsade de pointes (TdP). Analysis of ventricular repolarization through electrocardiographic T-wave features represents a noninvasive way to accurately evaluate the TdP risk in drug-safety studies. This study proposes an artificial neural network (ANN) for noninvasive electrocardiography-based classification of the hERG potassium-channel block. METHODS: The data were taken from the "ECG Effects of Ranolazine, Dofetilide, Verapamil, and Quinidine in Healthy Subjects" Physionet database; they consisted of median vector magnitude (VM) beats of 22 healthy subjects receiving a single 500 µg dose of dofetilide. Fourteen VM beats were considered for each subject, relative to time-points ranging from 0.5 hr before to 14.0 hr after dofetilide administration. For each VM, changes in two indexes accounting for the early and the late phases of repolarization, ΔERD30% and ΔTS/A , respectively, were computed as difference between values at each postdose time-point and the predose time-point. Thus, the dataset contained 286 ΔERD30% -ΔTS/A pairs, partitioned into training, validation, and test sets (114, 29, and 143 pairs, respectively) and used as inputs of a two-layer feedforward ANN with two target classes: high block (HB) and low block (LB). Optimal ANN (OANN) was identified using the training and validation sets and tested on the test set. RESULTS: Test set area under the receiver operating characteristic was 0.91; sensitivity, specificity, accuracy, and precision were 0.93, 0.83, 0.92, and 0.96, respectively. CONCLUSION: OANN represents a reliable tool for noninvasive assessment of the hERG potassium-channel block.

Quantitative determination of talatisamine and its pharmacokinetics and bioavailability in mouse plasma by UPLC-MS/MS.

Talatisamine, as the efficacy ingredient of Aconitum, was known as a novel specific blocker for the delayed rectifier K+ channels in rat hippocampal neurons. In this study, a rapid, selective and reproducible UPLC-MS/MS separation method was established and fully validated for the quantitative determination of talatisamine levels in ICR (Institute of Cancer Research) mouse blood. A total of 24 healthy male ICR mice were divided into four groups that was administered talatisamine via intravenous at a dose of 1 mg/kg and oral administration of three doses (2, 4, 8 mg/kg). All blood samples were protein precipitate by using acetonitrile with an internal standard (IS) deltaline. The effective chromatographic separation was carried out through an UPLC BEH C18 analytical column (2.1 mm × 50 mm, 1.7 µm) with an initial mobile phase that consisted of acetonitrile and 10 mmol/L ammonium acetate aqueous solution (containing 0.1% formic acid) with a gradient elution pumped at a flow rate of 0.4 mL/min. Also, an electrospray ionization (ESI) was applied to quantify the talatisamine in the positive ions mode. The method validation demonstrated good linearity over the range of 1-1000 ng/mL (r2 ≥ 0.9993) for talatisamine in mouse blood with a lower limit of quantification (LLOQ) at 1 ng/mL. The accuracy values of the method were within 89.4% to 113.3%, and the matrix effects were between 103.2% and 106.3%. The mean extraction recoveries for talatisamine obtained from four concentrations of QC blood samples were exceeded 71.7%, and the relative standard deviation (RSD) both of intra- and inter-day precision values for replicate quality control samples did not exceed 15% respectively for all analytes during the assay validation. This method was successfully applied to the evaluation of the pharmacokinetic of talatisamine, regardless of intragastric or intravenous administration in mice. Based on the pharmacokinetics data, the bioavailability of talatisamine in mice was >65.0% after oral administration, exhibiting an excellent oral absorption.

Inhibition of protein kinase A and GIRK channel reverses fentanyl-induced respiratory depression.

Opioid-induced respiratory depression is a major obstacle to improving the clinical management of moderate to severe chronic pain. Opioids inhibit neuronal activity via various pathways, including calcium channels, adenylyl cyclase, and potassium channels. Currently, the underlying molecular pathway of opioid-induced respiratory depression is only partially understood. This study aimed to investigate the mechanisms of opioid-induced respiratory depression in vivo by examining the effects of different pharmacological agents on fentanyl-induced respiratory depression. Respiratory parameters were detected using whole body plethysmography in conscious rats. We show that pre-treatment with the protein kinase A (PKA) inhibitor H89 reversed the fentanyl-related effects on respiratory rate, inspiratory time, and expiratory time. Pre-treatment with the G protein-gated inwardly rectifying potassium (GIRK) channel blocker Tertiapin-Q dose-dependently reversed the fentanyl-related effects on respiratory rate and inspiratory time. A phosphodiesterase 4 (PDE4) inhibitor and cyclic adenosine monophosphate (cAMP) analogs did not affect fentanyl-induced respiratory depression. These findings suggest that PKA and GIRK may be involved in fentanyl-induced respiratory depression and could represent useful therapeutic targets for the treatment of fentanyl-induced ventilatory depression.

[A retrospective study of the effects of 3,4-diaminopyridine treatment in Lambert-Eaton myasthenic syndrome].

In this independent clinical study, we analyzed retrospectively the clinical features of 9 cases (6 male and 3 female) of Lambert-Eaton myasthenic syndrome that were administered 3,4-diaminopyridine (3,4-DAP). Four cases showed no cancer and 5 cases had small cell lung carcinoma. Seven cases were positive for anti voltage-gated calcium channel antibodies. Activities of daily living (ADL) were improved by 3,4-DAP in 8 cases that showed mainly weakness of the extremities, but did not improve ADL in 1 case with cerebellar ataxia of paraneoplastic cerebellar degeneration (PCD). Seven cases showed autonomic symptoms, and 6 cases were improved with 3,4-DAP. The maintenance dose varied widely among individuals, with a single dose ranging from 10 to 40 mg. Each patient was prescribed a maintenance dose 3 to 7 times a day. The daily dosage ranged from 36 to 100 mg. Two cases showed adverse effects to the treatment. Of those 2 cases, 1 case treated at 45 mg/day discontinued treatment, but another case treated at 100 mg/day reduced the dosage and continued treatment. The administration period was 1 to 149 months. Three cases have continued 3,4-DAP for more than 10 years. Four cases have discontinued 3,4-DAP, with 2 cases discontinuing due to death, 1 case discontinuing due to progression of cancer, and 1 case discontinuing due to an adverse reaction. Our results suggest that 3,4-DAP treatment is effective for weakness and autonomic symptoms, but may be ineffective for ataxia of PCD. Treatment with 3,4-DAP can be tolerated for a long period, but the optimal dosage varies widely among individuals.

Targeting Astrocytes for Treatment in Amyotrophic Lateral Sclerosis.

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disorder affecting upper and lower motoneurons. The two types, sporadic and familial differ in the aetiopathogenesis but have a similar neuropathology characterized by oxidative stress, excitotoxicity and inflammation. The disease is also characterized by a non-cell autonomous mechanism with astrocytes playing a central role by affecting synaptic glutamate, the blood-brain barrier, and metabolic and trophic support. Two types of therapeutic approaches focusing on astrocytes are presented: a) emerging molecular targets (potassium inward rectifier channels and aquaporins at the astrocyte endfeet, and IP3 receptor signaling pathway), and b) cell therapy with stem cell - generated and transplanted astrocytes.

Short- and long-term clinical predictors of pharmacological cardioversion of persistent atrial fibrillation by dofetilide: A retrospective cohort study of 160 patients.

INTRODUCTION: Dofetilide is a class III antiarrhythmic prescribed to cardiovert persistent atrial fibrillation (AF) to sinus rhythm (SR). HYPOTHESIS: To determine the clinical predictors of cardioversion and readmission in persistent AF patients on dofetilide. METHODS: We analyzed 160 patients with persistent AF who were started on dofetilide and followed for 1 year. We examined age, sex, race, hypertension, diabetes, smoking, dyslipidemia, CAD, left ventricular ejection fraction (LVEF), creatinine, BMI and concomitant use of calcium channel blockers (CCB), ß-blockers in a multivariable logistic regression model. We also examined the same predictors in Cox regression model for AF-related readmission within 1 year of follow-up. RESULTS: 13.5% individuals did not convert to SR on dofetilide. 55.6% converted on the first dose and 83.1% converted by the fourth dose. In multivariable logistic models, dyslipidemia (OR: 2.4, CI: 1.12-5.16) and LVEF (OR: 3.83,CI: 1.37-10.8) were associated with failure to convert with the first dose. Female sex and LVEF also were associated with increased risk of failure to convert at all. Concomitant use of CCB associated with decreased risk of failure to convert to SR. In Cox proportional model, female sex, age <63 years and CAD were associated with increased AF readmission within 1 year. CONCLUSIONS: Dyslipidemia and LVEF <40% were associated with failure to cardiovert after first dose, and female sex and LVEF 40% were related to failure to convert at all on dofetilide in persistent AF patients. After 1-year follow-up, female sex, known CAD, and age <63 years were associated with increased AF readmissions.

The effects of pure potassium channel blocker nifekalant and sodium channel blocker mexiletine on malignant ventricular tachyarrhythmias.

BACKGROUND: Patients with repetitive ventricular tachyarrhythmias - so-called electrical storm - frequently require antiarrhythmic drugs. Amiodarone is widely used for the treatment of electrical storm but is ineffective in some patients. Therefore, we investigated the efficacy of stepwise administration of nifekalant, a pure potassium channel blocker, and mexiletine for electrical storm. METHODS: This study included 44 patients with repetitive ventricular tachyarrhythmias who received stepwise therapy with nifekalant and mexiletine for electrical storm. Nifekalant was initially administered, and mexiletine was subsequently added if nifekalant failed to control ventricular tachyarrhythmias. RESULTS: Nifekalant completely suppressed recurrences of ventricular arrhythmias in 28 patients (64%), including 6 patients in whom oral amiodarone failed to control arrhythmias. In 9 of 16 patients in whom nifekalant was partially effective but failed to suppress ventricular arrhythmias, mexiletine was added. The addition of mexiletine prevented recurrences of ventricular tachyarrhythmias in 5 of these 9 patients (56%). There was no death associated with electrical storm. In total, the stepwise treatment with nifekalant and mexiletine was effective in preventing ventricular tachyarrhythmias in 33 of 44 patients (75%). There was no difference in cycle length of the ventricular tachycardia, QRS interval, QT interval, or left ventricular ejection fraction between patients who responded to antiarrhythmic drugs and those who did not. During follow-up, 8 patients had repetitive ventricular tachyarrhythmia recurrences, and the stepwise treatment was effective in 6 of these 8 patients (75%). CONCLUSIONS: The stepwise treatment with nifekalant and mexiletine was highly effective in the suppression of electrical storm.

An Accelerator Mass Spectrometry-Enabled Microtracer Study to Evaluate the First-Pass Effect on the Absorption of YH4808.

14 C-labeled YH4808, a novel potassium-competitive acid blocker, was intravenously administered as a microtracer at 80 µg (11.8 kBq or 320 nCi) concomitantly with the nonradiolabeled oral drug at 200 mg to determine the absolute bioavailability and to assess the effect of pharmacogenomics on the oral absorption of YH4808. The absolute bioavailability was low and highly variable (mean, 10.1%; range, 2.3-19.3%), and M3 and M8, active metabolites of YH4808, were formed 22.6- and 38.5-fold higher after oral administration than intravenous administration, respectively. The product of the fraction of an oral YH4808 dose entering the gut wall and the fraction of YH4808 passing on to the portal circulation was larger in subjects carrying the variants of the CHST3, SLC15A1, and SULT1B1 genes. A combined LC+AMS is a useful tool to construct a rich and highly informative pharmacokinetic knowledge core in early clinical drug development at a reasonable cost.

Clemizole hydrochloride blocks cardiac potassium currents stably expressed in HEK 293 cells.

BACKGROUND AND PURPOSE: Clemizole, a histamine H1 receptor antagonist has a potential therapeutic effect on hepatitis C infection and also potently inhibits TRPC5 ion channels. The aim of the present study was to investigate whether clemizole blocks cardiac K+ currents and thus affects cardiac repolarization. EXPERIMENTAL APPROACH: Whole-cell patch techniques was used to examine the effects of clemizole on hERG channel current, IKs and Kv 1.5 channel current in HEK 293 cell expression systems as well as on ventricular action potentials of guinea pig hearts. Isolated hearts from guinea pigs were used to determine the effect on the ECG. KEY RESULTS: Clemizole decreased hERG current by blocking both open and closed states of the channel in a concentration-dependent manner (IC50 : 0.07 µM). The S631A, S636A, Y652A and F656V hERG mutant channels reduced the inhibitory effect of clemizole (IC50 : 0.82, 0.89, 1.49 and 2.98 µM, respectively), suggesting that clemizole is a pore blocker of hERG channels. Clemizole also moderately decreased IKs and human Kv 1.5 channel current. Moreover, clemizole increased the duration of the ventricular action potential in guinea pig hearts and the QTc interval in isolated perfused hearts from guinea pigs, in a concentration-dependent manner (0.1-1.0 µM). CONCLUSION AND IMPLICATIONS: Our results provide the first evidence that clemizole potently blocks hERG channels, moderately inhibits cardiac IKs , delays cardiac repolarization and thereby prolongs QT interval. Thus, caution should be taken when clemizole is used as a TRPC5 channel blocker or for treating hepatitis C infection.

A Physiologically Based Pharmacokinetic Model of Amiodarone and its Metabolite Desethylamiodarone in Rats: Pooled Analysis of Published Data.

BACKGROUND AND OBJECTIVE: Amiodarone (AMD) is one of the most effective drugs for rhythm control of atrial fibrillation. The use of AMD is also associated with adverse effects in multiple tissues. Both the parent compound and its major metabolite desethylamiodarone (DEA) contribute to the drug's therapeutic and toxic action. The present study aimed to build a whole-body physiologically based pharmacokinetic (PBPK) model for AMD and DEA in rats. METHODS: Pharmacokinetic data from multiple studies were collected. Some of the data were pooled together to develop the PBPK model; others were used to evaluate the model. Development of the model also involved in vitro to in vivo extrapolation based on in vitro metabolism data. RESULTS: The final model consisted of 11 tissue compartments, including therapeutic target organs and those to which AMD and DEA may be harmful. Model simulations were in good agreement with the observed time courses of the drug-metabolite pair in tissues, under various dosing scenarios. The key pharmacokinetic properties of AMD, such as extensive tissue distribution, substantial storage in the fat tissue, and long half-lives in many tissues, were closely reflected. CONCLUSION: The developed PBPK model can be regarded as the first step towards a PBPK-pharmacodynamic model that can used to mechanistically evaluate and explain the high adverse event rate and potentially to determine which factors are the primary drives for experiencing an adverse event.

A distinct three-helix centipede toxin SSD609 inhibits I(ks) channels by interacting with the KCNE1 auxiliary subunit.

KCNE1 is a single-span transmembrane auxiliary protein that modulates the voltage-gated potassium channel KCNQ1. The KCNQ1/KCNE1 complex in cardiomyocytes exhibited slow activated potassium (I(ks)) currents. Recently, a novel 47-residue polypeptide toxin SSD609 was purified from Scolopendra subspinipes dehaani venom and showed I(ks) current inhibition. Here, chemically synthesized SSD609 was shown to exert I(ks) inhibition in extracted guinea pig cardiomyocytes and KCNQ1/KCNE1 current attenuation in CHO cells. The K(+) current attenuation of SSD609 showed decent selectivity among different auxiliary subunits. Solution nuclear magnetic resonance analysis of SSD609 revealed a distinctive three-helix conformation that was stabilized by a new disulfide bonding pattern as well as segregated surface charge distribution. Structure-activity studies demonstrated that negatively charged Glu19 in the amphipathic extracellular helix of KCNE1 was the key residue that interacted with SSD609. The distinctive three-helix centipede toxin SSD609 is known to be the first polypeptide toxin acting on channel auxiliary subunit KCNE1, which suggests a new type of pharmacological regulation for ion channels in cardiomyocytes.

Long-term observation of incremental response and antibodies to voltage-gated calcium channels in patients with Lambert-Eaton myasthenic syndrome: two case reports.

INTRODUCTION: Lambert-Eaton myasthenic syndrome is a rare autoimmune disorder of neuromuscular transmission due to the presence of antibodies to presynaptic P/Q-type voltage-gated calcium channels. The gold standard of therapy is the potassium channel blocker 3,4-diaminopyridine. To the best of our knowledge, no clinical reports have been published to date about long-term follow-up outcomes in patients who discontinued 3,4-diaminopyridine therapy. In addition, we know of no recent articles in which the natural history in patients with autoimmune-mediated Lambert-Eaton myasthenic syndrome has been addressed. In this report, we describe the cases of two such patients. CASE PRESENTATION: Patient 1 was a Caucasian man who had been diagnosed at age 15 years with Lambert-Eaton myasthenic syndrome with symptoms of fluctuating muscle weakness and easy fatigability. These symptoms stabilized, and his electrophysiological parameters normalized, during treatment with a maintenance dose of 50mg/day of 3,4-diaminopyridine. After 5.5 years, however, he wished to discontinue the treatment. After that point, his electrophysiological parameters and presynaptic P/Q-type voltage-gated calcium-channel antibody titer remained stable. During the 15-year follow-up period, patient 1 reported mild exertion-induced complaints but did not feel restricted in his occupation and most daily activities. Patient 2 was a Caucasian man diagnosed at 32 years of age with a moderate limb girdle syndrome. He was treated with up to 80 mg/day of 3,4-diaminopyridine. Because of the drug's very short-lasting effect (<1 hour), however, he took it mostly irregularly (≤ 1 × 20 mg/day). During the 14- year period of observation, his repetitive nerve stimulation responses and presynaptic P/Q-type voltage-gated calcium-channel antibody titer remained stable, his compound muscle action potential amplitudes were decreasing and his clinical symptoms did not deteriorate. At his last follow-up examination, patient 2 was independent in all of his daily activities. CONCLUSION: Some patients with autoimmune-mediated Lambert-Eaton myasthenic syndrome show a stable clinical long-term course without treatment. The benefit of each long-term therapy should be critically assessed during follow-up, and possible side effects should be balanced against the quality of life in these patients.

Antipsychotic drugs and the risk of ventricular arrhythmia and/or sudden cardiac death: a nation-wide case-crossover study.

BACKGROUND: Antipsychotics have been linked to prolongation of the QT interval. However, little is known about the risk of ventricular arrhythmia (VA) and/or sudden cardiac death (SCD) associated with individual antipsychotic drug use. This study was designed to investigate the association between specific antipsychotic drugs and the risk of VA and/or SCD. METHODS AND RESULTS: We conducted a case-crossover study using a nation-wide population-based sample obtained from Taiwan's National Health Insurance Research Database. A total of 17 718 patients with incident VA and/or SCD were enrolled. Conditional logistic regression models were applied to examine the effects of antipsychotic drug use on the risk of VA/SCD during various case and control time windows of 7, 14, and 28 days. The effect of the potency of a human ether-à-go-go-related gene (hERG) potassium channel blockade was also assessed. Antipsychotic drug use was associated with a 1.53-fold increased risk of VA and/or SCD. Antipsychotic drugs with increased risk included clothiapine, haloperidol, prochlorperazine, thioridazine, olanzapine, quetiapine, risperidone, and sulpiride. The association was significantly higher among those with short-term use. Antipsychotics with a high potency of the hERG potassium channel blockade had the highest risk of VA and/or SCD. CONCLUSION: Use of antipsychotic drugs is associated with an increased risk of VA and/or SCD. Careful evaluations of the risks and benefits of antipsychotic treatment are highly recommended.

Voltage­gated K+ channel blocker quinidine inhibits proliferation and induces apoptosis by regulating expression of microRNAs in human glioma U87­MG cells.

Accumulating evidence has proved that potassium channels (K+ channels) are involved in regulating cell proliferation, cell cycle progression and apoptosis of tumor cells. However, the precise cellular mechanisms are still unknown. In the present study, we investigated the effect and mechanisms of quinidine, a commonly used voltage-gated K+ channel blocker, on cell proliferation and apoptosis of human glioma U87-MG cells. We found that quinidine significantly inhibited the proliferation of U87-MG cells and induced apoptosis in a dose-dependent manner. The results of caspase colorimetric assay showed that the mitochondrial pathway was the main mode involved in the quinidine-induced apoptotic process. Furthermore, the concentration range of quinidine, which inhibited voltage-gated K+ channel currents in electrophysiological assay, was consistent with that of quinidine inhibiting cell proliferation and inducing cell apoptosis. In U87-MG cells treated with quinidine (100 µmol/l), 11 of 2,042 human microRNAs (miRNAs) were upregulated and 16 were downregulated as detected with the miRNA array analysis. The upregulation of miR-149-3p and downregulation of miR-424-5p by quinidine treatment were further verified by using quantitative real-time PCR. In addition, using miRNA target prediction program, putative target genes related to cell proliferation and apoptosis for two differentially expressed miRNAs were predicted. Taken together, these data suggested that the anti-proliferative and pro-apoptosis effect of voltage-gated K+ channel blocker quinidine in human glioma cells was mediated at least partly through regulating expression of miRNAs, and provided further support for the mechanisms of voltage-gated K+ channels in mediating cell proliferation and apoptosis.

Reactive hyperemia occurs via activation of inwardly rectifying potassium channels and Na+/K+-ATPase in humans.

RATIONALE: Reactive hyperemia (RH) in the forearm circulation is an important marker of cardiovascular health, yet the underlying vasodilator signaling pathways are controversial and thus remain unclear. OBJECTIVE: We hypothesized that RH occurs via activation of inwardly rectifying potassium (KIR) channels and Na(+)/K(+)-ATPase and is largely independent of the combined production of the endothelial autocoids nitric oxide (NO) and prostaglandins in young healthy humans. METHODS AND RESULTS: In 24 (23±1 years) subjects, we performed RH trials by measuring forearm blood flow (FBF; venous occlusion plethysmography) after 5 minutes of arterial occlusion. In protocol 1, we studied 2 groups of 8 subjects and assessed RH in the following conditions. For group 1, we studied control (saline), KIR channel inhibition (BaCl2), combined inhibition of KIR channels and Na(+)/K(+)-ATPase (BaCl2 and ouabain, respectively), and combined inhibition of KIR channels, Na(+)/K(+)-ATPase, NO, and prostaglandins (BaCl2, ouabain, L-NMMA [N(G)-monomethyl-L-arginine] and ketorolac, respectively). Group 2 received ouabain rather than BaCl2 in the second trial. In protocol 2 (n=8), the following 3 RH trials were performed: control; L-NMMA plus ketorolac; and L-NMMA plus ketorolac plus BaCl2 plus ouabain. All infusions were intra-arterial (brachial). Compared with control, BaCl2 significantly reduced peak FBF (-50±6%; P<0.05), whereas ouabain and L-NMMA plus ketorolac did not. Total FBF (area under the curve) was attenuated by BaCl2 (-61±3%) and ouabain (-44±12%) alone, and this effect was enhanced when combined (-87±4%), nearly abolishing RH. L-NMMA plus ketorolac did not impact total RH FBF before or after administration of BaCl2 plus ouabain. CONCLUSIONS: Activation of KIR channels is the primary determinant of peak RH, whereas activation of both KIR channels and Na(+)/K(+)-ATPase explains nearly all of the total (AUC) RH in humans.