Evaluation of Batch Variations in Induced Pluripotent Stem Cell-Derived Human Cardiomyocytes from 2 Major Suppliers.

Drug-induced proarrhythmia is a major safety issue in drug development. Developing sensitive in vitro assays that can predict drug-induced cardiotoxicity in humans has been a challenge of toxicology research for decades. Recently, induced pluripotent stem cell-derived human cardiomyocytes (iPSC-hCMs) have become a promising model because they largely replicate the electrophysiological behavior of human ventricular cardiomyocytes. Patient-specific iPSC-hCMs have been proposed for personalized cardiac drug selection and adverse drug response prediction; however, many procedures are involved in cardiomyocytes differentiation and purification process, which may result in large line-to-line and batch-to-batch variations. Here, we examined the purity, cardiac ion channel gene expression profile, and electrophysiological response of 3 batches of iPSC-hCMs from each of 2 major cell suppliers. We found that iPSC-hCMs from both vendors had similar purities. Most of the cardiac ion channel genes were expressed uniformly among different batches of iCells, while larger variations were found in Cor.4U cells, particularly in the expression of CACNA1C, KCND2, and KCNA5 genes, which could underlie the differences in baseline beating rate (BR) and field potential duration (FPD) measurements. Although, in general, the electrophysiological responses of different batches of cells to Na+, Ca2+, Ikr, and Iks channel blockers were similar, with Ikr blocker-induced proarrhythmia, the sensitivities were depended on baseline BR and FPD values: cells that beat slower had longer FPD and greater sensitivity to drug-induced proarrhythmia. Careful evaluation of the performance of iPSC-hCMs and methods of data analysis is warranted for shaping regulatory standards in qualifying iPSC-hCMs for drug safety testing.

Bioelectronic neural pixel: Chemical stimulation and electrical sensing at the same site.

Local control of neuronal activity is central to many therapeutic strategies aiming to treat neurological disorders. Arguably, the best solution would make use of endogenous highly localized and specialized regulatory mechanisms of neuronal activity, and an ideal therapeutic technology should sense activity and deliver endogenous molecules at the same site for the most efficient feedback regulation. Here, we address this challenge with an organic electronic multifunctional device that is capable of chemical stimulation and electrical sensing at the same site, at the single-cell scale. Conducting polymer electrodes recorded epileptiform discharges induced in mouse hippocampal preparation. The inhibitory neurotransmitter, γ-aminobutyric acid (GABA), was then actively delivered through the recording electrodes via organic electronic ion pump technology. GABA delivery stopped epileptiform activity, recorded simultaneously and colocally. This multifunctional "neural pixel" creates a range of opportunities, including implantable therapeutic devices with automated feedback, where locally recorded signals regulate local release of specific therapeutic agents.

Serum albumin attenuates the open-channel blocking effects of propofol on the human Kv1.5 channel.

The intravenous anesthetic propofol modulates various ion channel functions. It is generally accepted that approximately 98% of propofol binds to blood constituents and that the free (unbound) drug preferentially affects target proteins including ion channels. However, modulatory effects of propofol on ion channels have not been previously explored in the presence of serum albumin. This study was designed to investigate the effects of serum albumin on the blocking action of propofol on the human Kv1.5 (hKv1.5) current. Whole-cell patch-clamp method was used to record the hKv1.5 channel current, heterologously expressed in Chinese hamster ovary cells, in the absence and presence of bovine serum albumin (BSA). Propofol induced a time-dependent decline of the hKv1.5 current during depolarizing steps and slowed the time course of tail current decay upon repolarization, supporting that propofol acts as an open-channel blocker. This blocking effect was reversible and concentration-dependent with an IC50 of 62.9±3.1µM (n = 6). Bath application of 1% BSA markedly reduced the blocking potency of propofol on hKv1.5 current (IC50 of 1116.0±491.4µM; n = 6). However, in the presence of BSA, the propofol-induced inhibition of hKv1.5 current was also accompanied by a gradual decline of activated current during depolarization and deceleration of deactivating tail current upon repolarization. The presence of BSA greatly attenuated the blocking potency of propofol on hKv1.5 channel without affecting the mode of action of propofol on the channel. Serum albumin thus appears to bind to propofol and thereby reducing effective concentrations of the drug for inhibition of hKv1.5 channel.

In silico analysis of potential inhibitors of Ca(2+) activated K(+) channel blocker, Charybdotoxin-C from Leiurus quinquestriatus hebraeus through molecular docking and dynamics studies.

OBJECTIVE: Charybdotoxin-C (ChTx-C), from the scorpion Leiurus, quinquestriatus hebraeus blocks the calcium-activated potassium channels and causes hyper excitability of the nervous system. Detailed understanding the structure of ChTx-C, conformational stability, and intermolecular interactions are required to select the potential inhibitors of the toxin. MATERIALS AND METHODS: The structure of ChTx-C was modeled using Modeller 9v7. The amino acid residues lining the binding site were predicted and used for toxin-ligand docking studies, further, selected toxin-inhibitor complexes were studied using molecular dynamics (MD) simulations. RESULTS: The predicted structure has 91.7% of amino acids in the core and allowed regions of Ramachandran plot. A total of 133 analog compounds of existing drugs for scorpion bites were used for docking. As a result of docking, a list of compounds was shown good inhibiting properties with target protein. By analyzing the interactions, Ser 15, Lys 32 had significant interactions with selected ligand molecules and Val5, which may have hydrophobic interaction with the cyclic group of the ligand. MD simulation studies revealed that the conformation and intermolecular interactions of all selected toxin-inhibitor complexes were stable. CONCLUSION: The interactions of the ligand and active site amino acids were found out for the best-docked poses in turn helpful in designing potential antitoxins which may further be exploited in toxin based therapies.

Underlying mechanism of regulatory actions of diclofenac, a nonsteroidal anti-inflammatory agent, on neuronal potassium channels and firing: an experimental and theoretical study.

Diclofenac (DIC), a nonsteroidal anti-inflammatory drug, is known to exert anti-nociceptive and anti-convulsant actions; however, its effects on ion currents, in neurons remain debatable. We aimed to investigate (1) potential effects of diclofenac on membrane potential and potassium currents in differentiated NSC-34 neuronal cells and dorsal root ganglion (DRG) neurons with whole-cell patch-clamp technology, and (2) firing of action potentials (APs), using a simulation model from hippocampal CA1 pyramidal neurons based on diclofenac's effects on potassium currents. In the NSC-34 cells, diclofenac exerted an inhibitory effect on delayed-rectifier K⁺ current (I(KDR)) with an IC50 value of 73 µM. Diclofenac not merely inhibited the I(KDR) amplitude in response to membrane depolarization, but also accelerated the process of current inactivation. The inhibition by diclofenac of IK(DR) was not reversed by subsequent application of either naloxone. Importantly, diclofenac (300 µM) increased the amplitude of M-type K⁺ current (I)(KM)), while flupirtine (10 µM) or meclofenamic acid (10 µM) enhanced it effectively. Consistently, diclofenac (100 µM) increased the amplitude of I(KM) and diminished the I(KDR) amplitude, with a shortening of inactivation time constant in DRG neurons. Furthermore, by using the simulation modeling, we demonstrated the potential electrophysiological mechanisms underlying changes in AP firing caused by diclofenac. During the exposure to diclofenac, the actions on both I(KM) and I(KDR) could be potential mechanism through which it influences the excitability of fast-spiking neurons. Caution needs to be made in attributing the effects of diclofenac primarily to those produced by the activation of I(KM).

Chloride channel blockers promote relaxation of TEA-induced contraction in airway smooth muscle.

Enhanced airway smooth muscle (ASM) contraction is an important component in the pathophysiology of asthma. We have shown that ligand gated chloride channels modulate ASM contractile tone during the maintenance phase of an induced contraction, however the role of chloride flux in depolarization-induced contraction remains incompletely understood. To better understand the role of chloride flux under these conditions, muscle force (human ASM, guinea pig ASM), peripheral small airway luminal area (rat ASM) and airway smooth muscle plasma membrane electrical potentials (human cultured ASM) were measured. We found ex vivo guinea pig airway rings, human ASM strips and small peripheral airways in rat lungs slices relaxed in response to niflumic acid following depolarization-induced contraction induced by K(+) channel blockade with tetraethylammonium chloride (TEA). In isolated human airway smooth muscle cells TEA induce depolarization as measured by a fluorescent indicator or whole cell patch clamp and this depolarization was reversed by niflumic acid. These findings demonstrate that ASM depolarization induced contraction is dependent on chloride channel activity. Targeting of chloride channels may be a novel approach to relax hypercontractile airway smooth muscle in bronchoconstrictive disorders.

Pharmacological removal of human ether-à-go-go-related gene potassium channel inactivation by 3-nitro-N-(4-phenoxyphenyl) benzamide (ICA-105574).

Human ether-à-go-go-related gene (hERG) potassium channel activity helps shape the cardiac action potential and influences its duration. In this study, we report the discovery of 3-nitro-N-(4-phenoxyphenyl) benzamide (ICA-105574), a potent and efficacious hERG channel activator with a unique mechanism of action. In whole-cell patch-clamp studies of recombinant hERG channels, ICA-105574 steeply potentiated current amplitudes more than 10-fold with an EC(50) value of 0.5 +/- 0.1 microM and a Hill slope (n(H)) of 3.3 +/- 0.2. The effect on hERG channels was confirmed because the known hERG channel blockers, N-[4-[[1-[2-(6-methyl-2-pyridinyl)ethyl]-4-piperidinyl]carbonyl]phenyl]methanesulfonamide, 2HCl (E-4031) and BeKm-1, potently blocked the stimulatory effects of ICA-105574. The primary mechanism by which ICA-105574 potentiates hERG channel activity is by removing hERG channel inactivation, because ICA-105574 (2 microM) shifts the midpoint of the voltage-dependence of inactivation by >180 mV from -86 to +96 mV. In addition to the effects on inactivation, greater concentrations of ICA-105574 (3 microM) produced comparatively small hyperpolarizing shifts (up to 11 mV) in the voltage-dependence of channel activation and a 2-fold slowing of channel deactivation. In isolated guinea pig ventricular cardiac myocytes, ICA-105574 induced a concentration-dependent shortening of action potential duration (>70%, 3 microM) that could be prevented by preincubation with E-4031. In conclusion, we identified a novel agent that can prevent the inactivation of hERG potassium channels. This compound may provide a useful tool to further understand the mechanism by which hERG channels inactivate and affect cardiac function in addition to the role of hERG channels in other cell systems.

Nicotinic receptor-evoked hippocampal norepinephrine release is highly sensitive to inhibition by isoflurane.

BACKGROUND: Inhaled anaesthetics (IAs) produce multiple dose-dependent behavioural effects including amnesia, hypnosis, and immobility in response to painful stimuli that are mediated by distinct anatomical, cellular, and molecular mechanisms. Amnesia is produced at lower anaesthetic concentrations compared with hypnosis or immobility. Nicotinic acetylcholine receptors (nAChRs) modulate hippocampal neural network correlates of memory and are highly sensitive to IAs. Activation of hippocampal nAChRs stimulates the release of norepinephrine (NE), a neurotransmitter implicated in modulating hippocampal synaptic plasticity. We tested the hypothesis that IAs disrupt hippocampal synaptic mechanisms critical to memory by determining the effects of isoflurane on NE release from hippocampal nerve terminals. METHODS: Isolated nerve terminals prepared from adult male Sprague-Dawley rat hippocampus were radiolabelled with [(3)H]NE and either [(14)C]GABA or [(14)C]glutamate and superfused at 37 degrees C. Release evoked by a 2 min pulse of 100 microM nicotine or 5 microM 4-aminopyridine was evaluated in the presence or absence of isoflurane and/or selective antagonists. RESULTS: Nicotine-evoked NE release from rat hippocampal nerve terminals was nAChR- and Ca(2+)-dependent, involved both alpha7 and non-alpha7 subunit-containing nAChRs, and was partially dependent on voltage-gated Na(+) channel activation based on sensitivities to various antagonists. Isoflurane inhibited nicotine-evoked NE release (IC(50)=0.18 mM) more potently than depolarization-evoked NE release (IC(50)=0.27 mM, P=0.014), consistent with distinct presynaptic mechanisms of IA action. CONCLUSIONS: Inhibition of hippocampal nAChR-dependent NE release by subanaesthetic concentrations of isoflurane supports a role in IA-induced amnesia.

Antiepileptic effect of carbenoxolone on seizures induced by 4-aminopyridine: a study in the rat hippocampus and entorhinal cortex.

We have examined the effects of the gap junction blocker carbenoxolone (CBX) on the generation and propagation of epileptiform activity induced by 4-aminopyridine (4-AP) in the rat entorhinal cortex and hippocampus. We analyzed the epileptiform pattern generated on awaked rats by administering 10 nmol of 4-AP and we studied the effect of administering CBX (50 nmol) 30 min later by injection into the entorhinal cortex. The injection of 4-AP produced an epileptiform pattern in EEG recordings characterized by an initial hypersynchronic activity followed by trains of high-amplitude epileptiform discharges. This pattern was associated with convulsive behavior rated as 0, 1 and 3 in the Racine Scale. In contrast, no changes in electrical activity or behavior were observed in animals that received NaCl or CBX alone. The application of CBX to rats that had received 4-AP decreased the amplitude and frequency of the epileptiform discharges, as well as the number and duration of the epileptiform trains in the entorhinal cortex and hippocampus. Indeed, discharge trains were completely blocked by CBX after 22+/-4.4 min, and likewise CBX reverted the convulsive behavior of these animals. We conclude that Gap junctions participate in the generation and propagation of epileptiform activity induced by 4-AP in these regions, as well as blocking motor alterations.

The IKr drug response is modulated by KCR1 in transfected cardiac and noncardiac cell lines.

The cardiac potassium channel encoded by the human ether-à-go-go related gene (HERG) is blocked by a diverse array of common therapeutic compounds. Even transient exposure to such agents may provoke the life-threatening cardiac arrhythmia torsades de pointes in some, but not all, individuals. Although the molecular and genetic factors predicting such wide variability in drug response remain unclear, known sequence variations within the coding region of HERG do not explain the adverse drug response in many cases. Although other proteins can modulate HERG function, no studies have identified protein partners capable of limiting the pharmacological sensitivity of HERG. Here we show that KCR1, a protein identified previously in rat cerebellum, is a plasma membrane-associated protein expressed at the RNA level in the human heart and can be immunoprecipitated with HERG. Functionally, KCR1 reduces the sensitivity of HERG to classic proarrhythmic HERG blockers (sotalol, quinidine, dofetilide) in both cardiac and noncardiac cell lines. We propose that KCR1, when coupled to HERG, may limit the sensitivity of HERG to proarrhythmic drug blockade and may be a rational target for modifying the proarrhythmic effects of otherwise clinically useful compounds.

Testosterone diminishes the proarrhythmic effects of dofetilide in normal female rabbits.

BACKGROUND: Recent clinical and experimental data suggest that testosterone may protect males against the deleterious effects of repolarization-prolonging drugs. This study tests the hypothesis that 5alpha-dihydrotestosterone (DHT) protects normal females against drug-induced excessive prolongation of repolarization. METHODS AND RESULTS: We used microelectrode techniques to study isolated preparations of rabbit ventricular endocardium from age-matched normal control female rabbits and female rabbits treated with DHT for 4 weeks. Serum 17beta-estradiol levels were identical in the control and DHT-treated animals, whereas DHT levels were high (equaling those in normal males) only in the DHT-treated animals. Basal action potential duration to 90% repolarization (APD90) was significantly shorter in DHT-treated (155+/-7.4 ms, n=32) than control females (178+/-6.7 ms, n=29; P<0.05) at cycle length=1000 ms. The increase in APD90 induced by 10(-8) mol/L dofetilide at cycle length=1000 ms was significantly less in DHT-treated females than normal females (DeltaAPD90=8+/-7 and 29+/-5 ms, respectively, P<0.05). At 10(-6) mol/L dofetilide, the incidence of early afterdepolarizations was 28% in DHT-treated and 55% in normal female rabbits (P<0.05). CONCLUSIONS: Elevating DHT levels diminishes the effects of dofetilide to increase APD and induce early afterdepolarizations in females. Moreover, treatment of females with DHT results in prolongation of APD and an incidence of early afterdepolarization equal to values previously reported by us for dofetilide-treated normal males. That serum levels of 17beta-estradiol were the same in DHT-treated and untreated females suggests that estradiol is not involved in the response to dofetilide. Thus, these data suggest that DHT and perhaps other androgenic hormones may protect normal females against the risk of dofetilide-induced arrhythmia.