Impairment of ciliary dynamics in an APP knock-in mouse model of Alzheimer's disease.

The primary cilium is a specialized microtubule-based sensory organelle that extends from the cell body of nearly all cell types. Neuronal primary cilia, which have their own unique signaling repertoire, are crucial for neuronal integrity and the maintenance of neuronal connectivity throughout adulthood. Dysfunction of cilia structure and ciliary signaling is associated with a variety of genetic syndromes, termed ciliopathies. One of the characteristic features of human ciliopathies is impairment of memory and cognition, which is also observed in Alzheimer's disease (AD). Amyloid ß peptide (Aß) is produced through the proteolytic processing of amyloid precursor protein (APP), and Aß accumulation in the brain is proposed to be an early toxic event in the pathogenesis of AD. To evaluate the effect of increased Aß level on primary cilia, we assessed ciliary dynamics in hippocampal neurons in an APP knock-in AD model (AppNL-G-F mice) compared to that in wild-type mice. Neuronal cilia length in the CA1, CA3, and dentate gyrus (DG) of wild-type mice increased significantly with age. In AppNL-G-F mice, such elongation was detected in the DG but not in the CA1 and CA3, where more Aß accumulation was observed. We further demonstrated that Aß1-42 treatment decreased cilia length both in hTERT-RPE1 cells and dissociated rat hippocampal neurons. There is growing evidence that reduced cilia length is associated with perturbations of synaptic connectivity and dendrite complexity. Thus, our observations raise the important possibility that structural alterations in neuronal cilia might have a role in AD development.

Adenosine A1 receptor antagonist-induced facilitation of postsynaptic AMPA currents in pyramidal neurons of the rat hippocampal CA2 area.

Adenosine A1 receptors (A1R) are widely expressed in hippocampal pyramidal neurons and their presynaptic terminals. It is well known that endogenous adenosine regulates hippocampal function through the activation of A1R in hippocampal pyramidal neurons and has been reported that blockade of A1R induces stronger potentiation of excitatory synaptic transmission in CA2 pyramidal neurons than in CA1 pyramidal neurons. This strong potentiation of CA2 neurons is thought to be caused by the specific modulation of excitatory synaptic transmission through postsynaptic A1R. However, the direct effects of A1R on postsynaptic AMPA channels remain unknown because of the technical difficulties of patch-clamp recording from mature hippocampal CA2 neurons. We recorded synaptic currents from pyramidal neurons in CA1 and CA2 and analyzed the effects of an A1R antagonist on stimulation-evoked synaptic transmission and local application-induced postsynaptic AMPA currents. The antagonist increased the amplitude of evoked synaptic transmission in neurons in both CA1 and CA2. This facilitation was larger in pyramidal neurons in CA2 than in CA1. The antagonist also increased postsynaptic AMPA currents in neurons in CA2 but not in CA1. This facilitation of CA2 AMPA currents was occluded by the intracellular application of a G-protein blocker. Even with the blockade of postsynaptic G-protein signaling, the A1R antagonist increased evoked synaptic transmission in neurons in CA2. These results suggest that synaptic transmission in pyramidal neurons in CA2 is regulated by both presynaptic and postsynaptic A1R. Moreover, A1R regulate excitatory synaptic transmission in pyramidal neurons in CA2 through the characteristic postsynaptic modulation of AMPA currents.

Neurons Induce Tiled Astrocytes with Branches That Avoid Each Other.

Neurons induce astrocyte branches that approach synapses. Each astrocyte tiles by expanding branches in an exclusive territory, with limited entries for the neighboring astrocyte branches. However, how astrocytes form exclusive territories is not known. For example, the extensive branching of astrocytes may sterically interfere with the penetration of other astrocyte branches. Alternatively, astrocyte branches may actively avoid each other or remove overlapped branches to establish a territory. Here, we show time-lapse imaging of the multi-order branching process of GFP-labeled astrocytes. Astrocyte branches grow in the direction where other astrocyte branches do not exist. Neurons that had just started to grow dendrites were able to induce astrocyte branching and tiling. Upon neuronal loss by glutamate excitotoxicity, astrocytes' terminal processes retracted and more branches went over other branches. Our results indicate that neurons induce astrocyte branches and make them avoid each other.

NMDA receptor-dependent and -independent effects of natural compounds and crude drugs on synaptic states as revealed by drebrin imaging analysis.

Effective drugs that can cure cognitive impairments remain elusive. Because synaptic dysfunction has been correlated with cognitive impairments, drug development to target synaptic dysfunction is important. Recently, natural compounds and crude drugs have emerged as potential therapeutic agents for cognitive disorders. However, their effects on synaptic function remain unclear, because of lack of evaluation system with high reproducibility. We have recently developed highly reproducible in vitro high-content imaging analysis system for evaluation of synaptic function using drebrin as a marker for synaptic states. Therefore, we aimed to examine the direct effects of well-known natural compounds and crude drugs on synaptic states using this system. Rat hippocampal neurons were treated using natural compounds (nobiletin, diosgenin and tenuifolin) and crude drugs (Uncaria Hook [UH], Bezoar Bovis [BB], Coptis Rhizome [CR], Phellodendron Bark [PB] and Polygala Root [PR]). Immunocytochemical analysis was performed, and dendrite lengths and drebrin cluster densities were automatically quantified. We found that diosgenin, tenuifolin, CR, PB and PR decreased drebrin cluster densities, and the effects of PB and PR were partially dependent on N-methyl-D-aspartic acid-type glutamate receptors (NMDARs). Nobiletin and UH did not show any effects, whereas low-dose BB treatment increased drebrin cluster densities. Our results showed that diosgenin, tenuifolin, BB, CR, PB and PR appeared to directly change synaptic states. Particularly, the NMDAR dependency of PB and PR appears to affect synaptic plasticity.

Hyaluronan synthesis supports glutamate transporter activity.

Hyaluronan is synthesized, secreted, and anchored by hyaluronan synthases (HAS) at the plasma membrane and comprises the backbone of perineuronal nets around neuronal soma and dendrites. However, the molecular targets of hyaluronan to regulate synaptic transmission in the central nervous system have not been fully identified. Here, we report that hyaluronan is a negative regulator of excitatory signals. At excitatory synapses, glutamate is removed by glutamate transporters to turn off the signal and prevent excitotoxicity. Hyaluronan synthesized by HAS supports the activity of glial glutamate transporter 1 (GLT1). GLT1 also retracted from cellular processes of cultured astrocytes after hyaluronidase treatment and hyaluronan synthesis inhibition. A serial knockout study showed that all three HAS subtypes recruit GLT1 to cellular processes. Furthermore, hyaluronidase treatment activated neurons in a dissociated rat hippocampal culture and caused neuronal damage due to excitotoxicity. Our findings reveal that hyaluronan helps to turn off excitatory signals by supporting glutamate clearance. Cover Image for this issue: doi: 10.1111/jnc.14516.

Characterization of Functional Primary Cilia in Human Induced Pluripotent Stem Cell-Derived Neurons.

Recent advances in human induced pluripotent stem cells (hiPSCs) offer new possibilities for biomedical research and clinical applications. Neurons differentiated from hiPSCs may be promising tools to develop novel treatment methods for various neurological diseases. However, the detailed process underlying functional maturation of hiPSC-derived neurons remains poorly understood. Here, we analyze the developmental architecture of hiPSC-derived cortical neurons, iCell GlutaNeurons, focusing on the primary cilium, a single sensory organelle that protrudes from the surface of most growth-arrested vertebrate cells. To characterize the neuronal cilia, cells were cultured for various periods and evaluated immunohistochemically by co-staining with antibodies against ciliary markers Arl13b and MAP2. Primary cilia were detected in neurons within days, and their prevalence and length increased with increasing days in culture. Treatment with the mood stabilizer lithium led to primary cilia length elongation, while treatment with the orexigenic neuropeptide melanin-concentrating hormone caused cilia length shortening in iCell GlutaNeurons. The present findings suggest that iCell GlutaNeurons develop neuronal primary cilia together with the signaling machinery for regulation of cilia length. Our approach to the primary cilium as a cellular antenna can be useful for both assessment of neuronal maturation and validation of pharmaceutical agents in hiPSC-derived neurons.

Systematic expression analysis of genes related to generation of action potentials in human iPS cell-derived cardiomyocytes.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are a valuable tool to characterize the pharmacology and toxic effects of drugs on heart cells. In particular, hiPSC-CMs can be used to identify drugs that generate arrhythmias. However, it is unclear whether the expression of genes related to generation of CM action potentials differs between hiPSC-CM cell lines and the mature human heart. To address this, we obtained accurate gene expression profiles of commercially available hiPSC-CM cell lines with quantitative real time RT-PCR analysis. Expression analysis of ten cardiac proteins important for generation of action potentials and three cardiac proteins important for muscle contractility was performed using GAPDH for normalization. Comparison revealed large variations in expression levels among hiPSC-CM cell lines and between hiPSC-CMs and normal human heart. In general, gene expression in hiPSC-CM cell lines was more similar to an immature, stem-like cell than a mature cardiomyocyte from human heart samples. These results provide quantitative information about differences in gene expression between hiPSC-CM cell lines, essential for interpreting pharmacology experiments. Our approach can be used as an experimental guideline for future research on gene expression in hiPSC-CMs.

Application of human induced pluripotent stem cell-derived cardiomyocytes sheets with microelectrode array system to estimate antiarrhythmic properties of multi-ion channel blockers.

We examined electrophysiological indices of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) sheets in order to quantitatively estimate Na+, K+ and Ca2+ channel blocking actions of bepridil and amiodarone using microelectrode array system in comparison with that of E-4031. We analyzed the field potential duration, effective refractory period, current threshold and conduction property using a programmed electrical stimulation protocol to obtain the post repolarization refractoriness and coefficient a of the relationship between the pacing cycle length and field potential duration. Electropharmacological profile of each drug was successfully characterized; namely, 1) the changes in the current threshold and conduction property provided basic information of Na+ channel blocking kinetics, 2) the relationship between pacing cycle length and field potential duration reflected drug-induced inhibition of human ether-à-go-go-related gene (hERG) K+ channel, 3) the post repolarization refractoriness indicated the relative contribution of these drugs to Na+ and K+ channel blockade, and 4) L-type Ca2+ channel blocking action was more obvious in the field potential waveform of the hiPSC-CMs sheets than that expected in the electrocardiogram in humans. Thus, this information may help to better utilize the hiPSC-CMs sheets for grasping the properties and net effects of drug-induced Na+, Ca2+ and K+ channel blockade.

Proarrhythmia risk prediction using human induced pluripotent stem cell-derived cardiomyocytes.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are expected to become a useful tool for proarrhythmia risk prediction in the non-clinical drug development phase. Several features including electrophysiological properties, ion channel expression profile and drug responses were investigated using commercially available hiPSC-CMs, such as iCell-CMs and Cor.4U-CMs. Although drug-induced arrhythmia has been extensively examined by microelectrode array (MEA) assays in iCell-CMs, it has not been fully understood an availability of Cor.4U-CMs for proarrhythmia risk. Here, we evaluated the predictivity of proarrhythmia risk using Cor.4U-CMs. MEA assay revealed linear regression between inter-spike interval and field potential duration (FPD). The hERG inhibitor E-4031 induced reverse-use dependent FPD prolongation. We next evaluated the proarrhythmia risk prediction by a two-dimensional map, which we have previously proposed. We determined the relative torsade de pointes risk score, based on the extent of FPD with Fridericia's correction (FPDcF) change and early afterdepolarization occurrence, and calculated the margins normalized to free effective therapeutic plasma concentrations. The drugs were classified into three risk groups using the two-dimensional map. This risk-categorization system showed high concordance with the torsadogenic information obtained by a public database CredibleMeds. Taken together, these results indicate that Cor.4U-CMs can be used for drug-induced proarrhythmia risk prediction.

The role of drebrin in dendritic spines.

Dendritic spines form typical excitatory synapses in the brain and their shapes vary depending on synaptic inputs. It has been suggested that the morphological changes of dendritic spines play an important role in synaptic plasticity. Dendritic spines contain a high concentration of actin, which has a central role in supporting cell motility, and polymerization of actin filaments (F-actin) is most likely involved in spine shape changes. Drebrin is an actin-binding protein that forms stable F-actin and is highly accumulated within dendritic spines. Drebrin has two isoforms, embryonic-type drebrin E and adult-type drebrin A, that change during development from E to A. Inhibition of drebrin A expression results in a delay of synapse formation and inhibition of postsynaptic protein accumulation, suggesting that drebrin A has an important role in spine maturation. In mature synapses, glutamate stimulation induces rapid spine-head enlargement during long-term potentiation (LTP) formation. LTP stimulation induces Ca2+ entry through N-methyl-d-aspartate (NMDA) receptors, which causes drebrin exodus from dendritic spines. Once drebrin exits from dendritic spine heads, the dynamic actin pool increases in spine heads to facilitate F-actin polymerization. To maintain enlarged spine heads, drebrin-decorated F-actin is thought to reform within the spine heads. Thus, drebrin plays a pivotal role in spine plasticity through regulation of F-actin.

The role of drebrin in neurons.

Drebrin is an actin-binding protein that changes the helical pitch of actin filaments (F-actin), and drebrin-decorated F-actin shows slow treadmilling and decreased rate of depolymerization. Moreover, the characteristic morphology of drebrin-decorated F-actin enables it to respond differently to the same signals from other actin cytoskeletons. Drebrin consists of two major isoforms, drebrin E and drebrin A. In the developing brain, drebrin E appears in migrating neurons and accumulates in the growth cones of axons and dendrites. Drebrin E-decorated F-actin links lamellipodium F-actin to microtubules in the growth cones. Then drebrin A appears at nascent synapses and drebrin A-decorated F-actin facilitates postsynaptic molecular assembly. In the adult brain, drebrin A-decorated F-actin is concentrated in the central region of dendritic spines. During long-term potentiation initiation, NMDA receptor-mediated Ca2+ influx induces the transient exodus of drebrin A-decorated F-actin via myosin II ATPase activation. Because of the unique physical characteristics of drebrin A-decorated F-actin, this exodus likely contributes to the facilitation of F-actin polymerization and spine enlargement. Additionally, drebrin reaccumulation in dendritic spines is observed after the exodus. In our drebrin exodus model of structure-based synaptic plasticity, reestablishment of drebrin A-decorated F-actin is necessary to keep the enlarged spine size during long-term potentiation maintenance. In this review, we introduce the genetic and biochemical properties of drebrin and the roles of drebrin in early stage of brain development, synaptic formation and synaptic plasticity. Further, we discuss the pathological relevance of drebrin loss in Alzheimer's disease. This article is part of the mini review series "60th Anniversary of the Japanese Society for Neurochemistry".

Development of correction formula for field potential duration of human induced pluripotent stem cell-derived cardiomyocytes sheets.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have been used in many studies to assess proarrhythmic risks of chemical compounds. In those studies, field potential durations (FPD) of hiPSC-CMs have been corrected by clinically used Fridericia's and/or Bazett's formulae, however, the rationale for the use of these formulae has not been well established. In the present study, we developed a correction formula for experiments using hiPSC-CMs. First, we analyzed the effect of beating rate on FPD in the hiPSC-CMs sheets with electrical stimuli and a HCN channel inhibitor zatebradine. Next, we examined the relationship between the electrophysiological properties and the expression levels of ion channel genes in the cell sheets. Zatebradine slowed the beating rate and allowed to analyze FPD changes at various pacing cycle lengths. Rate-dependent change in the repolarization period was smaller in the cell sheets than that reported on the human hearts, which can be partly explained by lower gene expression level of hKCNJ2 and hKCNE1. Thus, non-linear equation for correcting FPD in the cell sheet; FPDc = FPD/RR0.22 with RR given in second was obtained, which may make it feasible to assess net repolarization delay by various chemical compounds with a chronotropic action.

Overexpression of KCNJ2 in induced pluripotent stem cell-derived cardiomyocytes for the assessment of QT-prolonging drugs.

Human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes hold great potentials to predict pro-arrhythmic risks in preclinical cardiac safety screening, although the hiPSC cardiomyocytes exhibit rather immature functional and structural characteristics, including spontaneous activity. Our physiological characterization and mathematical simulation showed that low expression of the inward-rectifier potassium (IK1) channel is a determinant of spontaneous activity. To understand impact of the low IK1 expression on the pharmacological properties, we tested if transduction of hiPSC-derived cardiomyocytes with KCNJ2, which encodes the IK1 channel, alters pharmacological response to cardiac repolarization processes. The transduction of KCNJ2 resulted in quiescent hiPSC-derived cardiomyocytes, which need pacing to elicit action potentials. Significant prolongation of paced action potential duration in KCNJ2-transduced hiPSC-derived cardiomyocytes was stably measured at 0.1 µM E-4031, although the same concentration of E-4031 ablated firing of non-treated hiPSC-derived cardiomyocytes. These results in single cells were confirmed by mathematical simulations. Using the hiPSC-derived cardiac sheets with KCNJ2-transduction, we also investigated effects of a range of drugs on field potential duration recorded at 1 Hz. The KCNJ2 overexpression in hiPSC-derived cardiomyocytes may contribute to evaluate a part of QT-prolonging drugs at toxicological concentrations with high accuracy.

General Introduction to Drebrin.

Drebrin was first discovered by our group as "developmentally regulated brain protein" from the chicken optic tectum. Drebrin is an actin-binding protein, which is classified into two major isoforms produced by alternative splicing from a single DBN1 gene. The isoform predominantly expressed in the adult brain (drebrin A) is neuron specific, containing a neuron-specific sequence (Ins2) in the middle of the molecule. Drebrin A is highly concentrated in dendritic spines, and its accumulation level is regulated by synaptic activity. In contrast, drebrin E, which lacks Ins2, is found in widespread but not ubiquitous cell types in various tissues. The isoform conversion from drebrin E to drebrin A occurs in parallel with synaptogenesis. Drebrin decorating F-actin is found at the recipient side of cell-cell communication systems, such as gap junctions, adherens junctions, immunological synapses, and neuronal synapses. In addition, it is involved in the cellular mechanisms of cell migration, cell process formation, cancer metastasis, and spermatogenesis. Lack of drebrin leads to the dysfunction of cell-cell communication, resulting in aberrant migration of metastatic cancer cells, aberrant synaptic function in dementia, and rupture of endothelial integrity. Because drebrin forms a unique F-actin with a longer helical crossover, drebrin may create an F-actin platform for molecular assembly and play a pivotal role in intercellular communication.

Role of Drebrin in Synaptic Plasticity.

Synaptic plasticity underlies higher brain function such as learning and memory, and the actin cytoskeleton in dendritic spines composing excitatory postsynaptic sites plays a pivotal role in synaptic plasticity. In this chapter, we review the role of drebrin in the regulation of the actin cytoskeleton during synaptic plasticity, under long-term potentiation (LTP) and long-term depression (LTD). Dendritic spines have two F-actin pools, drebrin-decorated stable F-actin (DF-actin) and drebrin-free dynamic F-actin (FF-actin). Resting dendritic spines change their shape, but are fairly constant over time at steady state because of the presence of DF-actin. Accumulation of DF-actin is inversely regulated by the intracellular Ca2+ concentration. However, LTP and LTD stimulation induce Ca2+ influx through N-methyl-D-aspartate (NMDA) receptors into the potentiated spines, resulting in drebrin exodus via myosin II ATPase activation. The potentiated spines change to excited state because of the decrease in DF-actin and thus change their shape robustly. In LTP, the Ca2+ increase via NMDA receptors soon returns to the basal level, and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) expression at the postsynaptic membrane is increased. The Ca2+ recovery and AMPAR increase coordinately induce the re-accumulation of DF-actin and change the dendritic spines from the excited state to steady state during LTP maintenance. During LTD, the prolonged intracellular Ca2+ increase inhibits the re-accumulation of DF-actin, resulting in facilitation of AMPAR endocytosis. Because of the positive feedback loop of the AMPAR decrease and drebrin re-accumulation inhibition, the dendritic spines are instable during LTD maintenance. Taken together, we propose the presence of resilient spines at steady state and plastic spines at excited state and discuss the physiological and pathological relevance of the two-state model to synaptic plasticity.

Nicotine induces mitochondrial fission through mitofusin degradation in human multipotent embryonic carcinoma cells.

Nicotine is considered to contribute to the health risks associated with cigarette smoking. Nicotine exerts its cellular functions by acting on nicotinic acetylcholine receptors (nAChRs), and adversely affects normal embryonic development. However, nicotine toxicity has not been elucidated in human embryonic stage. In the present study, we examined the cytotoxic effects of nicotine in human multipotent embryonal carcinoma cell line NT2/D1. We found that exposure to 10 µM nicotine decreased intracellular ATP levels and inhibited proliferation of NT2/D1 cells. Because nicotine suppressed energy production, which is a critical mitochondrial function, we further assessed the effects of nicotine on mitochondrial dynamics. Staining with MitoTracker revealed that 10 µM nicotine induced mitochondrial fragmentation. The levels of the mitochondrial fusion proteins, mitofusins 1 and 2, were also reduced in cells exposed to nicotine. These nicotine effects were blocked by treatment with mecamylamine, a nonselective nAChR antagonist. These data suggest that nicotine degrades mitofusin in NT2/D1 cells and thus induces mitochondrial dysfunction and cell growth inhibition in a nAChR-dependent manner. Thus, mitochondrial function in embryonic cells could be used to assess the developmental toxicity of chemicals.

Microglia enhance neurogenesis and oligodendrogenesis in the early postnatal subventricular zone.

Although microglia have long been considered as brain resident immune cells, increasing evidence suggests that they also have physiological roles in the development of the normal CNS. In this study, we found large numbers of activated microglia in the forebrain subventricular zone (SVZ) of the rat from P1 to P10. Pharmacological suppression of the activation, which produces a decrease in levels of a number of proinflammatory cytokines (i.e., IL-1ß, IL-6, TNF-α, and IFN-γ) significantly inhibited neurogenesis and oligodendrogenesis in the SVZ. In vitro neurosphere assays reproduced the enhancement of neurogenesis and oligodendrogenesis by activated microglia and showed that the cytokines revealed the effects complementarily. These results suggest that activated microglia accumulate in the early postnatal SVZ and that they enhance neurogenesis and oligodendrogenesis via released cytokines.

Early-stage development of human induced pluripotent stem cell-derived neurons.

Recent advances in human induced pluripotent stem cells (hiPSCs) offer new possibilities for biomedical research and clinical applications. Differentiated neurons from hiPSCs are expected to be useful for developing novel methods of treatment for various neurological diseases. However, the detailed process of functional maturation of hiPSC-derived neurons (hiPS neurons) remains poorly understood. This study analyzes development of hiPS neurons, focusing specifically on early developmental stages through 48 hr after cell seeding; development was compared with that of primary cultured neurons derived from the rat hippocampus. At 5 hr after cell seeding, neurite formation occurs in a similar manner in both neuronal populations. However, very few neurons with axonal polarization were observed in the hiPS neurons even after 48 hr, indicating that hiPS neurons differentiate more slowly than rat neurons. We further investigated the elongation speed of axons and found that hiPS neuronal axons were slower. In addition, we characterized the growth cones. The localization patterns of skeletal proteins F-actin, microtubule, and drebrin were similar to those of rat neurons, and actin depolymerization by cytochalasin D induced similar changes in cytoskeletal distribution in the growth cones between hiPS neurons and rat neurons. These results indicate that, during the very early developmental stage, hiPS neurons develop comparably to rat hippocampal neurons with regard to axonal differentiation, but the growth of axons is slower.

Structural development of stabilized helical peptides as inhibitors of estrogen receptor (ER)-mediated transcription.

Three types of stabilized helical peptides containing disulfide bonds, C-C cross-linked side chains, or α,α-disubstituted amino acids (2-aminoisobutyric acid (Aib)) were designed and synthesized as inhibitors of estrogen receptor (ER)-coactivator interactions. Furthermore, heptaarginine (R7)-conjugated versions of the peptides were prepared, and their effects on ER-mediated transcription were evaluated at the cellular level (in ER-positive T47D cells). Among them, the R7-conjugated peptides 11 and 12 downregulated the mRNA expression of pS2 (an ER-mediated gene whose expression is upregulated by 17ß-estradiol) by 95% (at a dose of 10 µM) and 87% (at a dose of 3 µM), respectively.

Possible effects of inhibition of IKr and IKs on field-potential waveforms in the human iPS cell-derived cardiomyocytes sheet.

In order to investigate how IKr and IKs inhibitions affect waveforms of the field potential in the human iPS cell-derived cardiomyocytes sheet, we analyzed the effects of E-4031 and chromanol 293B on the maximum upslope and peak amplitude of its second wave (n = 7 for each drug). E-4031 in 10-100 nM as well as chromanol 293B in 3-30 µM prolonged the field-potential duration, whereas E-4031 decreased the upslope in 10-100 nM and amplitude at 100 nM, which was not observed by chromanol 293B. Thus, the decrease of the upslope can be used as a supplemental marker of drug-induced IKr inhibition.