Pharmacology of P2X3 and P2X2/3 receptors: An automated patch clamp study.

Interaction of gating-modifier tarantula toxins with voltage-gated sodium channels.

Electrical impedance spectroscopy for drug screening on ligand-gated ion channels.

Acute PKA modulation of the cardiac sodium current is mediated by 14-3-3.

Input of expressed hERG current into a complex neuron in silico cardiac atrial cell: Implications for cardiotoxicity screening.

The Kv11.1 protein encoded by the hERG gene forms the primary subunit of a voltage-sensitive ion channel responsible for IKr in cardiomyocytes. Mathematical models of the macroscopic current are fitted to data from patch-clamp experiments - in which the whole-cell current is recorded in response to an applied voltage protocol. These models are a valuable tool for understanding the proarrhythmic effects of drugs and mutations, as they can provide accurate, quantitative predictions of the macroscopic current. In recent years, information rich protocols (that do not rely on the channels returning to steady state between voltage pulses) were designed to calibrate mathematical IKr models using short, dense time series. These protocols have been adapted for use on high-throughput automated patch clamp machines in CHO cells overexpressing hERG at either room or physiological temperatures. There are many choices of such protocols to apply during a patch-clamp experiment. We designed twelve protocols under various criteria, all of which should provide enough information to fit simple models of IKr uniquely. However, the parameters in imperfect models are forced to make different compromises to fit data from different protocols. The results highlight the impact of model discrepancy (the difference between models and reality) on parameter estimation and prediction. In particular, we show that the parameter estimates obtained depend on the chosen protocol, and how parameters fitted to protocols which highlight a significant amount of model discrepancy can lead to poor predictions. These results motivate the need for new experimental design methods that account for model discrepancy and aid in model selection. Furthermore, we suggest cross-validation as a tool to help evaluate the trustworthiness of model predictions, which may help identify good models of IKr as well as other macroscopic currents.

Technologies capable of assessing cellular metabolites with high precision and temporal resolution are currently limited. Recent developments in the field of nanopore sensors allow the non-stochastic quantification of metabolites, where a nanopore is acting as an electrical transducer for selective substrate binding proteins (SBPs). Here we show that incorporation of the pore-forming toxin Cytolysin A (ClyA) into the plasma membrane of Chinese hamster ovary cells (CHO-K1) results in the appearance of single-channel conductance amenable to multiplexed automated patch-clamp (APC) electrophysiology. In CHO-K1 cells, SBPs modify the ionic current flowing though ClyA nanopores, thus demonstrating its potential for metabolite sensing of living cells. Moreover, we developed a graphical user interface for the analysis of the complex signals resulting from multiplexed APC recordings. This system lays the foundation to bridge the gap between recent advances in the nanopore field (e.g., proteomic and transcriptomic) and potential cellular applications.

A predictive model for seal condition in an automated patch clamp system

Introduction: Rare titin-truncating variants ( TTN tv) are associated with early-onset atrial fibrillation (AF) but the pathogenic mechanisms and therapeutic implications remain unclear. To determine the function of a highly conserved immunoglobulin-like domain of the A-band of TTN , a region enriched in AF-associated variants, we employed CRISPR-Cas9-mediated deletion of 9 amino acids (Δ9) in human induced pluripotent stem cells and then derived atrial cardiomyocytes (hiPSC-aCMs) for electrophysiological (EP) analysis. Hypothesis: We hypothesized that the TTN -Δ9 mutation results in augmentation of the slow delayed rectifier potassium current (I Ks ) resulting in shortened action potential duration (APD). Methods: TTN -WT hiPSC-aCMs (healthy control) and TTN -Δ9 hiPSC-aCMs (isogenic mutant) were matured with metabolic conditioning, electrical stimulation, co-culture with atrial fibroblasts, and micropatterning. We used transmission electron microscopy (TEM) to assess sarcomeric defects, RNA-sequencing and RT-qPCR to assess molecular ion channel remodeling, and high throughput automated patch clamp and optical voltage mapping to assess the EP properties of TTN -Δ9 hiPSC-aCMs. We also performed targeted pharmacological inhibition of I Ks . Results: We showed that TTN -Δ9 hiPSC-aCMs displayed disrupted organization and myofibril assembly ( Fig. 1A-B ), upregulated voltage-gated potassium channel complexes and increased KCNQ1 expression ( Fig 1C-D ), and shortened APD ( Fig. 1E-F ). I Ks was significantly augmented in TTN -Δ9 hiPSC-aCMs ( Fig. 1G-H ). Infusion of the I Ks -specific blocker HMR-1556, and not I Kr blocker dofetilide, fully restored the shortened APD 90 and partially recovered defects in contractility in TTN -Δ9 hiPSC-aCMs compared to TTN -WT hiPSC-aCMs ( Fig. 1I-J ). Conclusion: Our findings suggest that augmentation of I Ks contributes to the pathogenic mechanism of TTN -mediated AF, pointing to I Ks as a potential therapeutic target.

Clozapine is an atypical neuroleptic used to manage treatment-resistant schizophrenia which is known to inhibit cardiac hERG/KV11.1 potassium channels, a pharmacological property associated with increased risk of potentially fatal Torsades de Pointes (TdP) and sudden cardiac death (SCD). Yet, the long-standing clinical practice of clozapine does not show a consistent association with increased incidence of TdP, although SCD is considerably higher among schizophrenic patients than in the general population. Here, we have established the inhibitory profile of clozapine at the seven cardiac ion currents proposed by the ongoing comprehensive in vitro pro-arrhythmia (CiPA) initiative to better predict new drug cardio-safety risk. We found that clozapine inhibited all CiPA currents tested with the following rank order of potency: KV11.1 > NaV1.5 (late current) ≈ CaV1.2 ≈ NaV1.5 (peak current) ≈ KV7.1 > KV4.3 > Kir2.1 (outward current). Half-maximal inhibitory concentrations (IC50) at the repolarizing KV11.1 and KV7.1 channels, and at the depolarizing CaV1.2 and NaV1.5 channels fell within a narrow half-log 3-10µM concentration range, suggesting that mutual compensation could explain the satisfactory arrhythmogenic cardio-safety profile of clozapine. Although the IC50 values determined herein using an automated patch-clamp (APC) technique are at the higher end of clozapine plasmatic concentrations at target therapeutic doses, this effective antipsychotic appears prone to distribute preferentially into the cardiac tissue, which supports the clinical relevance of our in vitro pharmacological findings.

Background: Variants in KCNH2, encoding the human ether a-go-go (hERG) channel that is responsible for the rapid component of the cardiac delayed rectifier K+ current (IKr), are causal to long QT syndrome type 2 (LQTS2). We identified eight index patients with a new variant of unknown significance (VUS), KCNH2:c.2717C > T:p.(Ser906Leu). We aimed to elucidate the biophysiological effect of this variant, to enable reclassification and consequent clinical decision-making. Methods: A genotype–phenotype overview of the patients and relatives was created. The biophysiological effects were assessed independently by manual-, and automated calibrated patch clamp. HEK293a cells expressing (i) wild-type (WT) KCNH2, (ii) KCNH2-p.S906L alone (homozygous, Hm) or (iii) KCNH2-p.S906L in combination with WT (1:1) (heterozygous, Hz) were used for manual patching. Automated patch clamp measured the variants function against known benign and pathogenic variants, using Flp-In T-rex HEK293 KCNH2-variant cell lines. Results: Incomplete penetrance of LQTS2 in KCNH2:p.(Ser906Leu) carriers was observed. In addition, some patients were heterozygous for other VUSs in CACNA1C, PKP2, RYR2 or AKAP9. The phenotype of carriers of KCNH2:p.(Ser906Leu) ranged from asymptomatic to life-threatening arrhythmic events. Manual patch clamp showed a reduced current density by 69.8 and 60.4% in KCNH2-p.S906L-Hm and KCNH2-p.S906L-Hz, respectively. The time constant of activation was significantly increased with 80.1% in KCNH2-p.S906L-Hm compared with KCNH2-WT. Assessment of KCNH2-p.S906L-Hz by calibrated automatic patch clamp assay showed a reduction in current density by 35.6%. Conclusion: The reduced current density in the KCNH2-p.S906L-Hz indicates a moderate loss-of-function. Combined with the reduced penetrance and variable phenotype, we conclude that KCNH2:p.(Ser906Leu) is a low penetrant likely pathogenic variant for LQTS2.

Human acid-sensing ion channels (ASIC) are ligand-gated ionotropic receptors expressed widely in peripheral tissues as well as sensory and central neurons and implicated in detection of inflammation, tissue injury, and hypoxia-induced acidosis. This makes ASIC channels promising targets for drug discovery in oncology, pain and ischemia, and several modulators have progressed into clinical trials. We describe the use of hASIC1a as a case study for the development and validation of low, medium and high throughput automated patch clamp (APC) assays suitable for the screening and mechanistic profiling of new ligands for this important class of ligand-gated ion channel. Initial efforts to expand on previous manual patch work describing an endogenous hASIC1a response in HEK cells were thwarted by low current expression and unusual pharmacology, so subsequent work utilized stable hASIC1a CHO cell lines. Ligand-gated application protocols and screening assays on the Patchliner, QPatch 48, and SyncroPatch 384 were optimized and validated based on pH activation and nM-μM potency of reference antagonists (e.g., Amiloride, Benzamil, Memantine, Mambalgin-3, A-317567, PcTx1). By optimizing single and stacked pipette tip applications available on each APC platform, stable pH-evoked currents during multiple ligand applications enabled cumulative EC50 and IC50 determinations with minimized receptor desensitization. Finally, we successfully demonstrated for the first time on an APC platform the ability to use current clamp to implement the historical technique of input resistance tracking to measure ligand-gated changes in membrane conductance on the Patchliner platform.

Structure–activity relationship studies in a new series of 2-amino-N-phenylacetamide inhibitors of Slack potassium channels

Transient Receptor Potential Melastatin 8 (TRPM8) from the melastatin TRP channel subfamily is a non-selective Ca2+-permeable ion channel with multimodal gating which can be activated by low temperatures and cooling compounds, such as menthol and icilin. Different conditions such as neuropathic pain, cancer, overactive bladder syndrome, migraine, and chronic cough have been linked to the TRPM8 mode of action. Despite the several potent natural and synthetic inhibitors of TRPM8 that have been identified, none of them have been approved for clinical use. The aim of this study was to discover novel blocking TRPM8 agents using automated patch clamp electrophysiology combined with a ligand-based virtual screening based on the SwissSimilarity platform. Among the compounds we have tested, nebivolol and carvedilol exhibited the greatest inhibitory effect, with an IC50 of 0.97 ± 0.15 µM and 9.1 ± 0.6 µM, respectively. This study therefore provides possible candidates for future drug repurposing and suggests promising lead compounds for further optimization as inhibitors of the TRPM8 ion channel.

This popular meeting occurred for the fifth time, returning after a 2-year break, with some 150 people attending to fill the maximum capacity. The proceedings included 22 oral presentations and 15 posters, altogether representing 14 countries. The topics covered voltage-gated potassium, calcium, and sodium channels as well as ligand-gated and mechanogated (piezo) ion channels. The relevant range of physiologies and pathophysiologies covered included taste, pain, neurodegenerative diseases, epilepsy, atrial fibrillation, Parkinson's disease, respiratory disease, and cancer. Speakers also regularly discussed possible clinical applications of their data. In addition, the symposium covered the latest automated patch clamp technologies with exhibits.

Crucial conventional patch-clamp approaches to investigate cellular electrophysiology suffer from low-throughput and require considerable experimenter expertise. Automated patch-clamp (APC) approaches are more experimenter independent and offer high-throughput, but by design are predominantly limited to assays containing small, homogenous cells. In order to enable high-throughput APC assays on larger cells such as native cardiomyocytes isolated from mammalian hearts, we employed a fixed-well APC plate format. A broad range of detailed electrophysiological parameters including action potential, L-type calcium current and basal inward rectifier current were reliably acquired from isolated swine atrial and ventricular cardiomyocytes using APC. Effective pharmacological modulation also indicated that this technique is applicable for drug screening using native cardiomyocyte material. Furthermore, sequential acquisition of multiple parameters from a single cell was successful in a high throughput format, substantially increasing data richness and quantity per experimental run. When appropriately expanded, these protocols will provide a foundation for effective mechanistic and phenotyping studies of human cardiac electrophysiology. Utilizing scarce biopsy samples, regular high throughput characterization of primary cardiomyocytes using APC will facilitate drug development initiatives and personalized treatment strategies for a multitude of cardiac diseases.

Abstract Cancer cells typically exhibit altered ion channel expression and membrane potential, wich plays an important role in various processes such as proliferation or apoptosis Hence, therapeutic strategies that modulate ion channel activity or shift the membrane potential prove to be promising for cancer therapy. Since temperature significantly affects ion channel function, deviation from normal body temperture might provide akey factor in electrophysiological progression. In this pilot study, we focused on a first insight into the temperature-induced modulation of A549 cells using an automated patch clamp system. Measurements of 14 cells at hypo-, normo- and hypertermia were accomplished to investigate the temperature-dependent electophysiological behavior. The results revealed that both, temperatures below and above normal body temperature affect the current and potential of A549 cells. In hyperthermia the potential tends to more hyperpolarized values, while conversely, in hypothermic conditions we observer mainly a lower current reponse and thus a depolarization of the membrane potential.

Fluoride has been used in the internal recording solution for manual and automated patch clamp experiments for decades because it helps to improve the seal resistance and promotes longer lasting recordings. In manual patch clamp, fluoride has been used to record voltage-gated Na (NaV) channels where seal resistance and access resistance are critical for good voltage control. In automated patch clamp, suction is applied from underneath the patch clamp chip to attract a cell to the hole and obtain a good seal. Since the patch clamp aperture cannot be moved to improve the seal like the patch clamp pipette in manual patch clamp, automated patch clamp manufacturers use internal fluoride to improve the success rate for obtaining GΩ seals. However, internal fluoride can affect voltage-dependence of activation and inactivation, as well as affecting internal second messenger systems and therefore, it is desirable to have the option to perform experiments using physiological, fluoride-free internal solution. We have developed an approach for high throughput fluoride-free recordings on a 384-well based automated patch clamp system with success rates >40% for GΩ seals. We demonstrate this method using hERG expressed in HEK cells, as well as NaV1.5, NaV1.7, and KCa3.1 expressed in CHO cells. We describe the advantages and disadvantages of using fluoride and provide examples of where fluoride can be used, where caution should be exerted and where fluoride-free solutions provide an advantage over fluoride-containing solutions.

Channelrhodopsins (ChRs) are proteins that guide phototaxis in protists and exhibit light-gated channel conductance when their genes are heterologously expressed in mammalian cells. ChRs are widely used as molecular tools to control neurons and cardiomyocytes with light (optogenetics). Cation- and anion-selective ChRs (CCRs and ACRs, respectively) enable stimulation and inhibition of neuronal activity by depolarization and hyperpolarization of the membrane, respectively. More than 400 natural ChR variants have been identified so far, and high-throughput polynucleotide sequencing projects add many more each year. However, electrophysiological characterization of new ChRs lags behind because it is mostly done by time-consuming manual patch clamp (MPC). Here we report using a high-throughput automated patch clamp (APC) platform, SyncroPatch 384i from Nanion Technologies, for ChR research. We find that this instrument can be used for determination of the light intensity dependence and current-voltage relationships in ChRs and discuss its advantages and limitations.

High throughput measurement of hERG drug block kinetics using the CiPA dynamic protocol