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Quinoline-related antimalarial drugs have been associated with cardiotoxicity risk, in particular QT prolongation and QRS complex widening. In collaboration with Medicines for Malaria Venture, we discovered novel plasmepsin X (PMX) inhibitors for malaria treatment. The first lead compounds tested in anesthetized guinea pigs (GPs) induced profound QRS widening, although exhibiting weak inhibition of NaV1.5-mediated currents in standard patch clamp assays. To understand the mechanism(s) underlying QRS widening to identify further compounds devoid of such liability, we established a set of in vitro models including CaV1.2, NaV1.5 rate-dependence, and NaV1.8 patch clamp assays, human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM), and Langendorff-perfused isolated GP hearts. Six compounds were tested in all models including anesthetized GP, and 8 additional compounds were tested in vitro only. All compounds tested in anesthetized GP and isolated hearts showed a similar cardiovascular profile, consisting of QRS widening, bradycardia, negative inotropy, hypotension, and for some, QT prolongation. However, a left shift of the concentration–response curves was noted from in vitro to in vivo GP data. When comparing in vitro models, there was a good consistency between decrease in sodium spike amplitude in hiPSC-CM and QRS widening in isolated hearts. Patch clamp assay results showed that the QRS widening observed with PMX inhibitors is likely multifactorial, primarily due to NaV1.8 and NaV1.5 rate-dependent sodium blockade and/or calcium channel-mediated mechanisms. In conclusion, early de-risking of QRS widening using a set of different in vitro assays allowed to identify novel PMX inhibitors with improved cardiac safety profile. [ABSTRACT FROM AUTHOR]

Out of every 1000 people, 4 to 10 are estimated to have current epilepsy, which means they either still have seizures or need medication. Worldwide, an estimated 5 million people are diagnosed with epilepsy each year. The cause of epilepsy is still not entirely understood. Nonetheless, overactivation of voltagegated calcium (VGCC) and sodium (VGSC) channels as well as inhibition of potassium and chloride channels are some of the suggested mechanisms. As a result, modern antiepileptic medications prevent an excessive inflow of calcium and sodium. Nevertheless, the antiepileptic medications used today either have unfavorable side effects or a restricted ability to guard against seizures. VGCC and VGSC mutations are significant risk factors for a number of epilepsy types. Usually, the changes result in an increase in function by altering the biophysical characteristics of the channels. The development of medications that interact with several disease-causing targets is a contemporary tactic to increase the effectiveness of anticonvulsant medications and decrease their side effects. VGCC and one isoform of tetrodotoxin (TTX)-sensitive VGSC were found to be viable targets. Automated patch-clamping was utilized to test a greater number of chemicals. Stable transfected cell lines with consistently high expression levels were created and biophysically assessed prior to initiating the screening of chemical libraries. [ABSTRACT FROM AUTHOR]

It has been recently reported that the essential antioxidant element selenium has protective effects on cytosolic Ca2+ levels in cell lines. However, the effects of selenium on like transient receptor potential melastatin 2 ( TRPM2) in response to oxidative stress ( H2 O2) are not well understood. We investigated the effects of selenium on H2 O2-induced TRPM2 channel currents in the Chinese hamster ovary ( CHO) cell line using patch-clamp and fura-2 fluorescence imaging techniques. [ABSTRACT FROM AUTHOR]

Epilepsy is the fourth most common neurological disorder and affects people of all ages. Medication for epilepsy is often life-long and has a major impact on the quality of life - mostly being related to substantial adverse effects. Therefore, over 30% of people with epilepsy do not achieve sufficient seizure control whilst effective medication being available. Ion channels are often primary targets of anticonvulsant drugs. They can either act as blockers for voltage gated sodium and calcium channels or as activators for potassium or chloride channels. Additionally, modulators of ligand gated ion channels (GABAA or Glutamate receptors) are frequently used to treat epilepsy. Employing a panel of functional electrophysiological assays using patch-clamping on a broad range of voltage and ligand gated ion channels, we were able to successfully screen for drugs with a beneficial action profile. In successful leads we found drugs that selectively interacted with TTX sensitive, neuronal voltage gated sodium channels. Activation and fast inactivation were unchanged, while an increased affinity in the slow inactivated state was observed. This is a modern mode of action for anticonvulsive drugs. In contrast, traditional anticonvulsant drugs often show their major effects on the fast inactivated state of voltage gated sodium channels. For further improvement, new anticonvulsants interacting with multiple ion channels as primary targets should be developed. As promising targets one isoform of the TTX sensitive voltage gated sodium channels and a voltage gated calcium channel were identified. For the screening of larger number of compounds, automated patch-clamping was used. Before starting the screening of compound libraries, stably transfected cell lines with constant expression levels were developed and biophysically characterized. Based on the results of these experiments an assay was developed to be able to reliably differentiate effects on ion channels in certain states and at high throughput. [ABSTRACT FROM AUTHOR]

Epilepsy is the fourth most common neurological disorder and affects people of all ages. Medication for epilepsy is often life-long and has a major impact on the quality of life - mostly being related to substantial adverse effects. Therefore, over 30% of people with epilepsy do not achieve sufficient seizure control whilst effective medication being available. Ion channels are often primary targets of anticonvulsant drugs. They can either act as blockers for voltage gated sodium and calcium channels or as activators for potassium or chloride channels. Additionally, modulators of ligand gated ion channels (GABAA or Glutamate receptors) are frequently used to treat epilepsy. Employing a panel of functional electrophysiological assays using fluorescence based methods and patch-clamping on a broad range of voltage and ligand gated ion channels, we were able to successfully screen for drugs with a beneficial action profile. In successful leads we found drugs that selectively interacted with TTX sensitive, neuronal voltage gated sodium channels. Activation and fast inactivation were unchanged, while an increased affinity in the slow inactivated state was observed. This is a modern mode of action for anticonvulsive drugs. In contrast, traditional anticonvulsant drugs often show their major effects on the fast inactivated state of voltage gated sodium channels. One of the tested drugs showed substantial shifts of the voltage dependence of the slow inactivation only for NaV1.2 and 1.6. This favours this drug for treating patients with diseases with compromised NaV1.1 function in interneurons, such as Alzheimer's disease. For further improvement of anticonvulsants interacting with ion channels as primary targets, compound libraries are screened to identify drugs with multiple ion channel effects like blockers of TTX sensitive NaV channels and T type calcium channels. For this purpose, assays need to be improved and new assays need to be developed, to be able to reliably differentiate effects on ion channels in certain states and at high throughput. [ABSTRACT FROM AUTHOR]

An abstract of the research paper "Voltage gated sodium channels and epilepsy" by Simon Hebeisen that was presented in the conference 1st International Brain Research School held in August-September 2015, is presented.

ClC- channels play important physiological roles in all known phyla, from bacteria over plants to man. In mammalians nine isoforms have been identified. They can be divided in two branches. ClC-0 - ClC-k are expressed in the plasma membranes, while ClC-3 - ClC-7 were found in intracellular membranes. The channels expressed in the plasma membrane were characterized very well using electrophysiological methods like two electrode voltage clamp and the patch clamp technique, while little is known about the function and the properties of the intracellular vesicular ClC-channels. The crystallization of two bacterial ClC-channels showed that the functional unit consists of dimers, with each monomer forming its own ion pore. That result proved electrophysiological results which were done several years before the first ion channel was crystallized. During the electrophysiological analysis of the bacterial isoforms reconstituted in artificial lipid bilayers, it came out that these isoforms rather function as electrogenic Cl-/H+ exchangers than as ion channels. The same was shown recently for ClC-4 and ClC-5. This finding could help to stop the controversial discussion about the biophysical properties of these isoforms. So far only two auxiliary q-subunits are known for ClC-proteins. Barttin associates specifically with ClC-K channels, while Ostm1 binds to ClC-7. Barttin dramatically increases the surface expression and influences the biophysical properties of the ClC-K channels. As ClC-K channels are expressed in kidney and in the inner ear, mutated Barttin proteins lead to Bartter syndrome IV, a disease characterized by decreased renal salt reabsorption and deafness. [ABSTRACT FROM AUTHOR]

A correction to the article related to the mutation in CLCN2 encoding a voltage-gated chloride channel which are associated with idiopathic generalized epilepsies that was published in the March 3, 2003 issue is presented.