Extracellular hemin is a reverse use-dependent gating modifier of cardiac voltage-gated Na channels.

Heme (Fe-protoporphyrin IX) is a well-known protein prosthetic group; however, heme and hemin (Fe-protoporphyrin IX) are also increasingly viewed as signaling molecules. Among the signaling targets are numerous ion channels, with intracellular-facing heme-binding sites modulated by heme and hemin in the sub-µM range. Much less is known about extracellular hemin, which is expected to be more abundant, in particular after hemolytic insults.

Intracellular hemin is a potent inhibitor of the voltage-gated potassium channel Kv10.1.

Heme, an iron-protoporphyrin IX complex, is a cofactor bound to various hemoproteins and supports a broad range of functions, such as electron transfer, oxygen transport, signal transduction, and drug metabolism. In recent years, there has been a growing recognition of heme as a non-genomic modulator of ion channel functions. Here, we show that intracellular free heme and hemin modulate human ether à go-go (hEAG1, Kv10.

Fe-Mediated Activation of BK Channels by Rapid Photolysis of CORM-S1 Releasing CO and Fe.

Heme catabolism by heme oxygenase (HO) with a decrease in intracellular heme concentration and a concomitant local release of CO and Fe has the potential to regulate BK channels. Here, we show that the iron-based photolabile CO-releasing molecule CORM-S1 [dicarbonyl-bis(cysteamine)iron(II)] coreleases CO and Fe, making it a suitable light-triggered source of these downstream products of HO activity. To investigate the impact of CO, iron, and cysteamine on BK channel activation, human Slo1 (hSlo1) was expressed in HEK293T cells and studied with electrophysiological methods.

Linkage Evidence for a Two-Locus Inheritance of LQT-Associated Seizures in a Multigenerational LQT Family With a Novel Loss-of-Function Mutation.

Mutations in several genes encoding ion channels can cause the long-QT (LQT) syndrome with cardiac arrhythmias, syncope and sudden death. Recently, mutations in some of these genes were also identified to cause epileptic seizures in these patients, and the sudden unexplained death in epilepsy (SUDEP) was considered to be the pathologic overlap between the two clinical conditions. For LQT-associated mutations, only few investigations reported the coincidence of cardiac dysfunction and epileptic seizures.

Disruption of Membrane Integrity by the Bacterium-Derived Antifungal Jagaricin.

Jagaricin is a lipopeptide produced by the bacterial mushroom pathogen , the causative agent of mushroom soft rot disease. Apart from causing lesions in mushrooms, jagaricin is a potent antifungal active against human-pathogenic fungi. We show that jagaricin acts by impairing membrane integrity, resulting in a rapid flux of ions, including Ca, into susceptible target cells.

ANK2 functionally interacts with KCNH2 aggravating long QT syndrome in a double mutation carrier.

Pathogenic long QT mutations often comprise high phenotypic variability and particularly variants in ANK2 (long QT syndrome 4) frequently lack QT prolongation. We sought to elucidate the genetic and functional background underlying the clinical diversity in a 3-generation family with different cardiac arrhythmias. Next-generation sequencing-based screening of patients with QT prolongation identified the index patient of the family carrying an ANK2-E1813K variant and a previously uncharacterized KCNH2-H562R mutation in a double heterozygous conformation.

CO-independent modification of K channels by tricarbonyldichlororuthenium(II) dimer (CORM-2).

Although toxic when inhaled in high concentrations, the gas carbon monoxide (CO) is endogenously produced in mammals, and various beneficial effects are reported. For potential medicinal applications and studying the molecular processes underlying the pharmacological action of CO, so-called CO-releasing molecules (CORMs), such as tricabonyldichlororuthenium(II) dimer (CORM-2), have been developed and widely used. Yet, it is not readily discriminated whether an observed effect of a CORM is caused by the released CO gas, the CORM itself, or any of its intermediate or final breakdown products.

Synthesis and solution stability of water-soluble κN,κO-bis(3,5-dimethylpyrazolyl)ethanol manganese(i) tricarbonyl bromide (CORM-ONN1).

The reaction of (OC)MnBr with bis(3,5-dimethyl-1-pyrazolyl)methane yields [{(Pz)CH}Mn(CO)Br] (1). The use of tridentate heteroscorpionates such as bis(3,5-dimethyl-1-pyrazolyl)acetic acid and 2,2-bis(3,5-dimethyl-1-pyrazolyl)ethanol leads to the formation of mononuclear [(OC)Mn{(Pz)CH-CO}] (2) and [(OC)Mn{(Pz)CH-CHOH}]Br (3, CORM-ONN1). Salt-like photoCORM 3 is soluble in aqueous media up to a concentration of 200 μM, non-toxic up to an approx.

CORM-EDE1: A Highly Water-Soluble and Nontoxic Manganese-Based photoCORM with a Biogenic Ligand Sphere.

[Mn(CO)5Br] reacts with cysteamine and 4-amino-thiophenyl with a ratio of 2:3 in refluxing tetrahydrofuran to the complexes of the type [{(OC)3Mn}2(μ-SCH2CH2NH3)3]Br2 (1, CORM-EDE1) and [{(OC)3Mn}2(μ-SC6H4-4-NH3)3]Br2 (2, CORM-EDE2). Compound 2 precipitates during refluxing of the tetrahydrofuran solution as a yellow solid whereas 1 forms a red oil that slowly solidifies. Recrystallization of 2 from water yields the HBr-free complex [{(OC)3Mn}2(μ-S-C6H4-4-NH2)2(μ-SC6H4-4-NH3)] (3).

Carbon monoxide release properties and molecular structures of phenylthiolatomanganese(I) carbonyl complexes of the type [(OC)4Mn(μ-S-aryl)]2.

Several phenylthiolatomanganese carbonyl complexes of the type [(OC)4Mn(μ-SR)]2 (R = Ph (), C6H4-4-CH3 (), C6H4-4-CF3 (), C6H4-4-F (), C6H4-4-Cl (), C6H4-4-OMe (), C6F5 (), and CH2C6H4-4-Cl ()) have been prepared via the reaction of Mn2(CO)10 with diaryldisulfane or via the reaction of [(OC)5MnBr] with arylthiols. These complexes lose two carbon monoxide molecules quite easily yielding tetranuclear [(OC)3Mn(μ3-SR)]4 (). Derivatives with fluoro-substituted aryl groups commonly form mixtures of dinuclear and tetranuclear which can quantitatively be converted to by heating of the corresponding reaction mixtures.

Critical role of large-conductance calcium- and voltage-activated potassium channels in leptin-induced neuroprotection of N-methyl-d-aspartate-exposed cortical neurons.

In the present study, the neuroprotective effects of the adipokine leptin, and the molecular mechanism involved, have been studied in rat and mice cortical neurons exposed to N-methyl-d-aspartate (NMDA) in vitro. In rat cortical neurons, leptin elicited neuroprotective effects against NMDA-induced cell death, which were concentration-dependent (10-100 ng/ml) and largest when the adipokine was preincubated for 2h before the neurotoxic stimulus. In both rat and mouse cortical neurons, leptin-induced neuroprotection was fully antagonized by paxilline (Pax, 0.

Molecular mechanism of pharmacological activation of BK channels.

Large-conductance voltage- and Ca(2+)-activated K(+) (Slo1 BK) channels serve numerous cellular functions, and their dysregulation is implicated in various diseases. Drugs activating BK channels therefore bear substantial therapeutic potential, but their deployment has been hindered in part because the mode of action remains obscure. Here we provide mechanistic insight into how the dehydroabietic acid derivative Cym04 activates BK channels.

Dicarbonyl-bis(cysteamine)iron(II): a light induced carbon monoxide releasing molecule based on iron (CORM-S1).

Carbon monoxide releasing molecules (CORMs) deliver controlled amounts of CO to biological targets and organs. The reaction of cysteamine with triirondodecacarbonyl yields dicarbonyl bis(aminoethylthiolato)iron(II) that represents an iron-based CORM with biogenic ligands. X-ray diffraction studies at a single crystal show a cis-arrangement of the carbonyl ligands in trans-position to the amino groups with average Fe-C and C-O distances of 176.

Cysteine 723 in the C-linker segment confers oxidative inhibition of hERG1 potassium channels.

Excess reactive oxygen species (ROS) play a crucial role under pathophysiological conditions, such as ischaemia/reperfusion and diabetes, potentially contributing to cardiac arrhythmia. hERG1 (KCNH2) potassium channels terminate the cardiac action potential and malfunction can lead to long-QT syndrome and fatal arrhythmia. To investigate the molecular mechanisms of hERG1 channel alteration by ROS, hERG1 and mutants thereof were expressed in HEK293 cells and studied with the whole-cell patch-clamp method.

The amiodarone derivative KB130015 activates hERG1 potassium channels via a novel mechanism.

Human ether à go-go related gene (hERG1) potassium channels underlie the repolarizing I(Kr) current in the heart. Since they are targets of various drugs with cardiac side effects we tested whether the amiodarone derivative 2-methyl-3-(3,5-diiodo-4-carboxymethoxybenzyl)benzofuran (KB130015) blocks hERG1 channels like its parent compound. Using patch-clamp and two-electrode voltage-clamp techniques we found that KB130015 blocks native and recombinant hERG1 channels at high voltages, but it activates them at low voltages.

A mutually exclusive alternative exon of slo1 codes for a neuronal BK channel with altered function.

Large-conductance Ca(2+)- and voltage-activated K(+) (BK) channels are comprised of four pore-forming -subunits (Slo1), whose mRNA is alternatively spliced in a cell-specific manner. Here we report the first case of a correctly spliced mutually exclusive exon in a mammalian (human and mouse) BK channel; an exon coding for the region from S6 to the RCK1 domain is exchanged for an alternative exon of the same length. The slo1 transcript with this novel exon is present in native brain tissues and inclusion of the alternative exon profoundly alters the channel's gating characteristics: faster activation at low Ca(2+) concentrations and greater open probability at resting membrane potential at high Ca(2+) concentrations.

The amiodarone derivative 2-methyl-3-(3,5-diiodo-4-carboxymethoxybenzyl)benzofuran (KB130015) opens large-conductance Ca2+-activated K+ channels and relaxes vascular smooth muscle.

2-methyl-3-(3,5-diiodo-4-carboxymethoxybenzyl)benzofuran (KB130015) has been developed to retain the antiarrhythmic properties of the parent molecule amiodarone but to eliminate its undesired side effects. In patch-clamp experiments, KB130015 activated large-conductance, Ca2+-activated BK(Ca) channels formed by hSlo1 (alpha) subunits in HEK 293 cells. Channels were reversibly activated by shifting the open-probability/voltage (P(o)/V) relationship by about -60 mV in 3 muM intracellular free Ca2+ ([Ca2+]in).

In vivo targeting of ERG potassium channels in mice and dogs by a positron-emitting analogue of fluoroclofilium.

The antiarrhythmic clofilium is an efficient blocker of hERG1 potassium channels that are strongly expressed in the heart. Therefore, derivatives of clofilium that emit positrons might be useful tools for monitoring hERG1 channels in vivo. Fluoro- clofilium (F-clofilium) was synthesized and its channel-blocking properties were determined for hERG1 and hEAG1 channels expressed in HEK?293 cells and in Xenopus oocytes.

Molecular determinants for high-affinity block of human EAG potassium channels by antiarrhythmic agents.

Undesired block of human ERG1 potassium channels is the basis for cardiac side effects of many different types of drugs. Therefore, it is important to know exactly why some drugs particularly bind to these channels with high affinity. Upon expression in mammalian cells and Xenopus laevis oocytes, we investigated the inhibition of the closely related hEAG1 and hEAG2 channels by agents that have previously been reported to block hERG1 channels.

Inhibition of hEAG1 and hERG1 potassium channels by clofilium and its tertiary analogue LY97241.

1 We investigated the inhibition of hEAG1 potassium channels, expressed in mammalian cells and Xenopus oocytes, by several blockers that have previously been reported to be blockers of hERG1 channels. 2 In the whole-cell mode of mammalian cells, LY97241 was shown to be a potent inhibitor of both hEAG1 and hERG1 channels (IC(50) of 4.9 and 2.

Functional distinction of human EAG1 and EAG2 potassium channels.

Human ether à go-go potassium channel 2 (hEAG2) was cloned and its properties were compared with the previously characterized isoform hEAG1. In the Xenopus oocyte expression system the time course of activation was about four times slower and the voltage required for half-maximal subunit activation was about 10 mV greater for hEAG2 channels. However, its voltage dependence was smaller and, therefore, hEAG2 channels start to open at more negative voltages than hEAG1.