Inhibition of the voltage-gated potassium channel Kv1.5 by hydrogen sulfide attenuates remodeling through S-nitrosylation-mediated signaling.

The voltage-gated K channel plays a key role in atrial excitability, conducting the ultra-rapid rectifier K current (I) and contributing to the repolarization of the atrial action potential. In this study, we examine its regulation by hydrogen sulfide (HS) in HL-1 cardiomyocytes and in HEK293 cells expressing human Kv1.5.

Flecainide induces a sustained countercurrent dependent effect on RyR2 in permeabilized WT ventricular myocytes but not in intact cells.

While flecainide is now an accepted treatment for arrhythmias associated with catecholaminergic polymorphic ventricular tachycardia (CPVT), its mechanism of action remains controversial. In studies on myocytes from CPVT mice, inhibition of proarrhythmic Ca waves was initially attributed to a novel action on the type-2 ryanodine receptor (RyR2). However, subsequent work on wild type (WT) myocytes questioned the conclusion that flecainide has a direct action on RyR2.

Action potential responses to changes in stimulation frequency and isoproterenol in rat ventricular myocytes.

Purpose: Current understanding of ventricular action potential adaptation to physiological stress is generally based on protocols using non-physiological rates and conditions isolating rate effects from escalating adrenergic stimulation. To permit refined understanding, ventricular action potentials were assessed across physiological pacing frequencies in the presence and absence of adrenergic stimuli. Isolated and combined effects were analyzed to assess their ability to replicate in-vivo responses.

Deterministic and Stochastic Cellular Mechanisms Contributing to Carbon Monoxide Induced Ventricular Arrhythmias.

Chronic exposure to low levels of Carbon Monoxide is associated with an increased risk of cardiac arrhythmia. Microelectrode recordings from rat and guinea pig single isolated ventricular myocytes exposed to CO releasing molecule CORM-2 and excited at 0.2/s show repolarisation changes that develop over hundreds of seconds: action potential prolongation by delayed repolarisation, EADs, multiple EADs and oscillations around the plateau, leading to irreversible repolarisation failure.

Hydrogen sulfide regulates hippocampal neuron excitability via S-sulfhydration of Kv2.1.

Hydrogen sulfide (HS) is gaining interest as a mammalian signalling molecule with wide ranging effects. S-sulfhydration is one mechanism that is emerging as a key post translational modification through which HS acts. Ion channels and neuronal receptors are key target proteins for S-sulfhydration and this can influence a range of neuronal functions.

Kv1.3 voltage-gated potassium channels link cellular respiration to proliferation through a non-conducting mechanism.

Cellular energy metabolism is fundamental for all biological functions. Cellular proliferation requires extensive metabolic reprogramming and has a high energy demand. The Kv1.

Divergent skeletal muscle mitochondrial phenotype between male and female patients with chronic heart failure.

Background: Previous studies in heart failure with reduced ejection fraction (HFrEF) suggest that skeletal muscle mitochondrial impairments are associated with exercise intolerance in men. However, the nature of this relationship in female patients remains to be elucidated. This study aimed to determine the relationship between skeletal muscle mitochondrial impairments and exercise intolerance in male and female patients with HFrEF.

Coupling of Smoothened to inhibitory G proteins reduces voltage-gated K currents in cardiomyocytes and prolongs cardiac action potential duration.

SMO (Smoothened), the central transducer of Hedgehog signaling, is coupled to heterotrimeric G proteins in many cell types, including cardiomyocytes. In this study, we report that activation of SMO with SHH (Sonic Hedgehog) or a small agonist, purmorphamine, rapidly causes a prolongation of the action potential duration that is sensitive to a SMO inhibitor. In contrast, neither of the SMO agonists prolonged the action potential in cardiomyocytes from transgenic GCT/TTA mice, in which G signaling is impaired, suggesting that the effect of SMO is mediated by G proteins.

Multiple mechanisms mediating carbon monoxide inhibition of the voltage-gated K channel Kv1.5.

The voltage-gated K channel has key roles in the vasculature and in atrial excitability and contributes to apoptosis in various tissues. In this study, we have explored its regulation by carbon monoxide (CO), a product of the cytoprotective heme oxygenase enzymes, and a recognized toxin. CO inhibited recombinant Kv1.

A key role for peroxynitrite-mediated inhibition of cardiac ERG (Kv11.1) K channels in carbon monoxide-induced proarrhythmic early afterdepolarizations.

Exposure to CO causes early afterdepolarization arrhythmias. Previous studies in rats have indicated that arrhythmias arose as a result of augmentation of the late Na current. The purpose of the present study was to examine the basis for CO-induced arrhythmias in guinea pig myocytes in which action potentials (APs) more closely resemble those of human myocytes.

Heme oxygenase-1 derived carbon monoxide suppresses Aβ toxicity in astrocytes.

Neurodegeneration in Alzheimer's disease (AD) is extensively studied, and the involvement of astrocytes and other cell types in this process has been described. However, the responses of astrocytes themselves to amyloid β peptides ((Aβ; the widely accepted major toxic factor in AD) is less well understood. Here, we show that Aβ is toxic to primary cultures of astrocytes.

Epac2-Rap1 Signaling Regulates Reactive Oxygen Species Production and Susceptibility to Cardiac Arrhythmias.

Aims: In the heart, β-adrenergic signaling involves cyclic adenosine monophosphate (cAMP) acting via both protein kinase-A (PKA) and exchange protein directly activated by cAMP (Epac): a guanine nucleotide exchange factor for the small GTPase Rap1. Inhibition of Epac-Rap1 signaling has been proposed as a therapeutic strategy for both cancer and cardiovascular disease. However, previous work suggests that impaired Rap1 signaling may have detrimental effects on cardiac function.

Heme Oxygenase-1 Influences Apoptosis via CO-mediated Inhibition of K+ Channels.

Hypoxic/ischemic episodes can trigger oxidative stress-mediated loss of central neurons via apoptosis, and low pO2 is also a feature of the tumor microenvironment, where cancer cells are particularly resistant to apoptosis. In the CNS, ischemic insult increases expression of the CO-generating enzyme heme oxygenase-1 (HO-1), which is commonly constitutively active in cancer cells. It has been proposed that apoptosis can be regulated by the trafficking and activity of K(+) channels, particularly Kv2.

T-Type Ca2+ Channel Regulation by CO: A Mechanism for Control of Cell Proliferation.

T-type Ca(2+) channels regulate proliferation in a number of tissue types, including vascular smooth muscle and various cancers. In such tissues, up-regulation of the inducible enzyme heme oxygenase-1 (HO-1) is often observed, and hypoxia is a key factor in its induction. HO-1 degrades heme to generate carbon monoxide (CO) along with Fe(2+) and biliverdin.

Heme oxygenase-1 regulates cell proliferation via carbon monoxide-mediated inhibition of T-type Ca2+ channels.

Induction of the antioxidant enzyme heme oxygenase-1 (HO-1) affords cellular protection and suppresses proliferation of vascular smooth muscle cells (VSMCs) associated with a variety of pathological cardiovascular conditions including myocardial infarction and vascular injury. However, the underlying mechanisms are not fully understood. Over-expression of Cav3.

Carbon monoxide mediates the anti-apoptotic effects of heme oxygenase-1 in medulloblastoma DAOY cells via K+ channel inhibition.

Tumor cell survival and proliferation is attributable in part to suppression of apoptotic pathways, yet the mechanisms by which cancer cells resist apoptosis are not fully understood. Many cancer cells constitutively express heme oxygenase-1 (HO-1), which catabolizes heme to generate biliverdin, Fe(2+), and carbon monoxide (CO). These breakdown products may play a role in the ability of cancer cells to suppress apoptotic signals.

Cellular consequences of the expression of Alzheimer's disease-causing presenilin 1 mutations in human neuroblastoma (SH-SY5Y) cells.

Mutations in the presenilin 1 (PS1) gene lead to early-onset Alzheimer's disease with the S170F mutation causing the earliest reported age of onset. Expression of this, and other PS1 mutations, in SH-SY5Y cells resulted in significant loss of cellular viability compared to control cells. Basal Ca2+ concentrations in PS1 mutants were never lower than controls and prolonged incubation in Ca2+ -free solutions did not deplete Ca2+ stores, demonstrating there was no difference in Ca2+ leak from endoplasmic reticulum (ER) stores in PS1 mutants.

Virtual tissue engineering of the human atrium: modelling pharmacological actions on atrial arrhythmogenesis.

Computational models of human atrial cells, tissues and atria have been developed. Cell models, for atrial wall, crista terminalis, appendage, Bachmann's bundle and pectinate myocytes are characterised by action potentials, ionic currents and action potential duration (APD) restitution. The principal effect of the ion channel remodelling of persistent atrial fibrillation (AF), and a mutation producing familial AF, was APD shortening at all rates.

Quantitative prediction of the arrhythmogenic effects of de novo hERG mutations in computational models of human ventricular tissues.

Mutations to hERG which result in changes to the rapid delayed rectifier current I(Kr) can cause long and short QT syndromes and are associated with an increased risk of cardiac arrhythmias. Experimental recordings of I(Kr) reveal the effects of mutations at the channel level, but how these changes translate to the cell and tissue levels remains unclear. We used computational models of human ventricular myocytes and tissues to predict and quantify the effects that de novo hERG mutations would have on cell and tissue electrophysiology.

Role of intracellular domains in the function of the herg potassium channel.

The functional role of the large intracellular regions (which include the cyclic nucleotide binding domain, cNBD, and the Per-Arnt-Sim domain, PAS) in the herg channel is not well understood. We have studied possible interactions of the cNBD with other parts of the channel protein using lysine mutations to disrupt such interactions. Some lysine mutations caused significant right shifts in the voltage dependence of inactivation; almost all the mutants caused speeding up of deactivation time course.

A systematic analysis of backbone amide assignments achieved via combinatorial selective labelling of amino acids.

With the advent of high-yield cell-free expressions systems, many researchers are exploiting selective isotope labelling of amino acids to increase the efficiency and accuracy of the NMR assignment process. We developed recently a combinatorial selective labelling (CSL) method capable of yielding large numbers of residue-type and sequence-specific backbone amide assignments, which involves comparing cross-peak intensities in 1H- 15N HSQC and 2D 1H- 15N HNCO spectra collected for five samples containing different combinations of 13C- and 15N-labelled amino acids [Parker MJ, Aulton-Jones M, Hounslow A, Craven C J (2004) J Am Chem Soc 126:5020-5021]. In this paper we develop a robust method for establishing the reliability of these assignments.

Human non-pregnancy ribonuclease with anti-Kaposi's sarcoma activity.

Our demonstration of a 19kDa anti-Kaposi's sarcoma (KS) ribonuclease (RNase) in urine from a non-pregnant female may provide at least part of the explanation for the low incidence of KS in human females. N-terminal sequence analysis and isoelectric focusing of the purified RNase, coupled with the very low levels of anti-KS activity noted for recombinant forms of human eosinophil derived neurotoxin and human eosinophil cationic protein, suggest that the 19kDa enzyme is an eosinophilic protein whose potent anti-KS activity is dependent upon post-translational modifications that occur only in human cells.