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Key points Channelopathies of autoimmune origin are novel and are associated with corrected QT (QTc) prolongation and complex ventricular arrhythmias., We have recently demonstrated that anti-SSA/Ro antibodies from patients with autoimmune diseases and with QTc prolongation on the ECG target the human ether-à-go-go-related gene (HERG) K+ channel by inhibiting the corresponding current, IKr, at the pore region., Immunization of guinea-pigs with a peptide (E-pore peptide) corresponding to the extracellular loop region connecting the S5 and S6 segments of the HERG channel induces high titres of antibodies that inhibit IKr, lengthen the action potential and cause QTc prolongation on the surface ECG. In addition, anti-SSA/Ro-positive sera from patients with connective tissue diseases showed high reactivity to the E-pore peptide., The translational impact is the development of a peptide-based approach for the diagnosis and treatment of autoimmune-associated long QT syndrome., Abstract We recently demonstrated that anti-SSA/52 kDa Ro antibodies (Abs) from patients with autoimmune diseases and corrected QT (QTc) prolongation directly target and inhibit the human ether-à-go-go-related gene (HERG) K+ channel at the extracellular pore (E-pore) region, where homology with SSA/52 kDa Ro antigen was demonstrated. We tested the hypothesis that immunization of guinea-pigs with a peptide corresponding to the E-pore region (E-pore peptide) will generate pathogenic inhibitory Abs and cause QTc prolongation. Guinea-pigs were immunized with a 31-amino-acid peptide corresponding to the E-pore region of HERG. On days 10-62 after immunization, ECGs were recorded and blood was sampled for the detection of E-pore peptide Abs. Serum samples from patients with autoimmune diseases were evaluated for reactivity to E-pore peptide by enzyme-linked immunosorbent assay (ELISA), and histology was performed on hearts using Masson's Trichrome. Inhibition of the HERG channel was assessed by electrophysiology and by computational modelling of the human ventricular action potential. The ELISA results revealed the presence of high titres of E-pore peptide Abs and significant QTc prolongation after immunization. High reactivity to E-pore peptide was found using anti-SSA/Ro Ab-positive sera from patients with QTc prolongation. Histological data showed no evidence of fibrosis in immunized hearts. Simulations of simultaneous inhibition of repolarizing currents by anti-SSA/Ro Ab-positive sera showed the predominance of the HERG channel in controlling action potential duration and the QT interval. These results are the first to demonstrate that inhibitory Abs to the HERG E-pore region induce QTc prolongation in immunized guinea-pigs by targeting the HERG channel independently from fibrosis. The reactivity of anti-SSA/Ro Ab-positive sera from patients with connective tissue diseases with the E-pore peptide opens novel pharmacotherapeutic avenues in the diagnosis and management of autoimmune-associated QTc prolongation. [ABSTRACT FROM AUTHOR]

Mancarella S, Yue Y, Karnabi E, Qu Y, El-Sherif N, Boutjdir M. Impaired Ca[sup2+] homeostasis is associated with atrial fibrillation in the α1D L-type Ca[sup2+] channel KU mouse. Am J Physiol Heart Circ Physiol 295: H2017-H2024, 2008. First published September 12, 2008; doi: 10.1152/ajpheart.00537.2008.-The novel α1D Ca[sup2+] channel together with α1D Ca[sup2+] channel contribute to the L-type Ca[sup2+] current (I[subCa-L]) in the mouse supraventricular tissue. However, its functional role in the heart is just emerging. We used the α1D gene knockout (KO) mouse to investigate the electrophysiological features, the relative contribution of the α1D Ca[sup2+] channel to the global I[subCa-L], the intracellular Ca[sup2+] transient, the Ca[sup2+] handling by the sarcoplasmic reticulum (SR), and the inducibility of atrial fibrillation (AF). In vivo and ex vivo ECG recordings from α1D KO mice demonstrated significant sinus bradycardia, atrioventricular block, and vulnerability to AF. The wild-type mice showed no ECG abnormalities and no AF. Patch-clamp recordings from isolated α1D KO atrial myocytes revealed a significant reduction of I[subCa-L] (24.5%; P < 0.05). However, there were no changes in other currents such as I[subNa], I[subCa-T], I[subK], If, and I[subf] and no changes in α[subIC] mRNA levels of α1D KO atria. Fura 2-loaded atrial myocytes showed reduced intracellular Ca[sup2+] transient (-40%; P < 0.05) and rapid caffeine application caused a 17% reduction of the SR Ca[sup2+] content (P < 0.05) and a 28% reduction (P < 0.05) of fractional SR Ca[sup2+] release in α1D KO atria. In conclusion, genetic deletion of α1D Ca[sup2+] channel in mice results in atrial electrocardiographic abnormalities and AF vulnerability. The electrical abnormalities in the α1D KO mice were associated with a decrease in the total I[subCa-L] density, a reduction in intracellular Ca[sup2+] transient, and impaired intracellular Ca[sup2+] handling. These findings provide new insights into the mechanism leading to atrial electrical dysfunction in the α1D KO mice. [ABSTRACT FROM AUTHOR]

Objectives: Ischemic preconditioning (PC) reduces myocardial infarction by a mechanism that involves opening of mitochondrial ATP-dependent potassium channels (mKATP), reactive oxygen species (ROS), and possibly activation of p38 mitogen-activated protein kinase (p38 MAPK). The actual order of these steps, however, is a matter of current debate. This study examined whether protection afforded by menadione, which protects by causing mitochondria to produce ROS, requires mKATP opening. In addition, we tested whether protection from anisomycin, a p38 MAPK activator, is dependent on ROS production. Methods and Results: Isolated, buffer-perfused rat hearts were pretreated with menadione, and infarction was assessed after 30 min of regional ischemia and 120 min of reperfusion. Menadione reduced infarction in a dose-dependent manner with an EC50 of 270 nM. Menadione’s infarct-limiting effect was insensitive to 200 μM 5-hydroxydecanoate (5HD), an mKATP channel blocker, whereas protection by diazoxide and PC were blocked by 5HD. Anisomycin caused hearts to resist infarction and this protective effect was abrogated by SB203580, a p38 MAPK inhibitor, and 2-mercaptopropionylglycine (MPG), a free radical scavenger. Conclusions: These results indicate that mKATP opening occurs upstream of mitochondrial ROS generation in the protective pathway. Furthermore, protection afforded by anisomycin was p38 MAPK- and ROS-dependent. [Copyright &y& Elsevier]

Presents a study which examined the role of mitochondrial free radicals in the cardioprotective effect of ischemic preconditioning in isolated rat hearts. Methodology; Results; Discussion.

There is debate concerning the involvement of p38 mitogen activated protein kinase (MAPK) in the mediation of ischaemic preconditioning. Pharmacological inhibition of p38 MAPK with SB203580 has been reported to block preconditioning in some studies but not in others. We hypothesised that this divergence could be due to differences in the timing of inhibitor administration. Isolated rat hearts were perfused in the Langendorff mode and subjected to 35 min regional ischaemia followed by 120 min reperfusion. Hearts were then double stained with Evans' blue and triphenyltetrazolium chloride to determine risk (R) and infarct zones (I), expressed as I/R% ratios. Preconditioned hearts were subjected to 2 times 5 min global ischaemia with 10 min intervening reperfusion. SB203580 10 μ M was perfused either during the preconditioning protocol (PC+SB-early), just prior to and during the first 15 min of the lethal ischaemia (PC+SB-late) or prior to regional ischaemia in the absence of preconditioning. Ischaemic preconditioning significantly limited infarct size (I/R 38.9 ± 3.0% in control vs 13.4 ± 2.4%, P < 0.01). In the PC+SB-early group, preconditioning was still fully protective (I/R% 14.6 ± 1.0). However, in the PC+SB-late group, SB203580 completely blocked the protection afforded by preconditioning (I/R% 33.6 ± 4.4%, P < 0.01 vs 13.4 ± 2.4% in preconditioned hearts, p < 0.05). SB203580 alone did not affect infarct size when given prior to and during regional ischaemia (I/R 36.2 ± 2.7%). These histological data are corroborated by a significant increase in p38 MAPK activation in the preconditioned hearts during sustained ischaemia in comparison with the controls. In conclusion the activation of p38 MAPK during lethal ischaemia, but not during the ischaemic preconditioning protocol, is essential for the mediation of protection and may resolve some of the earlier controversy surrounding the use of SB203580 in preconditioning studies. [ABSTRACT FROM AUTHOR]