Background-Congenital heart block (CHB) is an autoimmune disease that affects fetuses/infants born to mothers with anti-Ro/La antibodies (positive IgG). Although the hallmark of CHB is complete atrioventricular block, sinus bradycardia has been reported recently in animal models of CHB. Interestingly, knockout of the neuroendocrine ␣ 1D Ca channel in mice results in significant sinus bradycardia and atrioventricular block, a phenotype reminiscent to that seen in CHB. Here, we tested the hypothesis that the ␣ 1D Ca channel is a novel target for positive IgG.

A novel acquired autoimmune-associated LQTS has been recently reported in adult patients carrying anti-Ro antibodies (anti-Ro Abs), 7-10 which result from an autoimmune response against the intracellular ribonucleoprotein, SSA/Ro antigen (Ro). The detection of circulating anti-Ro Abs is relatively Background-Emerging clinical evidence demonstrates high prevalence of QTc prolongation and complex ventricular arrhythmias in patients with anti-Ro antibody (anti-Ro Ab)-positive autoimmune diseases. We tested the hypothesis that anti-Ro Abs target the HERG (human ether-a-go-go-related gene) K + channel, which conducts the rapidly activating delayed K + current, I Kr , thereby causing delayed repolarization seen as QT interval prolongation on the ECG. Methods and Results-Anti-Ro Ab-positive sera, purified IgG, and affinity-purified anti-52kDa Ro Abs from patients with autoimmune diseases and QTc prolongation were tested on I Kr using HEK293 cells expressing HERG channel and native cardiac myocytes. Electrophysiological and biochemical data demonstrate that anti-Ro Abs inhibit I Kr to prolong action potential duration by directly binding to the HERG channel protein. The 52-kDa Ro antigen-immunized guinea pigs showed QTc prolongation on ECG after developing high titers of anti-Ro Abs, which inhibited native I Kr and crossreacted with guinea pig ERG channel. Conclusions-The data establish that anti-Ro Abs from patients with autoimmune diseases inhibit I Kr by cross-reacting with the HERG channel likely at the pore region where homology between anti-52-kDa Ro antigen and HERG channel is present. The animal model of autoimmune-associated QTc prolongation is the first to provide strong evidence for a pathogenic role of anti-Ro Abs in the development of QTc prolongation. It is proposed that adult patients with anti-Ro Abs may benefit from routine ECG screening and that those with QTc prolongation should receive counseling about drugs that may increase the risk for life-threatening arrhythmias. (QTc prolongation) 7-10 but not with conduction abnormalities (complete atrioventricular block), which is well described in children born to mothers with anti-Ro Abs.13,14 Accordingly, it is assumed that the adult heart does not represent an immunological target for anti-Ro Abs. However, emerging clinical observations suggest that anti-Ro Abs may be arrhythmogenic for the adult heart by causing QT interval prolongation.7-10 Specifically, in a cohort of CTD patients, more than half (58%) of patients with anti-Ro Abs displayed a prolonged QTc, with a mean QTc duration significantly longer in anti-Ro Ab-positive versus anti-Ro Ab-negative patients. 7 In a subsequent study, patients with CTD and anti-Ro Ab showed 5-fold higher incidence of complex ventricular arrhythmias compared with anti-Ro Ab-negative patients.9 Despite this high incidence of QTc prolongation and ventricular arrhythmias in patients with CTD, the pathogenesis of this autoimmuneassociated QTc prolongation in the adult remains poorly understood. Methods Study PopulationSe...

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 microM 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.

The recent discovery of zinc signals and their essential role in the redox signaling network implies that zinc homeostasis and the function of zinc-containing proteins are probably altered as a result of oxidative stress, suggesting new targets for pharmacological intervention. We hypothesized that the level of intracellular labile zinc is changed in hearts subjected to ischemia/reperfusion (I/R) and investigated whether the maintenance of myocardial zinc status protected heart functions. Using fluorescent imaging, we demonstrated decreased levels of labile zinc in the I/R hearts. Phorbol 12-myristate 13-acetate, a known trigger of zinc release, liberated zinc ions in control hearts but failed to produce any increase in zinc levels in the I/R rat hearts. Adding the zinc ionophore pyrithione at reperfusion improved myocardial recovery up to 100% and reduced the incidence of arrhythmias more than 2-fold. This effect was dose-dependent, and high concentrations of zinc were toxic. Adding membrane-impermeable zinc chloride was ineffective. Hearts from rats receiving zinc pyrithione supplements in their diet fully recovered from I/R. The recovery was associated with the prevention of degradation of the two protein kinase C isoforms, ␦ and , during I/R. In conclusion, our results suggest a protective role of intracellular zinc in myocardial recovery from oxidative stress imposed by I/R. The data support the potential clinical use of zinc ionophores in the settings of acute redox stress in the heart.