De novo mutation responsible for atrial fibrillation in utero

Session 7 tigated patterns of gene expression in atrial tissues associated with the subsequent development of post-operative AF. Methods and Results: We obtained tissue at the time of cardiopulmonary bypass from the right atria of patients undergoing cardiac surgery, primarily coronary artery bypass grafting. Probes prepared from total RNA from these tissues were hybridized to the u95av2 Affymetrix microarray representing approximately 12,600 transcripts. We compared the gene expression profiles from the atria samples of patients who would subsequently develop post-operative AF to patients who would remain in sinus rhythm. We have successfully identified clusters of genes whose expression patterns are highly predictive for development of post-op AF. In our preliminary analysis, using just the gene expression profile, we can predict whether an atrial sample came from a patient who would go on to develop post-op AF with 75% accuracy. Many of the genes represented in these clusters have been shown to be involved in signal transduction pathways related to cell cycle control and apoptosis. Another functional category represented in the clusters includes those genes involved in cell-cell or cell-extracellular matrix signaling. Interestingly, there is relatively less representation of genes encoding ion channels or cytoskeletal proteins within these clusters. Furthermore there is little representation of genes involved in energetics and metabolism. Conclusion: Our genomic phenotyping of human atrial tissues revealed expression patterns that are predictive for the development of post-operative AF. Further investigation of the genes identified in this study may add to our understanding of the factors leading to susceptibility to this complication. AB7-2 DE NOVO MUTATION RESPONSIBLE FOR ATRIAL FIBRILLATION IN UTERO Kui Hong, MD, PhD, David R. Piper, Aurora DiazValdecantos, MD, Josep Brugada, MD, PhD, Elena Burashnikov, MS, Jose´ Santos-De-soto, MD, Josefina GruesoMontero, MD, Pedro Brugada, MD, PhD, Michael C. Sanguinetti, PhD and Ramo´n Brugada, MD. Masonic Medical Research Laboratory, Utica, NY, Department of Physiology and Nora Eccles Harrison Cardiovascular Research & Training Institute, University of Utah, Salt Lake City, UT, Hospital Virgen Macarena, Sevilla, Spain, Hospital Clinic, Barcelona, Spain, Hospital Virgen Rocio, Sevilla, Spain and Cardiovascular Research and Teaching Institute, Aalst, Belgium. Background: A gain-of-function mutation in KCNQ1 has been previously associated with familial atrial fibrillation. However, the presence of long QT in some of the members is inconsistent with the hastening of ventricular repolarization expected to be associated with a gain of function mutation. This study describes a novel genetic defect responsible for atrial fibrillation in utero and examines its biophysical basis. Methods and Results: A baby girl was born at 38 weeks after induction of delivery due to bradycardia since the 6th month. Echocardiogram showed a structurally normal heart. ECG revealed atrial fibrillation with slow ventricular response and short QT interval. Genetic analysis identified a missense mutation in KCNQ1 (V141M) present in the affected individual, but not present in the biological parents. To characterize the physiological consequences of the V141M mutation, Xenopus laevis oocytes were injected with cRNA encoding wild-type KCNQ1 (wt Q1) or mutant KCNQ1 subunits (V141M Q1) with or without the accessory subunit minK. Ionic currents were recorded using standard two-microelectrode voltage clamp techniques. In the absence of minK, wt Q1 and V141M Q1 currents had similar biophysical properties. Coexpression of wt Q1 ⫹ minK subunits induced the typical slowly activating and voltage-dependent IKs. In contrast, oocytes injected with cRNA encoding V141M Q1 ⫹ minK subunits exhibited an instantaneous and voltage-independent K⫹-selective current. Conclusion: Chronic atrial fibrillation in the young individual with a structurally normal heart is a very rare finding. The description of a novel, de novo gain of function mutation in KCNQ1, responsible for atrial fibrillation in utero indicates that some of these cases may have a genetic

S13 basis. Under physiological conditions, V141M Q1/minK channels would be expected to conduct a much greater outward current than wt channels and would hasten ventricular repolarization and shorten the QT interval. AB7-3 THE 825T-ALLELE OF THE GNB3 GENE IS ASSOCIATED WITH HIGHER BASAL INWARD RECTIFIER CURRENT IN HUMAN CHRONIC ATRIAL FIBRILLATION Dobromir Dobrev, MD, Adina Friedrich, Dorit Knuschke, Torsten Christ, MD, Erich Wettwer, PhD, Michael Knaut, MD and Ursula Ravens, MD. Department of Pharmacology and Toxicology, Dresden, Germany and Heart Centre, Dresden, Germany. The G-protein ␤3 subunit gene (GNB3) contains a C825T-polymorphism by which homozygous 825T-allele carriers exhibit higher basal inward rectifier current than the other genotypes. In addition, C825-allele carriers developing atrial fibrillation (AF) had higher IK1 than those in sinus rhythm (SR). Here we studied the interaction effects between GNB3 status and AF on inward rectifier current in voltage-clamped human atrial myocytes. Since at whole cell level we cannot differentiate between contribution of IK1 and the acetylcholine-activated current IK,ACh to enhanced basal current we tested the hypothesis that IK,ACh is constitutively active by using the selective IK,ACh blocker tertiapin. The patients were genotyped by PCR and restriction analysis. Basal current was larger in AF than in SR (at -100 mV: -21.9⫾1.0 pA/pF, n⫽169/55 [myocytes/patients] vs. -11.4⫾0.4 pA/pF, n⫽335/115, P⬍0.05). In SR, patients with TT genotype exhibited higher basal current than that with CC- and CT-genotype (TT, -15.8⫾1.3 pA/pF, n⫽17/7 vs. CC, -11.3⫾0.5 pA/pF, n⫽160/56 and CT, -11.1⫾0.7 pA/pF, n⫽158/52, P⬍0.05). The selective IK,ACh current blocker tertiapin (10 nM) had no effect on basal current of C825-allele carriers in SR but reduced it in patients with TT genotype (tertiapin-sensitive current: -3.1⫾0.6 pA/pF, n⫽5/2) suggesting basal IK,ACh activity in TT genotype. Stratifying the AF patients by GNB3 genotype revealed that basal current is higher in AF than in SR within all genotypes. However, 825T-allele carriers with AF had higher basal current than homozygous C825-allele carriers developing AF (CT, -25.2⫾1.6 pA/pF, n⫽79/24 and TT, 26.3⫾3.2 pA/pF, n⫽24/8 vs. CC, -16.5⫾1.1 pA/pF, n⫽66/23, P⬍0.05) suggesting higher basal current in 825T-allele carriers. Again, tertiapin (10 nM) blocked basal current of C825-allele carriers in AF yielding a tertiapin-sensitive current of 6.4⫾1.2 pA/pF (n⫽16/6). Our data suggests that increased basal inward rectifier current in homozygous 825T-allele carriers and patients with AF is associated with constitutively active IK,ACh current which may contribute to the initiation and/or perpetuation of AF. AB7-4 THE ITO/IKUR-BLOCKER AVE0118 INCREASES ATRIAL CONTRACTILITY BY ENHANCEMENT OF REVERSE MODE NAⴙ/ CA2ⴙ-EXCHANGE Ulrich Schotten, MD, PhD, Michelle Lamorgese, Laurie Castel, Erik Harks, PhD, Heinz Goegelein, PhD and David R. Van Wagoner, PhD. University of Maastricht, Maastricht, Netherlands, Cleveland Clinic Foundation, Cleveland, OH and Sanofi-Aventis, Frankfurt, Germany. Background: Loss of atrial contractility after cardioversion of atrial fibrillation (AF) contributes to the thromboembolic risk associated with this arrhythmia. We recently demonstrated that AVE0118, a newly developed blocker of ultrarapid delayed rectifier current (IKur) and transient outward current (Ito), enhances atrial contractility in patients with chronic AF. This study was designed to determine the cellular mechanisms of the positive inotropic effect of AVE0118. Methods: Cell shortening and transmembrane action potentials of freshly isolated canine atrial myocytes were recorded under current clamp conditions with the perforated patch technique (37°C). In action potential clamp experiments, the effect of the stored action potentials on cell shortening and the L-type Ca2⫹ current (ICaL) was studied. Ca2⫹ transients were recorded