Abstract 15732: Focal Non-Viral Gene Transfection of Ventricular Cardiomyocytes With Hcn1-hcn2 Channels Generates Ventricular Pacemakers in a Mouse Model of Complete Atrioventricular Block
We propose to develop biological cardiac pacemakers by in vivo non-viral gene transfer. We have shown that focal injection of plasmids coding the pacemaker channel Hcn2 and the β2-adrenoceptor (Adrb2) mixed with tetronic 614, a poloxamine block copolymer, in mice in complete atrioventricular block (CAVB) could generate ventricular pacemakers beating, 37% faster than ventricular escape rhythms in sham mice (non-coding plasmid). Our objective is now to improve the efficiency of our engineered biological pacemakers. Based on the functional differences between Hcn1 and Hcn2 isoforms, we engineered a pcDNA3-plasmid coding an Hcn1-Hcn2 fusion protein. Plasmids coding Hcn1-Hcn2 and Adrb2 mixed with tetronic 614 were injected focally in the left ventricular free wall of mice 7 days before CAVB obtained by radiofrequency-mediated ablation of the AV node. Hcn1-Hcn2 channel activated faster and at more positive voltages than Hcn2 (half-activation at −61±3 mV and −75±4 mV, respectively). Five days after AV node ablation, spontaneous ventricular escape rhythms were 41% faster in HCN1-HCN2/Adrb2 mice than in sham mice. This difference persisted over time: 15 and 25 days after ablation, Hcn1-Hcn2/Adrb2 had escape rhythms 57% and 56% faster respectively (RR of 230±22 ms and 240±27 ms) than in sham mice (RR of 363±38 ms and 361±28 ms; p<0.01 in both cases). These rhythms were also faster than in Hcn2/Adrb2 mice. Hcn1-Hcn2/Adrb2 mice were characterized by abnormal QRS axes and longer QRS intervals than sham mice (17±1 ms vs 11±1 ms at day 15) suggesting abnormal ventricular activation. The β-adrenergic agonist isoproterenol (40 µg/kg ip) increased ventricular rhythms more in Hcn1-Hcn2/Adrb2 mice (+44±2%) than in sham mice (+30±2%).
- © 2010 by American Heart Association, Inc.