Caveolar Disruption Of L-Type Calcium Channel And Ryanodine Receptor Facilitates Atrial Ectopy And Arrhythmogenesis In Heart Failure Mice

Atrial fibrillation (AF) often occurs during heart failure (HF). Ectopic foci that trigger AF, are linked to discrete atrial regions that experience the highest remodeling and clinically used for AF ablation; however, mechanisms of their arrhythmogenic propensity remain elusive. We employed in vivo ECG telemetry, in vitro optical mapping and confocal imaging of Ca 2+ transients (CaT) from myocytes isolated from the right atrial appendage (RAA) and inter-caval region (ICR) of wild type (WT, n=10), caveolin-3 knockout (KO, n=6) and 8-weeks post-myocardial infarction HF (n=8) mice. HF and KO mice showed an increased susceptibility to pacing-induced AF and enhanced ectopy originated exclusively from ICR. Optical mapping in isolated atria showed prolongation of CaT rise up time (CaT-RT) in HF ICR, which suggested a remodeled coupling between L-type Ca 2+ channels (LTCCs) and ryanodine receptors (RyRs) in this specific region. In WT mice, RAA consists of structured myocytes with a prominent transverse-axial tubular system (TATS) while ICR myocytes don’t have TATS. In RAA, CaT-RT depends on LTCCs in TATS triggering RyR, while in ICR, all the LTCCs are localized in surface caveolae where they can activate subsarcolemmal RyRs and lead to a slow diffusion of Ca 2+ inside the cell interior. Downregulation of caveolae was observed specifically in HF ICR. To mimic this, we used cav3-KO mice. Triggered activities were observed in myocytes isolated from HF and KO ICR, which presumably underlie the ectopic activities in tissue level. These myocytes presented significantly unsynchronized sarcoplasmic reticulum (SR) Ca 2+ releases (synchronization index: 10.8±0.9 in WT vs 38.3±4.1 in HF vs 21.5±2.1 in KO, p <0.01 for HF and KO vs WT respectively) especially at the subsarcolemmal space that prolongs CaT-RT (62.2±4.1 ms in WT vs 122.5±12.8 ms in KO, p <0.01). In addition, failing ICR myocytes showed a higher occurrence and size of spontaneous Ca 2+ sparks which were linked to CaMKII activity and associated phosphorylation of RyR. Our findings demonstrate that in HF, caveolar disruption creates “hot spots” for arrhythmogenic ectopic activity emanated from discrete vulnerable regions of the right atrium which are associated with desynchronized SR Ca 2+ release and elevated fibrosis.