Abstract 13169: In vivo TRPC3 Channel Blockade Suppresses Atrial Fibroblast Remodeling and AF Substrate in Dogs
Background: Cardiac fibroblast (FB) proliferation and differentiation plays a role in atrial fibrillation (AF), via profibrotic production of extracellular matrix (ECM) proteins and/or arrhythmogenic FB-cardiomyocyte electrical interaction. Ca2+-permeable transient receptor potential canonical (TRPC) channels couple mechanical stretch to cell-activation. Stretch is a strong FB activator, but the signaling pathways are poorly known. We previously reported TRPC3 dependent FB activation in a canine AF model based on in vitro work: AF increased fibroblast proliferation, differentiation and ECM gene expression; treatment with a selective TRPC3-blocker, pyrazole3 (Pyr3), suppressed the responses. Here, we tested the effect of TRPC3-blockade with Pyr3 on AF dogs in vivo.
Methods: Dogs kept in AF for 1 week by atrial pacing at 600 beats/min were treated with Pyr3 (n=7, 0.1 mg/kg/day), or vehicle (CTL, n=7). The drug was administrated continuously by osmotic pump. Cultured or freshly-isolated left atrial (LA) FBs were used for cell cycle analysis (flow cytometry) and qPCR.
Results: At terminal electrophysiological study, Pyr3 treated dogs showed significant decreases in spontaneously-maintained AF duration from 1197±245 s to 442±243* s (*p<0.05 vs. vehicle). They also had slightly but significantly greater effective refractory period at short cycle lengths (e.g. 80±6 ms vs. 96±5 ms* at 150 ms). Pyr3 treated dogs showed decreased vimentin protein expression (a FB marker, by 39%*) in LA tissues, suggesting decreased fibroblast density. In proliferation analysis, LA fibroblasts isolated from Pyr3-treated dogs showed decreased G2/M cell content (an index of cell division), by 5.2%* on Day 2 of culture, and decreased cell-number on Day 3, by 38%*, indicating decreased FB proliferation. In freshly isolated LA FBs, collagen-1 α1, collagen-1 α2, collagen-3 and fibrobectin-1 gene expression decreased in Pyr3-treated dogs by 71%*, 45%*, 34% (p=0.12) and 38% (p=0.09) respectively, indicating decreased ECM protein secretion.
Conclusions: In vivo treatment with Pyr3 suppresses FB proliferation, ECM gene expression and AF duration in AF dogs. TRPC3 channels are key signaling components for FB-remodeling and may represent an interesting anti-AF target.
- © 2012 by American Heart Association, Inc.