Abstract 9723: Calcium Loading Induces a PKC Isoform Switch That Activates Constitutive Acetylcholine Regulated Potassium Current in Atrial Fibrillation-Related Remodeling
Background: AF causes atrial tachycardia remodeling (ATR), with enhanced constitutive acetylcholine regulated K+ current (IKAChc) contributing to ATR-induced APD shortening and AF promotion. The present study examined the mechanisms underlying IKAChc activation; based on preliminary evidence for an essential role of phosphorylation, we evaluated the participation of protein kinase C (PKC).
Methods: Cultured dog atrial cardiomyocytes in vitro tachypaced (TP) at 3 Hz for 24 hours were compared to parallel 1 Hz paced cells and cells from ATR dogs (paced in vivo at 400 bpm x 1 week). IKAChc single channel activity was assessed in cell attached and cell free (I-O) patches. Protein expression was assessed by Western blot.
Results: In vitro TP for 24 hours activated IKAChc (Fig A), mimicking effects of in vivo ATR. The classical PKC isoform PKCα inhibited, whereas the novel isoform PKCε enhanced, IKAChc when applied to the intracellular side of I-O patches. TP and ATR downregulated PKCα (by 33, 37% respectively) and caused membrane translocation of PKCε, switching PKC-predominance to the stimulatory novel isoform. TP increased [Ca2+]i at 2 hours by 30% (Fig B), with subsequent return to baseline at 24 hrs. Ca2+ activates calpain, which breaks down proteins. Decreasing calpain activity during TP with PD150606 (20 µM) prevented TP enhancement of IKAChc (Fig C). Decreasing [Ca2+]i during TP with BAPTA-AM (1 µM), a cell permeable Ca2+ chelator, also prevented TP-enhancement of IKAChc (Fig D). Both PD150606 and BAPTA-AM prevented downregulation of PKCα protein expression by TP. Exposure of TP cells to a PKCε inhibitor (Fig E) suppressed TP-induced IKAChc activation, whereas a PKCα inhibitor (Fig F) enhanced IKAChc activity in 1 Hz cells.
Conclusions: Rate-related [Ca2+]i loading due to ATR causes a PKC isoform switch, with downregulation of inhibitory PKCα and membrane translocation (activation) of stimulatory PKCε, which enhances IKAChc causing APD shortening and AF promotion.
- © 2011 by American Heart Association, Inc.