Abstract 15832: Suppression of Rad Activity Regulates L-type Ca2+ Channels and Causes Triggered Activities in Mouse Hearts
Background: We have reported that the ras-related small G-protein Rad plays a critical role in generating arrhythmias. However, its mechanism has not been fully understood. This study was designed to demonstrate the role of Rad in the heart by cardiac-specific overexpression or dominant negative suppression of Rad.
Methods and Results: Transgenic (TG) mice that overexpress wild type (WT) or dominant negative mutant Rad (S105N Rad) driven by α-myosin heavy chain promoter were generated. We recorded L-type calcium currents (ICa-L) and action potentials (APs) from isolated ventricular cardiomyocytes by voltage or current clamp mode using whole cell patch-clamp technique. The peak ICa-L was dramatically larger in the S105N Rad TG cells than in controls (−15.9 ± 1.0 pA/pF at 5mV [n=4] in S105N Rad versus −9.4 ± 0.9 pA/pF at 5mV [n=8] in controls; P < 0.01), whereas ICa-L was smaller in WT Rad TG cells (−6.4 ± 0.9 pA/pF at 5mV [n=10] in WT Rad versus control; P=0.03). In steady-state activation curves, there was no significant difference between S105N Rad cells and controls. However, the activation curves in WT Rad was shifted to depolarized direction (V1/2: −1.7 ± 1.5 mV [n=10] in WT Rad versus −6.4 ±0.8 mV [n=8] in controls; P=0.02). There were no significant differences in steady-state inactivation curves among these three groups. Recovery from inactivation in S105N Rad was faster than in controls (TAU: 174.2 ± 5.7ms [n=3] in S105N Rad versus 285.8 ± 15.7 ms [n=3] in controls; P<0.01). Action potential duration at 90% repolarization (APD90) in WT Rad was significantly shortened compared with control cells (APD90: 19.2 ± 3.1 msec [n=4] in WT Rad versus 30.8 ± 4.6msec [n=7] in controls; P=0.04), whereas it was significantly prolonged in S105N Rad cells (APD90: 54.7 ± 6.8 msec [n=7] in S105N Rad versus controls; P=0.01). Consistent with the prolonged APD90, Early afterdepolarization (EAD) and delayed afterdepolarization (DAD) were frequently observed in S105N Rad, despite no induction in WT Rad and control cells.
Conclusions: Our results provided the evidence that Rad regulated ICa-L as well as APD in mouse hearts, which leads to the induction of triggered activities. Thus, Rad might play a critical role in arrhythmogenesis.
- © 2010 by American Heart Association, Inc.