Abstract 15009: Caveolin-3 Regulates Cardiac Repolarization by Integrated Regulation of Multiple Ionic Currents
Caveolae are discrete microdomains in cardiomyocytes in which a subset of ion channels and signaling proteins localize. Caveolin-3 (Cav3) is a muscle specific protein integral to caveolae in the cardiomyocytes. A reduction in caveolae and Cav3 expression is observed in cardiomyocytes in many cardiac diseases that are associated with prolonged cardiac repolarization, which puts patients at increased risk for arrhythmias and sudden cardiac death. Mutations in the CAV3 gene are also linked to congenital Long QT syndrome (LQT9). We hypothesize that cardiac caveolae provide integrated regulation of cardiac repolarization by controlling the functional properties of multiple types of ion channels. The impact of Cav3 expression levels on cardiac repolarization was determined using cardiac-specific conditional Cav3 knockout (Cav3-/-) mouse. Western blot and electron microscopy analysis demonstrated reduced expression Cav3 (88%) and the absence of caveolae in the ventricular myocytes of Cav3-/- mice compared to littermate wild type (WT) mice. The Cav3-/- mice demonstrated a significant increase in the conscious ECG QT interval determined by telemetry. Action potential duration (APD) measured in isolated ventricular myocytes at 1 Hz from Cav3-/- mice were significantly increased APD90: 87 ± 15 ms compared to WT cells (APD90: 18 ± 6 ms; n = 10, p<0.001). Whole-cell voltage clamp experiments in ventricular myocytes from the Cav3-/- mice demonstrated changes in a number of ionic currents including reduced peak Ito (19.6 ± 2.4 pA/pF compared to 11 ± 1.4 pA/pF in WT cells; n = 8, p<0.001), significant increase in late INa and delayed inactivation of ICa,L, but the peak INa and IK1 densities remain unchanged. Likewise, shRNA mediated knock down of Cav3 in human induced pluripotent stem cell derived cardiomyocytes resulted in significant prolongation of APD90: 758 ± 54 compared to control cells (APD90: 464 ± 48; n = 6, p<0.005). Our data demonstrate that a loss of Cav3 expression impacts the function of multiple types of ion channels in cardiomyocytes and causes prolongation of APD. We conclude that reduced Cav3 expression results in delayed cardiac repolarization and may be integrally linked to arrhythmias and sudden cardiac death in many prevalent forms of cardiac diseases.
- © 2013 by American Heart Association, Inc.