Abstract 3814: Caveolin-3 Associates With and Regulates the Function of Re-expressed T-type Ca2+ Channels in Ventricular Myocytes in Pressure Overload Induced Cardiac Hypertrophy
Voltage gated T-type Ca2+ channels (TTCC) are normally expressed during cardiac development but are not expressed in adult cardiomyocytes. Cardiac TTCC isoforms, Cav3.1 and Cav3.2, are up regulated in cardiac hypertrophy and may contribute to the altered intracellular Ca2+ during this disease. However, the mechanism of altered Ca2+ signaling in cardiac hypertrophy is not clearly known. Caveolae containing scaffolding protein caveolin-3 (Cav-3), provide temporal and spatial regulation of intracellular Ca2+ in cardiomyocytes. The purpose of this study was to define the source of signaling Ca2+ involved and basis of dysregulated contractile function in cardiac hypertrophy. To investigate the role of caveolae and TTCC in the regulation of Ca2+ signaling in cardiomyocytes in cardiac hypertrophy, we used a pressure-overload induced (transverse aortic constriction; TAC) mouse model of cardiac hypertrophy. Western blot analysis revealed re expression of Cav3.1 and Cav3.2 proteins in adult ventricular tissue from TAC mice but not from control mice. Also, the expression of Cav-3 was significantly increased in the TAC mouse hearts compared to sham hearts. Transmission electron microscopy analysis demonstrated a significant increase in the number of caveolae and co-localization of Cav3.2 and Cav-3 in the ventricular myocytes in the TAC hearts. Immunoprecipitation and Western blot analysis from ventricular myocytes using anti Cav-3 antibody revealed that re-expressed Cav3.2 co-immunoprecipitates with Cav-3 in the TAC hearts, but not in sham hearts. Impact of Cav-3 association with CaV3.2 was analyzed by whole cell patch clamp technique in HEK293 cells co-expressed with CaV3.2 and either the wild-type Cav-3 or a dominant negative mutation of Cav-3 (P104L) that does not localize to plasmamembrane. Co-expression of Cav3.2 + Cav-3 significantly decreased the peak ICa,T (−15±2.5 pA/pF, n=10) compared to Cav3.2 + GFP (−37±3 pA/pF, n=9). Co-expression of Cav3.2 + P104LCav-3 almost completely inhibited peak ICa,T (−1.7±1 pA/pF, n=12). Our data demonstrate that increased expression of caveolae and Cav-3 in ventricular myocytes modulate T-type Ca2+ channel function and may play a crucial role in regulation of Ca2+ signaling during hypertrophic cardiomyopathy.
This research has received full or partial funding support from the American Heart Association, National Center.