Caveolin-3 KO disrupts t-tubule structure and decreases t-tubular I(Ca) density in mouse ventricular myocytes

Caveolin-3 (Cav-3) is a protein that has been implicated in t-tubule formation and function in cardiac ventricular myocytes. In cardiac hypertrophy and failure, Cav-3 expression decreases, t-tubule structure is disrupted, and excitation-contraction coupling is impaired. However, the extent to which the decrease in Cav-3 expression underlies these changes is unclear. We therefore investigated the structure and function of myocytes isolated from the hearts of Cav-3 knockout (KO) mice. These mice showed cardiac dilatation and decreased ejection fraction in vivo compared with wild-type control mice. Isolated KO myocytes showed cellular hypertrophy, altered t-tubule structure, and decreased L-type Ca(2+) channel current (I(Ca)) density. This decrease in density occurred predominantly in the t-tubules, with no change in total I(Ca), and was therefore a consequence of the increase in membrane area. Cav-3 KO had no effect on L-type Ca(2+) channel expression, and C3SD peptide, which mimics the scaffolding domain of Cav-3, had no effect on I(Ca) in KO myocytes. However, inhibition of PKA using H-89 decreased I(Ca) at the surface and t-tubule membranes in both KO and wild-type myocytes. Cav-3 KO had no significant effect on Na(+)/Ca(2+) exchanger current or Ca(2+) release. These data suggest that Cav-3 KO causes cellular hypertrophy, thereby decreasing t-tubular I(Ca) density. NEW & NOTEWORTHY Caveolin-3 (Cav-3) is a protein that inhibits hypertrophic pathways, has been implicated in the formation and function of cardiac t-tubules, and shows decreased expression in heart failure. This study demonstrates that Cav-3 knockout mice show cardiac dysfunction in vivo, while isolated ventricular myocytes show cellular hypertrophy, changes in t-tubule structure, and decreased t-tubular L-type Ca(2+) current density, suggesting that decreased Cav-3 expression contributes to these changes in cardiac hypertrophy and failure.