Adenylyl Cyclase Subtype-Specific Compartmentalization Differential Regulation of L-Type Ca2+ Current in Ventricular Myocytes

Rationale: Adenylyl cyclase (AC) represents one of the principal molecules in the beta-adrenergic receptor signaling pathway, responsible for the conversion of ATP to the second messenger, cAMP. AC types 5 (AC(V)) and 6 (AC(VI)) are the 2 main isoforms in the heart. Although highly homologous in sequence, these 2 proteins play different roles during the development of heart failure. Caveolin-3 is a scaffolding protein, integrating many intracellular signaling molecules in specialized areas called caveolae. In cardiomyocytes, caveolin is located predominantly along invaginations of the cell membrane known as t-tubules. Objective: We take advantage of AC(V) and AC(VI) knockout mouse models to test the hypothesis that there is distinct compartmentalization of these isoforms in ventricular myocytes. Methods and Results: We demonstrate that AC(V) and AC(VI) isoforms exhibit distinct subcellular localization. The AC(VI) isoform is localized in the plasma membrane outside the t-tubular region and is responsible for beta(1)-adrenergic receptor signaling-mediated enhancement of the L-type Ca2+ current (I-Ca,I-L) in ventricular myocytes. In contrast, the AC(V) isoform is localized mainly in the t-tubular region where its influence on I-Ca,I-L is restricted by phosphodiesterase. We further demonstrate that the interaction between caveolin-3 with AC(V) and phosphodiesterase is responsible for the compartmentalization of AC(V) signaling. Conclusions: Our results provide new insights into the compartmentalization of the 2 AC isoforms in the regulation of I-Ca,I-L in ventricular myocytes. Because caveolae are found in most mammalian cells, the mechanism of beta-adrenergic receptor and AC compartmentalization may also be important for beta-adrenergic receptor signaling in other cell types.