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 β-adrenergic receptor signaling pathway, responsible for the conversion of ATP to the second messenger, cAMP. AC types 5 (ACV) and 6 (ACVI) 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 ACV and ACVI knockout mouse models to test the hypothesis that there is distinct compartmentalization of these isoforms in ventricular myocytes. METHODS AND
RESULTS: We demonstrate that ACV and ACVI isoforms exhibit distinct subcellular localization. The ACVI isoform is localized in the plasma membrane outside the t-tubular region and is responsible for β1-adrenergic receptor signaling-mediated enhancement of the L-type Ca(2+) current (ICa,L) in ventricular myocytes. In contrast, the ACV isoform is localized mainly in the t-tubular region where its influence on ICa,L is restricted by phosphodiesterase. We further demonstrate that the interaction between caveolin-3 with ACV and phosphodiesterase is responsible for the compartmentalization of ACV signaling.
CONCLUSIONS: Our results provide new insights into the compartmentalization of the 2 AC isoforms in the regulation of ICa,L in ventricular myocytes. Because caveolae are found in most mammalian cells, the mechanism of β- adrenergic receptor and AC compartmentalization may also be important for β-adrenergic receptor signaling in other cell types.