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 (βAR) signaling pathway, responsible for the conversion of ATP to the second messenger, cAMP. AC type 5 (ACV) and 6 (ACVI) are the two main isoforms in the heart. While highly homologous in sequence, these two proteins nevertheless 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 predominantly located 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 two isoforms in ventricular myocytes.
Methods and Results: We demonstrate that ACV and ACVI isoforms exhibit distinct subcellular localization. ACVI isoform is localized in the plasma membrane outside of the t-tubular region, and is responsible for β1AR signaling-mediated enhancement of the L-type Ca2+ current (ICa,L) in ventricular myocytes. In contrast, ACV isoform is localized mainly in the t-tubular region where its influence on ICa,L is restricted by phosphodiesterase (PDE). We further demonstrate that the interaction between caveolin-3 with ACV and PDE is responsible for the compartmentalization of ACV signaling.
Conclusions: Our results provide new insights into the compartmentalization of the two AC isoforms in the regulation of ICa,L in ventricular myocytes. Since caveolae are found in most mammalian cells, the mechanism of βAR and AC compartmentalization may also be important for βAR signaling in other cell types.
- Adenylyl cyclase type 5
- adenylyl cyclase type 6
- caveolin 3
- calcium channel
- cardiac myocyte
- adrenergic receptor
- Received October 24, 2012.
- Revision received April 9, 2013.
- Accepted April 22, 2013.