Abstract 10586: Caveolin-3 Restores Local cAMP Signaling Without Restoring T-Tubules in Response to ß2 Adrenergic Receptor Stimulation in Heart Failure
Objectives: In ventricular myocytes, β2 adrenergic receptors (β2ARs) are associated with caveolin-3 (cav3) molecules in T-tubules (TTs). In heart failure, cav3 expression is reduced and TTs are degraded, resulting in cav3-free, or lone β2ARs. We aimed to investigate mechanisms underlying changes to cAMP signaling caused by these changes. We hypothesized that association of β2ARs with cav3 in TTs is crucial for spatially confining cAMP in response to local β2 stimulation.
Methods and Results: A FRET-based cAMP sensor was expressed in control and failing ventricular myocytes. Using scanning ion conductance, a pipette was positioned within a single TT where β2ARs were stimulated. In control, cAMP remained local, while in failure cAMP was detected at distal sites. To guide interpretation of these results, we developed a computer model based on the Heijman et al. formulation, modified to include 1-dimensional long axis spatial distribution. Volumes containing cav3/β2ARs were represented as discrete (local response, also for sarcolemmal caveolae/β2ARs). That is, diffusion from these volumes was indirect, via connected cav3-free space (extra-caveolae and cytosol). In contrast, diffusion from lone β2ARs in cav3-free space was direct (diffuse response). As in experiments, β2 stimulation in a single TT yielded confined cAMP (top) because 85% of β2ARs were cav3 associated and therefore discrete. As in previous experiments, TT degradation in failure destroyed cav3/β2ARs associations, and in remaining TTs cav3 was reduced by 75%. This left 82% of total β2ARs as cav3-free, allowing cAMP to freely diffuse (middle). Addition of cav3 restored the confined response by scavenging 75% of lone β2ARs (bottom).
Conclusions: Association of β2ARs with cav3 in TTs is disrupted in failing ventricular myocytes causing pathologically diffuse cAMP signaling. Simulations revealed that cav3 is necessary and sufficient to correct this abnormality, despite prevailing TT degradation.
- © 2013 by American Heart Association, Inc.