Functional LTCC-β₂AR Complex Needs Caveolin-3 and Is Disrupted in Heart Failure

Beta-2 adrenergic receptors (β₂ARs) but not beta-2 adrenergic receptors (β₁ARs) form a functional complex with L-type Ca²⁺ channels (LTCCs) on the cardiomyocyte membrane. However, how microdomain localization in the plasma membrane affects the function of these complexes is unknown. We aim to study the coupling between LTCC and β adrenergic receptors in different cardiomyocyte microdomains, the distinct involvement of PKA and CAMKII (Ca²⁺/calmodulin-dependent protein kinase II) and explore how this functional complex is disrupted in heart failure.

Global signaling between LTCCs and β adrenergic receptors was assessed with whole-cell current recordings and western blot analysis. Super-resolution scanning patch-clamp was used to explore the local coupling between single LTCCs and β₁AR or β₂AR in different membrane microdomains in control and failing cardiomyocytes.

LTCC open probability (Po) showed an increase from 0.054±0.003 to 0.092±0.008 when β₂AR was locally stimulated in the proximity of the channel (<350 nm) in the transverse tubule microdomain. In failing cardiomyocytes, from both rodents and humans, this transverse tubule coupling between LTCC and β₂AR was lost. Interestingly, local stimulation of β₁AR did not elicit any change in the Po of LTCCs, indicating a lack of proximal functional interaction between the two, but we confirmed a general activation of LTCC via β₁AR. By using blockers of PKA and CaMKII and a Caveolin-3-knockout mouse model, we conclude that the β₂AR-LTCC regulation requires the presence of caveolin-3 and the activation of the CaMKII pathway. By contrast, at a cellular "global" level PKA plays a major role downstream β₁AR and results in an increase in LTCC current.

Regulation of the LTCC activity by proximity coupling mechanisms occurs only via β₂AR, but not β₁AR. This may explain how β₂ARs tune the response of LTCCs to adrenergic stimulation in healthy conditions. This coupling is lost in heart failure; restoring it could improve the adrenergic response of failing cardiomyocytes.