Prolonged ATR activation induces Ca1.2 channel internalization in rat cardiomyocytes.

The cardiac L-type calcium channel is a multi-subunit complex that requires co-assembling of the pore-forming subunit Ca1.2 with auxiliary subunits Caαδ and Caβ. Its traffic has been shown to be controlled by these subunits and by the activation of various G-protein coupled receptors (GPCR). Here, we explore the consequences of the prolonged activation of angiotensin receptor type 1 (ATR) over Ca1.2 channel trafficking. Bioluminescence Resonance Energy Transfer (BRET) assay between β-arrestin and L-type channels in angiotensin II-stimulated cells was used to assess the functional consequence of ATR activation, while immunofluorescence of adult rat cardiomyocytes revealed the effects of GPCR activation on Ca1.2 trafficking. Angiotensin II exposure results in β-arrestin recruitment to the channel complex and an apparent loss of Ca1.2 immunostaining at the T-tubules. Accordingly, angiotensin II stimulation causes a decrease in L-type current, Ca transients and myocyte contractility, together with a faster repolarization phase of action potentials. Our results demonstrate that prolonged ATR activation induces β-arrestin recruitment and the subsequent internalization of Ca1.2 channels with a half-dose of AngII on the order of 100 nM, suggesting that this effect depends on local renin-angiotensin system. This novel ATR-dependent Ca1.2-trafficking modulation likely contributes to angiotensin II-mediated cardiac remodeling.