A junctional cAMP compartment regulates rapid Ca2+ signaling in atrial myocytes

2022 | journal article; research paper. A publication with affiliation to the University of Göttingen.

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​A junctional cAMP compartment regulates rapid Ca2+ signaling in atrial myocytes​
Brandenburg, S. ; Pawlowitz, J.; Steckmeister, V.; Subramanian, H.; Uhlenkamp, D.; Scardigli, M. & Mushtaq, M. et al.​ (2022) 
Journal of Molecular and Cellular Cardiology165 pp. 141​-157​.​ DOI: https://doi.org/10.1016/j.yjmcc.2022.01.003 

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Authors
Brandenburg, Sören ; Pawlowitz, Jan; Steckmeister, Vanessa; Subramanian, Hariharan; Uhlenkamp, Dennis; Scardigli, Marina; Mushtaq, Mufassra; Amlaz, Saskia I.; Kohl, Tobias ; Wegener, Jörg W.; Lehnart, Stephan E. 
Abstract
Axial tubule junctions with the sarcoplasmic reticulum control the rapid intracellular Ca2+-induced Ca2+ release that initiates atrial contraction. In atrial myocytes we previously identified a constitutively increased ryanodine receptor (RyR2) phosphorylation at junctional Ca2+ release sites, whereas non-junctional RyR2 clusters were phosphorylated acutely following β-adrenergic stimulation. Here, we hypothesized that the baseline synthesis of 3′,5′-cyclic adenosine monophosphate (cAMP) is constitutively augmented in the axial tubule junctional compartments of atrial myocytes. Confocal immunofluorescence imaging of atrial myocytes revealed that junctin, binding to RyR2 in the sarcoplasmic reticulum, was densely clustered at axial tubule junctions. Interestingly, a new transgenic junctin-targeted FRET cAMP biosensor was exclusively co-clustered in the junctional compartment, and hence allowed to monitor cAMP selectively in the vicinity of junctional RyR2 channels. To dissect local cAMP levels at axial tubule junctions versus subsurface Ca2+ release sites, we developed a confocal FRET imaging technique for living atrial myocytes. A constitutively high adenylyl cyclase activity sustained increased local cAMP levels at axial tubule junctions, whereas β-adrenergic stimulation overcame this cAMP compartmentation resulting in additional phosphorylation of non-junctional RyR2 clusters. Adenylyl cyclase inhibition, however, abolished the junctional RyR2 phosphorylation and decreased L-type Ca2+ channel currents, while FRET imaging showed a rapid cAMP decrease. In conclusion, FRET biosensor imaging identified compartmentalized, constitutively augmented cAMP levels in junctional dyads, driving both the locally increased phosphorylation of RyR2 clusters and larger L-type Ca2+ current density in atrial myocytes. This cell-specific cAMP nanodomain is maintained by a constitutively increased adenylyl cyclase activity, contributing to the rapid junctional Ca2+-induced Ca2+ release, whereas β-adrenergic stimulation overcomes the junctional cAMP compartmentation through cell-wide activation of non-junctional RyR2 clusters.
Issue Date
2022
Journal
Journal of Molecular and Cellular Cardiology 
Project
EXC 2067: Multiscale Bioimaging 
SFB 1002: Modulatorische Einheiten bei Herzinsuffizienz 
SFB 1190: Transportmaschinen und Kontaktstellen zellulärer Kompartimente 
SFB 1190 | P03: Erhaltung und funktionelle Kopplung von ER-Kontakten mit der Plasmamembran 
Working Group
RG Hasenfuß 
RG Lehnart 
RG Voigt (Molecular Pharmacology) 
RG Brandenburg 
RG Nikolaev (Cardiovascular Research Center) 
ISSN
0022-2828
Language
English

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