Sympathetic stimulation of adult cardiomyocytes requires association of AKAP5 with a subpopulation of L-type calcium channels.
BACKGROUND
Sympathetic stimulation of the heart increases the force of contraction and rate of ventricular relaxation by triggering protein kinase (PK)A-dependent phosphorylation of proteins that regulate intracellular calcium. We hypothesized that scaffolding of cAMP signaling complexes by AKAP5 is required for efficient sympathetic stimulation of calcium transients.


OBJECTIVE
We examined the function of AKAP5 in the β-adrenergic signaling cascade.


RESULTS
We used calcium imaging and electrophysiology to examine the sympathetic response of cardiomyocytes isolated from wild type and AKAP5 mutant animals. The β-adrenergic regulation of calcium transients and the phosphorylation of substrates involved in calcium handling were disrupted in AKAP5 knockout cardiomyocytes. The scaffolding protein, AKAP5 (also called AKAP150/79), targets adenylyl cyclase, PKA, and calcineurin to a caveolin 3-associated complex in ventricular myocytes that also binds a unique subpopulation of Ca(v)1.2 L-type calcium channels. Only the caveolin 3-associated Ca(v)1.2 channels are phosphorylated by PKA in response to sympathetic stimulation in wild-type heart. However, in the AKAP5 knockout heart, the organization of this signaling complex is disrupted, adenylyl cyclase 5/6 no longer associates with caveolin 3 in the T-tubules, and noncaveolin 3-associated calcium channels become phosphorylated after β-adrenergic stimulation, although this does not lead to an enhanced calcium transient. The signaling domain created by AKAP5 is also essential for the PKA-dependent phosphorylation of ryanodine receptors and phospholamban.


CONCLUSIONS
These findings identify an AKAP5-organized signaling module that is associated with caveolin 3 and is essential for sympathetic stimulation of the calcium transient in adult heart cells.
Nichols
C Blake
CB
Department of Pharmacology, University of Washington, Seattle, WA 98195, USA.
Rossow
Charles F
CF
Navedo
Manuel F
MF
Westenbroek
Ruth E
RE
Catterall
William A
WA
Santana
Luis F
LF
McKnight
G Stanley
GS
D054758:A Kinase Anchor Proteins / Q000378:metabolism* / Q000502:physiology; D000367:Age Factors; D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*
D054758:A Kinase Anchor Proteins; C520665:Akap5 protein, mouse; C514350:CACNA1C protein, mouse; D020746:Calcium Channels, L-Type; D011943:Receptors, Adrenergic, beta; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D007545:Isoproterenol