Beta-adrenergic signaling accelerates and synchronizes cardiac ryanodine receptor response to a single L-type Ca2+ channel.
As the most prototypical G protein-coupled receptor, beta-adrenergic receptor (betaAR) regulates the pace and strength of heart beating by enhancing and synchronizing L-type channel (LCC) Ca(2+) influx, which in turn elicits greater sarcoplasmic reticulum (SR) Ca(2+) release flux via ryanodine receptors (RyRs). However, whether and how betaAR-protein kinase A (PKA) signaling directly modulates RyR function remains elusive and highly controversial. By using unique single-channel Ca(2+) imaging technology, we measured the response of a single RyR Ca(2+) release unit, in the form of a Ca(2+) spark, to its native trigger, the Ca(2+) sparklet from a single LCC. We found that acute application of the selective betaAR agonist isoproterenol (1 microM, < or = 20 min) increased triggered spark amplitude in an LCC unitary current-independent manner. The increased ratio of Ca(2+) release flux underlying a Ca(2+) spark to SR Ca(2+) content indicated that betaAR stimulation helps to recruit additional RyRs in synchrony. Quantification of sparklet-spark kinetics showed that betaAR stimulation synchronized the stochastic latency and increased the fidelity (i.e., chance of hit) of LCC-RyR intermolecular signaling. The RyR modulation was independent of the increased SR Ca(2+) content. The PKA antagonists Rp-8-CPT-cAMP (100 microM) and H89 (10 microM) both eliminated these effects, indicating that betaAR acutely modulates RyR activation via the PKA pathway. These results demonstrate unequivocally that RyR activation by a single LCC is accelerated and synchronized during betaAR stimulation. This molecular mechanism of sympathetic regulation will permit more fundamental studies of altered betaAR effects in cardiovascular diseases.
Zhou
Peng
P
State Key Laboratory of Biomembrane and Membrane Biotechnology, College of Life Sciences, Peking University, Beijing 100871, China.
Zhao
Yan-Ting
YT
Guo
Yun-Bo
YB
Xu
Shi-Ming
SM
Bai
Shu-Hua
SH
Lakatta
Edward G
EG
Cheng
Heping
H
Hao
Xue-Mei
XM
Wang
Shi-Qiang
SQ
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D018613:Microscopy, Confocal; D009200:Myocardial Contraction / Q000502:physiology; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology
D000318:Adrenergic beta-Agonists; D020746:Calcium Channels, L-Type; D011943:Receptors, Adrenergic, beta; D019837:Ryanodine Receptor Calcium Release Channel; D017868:Cyclic AMP-Dependent Protein Kinases; D007545:Isoproterenol