β-Adrenergic signaling accelerates and synchronizes cardiac ryanodine receptor response to a single L-type Ca²⁺ channel

• Published in: Proceedings of the National Academy of Sciences - PNAS 2009, Vol.106 (42), p.18028-18033
• Main Authors: Zhou, Peng, Zhao, Yan-Ting, Guo, Yun-Bo, Xu, Shi-Ming, Bai, Shu-Hua, Lakatta, Edward G, Cheng, Heping, Hao, Xue-Mei, Wang, Shi-Qiang
• Format: Article
• Language: English
• Subjects: agonists; antagonists; calcium; cAMP-dependent protein kinase; cardiovascular diseases; G-protein coupled receptors; heart; image analysis; ryanodine receptors; sarcoplasmic reticulum
• ISSN: 0027-8424; 1091-6490

As the most prototypical G protein-coupled receptor, β-adrenergic receptor (βAR) regulates the pace and strength of heart beating by enhancing and synchronizing L-type channel (LCC) Ca²⁺ influx, which in turn elicits greater sarcoplasmic reticulum (SR) Ca²⁺ release flux via ryanodine receptors (RyRs). However, whether and how βAR-protein kinase A (PKA) signaling directly modulates RyR function remains elusive and highly controversial. By using unique single-channel Ca²⁺ imaging technology, we measured the response of a single RyR Ca²⁺ release unit, in the form of a Ca²⁺ spark, to its native trigger, the Ca²⁺ sparklet from a single LCC. We found that acute application of the selective βAR agonist isoproterenol (1 μM, [less-than or equal to]20 min) increased triggered spark amplitude in an LCC unitary current-independent manner. The increased ratio of Ca²⁺ release flux underlying a Ca²⁺ spark to SR Ca²⁺ content indicated that βAR stimulation helps to recruit additional RyRs in synchrony. Quantification of sparklet-spark kinetics showed that βAR 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 Ca²⁺ content. The PKA antagonists Rp-8-CPT-cAMP (100 μM) and H89 (10 μM) both eliminated these effects, indicating that βAR acutely modulates RyR activation via the PKA pathway. These results demonstrate unequivocally that RyR activation by a single LCC is accelerated and synchronized during βAR stimulation. This molecular mechanism of sympathetic regulation will permit more fundamental studies of altered βAR effects in cardiovascular diseases.