Live-cell photoactivated localization microscopy correlates nanoscale ryanodine receptor configuration to calcium sparks in cardiomyocytes
Yufeng Hou, Martin Laasmaa, Jia Li, Xin Shen, Ornella Manfra, Einar Sjaastad Nordén, Christopher Le, Lili Zhang, Ivar Sjaastad, Peter P. Jones, Christian Soeller, William E. Louch
Abstract
Abstract Ca 2+ sparks constitute the fundamental units of Ca 2+ release in cardiomyocytes. Here we investigate how ryanodine receptors (RyRs) collectively generate these events by employing a transgenic mouse with a photoactivated label on RyR2. This allowed correlative imaging of RyR localization, by super-resolution photoactivated localization microscopy, and Ca 2+ sparks, by high-speed imaging. Two populations of Ca 2+ sparks were observed: stationary events and ‘traveling’ events that spread between neighboring RyR clusters. Traveling sparks exhibited up to eight distinct releases, sourced from local or distal junctional sarcoplasmic reticulum. Quantitative analyses showed that sparks may be triggered by any number of RyRs within a cluster, and that acute β-adrenergic stimulation augments intracluster RyR recruitment to generate larger events. In contrast, RyR ‘dispersion’ during heart failure facilitates the generation of traveling sparks. Thus, RyRs cooperatively generate Ca 2+ sparks in a complex, malleable fashion, and channel organization regulates the propensity for local propagation of Ca 2+ release.