Nanoscale organization of junctophilin-2 and ryanodine receptors within peripheral couplings of rat ventricular cardiomyocytes.

The peripheral distributions of the cardiac ryanodine receptor (RyR) and a junctional protein, junctophilin-2 (JPH2), were examined using single fluorophore localization-based super-resolution microscopy in rat ventricular myocytes. JPH2 was strongly associated with RyR clusters. Estimates of the colocalizing fraction of JPH labeling with RyR was ~90% within 30 nm of RyR clusters. This is comparable to fractions estimated from confocal data (~87%). Similarly, most RyRs were associated with JPH2 labeling in super-resolution images (~81% within 30 nm of JPH2 clusters). The shape of associated RyR clusters and JPH2 clusters were very similar, but not identical, suggesting that JPH2 is dispersed throughout RyR clusters and that the packing of JPH2 into junctions and the assembly of RyR clusters are tightly linked.