Ryanodine receptor arrays: not just a pretty pattern?

Ryanodine receptors (RyRs) are colossal membrane protein complexes that reside in the endoplasmic reticulum of skeletal and cardiac muscle myocytes and neurons, in addition to many non-excitable cells. They comprise high-conductance ion channels that mediate the massive release of Ca2+ ions from the endoplasmic reticulum into the cytoplasm. This is the trigger for contraction during each muscle excitation-contraction coupling cycle. Individual RyRs are believed to network with other RyRs indirectly, through diffusion of released Ca2+ ions, namely the Ca2+-induced Ca2+ release phenomenon. However, RyRs can intrinsically organize into a regular array resembling a distinctive checkerboard pattern, with each square-shaped receptor appearing to abut four neighbours at each corner. In this opinion article, we describe recent data showing structural interactions between RyR oligomers in reconstituted arrays, and we suggest that this provides strong evidence for direct inter-RyR communication through a novel, allosteric regulatory mechanism.