Figure 2

Examples of loose dyads. Electron micrographs selected to illustrate structural variability of the loose type of dyads. Top left: A dyad with a regular t-tubule (*) surrounded by a cisterna filled with homogenous electron-dense material and extending away from the t-tubule (arrows). Top right: Two dyads in a microdomain. The loose dyad between Z-lines has the junctional surface of cisterna partially deflected from the t-tubule (short arrow) and RyRs exposed to cytosol (long arrows). The compact dyad between A-bands of myofibrils contains a part of the longitudinal t-tubule (*) with well adherent cisterna (arrowhead). Bottom left: Two dyads in a microdomain. The dyad indicated by arrows is of the loose type because the junctional membrane of its cisterna deflects (short arrow) and extends (long arrow) from the t-tubule. The dyad made of regular t-tubule profile (*) is of the compact type of dyads. Bottom right: A dyad made of two cisternae (long arrows) and a deformed t-tubule (*). Numerous vesicles are present near the t-tubule (short arrows). Note: The left and the right columns show images taken from control and injured myocardia, respectively, but they represent characteristic dyads of both experimental groups.