Fig. 2.

Freeze–fracture replicas of plasmalemma from RyRs-expressing myotubes. Like WT RyR1, Ch-4rev, Ch-4+D2, Ch-2, Ch-2rev+D2, and RyR1+D2 rescued arrays of tetrads, although some tetrads are incomplete. Orange dots marking the center of complete and incomplete tetrads appear equally spaced at ≈40-nm intervals from each other, following an orthogonal array. Presence of short-range order in the tetrad arrays for Ch-2, RyR1+D2, Ch-4rev, Ch-2rev, and Ch-4+D2 are consistent with the reduced skeletal muscle EC coupling efficiency presented by these constructs. (Insets) Higher-magnification views of representative tetrad array from each picture. Expression of WT RyR3 shows that DHPR particles do not form tetrads but are randomly arranged. The small images at the bottom right are examples of randomly dispersed particle clusters illustrating the frequency of three- to four-particle, tetrad-like arrangements (asterisks) due to random chance.