A model proposing the contribution of Tdn's to the jSR anchors and a possible positioning of Jct.
In the model the triad is seen in a view parallel to the T-tubule axis (as in Figs. 2 B–C and 3 B, D and F) and the RyR array is modeled as seen in this orientation. The proportion between RyR heights and their spacing is appropriate, as suggested to us by Dr M. Samso . Clusters (polymers) of six Tdn molecules, modeled roughly according to the topology proposed by Knudson et al., (1993) and Marty et al., (1995) are located between the RyRs as initially suggested by Fan et al. (1995). Their aggregated mass is responsible for the visible anchors, but the exact ratio of Tdns to anchors is not known. Individual triadin molecules are connected to RyRs and to a long linear CASQ polymer on the luminal side of the SR. The latter corresponds to the fine line visible in the EM images at the tips of anchors (see Fig. 2 C and inset). The jSR lumen is filled by long CASQ polymers that randomly intersect each other . Junctin is depicted as monomers associated with RyRs , . Although we cannot visualize them directly, it is likely that individual Jct molecules are positioned as indicated along the jSR face and also possibly at the sites where CASQ is linked to the lateral sides of the SR.