A) Two-dimensional section of a middle XY plane in the intermediate TAT structure shown in the companion paper (Zhang et al.). Surface coupled CRUs and inner coupled CRUs are in orange, and uncoupled CRUs are in light blue. B) Schematic of surface coupled (left), central coupled (middle), and uncoupled (right) CRUs when surface/inner CRU protein expression ratio > 1 (i) or < 1 (ii). When varying the NCX (yellow) distribution, we scale the NCX current density in inner coupled and surface coupled CRUs accordingly. When varying the RyR distribution, we scale the relative expression of RyRs (pink) in the inner (coupled and uncoupled) CRUs vs. surface coupled CRUs. When varying the CSQ (orange) distribution, we scale the relative CSQ expression in the inner (coupled and uncoupled) CRUs vs. surface coupled CRUs.