Energy profiles consistent with observations. Individual RYR tetramer energy (E) versus occupancy (o) for the low and high parameter sets as listed in Table 1. The large values at top of the graph (dashed lines) are energies in conditions of steric clash (occupancy of an adjacent protomer of an adjacent RYR tetramer). The observed configurations are those with occupancy 0, 3, and 4, found at E ≤ 2.