Allosteric model rules in example couplons. (A) Trio of RyRs, where each one interacts pairwise with the other two, transitions from configuration CCC to OCC. As indicated, the corresponding change in energy of the channel at top is Δε = 2(ε_OO - ε_OC) in kT units. e^−νΔε enters as a factor the calculation of the rate of the forward transition. (B) Four-channel couplon, with the rules of interaction satisfied by RyR1s in skeletal muscle (RyRs of one color only interact with RyRs of the other color.). Under these rules, the opening of channel 1 has the same energy cost as the example in A. (C) Generic opening transition in a generic 2N-channel couplon with skeletal muscle array interaction rules. The energy cost of the transition represented, ε_OC + ε_OO - 2ε_CC, depends on both the initial and final array configurations. Panel A copies an example in Fig. 3 of Groff and Smith (2008).