Fig. 6.

Dependence of relative RyR open probability on relative changes of Ca_SR and Ca_Dyad as well as Ca_Tot. Left: changes in the Ca²⁺ contents of SR (dashed line) and dyadic subspace (solid line) change the open probability of RyRs (here shown as steady-state open probability). Right: model-predicted changes of open probability when Ca_Tot is changed (dotted line) and due to the respective underlying changes of Ca_SR (dashed) and Ca_Dyad (solid line). Top to bottom: Matsuoka03, Iribe06, and Iyer07 models (results for the Shannon04 and Fink08 models were similar to the Iyer07 model). Note that in the Matsuoka03 model the RyR open probability was more sensitive to increasing SR content than to dyadic subspace, whereas the Iribe06 model showed a decrease in RyR open probability with increasing Ca_SR content. The sensitivity in the Matsuoka03 model to the SR content was more than compensated by the more drastic change in Ca_Dyad concentration (top right), leading to an overall higher sensitivity to Ca_Dyad.