Figure 5. Augmented Ca²⁺–CaM response in a spine head in the presence of ER depends on the synaptic input rate and is suppressed at higher frequencies.

A, the steady state open probability of an IP₃ receptor (P _open) as a function of (constant) glutamate and Ca²⁺ concentrations. B, maximum Ca²⁺ level attained during persistent stimulation at different frequencies in the reference ER⁻ spine (black) and equivalent ER⁺ spine with different numbers of IP₃Rs (coloured curves). C, non‐monotonic dependence of the differential Ca²⁺ responses in the ER⁺ spine on the input rate. D and E, the corresponding results for CaM activation as a function of the input rate. F, the maximum calcium influx rate through NMDA receptors (black) and different numbers of IP₃ receptors (coloured curves) in an ER⁺ spine plotted against the input rate. (All results for the model synapse with peak NMDAR‐mediated Ca²⁺ response ΔCa_EPSP = 0.2 μM.) [Color figure can be viewed at wileyonlinelibrary.com]