Figure 7. Free calcium dynamics and calmodulin activation during single APs and AP trains.

A, B. Model calculations for free calcium dynamics during a single AP (left panels) and during a train of 5 APs at 50 Hz (right panels) in spines (A) and dendrites (B). Plotted are the free calcium concentration traces of shells 2, 6, 10, 14, 18 and 22. C. Calmodulin activation during a single AP and an AP train. Of the total endogenous buffer, 10 µM was assumed to be calmodulin in both dendrites and spines. Shown traces for calcium-bound calmodulin are the total calmodulin signals determined from the relative contributions of all shells corrected for shell volume. D. Parameter space analysis of the effect of model parameters SVR and B_tot,endo on calmodulin activation in spines. Upper panels show 10–90% rise time and decay time of the calmodulin signal. Color bar indicates range for rise times (left scale) and decay times (right scale) in ms. Lower left panel shows calmodulin activation at the peak of the signal and lower right panel shows the total calmodulin activation defined as the integral of the calmodulin signal. Color bar indicates range for peak activation in µM (left scale) and total activation in µM ms (right scale). E. Effect of increasing concentrations of the mobile buffers parvalbumin or calbindin on free calcium dynamics in spines. These buffers were added on top of the endogenous buffer concentration. Traces are the average free calcium signals for different mobile buffer concentration obtained from the traces of all shells corrected for shell volume.