Fig 6. Dynamics of the Ca²⁺ concentration in the intracellular compartment during synaptic activation for different values of the maximal pump current of the Na⁺/Ca²⁺ exchanger (I_NCXmax).

The astrocytic compartment was stimulated for 200 seconds with a Poisson spike train of 100 Hz. The corresponding glutamate concentration in the extracellular compartment as a function of time was calculated using the Tsodyks and Markram model. a [Ca²⁺]_i as a function of the volume ratio (ratio_ER) of internal Ca²⁺ stores and the maximal pump current of the Na⁺/Ca²⁺ exchanger (I_NCXmax). The upper and lower symbols denote the average height of peaks and troughs of the emerging Ca²⁺ oscillations (in [μM]). In case no oscillations were present symbols denote the average concentration of Ca²⁺ over the stimulation period. b-d Time course of the Ca²⁺ concentration for ratio_ER = 0 and I_NCXmax equal to 0 $\frac{pA}{\mu m^2}$ (blue), 0.01 $\frac{pA}{\mu m^2}$(gray) and 1 $\frac{pA}{\mu m^2}$(red). e-g Time course of the Ca²⁺ concentration for ratio_ER = 0.15 and I_NCXmax equal to 0 $\frac{pA}{\mu m^2}$ (blue), 0.01 $\frac{pA}{\mu m^2}$(gray) and 1 $\frac{pA}{\mu m^2}$(red).