Fig 9. Ca²⁺ concentrations in the intracellular space, the internal Ca²⁺ store and the extracellular space, the IP₃ concentration in the intracellular space and the ratio h of active IP₃ receptor channels as a function of the maximal pump current of the Na⁺/Ca²⁺ exchanger (I_NCXmax) and the volume ratio between the internal Ca²⁺ store and the intracellular space (ratio_ER).

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. Blue, gray and red lines denote the dynamics of [IP₃]_i, h [Ca²⁺]_i, [Ca²⁺]_ER, [Ca²⁺]_o for values of I_NCXmax equal to 0 $\frac{pA}{\mu m^2}$, 0.001 $\frac{pA}{\mu m^2}$ and 1 $\frac{pA}{\mu m^2}$. a Analysis of the GluT-dependent pathway in isolation. [Ca²⁺]_i is shown as a function of ratio_ER and for different values of I_NCXmax. b-f Analysis of both the mGluR- and the GluT-dependent pathway. [IP₃]_i, h, [Ca²⁺]_i, [Ca²⁺]_ER and [Ca²⁺]_o are shown as a function of ratio_ER and for different values of I_NCXmax.