Figure 4. The velocity of calcium removal was faster in ground squirrel neurons than in rat neurons.

(A) A series of image frames of fluo-4 AM loaded neurons acquired by confocal microscopy. Glutamate (Glu) was applied between the second and the third frame (indicated by the red arrow). Then, glutamate was washed out approximately 2 s later (indicated by the black arrow). Scale bar, 20 µm. (B) Left: a typical example of [Ca²⁺]_i dynamics in response to glutamate administration (the black line). The decay phase is fit with a single exponential function (red line) to estimate the time constant (τ). Right: statistical results suggest that the calcium removal rate is markedly faster in ground squirrel neurons than rat neurons. n = 76 to 131 neurons, from 3 separate experiments, P<0.01. Scale bar, 5 s. (C) Effect of NCX blockade on the [Ca²⁺]_i decay rate. The result shows that the reduced τ value in ground squirrel neurons is abolished by administration of CB-DMB, a specific NCX blocker. n = 73 to 96 neurons, from 5 separate experiments. (D) Effect on the [Ca²⁺]_i decay rate of the inhibition of SERCA. The results show that the reduced calcium removal rate is similar in rat and ground squirrel neurons in response to TG, a SERCA blocker. n = 56 to 70 neurons, from 4 (rat) and 3 (GS) separate experiments.