During control stimulation of the presynaptic GABAergic neuron at 40 Hz for 1-2 s, DeltaF/F(0) increased rapidly to a peak value and started to decline shortly after the train ended, returning to baseline within 10-20 s. The L-type channel blocker, isradipine (5 microM), had no significant effect on the amplitude or kinetics of the Ca(2+) signal.