Figure 4. The blocking effect of 5 μm IEM-1925 at high (2.5 mm) and low (1 mm) calcium concentrations.
A, representative eEPSC recordings from the same FSI in control and in the presence of IEM-1925. Lowering of calcium concentration resulted in reduction of eEPSC amplitude. B, decrease in calcium concentration significantly increases PPR and decreases the block of eEPSCs by IEM-1925. Circles represent results obtained in cortical FSIs and squares represent results obtained in giant striatal interneurons. C, the blocking effect of IEM-1925 (5 μm) on kainate-induced current in isolated GIs is the same in low (1 mm) and normal (2.5 mm) calcium concentrations. It indicates that the observed reduction of IEM-1925 action in low calcium conditions (B, right panel) is not due to direct interrelation between IEM-1925 and calcium at the postsynaptic site. Rather the effect is mediated by calcium dependency of the synaptic release probability (**P < 0.01).