Figure 2.

Mechanism of afterdepolarization in granule cells. A₁, Cadmium (Cd; 200 μm) abolishes the afterdepolarization evoked in granule cells by 25 pA depolarizing steps in 2 μm CCh. A₂, Summary of the effect of Cd on ADP amplitude. *p < 0.01. B₁, Flufenamic acid (100 μm) blocks the ADP in CCh. B₂, Enlargement of CCh and CCh + FFA responses. Action potentials truncated in A₁ and B₂. C, ADPs evoked by Ca spikes in 2 μm CCh, 1 μm TTX, 25 mm TEA, 100 μm 4-AP and 4 mm CsCl. Reducing the Na driving force by applying an ACSF solution containing 99 mm NMG reversibly blocked the ADP (“+NMG”). Responses to 90 pA steps are truncated to illustrate afterpotentials. Example responses in CCh and CCh + NMG conditions shown in the insets. D, Thapsigarin (TG; 10 μm) did not reduce the ADP response in granule cells exposed to 2 μm CCh (50 pA step). E₁, Photolyzing NP-EGTA (2 mm; added to the internal solution) evokes a graded inward current in voltage-clamped granule cells. Horizontal lines above each trace indicate UV exposure time (100, 250, 500, and 1000 ms). E₂, UV exposure by itself does not evoke an inward current in control granule cells that were not loaded with NP-EGTA. F, Uncaging response reversed polarity at approximately −20 mV (data from 5 experiments). The inset shows example responses recorded at 0, −40, and −80 mV.