Fig. 3.

The frequency of mEPSCs is very low in clostridial toxin-treated cultures but is increased by large Ca²⁺ influx into the terminal in BoNT/A-treated, but not TeNT-treated, cultures. Each sweep shows a continuous recording before and after application of 3 μm PDAc (A, phorbol ester), the Ca²⁺ ionophore ionomycin (B), and α-LTx (C). A, PDAc did not increase mEPSC frequency in either TeNT- or BoNT/A-treated cultures (0.1 Hz before and 5 min after PDAc; 0.07 Hz before and 0.06 Hz 5 min after PDAc, respectively). B1, C1, Neither 2.5 μm ionomycin applied in control or 10 mmCa²⁺ containing saline nor 0.5 nmα-LTx applied in control saline or 3 nm α-LTx applied in 10 mm Ca²⁺ increased mEPSC frequency in TeNT-treated cultures (0.06 Hz in control, 0.07 Hz 5 min after ionomycin in 2.8 mm Ca²⁺, and 0.11 Hz 5 min after ionomycin in 10 mm Ca²⁺; 0.06 Hz in control, 0.05 Hz 5 min after 0.5 nm α-LTx in 2.8 mm Ca²⁺, and 0.05 Hz 5 min after 3 nm α-LTx in 10 mm Ca²⁺).B2, C2, Ionomycin and α-LTx increased mEPSC frequency only after [Ca²⁺]_o was raised from 2.8 (control) to 10 mm in BoNT/A-treated cultures (0.04 Hz in control, 0.07 Hz 5 min after ionomycin in 2.8 mmCa²⁺, and 3.6 Hz 5 min after ionomycin in 10 mm Ca²⁺; 0.06 Hz in control, 0.05 Hz 5 min after 0.5 nm α-LTx in 2.8 mmCa²⁺, and 5.2 Hz 5 min after 3 nmα-LTx in 10 mm Ca²⁺).