Figure 1.

Pharmacological dissection reveals three components of the presynaptic Ca²⁺ current in hippocampal MFBs. A, Presynaptic Ca²⁺ current evoked by a 20 ms pulse to 0 mV under control conditions, in the presence of 500 nm ω-agatoxin IVa (ω-aga), and after subsequent addition of 1 μm ω-conotoxin GVIa (ω-cono). The residual component was blocked by 200 μm Cd²⁺, confirming that it was mediated by Ca²⁺ channels. B, Plot of Ca²⁺ current amplitude against time during application of the toxins. The time of application of the blockers is indicated by the horizontal bars. Same bouton as shown in A. C, Summary bar graph illustrating the proportions of ω-agatoxin IVa-sensitive, ω-conotoxin GVIa-sensitive, and toxin-resistant component of the Ca²⁺ current. Symbols (triangles, inverted triangles, and circles) represent individual experiments, and bars represent mean ± SEM. Data are from 12, 9, and 15 boutons. D, Plot of the proportions (Prop.) of the three components against the total Ca²⁺ current amplitude. Note the lack of correlation (Pearson's r, 0.11, −0.01, and 0.28; p > 0.2 in all cases).