Figure 3.

High [Ca²⁺]_o promotes paired-pulse-depression of MPP fEPSPs under HP. (A) Single experiment shows the antagonistic effect of high (4 mM) [Ca²⁺]_o on HP (10.1 MPa) paired-pulse modulation. At 10.1 MPa the initial phase of paired-pulse-depression (PPD) was attenuated, while the later paired-pulse-facilitation (PPF) was increased. Increased [Ca²⁺]_o at HP partially restored the slope of E₁, but increased PPD for short ISI and abolished the later phase of PPF for ISI 35–120 ms. (B) Comparison between PPM at 5.1 MPa (2 mM [Ca²⁺]_o) and 10.1 MPa (4 mM [Ca²⁺]_o). Note that E₁ under these two conditions is almost equal; however PPD is much greater under the latter condition.