Figure 5.

SV2 regulates short-term plasticity but not the calcium dependence of release. Pairs of EPSCs separated by 45 ms were evoked in wild-type and SV2 knock-out neurons at a variety of calcium concentrations with constant magnesium (1.5 mm). Data points represent mean ± SEM. The numbers of cells analyzed are indicated in parentheses. Data are from littermate cultures of three WT and SV2A KO animals and five SV2B KO and double KO animals. Asterisks denote statistically significant differences (p < 0.05). A, Representative pairs of responses in 1, 2.5, and 10 mm external calcium from SV2B and SV2A/B double knock-out cells. B, Mean normalized amplitudes of responses to a single stimulus in varying concentrations of external calcium. For each cell, EPSC amplitudes were normalized to responses in 2.5 mm calcium. Note that synaptic responses increase identically in all four genotypes as calcium is elevated. C, D, Mean paired-pulse ratios at several calcium concentrations for wild-type and SV2A knock-out (C) and SV2B and SV2A/B double knock-out (D) neurons. Paired-pulse ratios in SV2A/B double knock-outs were increased relative to SV2B knock-outs. SV2A knock-outs show an intermediate phenotype.