Figure 6.

Pool Refilling Rate during HFS_100APs Predicts the Magnitude of PTP

(A–C) The PKA blocker H-89 (10 μM) inhibits PTP and pool refilling.

(A) Unitary EPSCs evoked by a train of 10 stimuli in the presynaptic terminal before application of H-89 (black), in the presence of H-89 before HFS_100APs (green), and in the presence of H-89 after HFS_100APs (red).

(B) Left: plot of EPSC₁ against experimental time. H-89 was applied during the horizontal green continuous line, and HFS_100APs was applied at the time point indicated by the vertical black dashed line. Note that H-89 reduced EPSC₁ peak amplitude and suppressed the induction of PTP after subsequent HFS_100APs. Right: summary bar graph. Data are from 7 pairs.

(C) Left: unitary EPSCs evoked by HFS_100APs under control conditions (black) and in the presence of H-89 (green). Right: plot of cumulative EPSC peak amplitude (100 stimuli, 100 Hz in presynaptic cell-attached stimulation) under control conditions (black) and in the presence of H-89 (green).

(D) Similar plots as shown in (C), but with the actin polymerization blockers latrunculin B (20 μM) and cytochalasin D (10 μM). Traces from different pairs; same control trace shown in (C, left) and (D, left).

(E) Comparison of RRP (left), P_r (center), and refilling rate (right) under control conditions (black), in the presence of H-89 (green), and in the presence of latrunculin B and cytochalasin D. RRP and P_r were unchanged, whereas the refilling rate was significantly reduced by H-89 and the actin polymerization blockers.

(F) Unitary EPSCs evoked by a train of 10 stimuli in the presynaptic terminal in the presence of latrunculin B and cytochalasin D before (orange) and after (red) HFS_100APs.

(G) Plot of EPSC₁ against experimental time. Latrunculin B and cytochalasin D were applied during the horizontal orange continuous line, and HFS_100APs was applied at the time point indicated by the vertical black dashed line. Actin polymerization blockers reduce synaptic transmission and inhibit PTP.

(H) Summary bar graph of the effects of H-89 and latrunculin B and cytochalasin D on PTP.

(I) Scatterplot of the magnitude of PTP against the refilling rate during HFS_100APs. Black, control data; green, data in the presence of H-89; orange, data in the presence of latrunculin B and cytochalasin D. The line represents linear regression to the data points (Spearman rank correlation coefficient ρ = 0.61, p = 0.0005, 28 pairs).

In (B), right, (E), and (H), boxes indicate mean values, error bars denote SEM, circles show data from individual experiments, and data from the same experiment are connected by lines. ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001.