Figure 3.

Effect of mobile CaM on short-term synaptic plasticity. (A) Schematic representation of the paired-pulse simulation experiment (Δt_AP = 20 ms) with mobile CaM, see text for details. (B) Comparison of [Ca²⁺] time courses at the vesicular release Ca²⁺ sensor for a representative coupling distance d = 40 nm during paired-pulse stimulation (AP 1 and AP 2) with and without mobile CaM in the presynaptic bouton. Left, [Ca²⁺] transients; right, net increase of [Ca²⁺] at the second AP (Δ[Ca²⁺]_AP2 = [Ca²⁺]_AP2 − [Ca²⁺]_AP1). (C) Dependencies of PPR[Ca²⁺]_peak = [Ca²⁺]^AP2_peak/[Ca²⁺]^AP1_peak and PPR_pv = p_v^AP2/p_v^AP1 on the coupling distance d. p_v^AP1 and p_v^AP2 were determined as the horizontal asymptotes of p_v^AP1(t) and p_v^AP2(t) after the first and the second APs respectively. (D–G) Snapshots of spatial distribution of Ca²⁺ (D, [Ca²⁺]), Ca²⁺ bound to CB (E, [CaCB] = [CaCB_fast] + [CaCB_slow]), and Ca²⁺ bound to the C-lobe (F, [CaCaM_C-lobe] = [CaC_TC_R] + 2 · [CaC_RCaC_R]) and the N-lobe (G, [CaCaM_N-lobe] = [CaN_TN_R] + 2 · [CaN_RCaN_R]) of CaM during paired-pulse stimulation. Side view, XZ plane through the center of the bouton (as in A); AZ, 10 nm thick plane immediately above the AZ. Scale bar 100 nm.