Fig. 9.

Predicted effects of added exogenous buffers and lowered extracellular [Ca²⁺] onP_r, calyx. A, Predicted effect of exogenous buffers onP_r, calyx for two topographies (reference topography versus periodic grid topography, withd = 60 nm) compared with experimental data.Filled squares, EGTA (experimental); filled triangles, BAPTA (experimental; mean ± SEM as shown in Table 2). Trace 1, EGTA (reference topography);Trace 2, BAPTA (reference topography); Trace 3, EGTA (grid topography); Trace 4, BAPTA (grid topography). Reaction volume and location of channels/vesicles are as in Figure 7A (reference topography) or Figure4A (grid topography). The same simulations with the stochastic i_Ca mode (data not shown) yielded the same results as the uniform i_Camode: EGTA (1 mm, 24.3% ± 0.5%; 10 mm,16.0% ± 0.3%) and BAPTA (1 mm, 7.5.% ± 0.3%; 10 mm, 0.1% ± 0.01%; mean ± SEM after 100–200 Monte Carlo simulations). B, PredictedP_r, calyx as a function of Ca²⁺ influx for the same topographies as inA compared with experimental data (see Table 2). Influx was reduced by reducing the single channel conductance from 1.2 pS (control; vertical dashed line) to 0.12 pS.Squares (uniform i_Ca mode) and circles (mean of stochastici_Ca mode) indicate the reference topography (circles are not plotted where indistinguishable fromsquares; SEMs, after 200 Monte Carlo simulations, are smaller than the dimension of the circles).Triangles (uniform i_Ca mode) indicate the grid topography (predicted slope, n = 4.4). Solid thin line indicates slope,n = 2.7; shaded area indicates range of slopes in experimental studies (n = 2.2–3.5). Each data set is normalized to (1, 1). Reaction volume and location of channels/vesicles are as in Figure 7A (reference topography) or Figure 4A (grid topography).P_r, calyx at control conditions is 25%.