Skip to main content
. 2002 Mar 1;22(5):1648–1667. doi: 10.1523/JNEUROSCI.22-05-01648.2002

Fig. 4.

Fig. 4.

Effect of Ca2+channel spacing on release probability. A, Reaction volume with the periodic grid topography used in the simulation; allnumbers are given in nanometers (not drawn to scale). Partial 5 and 20 nm grids indicate varying spatial resolution.Dashed lines indicate repetition of volume with the use of periodic boundary conditions (see Materials and Methods). Ca2+ channels are located on a uniform grid with grid constant d (example showsd = 60 nm). Readily releasable vesicles are located randomly anywhere on the membrane. B, Spatial profiles of [Ca2+] (traces 1–3, snapshot at time of peak ICa) and ofPr, vesicle (traces 4–6, after 5 msec; rightaxis) generated by ad = 60 nm regular grid of channels under different buffer conditions; single Ca2+ channel current the same as in D. Channels are at 30 and 90 nm.Traces 1, 4, Endogenous fixed buffer (EFB) and ATP (control condition). Traces 2, 5, EFB, ATP, and 10 mm EGTA. Traces 3, 6, EFB, ATP, and 1 mm BAPTA. Squares at left axis indicate average [Ca2+] across the membrane (7.4, 4.3, and 1.9 μm for control, EGTA, and BAPTA, respectively). Triangles atright axis indicate averagePr, vesicle (=Pr, calyx) across the membrane (25, 2.4, and 0.13% for control, EGTA, and BAPTA, respectively).C, Peaks of [Ca2+] transients for different grid constants and buffer conditions (1, 4,and 7; 2, 5, and 8;3, 6, and 9 as in B; single Ca2+ channel current same as inD). 1–3, Peak of transient at 10 nm above a channel. 4–6, Peak of average transient across the membrane. 7–9, Peak of transient at half-grid constant from two neighboring channels. D, Predicted average Pr, vesicle across the membrane (=Pr, calyx) as a function of grid constantd. Traces 1–6 showPr, calyx for six different buffer conditions. Trace 1, EFB and 50 μm BAPTA.Trace 2, EFB and ATP (control condition). Trace 3, EFB, ATP, and 10 mm EGTA-2. Trace 4, EFB, ATP, and 10 mm EGTA. Trace 5, EFB and 1 mm BAPTA. Trace 6, EFB, ATP, and 1 mm BAPTA. Trace 7, PeakiCa per channel required to achievePr, calyx ∼25% for the control condition (right axis).