Table 3.

Calibrated parameters.

Parameter	Calibrated value	Range in the literature
PMCA PUMPS
Density in spine membrane	998 μm−2	~300 μm−2 in neuronal cells, if total membrane protein density is taken as ~30,000 μm−2 and PMCA as 1% (Stauffer et al., 1995). This number is an estimate.
Density in shaft membrane	488 μm−2
NCX PUMPS
Density in spine membrane	143 μm−2	Little information on absolute density. Lörincz et al. (2007) report a ratio of ~7:1 for density on shaft vs. spine. Our best fit ratio is 3.4:1.
Density in shaft membrane	488 μm−2
Ratio of Ca2+ pumped by PMCAs and NCXs	1:1	Ratio of 1:1 determined by Scheuss et al. (2006).
VDCCs
Density in spine membrane	1.2 μm−2	Magee and Johnston (1995a) estimated a density of 1–2 μm−2for R-type Ca2+ channels on dendrites of CA1 pyramidal neurons. In contrast, using noise analysis, Sabatini and Svoboda (2000) predicted as high as 20 μm−2in spines.
Density in shaft membrane	2.67 μm−2
IMMOBILE CBPs
Concentration in cytosol	78.7 μM
kon	2.47 × 108 M−1s−1
koff	524 s−1

Nine parameters were calibrated to fit the experimental data in Sabatini et al. (2002) as described in the Results Section. The ratio of 1:1 for the amount of Ca²⁺ pumped by PMCAs and NCXs was set at 1:1 to match data in Scheuss et al. (2006), reducing the free parameters to seven.