Calcium transients in a 1.0 single cylindrical compartment, 1 μm in diameter and 1 μm in length (similar in size to a spine head). Initial concentration is 0.05 μM. Influx is due to a calcium current of 5 μA cm−2, starting at 20 ms for 2 ms, across the radial surface. Black line: accumulation of calcium with no decay or extrusion. Blue line: simple decay with τdec = 27 ms. Gray dashed line: instantaneous pump with Vpump = 4 × 10−6 μMs−1, equivalent to 10−11 mol cm−2 s−1 through the surface area of this compartment, Kpump = 10 μM, Jleak = 0.0199 × 10−6 μMs−1.
