TABLE 2.

Summary of parameter values estimated from model analysis

Parameter	Description	Value*	% Difference†
D	3′ PI diffusion coefficient	0.37 ± 0.25 μm2/s	11%
k	3′ PI turnover rate constant	1.18 ± 0.54 min−1	18%
tlag	Lag in PI 3-kinase activation	42 ± 35 s	47%
X0/Xss	Basal/steady-state 3′ PI ratio	0.14 ± 0.11	53%
σ	Fluorescence gain parameter	15.3 ± 5.0‡	30%‡
pss	Fraction of probe bound	0.67 ± 0.12‡	37%‡

^*Parameter values obtained with the applicable limiting constraints (up to six) for each cell were averaged, and the value reported is the average over all cells analyzed (mean ± SD). The standard deviation of this value is thus a measure of cell-to-cell variability.

^†The percent difference between the maximum and minimum parameter values obtained from the applicable limiting cases was calculated for each cell. Given is the median percent difference for the cells analyzed, a measure of the precision in the parameter value.

^‡Two out of 32 cells, yielding both arbitrarily high average σ values (175 and 123) and arbitrarily low p_ss values (0.20 and 0.082), were excluded from these statistics; the next highest average σ value was 29, and the next lowest average p_ss was 0.41.