Figure 3.

Modeling of observed calcium dynamics in N1E-115 neuroblastoma cells. a, Distributions of BKR and ER (SERCA2/InsP₃1-R) used for modeling. Cells were stained for antibodies against BKR, SERCA2, InsP₃1-R, and ER. Relative fluorescence intensities were measured on the confocal microscope and adjusted for convolution artifacts (Fink et al. 1998). Intensities were scaled such that the left half soma is equal to 1.0, and plotted (mean ± SEM; n = 20 cells) for six representative regions of the cell. There was no statistical difference (ANOVA; P > 0.05) between the distributions of InsP₃1-R, SERCA2, and ER, so they were plotted together. b, Simulation results for [Ca²⁺] and [InsP₃] in N1E-115 neuroblastoma cells (as modeled in a). Simulations were run for three conditions: global application of a saturating concentration of BK with the average receptor and ER distribution as shown in a; global application of a saturating concentration of BK with average ER (and InsP₃-R and SERCA) distributions, but with a uniform plasma membrane BKR distribution; and a step increase of [InsP₃] to 1.5 μM uniformly throughout the cytosol analogous to the uncaging experiment in Fig. 1 b. [InsP₃] and [Ca²⁺] have been pseudocolor scaled according to the color bar at the top of each column. Time is seconds after the simulated stimulus event (either BK exposure or InsP₃ uncaging). Below each column are plots of [InsP₃] or [Ca²⁺] versus time for a point in the soma or the neurite (indicated by the yellow or green dots on the 1.0 s image of the first column). For the [InsP₃] versus time plot for the average receptor distribution experiment, also plotted are the [InsP₃] values indicative of the average [InsP₃] for the whole cell (dotted white line) and the experimental [InsP₃] values determined with radioligand binding as shown in Fig. 2 d. This plot is taken to 30 s, whereas the other plots are all to 12 s.