To gain insight into the possible role of Ca2+ sparks, we modeled a cell and simulated sparks and examined the spatial and temporal profile of free Ca2+ that resulted at the plasma membrane where BK channels would localize. Finite difference approximations were used to solve a set of partial differential equations for the reaction-diffusion kinetics in a cylindrical coordinate system. The details of this approach were described previously (ZhuGe et al., 2000, 2002). The cell was modeled as a cylinder, 6 µm in diameter and 3 µm in height. The Ca2+ release site was modeled as a small cylinder, 20 nm in radius and height, with its end 20 nm from the plasma membrane. Three ICa(spark)s with the same waveform (a linear rise time of 9 ms and an exponential decay with a τ of 12 ms) and different amplitudes (i.e., 1.12, 3.36, and 10.08 pA) were used as input Ca2+ currents. This waveform and these amplitudes for ICa(spark) were selected to match and reflect measured ICa(spark)s in this study and in Bao et al. (2008). The total concentration of
