Figure 1: Diagram of the components and fluxes in a minimal subspace model. Calcium influx (in units of μM/s) leads to increased calcium concentration (units of μM) in a diadic subspace of volume (liters). Subspace calcium moves to the bulk passively via diffusion at rate (given by 0.01 ms^{−1}). Bulk calcium at the concentration μM returns to the subspace at the same rate. The equilibration time of subspace calcium is ms [27].