Figure 1. Amplitude and spatial extent of Ca²⁺ microdomains.

A and B, plots of the numerically calculated profile of a Ca²⁺ microdomain near an open L-type Ca²⁺ channel (A) and a CRAC channel (B). Single channel currents were 0.144 pA (Church & Stanley, 1996) and 1.5 fA (Zweifach & Lewis, 1995), respectively. Endogenous Ca²⁺ buffering was ignored. C, the distance (λ) a Ca²⁺ ion diffuses before it is captured by some widely used Ca²⁺ chelators is shown and is stated next to each chelator. All concentrations are in mm. D, various properties of widely used fluorescent dyes (Lattanzio. & Bartschat (1991) and the calculated λ. All concentrations were 100 μm, corresponding to the levels used experimentally. For C and D, resting Ca²⁺ was set at 100 nm and the free chelator concentration then calculated. λ is not a precise calculation because buffer is not present in excess.