Validity of the rapid buffering approximation near a point source
of calcium ions.
Biophys. J., 70 (6):
2527--2539 (June 1996)Abstract
In the presence of rapid buffers the full reaction-diffusion equations
describing Ca$^2+$ transport can be reduced using the rapid buffering
approximation to a single transport equation for Ca$^2+$. Here
we simulate the full and reduced equations, exploring the conditions
necessary for the validity of the rapid buffering approximation for
an isolated Ca$^2+$ channel or a cluster of channels. Using a
point source and performing numerical simulations of different durations,
we quantify the error of the rapid buffering approximation as a function
of buffer and source parameters as well as the time and spatial scale
set by the resolution of confocal microscopic measurements. We carry
out simulations of Ca$^2+$ "sparks" and "puffs," both with and
without the indicator dye Ca$^2+$ Green-1, and find that the
rapid buffering approximation is excellent. These calculations also
show that the traditional calculation of Ca$^2+$ from a fluorescence
signal may grossly underestimate the true value of Ca$^2+$
near a source. Finally, we use the full model to simulate the transient
Ca$^2+$ domain near the pore of an open Ca$^2+$ channel in
a cell dialyzed with millimolar concentrations of 1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic
acid or EGTA. In this regime, where the rapid buffering approximation
is poor. Neher's equation for the steady-state Ca$^2+$ profile
is shown to be a reliable approximation adjacent to the pore.
Description
The whole bibliography file I use.