Abstract
Immobile and mobile calcium buffers shape the calcium signal close
to a channel by reducing and localizing the transient calcium increase
to physiological compartments. In this paper, we focus on the impact
of mobile buffers in shaping steady-state calcium gradients in the
vicinity of an open channel, i.e. within its "calcium microdomain."
We present a linear approximation of the combined reaction-diffusion
problem, which can be solved explicitly and accounts for an arbitrary
number of calcium buffers, either endogenous or added exogenously.
It is valid for small saturation levels of the present buffers and
shows that within a few hundred nanometers from the channel, standing
calcium gradients develop in hundreds of microseconds after channel
opening. It is shown that every buffer can be assigned a uniquely
defined length-constant as a measure of its capability to buffer
calcium close to the channel. The length-constant clarifies intuitively
the significance of buffer binding and unbinding kinetics for understanding
local calcium signals. Hence, we examine the parameters shaping these
steady-state gradients. The model can be used to check the expected
influence of single channel calcium microdomains on physiological
processes such as excitation-secretion coupling or excitation-contraction
coupling and to explore the differential effect of kinetic buffer
parameters on the shape of these microdomains.
- 9278532
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