Abstract
Punctate releases of Ca$^2+$, called Ca$^2+$ sparks, originate
at the regular array of t-tubules in cardiac myocytes and skeletal
muscle. During Ca$^2+$ overload sparks serve as sites for the
initiation and propagation of Ca$^2+$ waves in myocytes. Computer
simulations of spark-mediated waves are performed with model release
sites that reproduce the adaptive Ca$^2+$ release observed for
the ryanodine receptor. The speed of these waves is proportional
to the diffusion constant of Ca$^2+$, D, rather than D, as is
true for reaction-diffusion equations in a continuous excitable medium.
A simplified "fire-diffuse-fire" model that mimics the properties
of Ca$^2+$-induced Ca$^2+$ release (CICR) from isolated sites
is used to explain this saltatory mode of wave propagation. Saltatory
and continuous wave propagation can be differentiated by the temperature
and Ca$^2+$ buffer dependence of wave speed.
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