SALTATORY PROPAGATION OF CA2+ WAVES BY CA2+ SPARKS

Punctate releases of Ca2+, called Ca2+ sparks, originate at the regula r array of t-tubules in cardiac myocytes and skeletal muscle. During C a2+ overload sparks serve as sites for the initiation and propagation of Ca2+ waves in myocytes. Computer simulations of spark-mediated wave s are performed with model release sites that reproduce the adaptive C a2+ release observed for the ryanodine receptor. The speed of these wa ves is proportional to the diffusion constant of Ca2+, D, rather than root D, as is true for reaction-diffusion equations in a continuous ex citable medium. A simplified ''fire-diffuse-fire'' model that mimics t he properties of Ca2+-induced Ca2+ 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 temperatu re and Ca2+ buffer dependence of wave speed.