A strong Ca2+ mediated coupling of Ca2+ release sites gives rise to stereotyped Ca2+ signals.

LUCÍA LOPEZ, ESTEFANÍA PIEGARI, LORENA SIGAUT, SILVINA PONCE DAWSON

Otro; XV Giambiagi Winter School; 2013

Intracellular Ca2+ signals usually involve Ca2+ release from the endoplasmic reticulum through IP3 receptors (IP3R´s). IP3R´s are typically organized in clusters. Their open probability depends on both the concentrations of IP3 and of cytosolic Ca2+. In the presence of a fixed IP3 concentration (a situation achieved in experiments), signal propagation is strongly dependent on cytosolic Ca2+ via the phenomenon known as Ca2+-InducedCa2+-Release (CICR). Once an IP3R becomes open and starts to release Ca2+, the ions released act upon other IP3R´s and can eventually induce their opening. This process occurs both at the intra and the intercluster level. Namely, depending on the amount of Ca2+ that is released from a cluster and the mechanisms of Ca2+ buffering, the opening of IP3R´s in a cluster can induce the opening of IP3R´s on others. In this way either localized signals (puffs) or waves that propagate throughout the cell can be evoked. In this work we investigate the ways in which the signal size (or spatial spread) is modulated by the various processes involved in their production. Using a simple model that is based in experimental observations we show that the signals sizes can span a wide range of values or can be stereotyped depending on the strength of Ca2+ intracluster coupling. In particular we show that if the clearance rate of Ca2+ is decreased the size distribution is almost Gaussian about a mean while it approximately follows a power law for larger values of this rate.