ELEMENTARY AND GLOBAL ASPECTS OF CALCIUM SIGNALING

Calcium is a ubiquitous second messenger used to regulate a wide range of cellular processes. This role in signalling has to be conducted ag ainst the rigid homeostatic mechanisms that ensure that the resting le vel of Ca2+ is kept low (i.e. between 20 and 100 nmol l(-1)) in order to avoid the cytotoxic effects of a prolonged elevation of [Ca2+]. Cel ls have evolved a sophisticated signalling system based on the generat ion of brief pulses of Ca2+ which enables this ion to be used as a mes senger, thus avoiding its toxic effects. Such Ca2+ spikes usually resu lt from the coordinated release of Ca2+ from internal stores using eit her inositol 1,4,5-trisphosphate or ryanodine receptors. Using Ca2+ im aging techniques, the opening of individual channels has now been visu alized and models have been proposed to explain how these elementary e vents are coordinated to generate the global Ca2+ signals that regulat e cellular activity.