The general objectives of this project are to clarify the contribution of intracellular organelles to the genesis of the Ca2 + signal and to its spatio-temporal characteristics. Organelles, capturing or releasing Ca2 + can modify the characteristics of the cytosolic signal and its propagation and / or generate microdomains with different concentrations of Ca2 +. Thanks to these actions, the subcellular specificity of messages can be refined, allowing the same messenger, Ca2 +, to transduce different messages depending on the encoding. Therefore, it is necessary to know the characteristics of the Ca2 + transport in the organelles to understand this modulation of the signals. The methodology we have developed allows accurate measurements of [Ca2 +] changes at the subcellular level, even at the molecular level, in the environment of a given molecule used to anchor the probe. On the other hand, changes in the concentration of Ca2 + inside the different organelles can have per se important physiological consequences. In mitochondria in relation to respiratory control and with the triggering of programmed cell death. In the endoplasmic reticulum, in relation to protein synthesis. In the nucleus in relation to gene expression. Alterations of Ca2 + homeostasis by intracellular organelles may also be related to different pathologies. We will study the interactions between organelles, focusing especially on the newest points.