Abstract: Calcium (Ca(2+)) is a ubiquitous second messenger which promotes cell responses through transient changes in intracellular concentrations. The prominent role of Ca(2+) in cell physiology is mediated by a whole set of proteins constituting a Ca(2+)-signalling toolkit involved in Ca(2+)-signal generation, deciphering and arrest. The different Ca(2+)-signalosomes deliver Ca(2+)-signals with spatial and temporal dynamics to control the function of specific cell types. Among the intracellular proteins involved in Ca(2+)-signal deciphering, calmodulin (CaM) plays a pivotal role in controlling Ca(2+)-homeostasis and downstream Ca(2+)-based signalling events. Due to its ubiquitous expression in eukaryotic cells and the variety of proteins it interacts with, CaM is central in Ca(2+)-signalling networks. For these reasons, it is expected that disrupting or modifying CaM interactions with its target proteins will affect Ca(2+)-homeostasis and cellular responses. The resulting calcium response will vary depending on which interactions between CaM and target proteins are altered by the molecules and on the specific Ca(2+)-toolkit expressed in a given cell, even in the resting state. In the present paper, the effect of six classical CaM interactors (W5, W7, W12, W13, bifonazole and calmidazolium) was studied on Ca(2+)-signalling in tumor initiating cells isolated from human glioblastoma (TG1) and tobacco cells (BY-2) using the fluorescent Ca(2+)-sensitive Indo-1 dye and aequorin, respectively. Various Ca(2+)-fingerprints were obtained depending both on the CaM interactor used and the cell type investigated. These data demonstrate that interaction between the antagonists and CaM results in a differential inhibition of CaM-dependent proteins involved in Ca(2+)-signal regulation. In addition, the distinct Ca(2+)-fingerprints in tobacco and human tumor initiating glioblastoma cells induced by a given CaM interactor highlight the specificity of the Ca(2+)-signalosome in eukaryotic cells.