Breast cancer is the leading cancer in terms of incidence and mortality in the French female population. Concerning the process of carcinogenesis, including deregulation of proliferation, migration and invasion of cancer cells, the role of ion channels is increasingly studied. The implication of Ca2+ signalling, particularly the one involving inositol (1,4,5)-trisphosphate receptors (IP3R) which includes 3 subtypes (IP3R1, IP3R2 and IP3R3), has been shown in several cancers. Furthermore, Ca2+-dependent K+ channels (KCa) are known for their roles in the development of many neoplasic diseases. A recent study from our laboratory has shown that IP3R3-mediated Ca2+ signalling is involved in the proliferation of human breast cancer MCF-7 cells. Likewise, our laboratory showed that KCa channels (BK and hIK1) are also involved in human breast cancer cells proliferation. In this context, we investigated the role of IP3-dependent Ca2+ signalling and its probable interaction with the BK channels in the pathophysiology of breast cancer cells. Our results show that IP3R3 and BK channels are expressed in normal and cancerous breast cell lines and that both proteins are overexpressed in breast cancer tissues. Moreover, our results are in favor of a functional coupling between IP3R3 and BK channels in MCF-7 cancerous cells. Indeed, application of ATP causes an elevation of internal Ca2+ triggering a TEA-sensitive membrane hyperpolarization that is very strongly reduced in cells in which IP3R3 or BK channels expression was silenced by the use of specific siRNAs. Furthermore, we show that ATP increases the proliferation of MCF-7 cells and that this effect is impaired in cells in which the expression of BK channels, IP3R3, or both has been reduced following transfection by specific siRNAs. Our results show also that BK channel and IP3R3 co-immunoprecipitate and that the interaction seems to occur via lipid rafts. However, in the normal breast cell line MCF10A, neither ATP application nor reduction of BK channel expression level by a specific siRNA affect the proliferation of these cells. Furthermore, IP3R3 and BK channels are not co-immunoprecipitated, suggesting the absence of a molecular coupling between BK channels and IP3R3. Taken together, our results suggest a molecular and functional interaction between BK channel and IP3R3 via lipid rafts in cancer cells. Moreover, while this interaction was highlighted in the tumor cell line MCF-7, it is, however, absent in the normal cell line MCF-10A. Our findings permit us to propose this coupling between BK and IP3R3 as a necessary mechanism for tumor cells proliferation.