Background All identified mammalian TRPC channels show a C-terminal calmodulin (CaM)- and inositol 1,4,5-trisphosphate receptors (IP 3Rs)-binding (CIRB) site involved in the regulation of TRPC channel function. Objectives To assess the basis of CaM/IP 3Rs binding to the CIRB site of TRPC6 and its role in platelet physiology. Methods Protein association was detected by co-immunoprecipitation and Western blotting, Ca 2+ mobilization was measured by fluorimetric techniques and platelet function was analyzed by aggregometry. Results Co-immunoprecipitation of TRPC6 with CaM or the IP 3Rs at different cytosolic free Ca 2+ concentrations ([Ca 2+] c) indicates that the association between these proteins is finely regulated by cytosolic Ca 2+ via association of CaM and displacement of the IP 3Rs at high [Ca 2+] c. Thrombin-stimulated association of TRPC6 with CaM or the IP 3Rs was sensitive to 2-APB and partially inhibited by dimethyl BAPTA loading, thus suggesting that the association between these proteins occurs through both Ca 2+-dependent and -independent mechanisms. Incorporation of an anti-TRPC6 C-terminal antibody, whose epitope overlaps the CIRB region, impaired the dynamics of the association of TRPC6 with CaM and the IP 3Rs, which lead to both inhibition and enhancement of thrombin- and thapsigargin-evoked Ca 2+ entry in the presence of low or high, respectively, extracellular Ca 2+ concentrations, as well as altered thrombin-evoked platelet aggregation. Conclusions Our results indicate that the CIRB site of TRPC6 plays an important functional role in platelets both modulating Ca 2+ entry and aggregation through its interaction with CaM and IP 3Rs.