Modulation on the duration of intracellular Ca2+ transients is essential for B-cell activation. We have previously shown that extra-cellular-signal-regulated kinase (ERK) can phosphorylate inositol 1,4,5-trisphosphate receptor type I (IP(3)R1) at serine 436 and regulate its calcium channel activity. Here we investigate the potential physiological interaction between ERK and IP(3)R1 using chicken DT40 B-cell line in which different mutants are expressed. The interaction between ERK and IP(3)R1 is confirmed by co-immunoprecipitation and fluorescence resonance energy transfer (FRET) assays. This constitutive interaction is independent of either ERK kinase activation or IP(3)R1 phosphorylation status. Back phosphorylation analysis further shows that type 1 IP3R (IP(3)R1) is phosphorylated by ERK in anti-IgM-activated DT40 cells. Finally, our data show that the phosphorylation of Ser 436 in the IP3-binding domain of IP(3)R1 leads to less Ca2+ release from endoplasmic reticulum (ER) microsomes and accelerates the declining of calcium increase in DT40 cells in response to anti-IgM stimulation. (c) 2006 Elsevier Inc. All rights reserved.