“…Early reports have suggested that their sensitivity to Ca 2ϩ is greater for IP 3 R3 than IP 3 R1; however, all three subtypes show a bell-shaped Ca 2ϩ dependence with the optimum cytosolic [Ca 2ϩ ] around 200 nM (26,29,30). In addition, IP 3 R subtypes are modulated differentially by kinases, phosphatases, proteolysis, transcriptional, post-transcriptional, and post-translational modifications (31)(32)(33)(34)(35)(36)(37)(38)(39). Consequently, it is widely held that these differences may underlie subtype-specific Ca 2ϩ patterns, and it follows that the particular cellular complement of IP 3 Rs may therefore dictate the spatio-temporal patterns of Ca 2ϩ signals evoked in response to IP 3 formation in an individual cell (13, 35, 40 -42).…”