Ins(1,3,5)P3 is a member of the inositol phosphate (InsP) family of second messengers that play a critical role in the transmission of cellular signals.{8672,8344} The most studied InsP, Ins(1,4,5)P3 is a second messenger produced in cells by PLC-mediated hydrolysis of PtdIns-4,5-biphosphate.{2429,5714} Binding of Ins(1,4,5)P3 to its receptor on the endoplasmic reticulum results in opening of the calcium channels and an increase in intracellular calcium.{5714,4096} Ins(1,3,5)P3 (tested as the meso compound) is 50-fold less potent than Ins(1,4,5)P3 at initiating Ca2+ release when injected into Xenopus oocytes.{13725}