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. 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. 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. 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.