The inositol phosphates (InsP) play a critical role as small, soluble second messengers in the transmission of cellular signals. The most studied InsP, Ins(1,4,5)P3, more commonly referred to as IP3, is a second messenger produced in cells by PLC-mediated hydrolysis of phosphatidylinositol-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(2,4,5)P3 is a metabolically stable analog of Ins(1,4,5)P3 that is commonly used to study Ca2+ signaling pathways. Ins(2,4,5)P3 acts as a partial agonist at rat hepatic IP3 receptors, exhibiting 65% of the maximal Ca2+ response obtained with Ins(1,4,5)P3.