Inositol 1,4,5 trisphosphate
Inositol 1,4,5-trisphosphate is an important second messenger that activates calcium channels in the Endoplasmic Reticulum. It is cleaved from PIP2 by Phospholipase C.
References:
Molecular Biology of the Cell’ by Alberts et al (4th Edn). Chapter 15 ‘Cell Communication’ pp859-865.