Practice question

Egg activation calcium wave absolutely requires inositol trisphosphate-mediated release of endoplasmic reticulum calcium stores rather than extracellular influx. Phospholipase C enzyme introduced by sperm factor and activated endogenous PLCγ via Src family tyrosine kinases cleaves abundant phosphatidylinositol 4,5-bisphosphate residing in egg plasma membrane inner leaflet generating two potent second messengers: membrane-bound diacylglycerol activating protein kinase C and soluble inositol 1,4,5-trisphosphate (IP3) that diffuses rapidly to bind IP3 receptors on endoplasmic reticulum opening ligand-gated Ca2+ channels. Resulting localized Ca2+ efflux triggers further calcium-induced calcium release propagating global wave. cAMP, DAG alone, ATP do not directly liberate calcium from internal stores.