In the GPCR (G-protein coupled receptor) - phospholipase C (PLC) signal transduction system, the second messengers involved are inositol trisphosphate (IP3) and diacylglycerol (DAG).
When a ligand binds to a GPCR, it activates the associated G-protein, which in turn activates phospholipase C (PLC). PLC catalyzes the hydrolysis of a membrane phospholipid called phosphatidylinositol 4,5-bisphosphate (PIP2). This hydrolysis results in the formation of two second messengers: IP3 and DAG.
IP3 diffuses into the cytoplasm and binds to specific IP3 receptors on the endoplasmic reticulum (ER), causing the release of calcium ions (Ca2+) from the ER stores into the cytoplasm. The increased cytoplasmic Ca2+ concentration serves as a second messenger, triggering various downstream cellular responses.
DAG, on the other hand, remains within the plasma membrane. It activates protein kinase C (PKC), which translocates to the plasma membrane in its active form upon binding to DAG. PKC phosphorylates various target proteins, initiating specific cellular signaling pathways.
Together, IP3 and DAG mediate the intracellular signaling cascade initiated by GPCR activation and PLC activation, leading to a wide range of cellular responses depending on the specific receptors and cell types involved.