Fate of phosphatidylinositol 4,5-biphosphate (PIP2) in platelets and second messenger production

This figure shows the outcome of agonist activation of platelet PLC beta (PLC) via the G alpha-q subunit and activation of PI3K via the G beta-gamma subunit. In both cases, the substrate is membrane-associated PIP2, shown in the top center of the figure. The dashed green arrows point to the number 1 and 3 carbons in the inositol ring. Hydrolysis of PIP2 by PLC yields IP3, which raises the cytosolic calcium concentration by releasing sequestered calcium from the dense tubular system and DAG, which activates protein kinase C. Phosphorylation of the number 3 inositol carbon of PIP2 by PI3K generates the second messenger PIP3, important for stable platelet aggregation.