Phosphatidylinositol -4 ,5- bisphosphate [ PI ( 4,5) P2 ] is a lipid contained primarily in the inner layer of the cell membrane . Lipid controls the activity of the selected channels and membrane pumps , and modulates the activity of multiple proteins podbłonowych , including actin cytoskeletal proteins . The hydrolysis and phosphorylation of PI ( 4,5) P2 generated second-order three relays : IP3 , DAG , and PI ( 3,4,5) P3.