EN
Platelets respond to stimuli by rapidly changing from discs into active forms having lamellipodia and filopodia. Actin filament fragmentation and assembly are essential for platelet shape change. Actin assembly is regulated by an intracellular signaling pathway that involves calcium and the activation of small GTPases and phosphatidylinositol kinases (PI-kinases). Polyphosphoinositides (ppIs), the final products of the PI-kinases, directly interact with a special class of actin associated proteins, the barbed end capping proteins, to initiate actin filament assembly in activated cells.