Figure 1. Signal transduction and intracellular Calcium2+ regulation in platelets. When thrombin binds to glycoprotein Ib-thrombin receptor complex at the membrane surface, phospholipase C is activated via G protein, resulting in the rapid hydrolysis of phosphatidylinositol 4,5-bisphosphate to inositol 1,4,5-triphosphate and 1,2-diacylglycerol, both of which act as second messengers. While 1,2-diacylglycerol activates Calcium2+ /phospholipid-dependent protein kinase at the membrane, inositol 1,4,5-triphosphate mobilizes Calcium2+ from intracellular stores, especially dense tubular systems. Adenylate cyclase is activated by some prostaglandins, resulting in the hydrolysis of adenosine triphosphate to cyclic 3',5'-adenosine monophosphate. Cyclic 3',5'-adenosine monophosphate activates cyclic 3',5'-adenosine monophosphate-dependent protein kinase. Gs: stimulating G protein.