* ''Membrane zone'' is made of two types of membrane. One, the open canicular system, is membrane not used when the platelet budded off the megakaryocyte. The other, the dense tubular system, is membrane from the rough endoplasmic reticulum and is involved in calcium ion storage and regulation. | * ''Membrane zone'' is made of two types of membrane. One, the open canicular system, is membrane not used when the platelet budded off the megakaryocyte. The other, the dense tubular system, is membrane from the rough endoplasmic reticulum and is involved in calcium ion storage and regulation. |