Ultrastructure of human platelets following indium-111 labeling in plasma

Platelets labeled with 111In have become increasingly useful in monitoring their role in hemostasis and response to vascular injury by external detection. Platelets (10(9) ml-1) labeled with 600 microCi 111In in saline have been shown previously to have an 'overdeveloped' canalicular system and to have aggregated dense bodies. We have labeled 1.35 X 10(9) human platelets with 367 to 1170 microCi 111In in plasma and studied their in vitro aggregability and ultrastructure by transmission electron microscopy for up to five days post labeling. Studies indicated that platelets labeled with 111In in plasma did not suffer from functional or ultrastructural changes keeping mitochondria, canalicular system, alpha granules and microtubules as structurally similar to those in unlabeled control platelets.