Subcellular localization of indium-111 in indium-111-labeled platelets

Human platelets labeled with [111In]oxine have been suggested for use in platelet kinetic studies, thrombus localization, detection of atherosclerotic lesions, and other scintigraphic techniques. To demonstrate the subcellular localization of indium-111 in labeled platelets, we did subcellular fractionation and measured the amount of indium-111 localized in major platelet components. Human platelets were labeled with [111In]oxine and disrupted by nitrogen cavitation. The cellular material was fractionated on sucrose density gradients. When the subcellular fractions were analyzed, more than 70% of the indium-111 was located in the cytoplasmic pool of the platelets. Chromatography on Sephadex G-100 of aliquots of the labeled cytosol material showed that most of the indium-111 was associated with components of approximately 46,000 daltons. This demonstrated that indium-111 in human platelets labeled with [111In]oxine is located predominantly in platelet cytosol and is associated with cytoplasmic components.