Localization in platelets of sodium 51Cr-chromate, 125I-antibody to whole membrane, and 3H-diisopropylfluorophosphate using electron microscopic autoradiography.

Platelets from the rabbit and rat, respectively, were incubated with sodium 51Cr-chromate and 3H-diisopropylfluorophosphate (3H-DFP) in the same manner as for platelet survival studies. A third isotope, 125I, was incorporated into a labeled antibody raised against a partially purified pig platelet membrane fraction. The 51Cr label was found to be concentrated predominantly in the cytoplasm, with a marked degree of association with mitochondria, whereas the tritium label appeared to be largely confined to the periphery of the platelet, particularly in association with the open canalicular system. The 125I-labeled antibody showed a very marked association with the plasma membrane and the open canalicular system, suggesting a membrane-bound affinity.