ULTRASTRUCTURAL-LOCALIZATION OF HUMAN-PLATELET THROMBOSPONDIN, FIBRINOGEN, FIBRONECTIN, AND VONWILLEBRAND-FACTOR IN FROZEN THIN-SECTION

  • 1 January 1985
    • journal article
    • research article
    • Vol. 65  (4) , 929-938
Abstract
The localization of thrombospondin (TSP), fibrinogen, fibronectin and von Willebrand factor in human platelets was investigated by transmission electron microscopy of antibody-stained ultrathin frozen sections. In negatively stained thin sections, .alpha. granules were identified on the basis of their smooth, roughly spherical shape, size, single limiting electron-lucent 100 .ANG. membrane and frequent presence of electron-dense nucleoid. In contrast, mitochondria exhibited characteristic double membranes and cristae. Sections were separately stained with affinity-purified polyclonal antibodies to these proteins as well as with 3 monoclonal anti-TSP antibodies. Antibody specificity was documented in radioimmunoassays, by immunofluorescent cross-blocking, and by staining of bands of appropriate mobility in Western blots of whole platelets. Bound antibody was visualized using a 5-nm colloidal Au-avidin conjugate. In resting cells, staining of virtually all .alpha. granules was observed for all 4 proteins. In contrast, consistent staining was absent from other organelles, including plasma membranes, mitochondria and vacuolar structures that may represent the open canalicular system.