G H R Rao*, J D PeIler, M G Doni & J G White
Departments of pediatrics, Laboratory Medicine and Pathology and Biomedical Engineering Institute, University of Minnesota, 55455
Institute of Fisiologia Umana, University of Padova, Italy.
Received 11th May, 2008; Revised 9th August 2008
Abstract : Platelet surface membrane receptors, glycoprotein (GP) 11B/111 A, and GP lb/1X, play a critical role in adhesion, activation, signal transduction, interaction with cell matrix components and adhesive proteins, as well as cell-cell aggregation. There is considerable interest in the mobility of these receptors, their up-regulation, down-regulation, internalization, and clearance from the plasma membrane surface. In this study, we have used specific monoclonal antibodies to localize these receptors on the plasma membrane surface of adherent and thrombin activated platelets. Using fluorescence imaging and confocal microscopy, we have followed the distribution of these receptors on surface-activated cells as well as thrombin-stimulated platelets. In some studies, we have used mild detergent treatment to show the presence of these receptors on internal membranes of the open canalicualar system (OCS). We also have used a membrane specific fluorescent probe, to show the internal membranes. Results of our studies demonstrate that the GP11b/111 a and GP 1 b/1X receptors are present in abundance on the surface membrane of adherent platelets. Thrombin-induced activation of adherent platelets did not result in significant loss of these receptors from the surface membrane. Permeabalized platelets had a significant internal pool of GP1b/1X, while non-permeabalized, thrombin-stimulated platelets failed to show significant changes in internal pool of these receptors. Surface activated platelets as well as those stimulated with thrombin retain significant quantities of these receptors on their plasma membrane.