Membrane alterations in connection with the release reaction in human platelets as studied by the lactoperoxidase-iodination technique and by agglutination with bovine factor VIII-related protein

Abstract

Changes in the platelet membrane surface as a result of the thrombin-induced release reaction have been examined by lactoperoxidase-catalyzed iodination and agglutination of the platelets with bovine factor VIII-related protein. The distribution of labeled substances after iodination was studied after sodium dodecyl sulphate polyacrylamide gel electrophoresis of platelet proteins. The major radioactive peaks in the control samples were associated with (glyco)polypeptides of estimated molecular weights about 100 000 and 120 000, and a smaller peak was observed at 147 000 daltons. Platelets labeled after the release reaction had been performed incorporated markedly less radioactive iodine into the membrane proteins than control platelets, i.e. 57.7% ± 9.2 (147 000), 26.6% ± 13.0 (120 000) and 20.6% ± 5.5 (100 000) of the corresponding peaks of the control. These platelets agglutinated poorly with bovine factor VIII-related protein. These effects were not seen when the platelets were preincubated with metabolic inhibitors to prevent secretion. After sodium dodecyl sulphate polyacrylamide gel electrophoresis of the soluble fraction from released platelets, the main glycoprotein band (GPS), when examined in unreduced form, showed slower migration than the corresponding band in the control sample. It is concluded, that the surface structure of thrombin-secreted platelets is different from that of untreated cells. This change is independent of the direct action of thrombin on the membrane, but may be a result of conformational alterations during the secretion process and/or adsorption of released material to the external membrane surface.