VESICULATION INDUCED BY AMPHIPHILES AND IONOPHORE A23187 IN PORCINE PLATELETS - A TRANSMISSION ELECTRON-MICROSCOPIC STUDY

Amphiphiles, known to induce exo- and endovesiculation in human erythr ocytes, were studied by means of transmission electron microscopy (TEM ) for their ability to induce shedding of vesicles (microparticles) fr om the porcine platelet plasma membrane. While echinocytogenic amphiph iles induced shedding of vesicles to the extracellular medium (exovesi culation), stomatocytogenic amphiphiles did not induce endovesiculatio n. The rapid (<1 min) formation of many thin spicules in platelets upo n treatment with echinocytogenic amphiphiles, indicates that spicule-f ormation is caused by a primary interaction of the amphiphile with the plasma membrane. Agonist-(Ca2+-ionophore A23187, thrombin and collage n) induced shape changes, however, seem to involve contractile cytoske letal processes since treated cells attained heavily irregular shapes with broad pseudopods. Our study indicates that the mechanisms involve d in amphiphile- and agonist-induced exovesiculation differ. Amphiphil e-induced exovesicles are mainly electron-dense spherical structures ( phi 150-200 mn) which originate from the formed spicules. Ionophore A2 3187-induced exovesicles are large (phi 200-800 nm) predominantly elec tron-lucent structures which are mainly shed from the cell body and se em to originate from extrusions of the canalicular system. Our study s hows that there are several similarities but also obvious differences in the response of platelets and erythrocytes to amphiphile-treatment.