PLASMA-MEMBRANE PROPERTIES IN HETEROGENEOUS HUMAN BLOOD-PLATELET SUBFRACTIONS MODULATE THE CELLULAR-RESPONSE AT THE 2ND MESSENGER LEVEL

Three subfractions of human blood platelets differing in density and f unction exhibited also differences when EPR (electron paramagnetic res onance) spin label measurements and fluorescence polarization were per formed. The membrane anisotropy in the plasma membranes was higher in low density platelets as compared with that of platelets of intermedia te and higher densities. This higher plasma membrane anisotropy correl ated with a significantly higher cholesterol-phospholipid (C:P) molar ratio in the plasma membranes of low density platelets. As compared wi th the other platelet subfractions the low density platelets exhibited the smallest cAMP increase after activation with the aggregation inhi bitor prostaglandin (PGE1), and the highest percentage of inositol pho sphate accumulation after thrombin stimulation. The results suggest a high correlation between functional parameters and the plasma membrane architecture of human blood platelets.