Specialized membrane areas in non-activated and thrombin-activated platelets.
Filipin, a complex of polyene antibiotics, forms morphologically distinctive complexes with cholesterol in cell membranes under proper experimental conditions. When applied to non-activated, discoid platelets, filipin-induced lesions (FIL) occurred in rows at the platelet equator, suggesting a specialized membrane organization at the platelets' largest circumference. In some thrombin-activated platelets we observed surface membrane blebbing and release of lipid vesicles that predominantly originated from the plasma membrane proper, but some originated from (unidentified) platelet granules. FIL were initially present in high numbers over the entire bleb, they accumulated later at the neck of blebs, while the released vesicle was free of FIL. Absence of intramembrane protein particles (IMP) from the membranes of blebs and vesicles suggests that released vesicles are essentially without cholesterol and intrinsic membrane proteins and may consist predominantly of phospholipids. Membrane blebbing and vesicle release may represent unmasking and release of procoagulant platelet factor 3 activity.
D001792:Blood Platelets / Q000187:drug effects* / Q000648:ultrastructure; D002462:Cell Membrane / Q000648:ultrastructure*; D002784:Cholesterol / Q000032:analysis; D005372:Filipin / Q000494:pharmacology; D005614:Freeze Fracturing; D006801:Humans; D008563:Membrane Lipids / Q000032:analysis; D010977:Platelet Factor 3 / Q000032:analysis; D013917:Thrombin / Q000494:pharmacology*
D008563:Membrane Lipids; D010977:Platelet Factor 3; D005372:Filipin; D002784:Cholesterol; D013917:Thrombin