Degrading and non-degrading pathways in fluid-phase (non-adsorptive) endocytosis in human blood platelets.
A morphological study of the endocytic pathways in non-activated human blood platelets has been made using fibrinogen-stabilized colloidal gold as a fluid-phase marker, and acid phosphatase as a marker for lysosomes. Two pathways of constitutive endocytosis were demonstrated: one pathway was mediated by clathrin coated vesicles which formed at the platelet surface and the surface-connected, canalicular membrane system and which fuse with and deliver their contents to the platelets' secretory alpha-granules. The other pathway follows a degrading, endosomal-lysosomal route and appears to be clathrin independent. Endosomes containing marker particles originate from the surface-connected canalicular system, through which ambient fluid percolates. An account is given of the pleomorphism of platelet lysosomes, and evidence is presented for a lysosomal, focal autophagia in platelets which may be linked to platelet senescence. Lysosomes in non-activated platelets are thus involved in the same processes as lysosomes in other cells.
Behnke
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Institute of Anatomy C, Panum Institute, University of Copenhagen, Denmark.
D000469:Alkaline Phosphatase / Q000302:isolation & purification; D001792:Blood Platelets / Q000502:physiology* / Q000648:ultrastructure; D003034:Coated Pits, Cell-Membrane / Q000502:physiology / Q000648:ultrastructure; D003594:Cytoplasmic Granules / Q000502:physiology / Q000648:ultrastructure; D004705:Endocytosis / Q000502:physiology*; D005340:Fibrinogen / Q000378:metabolism; D006056:Golgi Apparatus / Q000502:physiology / Q000648:ultrastructure; D006651:Histocytochemistry; D006801:Humans; D008247:Lysosomes / Q000502:physiology / Q000648:ultrastructure; D008561:Membrane Fusion; D008863:Microspheres
D005340:Fibrinogen; D000469:Alkaline Phosphatase