Phosphatidylserine exposure on the platelet plasma membrane during A23187-induced activation is independent of cytoskeleton reorganization.
Modifications in cytoskeleton organization (monitored by scanning electron microscopy study of platelet shape) and cytoskeleton proteolysis were investigated for their role in phosphatidylserine exposure (measured with spin-labeled analogues of phospholipids) during A23187-induced activation of human platelets. Resting platelets treated with combinations of calpeptin and cytoskeleton-disrupting agents (nocodazole or cytochalasin D) remained discoid, and there was no dense granule release, cytoskeleton proteolysis or vesicle shedding. Spin-labeled phosphatidylserine was fully and rapidly redistributed (t1/2 approximately 5 min) from the outer to the inner leaflet of the plasma membrane through ATP-dependent aminophospholipid translocase activity. In contrast, spin-labeled phosphatidylcholine was only partially and slowly redistributed (less than 20% within 60 min) to the inner leaflet. Filopod formation, vesicle shedding, and calpain-mediated proteolysis were inhibited during activation of platelets treated with calpeptin and cytoskeleton-disrupting agents. Moreover, regardless of whether platelets were treated or not, spin-labeled phosphatidylserine was rapidly (t1/2 < 1 min) and massively (50%) exposed on the outer leaflet of the plasma membrane, while the slow and slight spin-labeled phosphatidylcholine influx did not counterbalance spin-labeled phosphatidylserine outflux. These results demonstrated that phosphatidylserine exposure was not connected to the following activation-related processes: cytoskeleton modifications (actin and tubulin polymerization, submembrane skeleton proteolysis), inhibition of aminophospholipid translocase, and filopod formation. Moreover, the redistribution kinetics of spin-labeled phospholipids during activation strongly suggested the involvement of an aminophospholipid exposure mechanism that differs from a scrambling phenomenon.
URA 1856 CNRS, Département Biologie-Santé, Université Montpellier II, France.
P
P
Gaffet
N
N
Bettache
A
A
Bienvenüe
D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D015638:Cytochalasin D / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects / Q000502:physiology*; D004151:Dipeptides / Q000494:pharmacology; D005994:Glycerophosphates / Q000378:metabolism / Q000494:pharmacology; D005997:Glycerylphosphorylcholine / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D015739:Nocodazole / Q000494:pharmacology; D010718:Phosphatidylserines / Q000378:metabolism*; D015539:Platelet Activation; D012701:Serotonin / Q000378:metabolism
C088333:1-palmitoyl-2-(4-doxylpentanoyl)-glycerophosphoserine; D004151:Dipeptides; D005994:Glycerophosphates; D010718:Phosphatidylserines; C071482:calpeptin; D015638:Cytochalasin D; D012701:Serotonin; D000001:Calcimycin; D005997:Glycerylphosphorylcholine; C088332:1-palmitoyl-2-(4-doxylpentanoyl)glycerophosphocholine; D015739:Nocodazole