Increased aminophospholipid translocase activity in human platelets during secretion.
Fluorescent labeled analogs of phosphatidylcholine (NBD-PC) and phosphatidylserine (NBD-PS) were used to study transport of phospholipids from the outer to the inner leaflet of the plasma membrane of human platelets. Platelets were stimulated with thrombin or Ca2(+)-ionophore at various extracellular [Ca2+]. No significant transport of NBD-PC could be observed either in resting or stimulated platelets. NBD-PS transport in platelets stimulated with thrombin (with or without extracellular Ca2+), or ionophore in the presence of EGTA, was enhanced 4-fold (t1/2 approximately 2 min) compared to unstimulated controls (t1/2 approximately 8 min). Stimulation with ionophore at extracellular [Ca2+] exceeding 8 microM caused a gradual decrease in inward transport of NBD-PS. At 100 microM Ca2+, NBD-PS transport becomes as slow as that of NBD-PC. We conclude that platelet activation by agonists that induce secretion without appreciable shedding is accompanied by an increase in translocase activity that maintains asymmetry during fusion which occurs during exocytosis.
Tilly
R H
RH
Department of Biochemistry, University of Limburg, Maastricht, The Netherlands.
Senden
J M
JM
Comfurius
P
P
Bevers
E M
EM
Zwaal
R F
RF
D001692:Biological Transport; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids / Q000378:metabolism*; D015539:Platelet Activation / Q000187:drug effects; D013917:Thrombin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D002352:Carrier Proteins; D008565:Membrane Proteins; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids; D013917:Thrombin