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Increased aminophospholipid translocase activity in human platelets during secretion
R H Tilly1, J M Senden, P Comfurius
1Department of Biochemistry, University of Limburg, Maastricht, The Netherlands.
Biochimica Et Biophysica Acta
|November 2, 1990
Summary
Platelet activation enhances the inward transport of phosphatidylserine (NBD-PS) via increased translocase activity. This phospholipid asymmetry is maintained during exocytosis, crucial for platelet function.
Area of Science:
- Biochemistry
- Cell Biology
- Hematology
Background:
- Phospholipids are crucial components of cell membranes, maintaining asymmetry between leaflets.
- Platelet activation involves complex membrane events, including exocytosis and potential changes in phospholipid distribution.
Purpose of the Study:
- To investigate the transport of fluorescently labeled phospholipids, phosphatidylcholine (NBD-PC) and phosphatidylserine (NBD-PS), across the plasma membrane of human platelets.
- To determine how platelet activation by thrombin or Ca2(+)-ionophore affects phospholipid transport and membrane asymmetry.
Main Methods:
- Utilized fluorescently labeled analogs: NBD-PC and NBD-PS.
- Studied transport in human platelets under resting and stimulated conditions (thrombin, Ca2(+)-ionophore).
- Varied extracellular calcium concentrations ([Ca2+]) to assess its role in transport.
Main Results:
- No significant transport of NBD-PC was observed in resting or stimulated platelets.
- NBD-PS transport was significantly enhanced (4-fold) in thrombin- or ionophore-stimulated platelets, especially without extracellular Ca2+.
- High extracellular Ca2+ concentrations (>8 microM) reduced NBD-PS inward transport, slowing it to levels similar to NBD-PC at 100 microM Ca2+.
Conclusions:
- Platelet activation increases translocase activity, facilitating NBD-PS inward transport.
- This enhanced translocase activity is vital for maintaining phospholipid asymmetry during membrane fusion events in exocytosis.
- Calcium levels play a regulatory role in phospholipid transport during platelet activation.