Influence of ionized calcium on thrombin-induced down regulation of GPIb/IX receptors on human platelets.
The influence of ionized calcium on the down-regulation of GPIb/IX receptors on human platelets was evaluated by flow cytometry using monoclonal antibodies. Addition of EDTA alone to a washed platelet suspension did not cause decreased monoclonal antibody binding to the cells. However, introduction of thrombin to the washed platelets containing EDTA resulted in a marked decrease in binding of monoclonal antibodies to the GPIb/IX receptors. If calcium at 1-3 mmol/L was added to buffered platelets instead of EDTA before thrombin, down-regulation was prevented or significantly reduced. Restoring calcium to EDTA platelets after the thrombin-stimulated down-regulation had been in progress for 1-3 minutes caused reversal of decreased antibody binding by GPIb/IX to near resting levels. Results demonstrate that extracellular calcium is a major factor regulating thrombin-induced down-regulation.
Rao
G H
GH
Department of Laboratory Medicine, University of Minnesota Medical School, Minneapolis 55455, USA.
Peller
J D
JD
White
J G
JG
D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D015536:Down-Regulation; D004492:Edetic Acid; D005434:Flow Cytometry; D006801:Humans; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface / Q000378:metabolism*; D013917:Thrombin / Q000494:pharmacology*
D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; C032193:glycoprotein receptor GPIb-IX; D004492:Edetic Acid; D013917:Thrombin; D002118:Calcium