Porcine von Willebrand factor binding to human platelet GPIb induces transmembrane calcium influx.
Porcine von Willebrand factor (P-vWF) binds to human platelet glycoprotein (GP) Ib and, upon stirring (1500 rpm/min) at 37 degrees C, induces, in a dose-dependent manner, a transmembrane flux of Ca2+ ions and platelet aggregation with an increase in their intracellular concentration. The inhibition of P-vWF binding to GP Ib, obtained with anti GP Ib monoclonal antibody (LJ-Ib1), inhibits the increase of intracellular Ca2+ concentration ([Ca2+]i) and platelet aggregation. This effect is not observed with LJ-Ib10, an anti GP Ib monoclonal antibody which does not inhibit the vWF binding to GP Ib. An anti GP IIb-IIIa monoclonal antibody (LJ-CP8) shown to inhibit the binding of both vWF and fibrinogen to the GP IIb-IIIa complex, had only a slight effect on the [Ca2+]i rise elicited by the addition of P-vWF. No inhibition was also observed with a different anti GP IIb-IIIa monoclonal antibody (LJ-P5), shown to block the binding of vWF and not that of fibrinogen to the GP IIb-IIIa complex. PGE1, apyrase and indomethacin show a minimal effect on [Ca2+]i rise, while EGTA completely blocks it. The GP Ib occupancy by recombinant vWF fragment rvWF445-733 completely inhibits the increase of [Ca2+]i and large aggregates formation. Our results suggest that, in analogy to what is seen with human vWF under high shear stress, the binding of P-vWF to platelet GP Ib, at low shear stress and through the formation of aggregates of an appropriate size, induces a transmembrane flux of Ca2+, independently from platelet cyclooxygenase metabolism, perhaps through a receptor dependent calcium channel. The increase in [Ca2+]i may act as an intracellular message and cause the activation of the GP IIb-IIIa complex.
Mazzucato
M
M
Servizio Immunotrasfusionale e Analisi Cliniche, I.R.C.C.S., C.R.O., Aviano, PN, Italy.
De Marco
L
L
Pradella
P
P
Masotti
A
A
Pareti
F I
FI
D000818:Animals; D000911:Antibodies, Monoclonal; D002118:Calcium / Q000097:blood*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism*; D006801:Humans; D007213:Indomethacin / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism*; D011485:Protein Binding; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011994:Recombinant Proteins / Q000494:pharmacology; D015290:Second Messenger Systems / Q000502:physiology*; D013314:Stress, Mechanical; D013552:Swine; D014700:Verapamil / Q000494:pharmacology; D014841:von Willebrand Factor / Q000378:metabolism* / Q000494:pharmacology
D000911:Antibodies, Monoclonal; D002121:Calcium Channel Blockers; D010446:Peptide Fragments; D019038:Platelet Glycoprotein GPIb-IX Complex; D011500:Protein Synthesis Inhibitors; D011994:Recombinant Proteins; D014841:von Willebrand Factor; C081839:von Willebrand factor (445-733); D014700:Verapamil; D002118:Calcium; D007213:Indomethacin