scholarly journals Shear-induced platelet aggregation requires von Willebrand factor and platelet membrane glycoproteins Ib and IIb-IIIa

Blood ◽  
1987 ◽  
Vol 69 (2) ◽  
pp. 625-628 ◽  
Author(s):  
DM Peterson ◽  
NA Stathopoulos ◽  
TD Giorgio ◽  
JD Hellums ◽  
JL Moake
Keyword(s):  
Shear Stress ◽  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Platelet Rich Plasma ◽  
Shear Stresses ◽  
Membrane Glycoprotein ◽  
Membrane Glycoproteins ◽  
Von Willebrand ◽  
Induced Aggregation ◽  
Willebrand Factor

Abstract Different types of platelets in various types of plasma were subjected to levels of shear stress that produce irreversible platelet aggregation in normal platelet-rich plasma (PRP). At shear stresses of 90 or 180 dyne/cm2 applied for 30 seconds or five minutes, aggregation was either absent or only transient and reversible using severe von Willebrand's disease (vWD) PRP (less than 1% von Willebrand factor, vWF); Bernard-Soulier syndrome (BSS) PRP (platelets deficient in the membrane glycoprotein Ib, GPIb); normal PRP plus monoclonal antibody (MoAb) to GPIb; thrombasthenic PRP (platelets deficient in membrane glycoprotein IIb-IIIa complex, GPIIb-IIIa); and normal PRP plus MoAb to GPIIb-IIIa. Shear-induced aggregation was inhibited under the above conditions, even though the platelets were activated to release their granular contents. Sheared normal platelets in vWD plasma aggregated in response to added vWF. These studies demonstrate that the formation of stable platelet aggregates under conditions of high shear requires vWF and the availability of both GPIb and GPIIb-IIIa on platelet membranes. The experiments demonstrate that vWF-platelet interactions can occur in the absence of artificial agonists or chemical modification of vWF. They suggest a possible mechanism for platelet aggregation in stenosed or partially obstructed arterial vessels in which the platelets are subjected to relatively high levels of shear stress.

scholarly journals Shear-induced platelet aggregation requires von Willebrand factor and platelet membrane glycoproteins Ib and IIb-IIIa

Blood ◽  
1987 ◽  
Vol 69 (2) ◽  
pp. 625-628 ◽  
Author(s):  
DM Peterson ◽  
NA Stathopoulos ◽  
TD Giorgio ◽  
JD Hellums ◽  
JL Moake
Keyword(s):  
Shear Stress ◽  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Platelet Rich Plasma ◽  
Shear Stresses ◽  
Membrane Glycoprotein ◽  
Membrane Glycoproteins ◽  
Von Willebrand ◽  
Induced Aggregation ◽  
Willebrand Factor

Different types of platelets in various types of plasma were subjected to levels of shear stress that produce irreversible platelet aggregation in normal platelet-rich plasma (PRP). At shear stresses of 90 or 180 dyne/cm2 applied for 30 seconds or five minutes, aggregation was either absent or only transient and reversible using severe von Willebrand's disease (vWD) PRP (less than 1% von Willebrand factor, vWF); Bernard-Soulier syndrome (BSS) PRP (platelets deficient in the membrane glycoprotein Ib, GPIb); normal PRP plus monoclonal antibody (MoAb) to GPIb; thrombasthenic PRP (platelets deficient in membrane glycoprotein IIb-IIIa complex, GPIIb-IIIa); and normal PRP plus MoAb to GPIIb-IIIa. Shear-induced aggregation was inhibited under the above conditions, even though the platelets were activated to release their granular contents. Sheared normal platelets in vWD plasma aggregated in response to added vWF. These studies demonstrate that the formation of stable platelet aggregates under conditions of high shear requires vWF and the availability of both GPIb and GPIIb-IIIa on platelet membranes. The experiments demonstrate that vWF-platelet interactions can occur in the absence of artificial agonists or chemical modification of vWF. They suggest a possible mechanism for platelet aggregation in stenosed or partially obstructed arterial vessels in which the platelets are subjected to relatively high levels of shear stress.

scholarly journals Platelet-collagen interaction: inhibition by ristocetin and enhancement by von Willebrand factor-platelet binding

Blood ◽  
1986 ◽  
Vol 68 (4) ◽  
pp. 927-937
Author(s):  
FM LaDuca ◽  
RE Bettigole ◽  
WR Bell ◽  
EB Robson
Keyword(s):  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Platelet Rich Plasma ◽  
Platelet Membrane ◽  
Type I ◽  
Membrane Glycoproteins ◽  
Platelet Binding ◽  
Von Willebrand ◽  
Willebrand Factor

The contribution of von Willebrand factor (vWF)-platelet binding to platelet-collagen interaction was examined in vitro. The binding of vWF to platelets was mediated and regulated by ristocetin. Subthreshold concentrations of ristocetin (less than or equal to 1 mg/mL), insufficient to cause ristocetin-induced platelet aggregation (RIPA), were added to platelet-rich plasma (PRP) prior to the addition of collagen. The collagen-induced platelet aggregation (CIPA) was modified by ristocetin and the degree of alteration was dependent on the ristocetin concentration. Response as a function of ristocetin concentration was designated the Collagen-Platelet Aggregation Response (CoI-PAR). In normal PRP the CoI-PAR was a progressive inhibition followed by decreasing inhibition and then an enhanced response. The enhanced response occurred over a narrow range of ristocetin concentrations (0.8 to 1.0 mg/mL). In the absence of vWF (severe von Willebrand's disease, Type I, vWF less than 1%) the CoI-PAR was a progressive, eventually complete inhibition with no enhanced response (with ristocetin concentrations up to 3.0 mg/mL). With addition of vWF to this PRP an enhanced response was observed at a ristocetin concentration inversely proportional to the vWF level. PRP from a patient with severe Hemophilia A showed a response within the normal range. Subthreshold ristocetin did not cause plasma protein precipitation or platelet release of 3H-serotonin, nor induce micro platelet aggregate formation. Digestion of platelet membrane glycoproteins (GP(s] with chymotrypsin demonstrated that upon removal of GPI, RIPA was absent, CIPA retained and the CoI-PAR was progressive inhibition, with no enhancement. With removal of GPs I, II, and III, RIPA, CIPA, and the CoI-PAR were absent. A dose-response 125I-vWF- platelet binding occurred with increasing ristocetin concentrations which was unchanged by the addition of collagen. These results demonstrated that ristocetin-platelet association inhibited CIPA, and vWF-platelet binding enhanced platelet-collagen adhesion and platelet aggregation. The in vitro-enhanced CIPA represents a vWF-dependent aggregation of sufficient magnitude to overcome the inhibitory effect of ristocetin. These studies demonstrate an influential interaction of ristocetin, vWF, and collagen with the platelet membrane and imply an important hemostatic contribution of vWF-platelet binding in platelet- collagen interaction.

scholarly journals Shear stress-induced von Willebrand factor binding to platelet glycoprotein Ib initiates calcium influx associated with aggregation

Blood ◽  
1992 ◽  
Vol 80 (1) ◽  
pp. 113-120 ◽  
Author(s):  
TW Chow ◽  
JD Hellums ◽  
JL Moake ◽  
MH Kroll
Keyword(s):  
Monoclonal Antibody ◽  
Shear Stress ◽  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Fluid Shear Stress ◽  
Platelet Glycoprotein ◽  
Platelet Surface ◽  
Von Willebrand ◽  
Induced Aggregation ◽  
Willebrand Factor

Platelets subjected to elevated levels of fluid shear stress in the absence of exogenous agonists will aggregate. Shear stress-induced aggregation requires von Willebrand factor (vWF) multimers, extracellular calcium (Ca2+), adenosine diphosphate (ADP), and platelet membrane glycoprotein (GP)Ib and GPIIb-IIIa. The sequence of interaction of vWF multimers with platelet surface receptors and the effect of these interactions on platelet activation have not been determined. To elucidate the mechanism of shear stress-induced platelet aggregation, suspensions of washed platelets were subjected to different levels of uniform shear stress (15 to 120 dyne/cm2) in an optically modified cone and plate viscometer. Cytoplasmic ionized calcium ([Ca2+]i) and aggregation of platelets were monitored simultaneously during the application of shear stress; [Ca2+]i was measured using indo-1 loaded platelets and aggregation was measured as changes in light transmission. Basal [Ca2+]i was approximately 60 to 100 nmol/L. An increase of [Ca2+]i (up to greater than 1,000 nmol/L) was accompanied by synchronous aggregation, and both responses were dependent on the shear force and the presence of vWF multimers. EGTA chelation of extracellular Ca2+ completely inhibited vWF-mediated [Ca2+]i and aggregation responses to shear stress. Aurin tricarboxylic acid, which blocks the GPIb recognition site on the vWF monomer, and 6D1, a monoclonal antibody to GPIb, also completely inhibited platelet responses to shear stress. The tetrapeptide RGDS and the monoclonal antibody 10E5, which inhibit vWF binding to GPIIb-IIIa, partially inhibited shear stress-induced [Ca2+]i and aggregation responses. The combination of creatine phosphate/creatine phosphokinase, which converts ADP to adenosine triphosphate and blocks the effect of ADP released from stimulated platelets, inhibited shear stress-induced platelet aggregation without affecting the increase of [Ca2+]i. Neither the [Ca2+]i nor aggregation response to shear stress was inhibited by blocking platelet cyclooxygenase metabolism with acetylsalicylic acid. These results indicate that GPIb and extracellular Ca2+ are absolutely required for vWF-mediated [Ca2+]i and aggregation responses to imposed shear stress, and that the interaction of vWF multimers with GPIIb-IIIa potentiates these responses. Shear stress-induced elevation of platelet [Ca2+]i, but not aggregation, is independent of the effects of release ADP, and both responses occur independently of platelet cyclooxygenase metabolism. These results suggest that shear stress induces the binding of vWF multimers to platelet GPIb and this vWF-GPIb interaction causes an increase of [Ca2+]i and platelet aggregation, both of which are potentiated by vWF binding to the platelet GPIIb-IIIa complex.

Surface-Secreted von Willebrand Factor Mediates Aggregation of ADP-Activated Platelets at Moderate Shear Stress: Facilitated by GPIb but Controlled by GPIIb-IIIa

1997 ◽  
Vol 77 (03) ◽  
pp. 568-576 ◽  
Author(s):  
M M Frojmovic ◽  
A Kasirer-Friede ◽  
H L Goldsmith ◽  
E A Brown
Keyword(s):  
Shear Stress ◽  
Von Willebrand Factor ◽  
Poiseuille Flow ◽  
Binding Domain ◽  
Shear Stresses ◽  
Shear Rates ◽  
Activated Platelets ◽  
Von Willebrand ◽  
Induced Aggregation ◽  
Willebrand Factor

SummaryWe previously showed that ADP activation of washed human platelets in plasma-free suspensions supports aggregation at moderate shear stress (0.4-1.6 Nm-2) in Poiseuille flow. Although most activated platelets expressed maximal fibrinogen-occupied GPIIb-IIIa receptors, aggregation appeared to be independent of bound fibrinogen, but blocked by the hexapeptide GRGDSP. Here, we tested the hypothesis that von Willebrand factor (vWF) secreted and expressed on activated platelets mediates aggregation at moderate shear rates from 300 to 1000 s_1 corresponding to shear stresses from 0.3 to 1.1 Nm-2. Relatively unactivated platelets (<15% expressing prebound fibrinogen) were prepared from acidified citrated platelet rich plasma (cPRP) by single centrifugation with 50 nM stable prostacyclin derivative ZK 36374 and resuspended in Tyrodes-albumin at 5 X 104 cells ε_1. Flow cytometric measurements with monoclonal antibody (mAb) 2.2.9 reporting on surface-bound vWF, and with mAb S12 reporting on a-granule secreted P-selectin, showed that 65% and 80%, respectively, of all platelets were maximally activated with respect to maximal secretion and surface expression of these proteins. “Resting” washed platelets exhibited both surface-bound vWF and significant P-selectin secretion. We showed that mAbs 6D1 and NMC4, respectively blocking the adhesive domains on the GPIb receptor recognizing vWF, and on the vWF molecule recognizing the GPIb receptor, partially inhibited ADP-induced aggregation under shear in Couette flow, the degree of inhibition increasing with increasing shear stress. In contrast, mAb 10E5, blocking the vWF binding domain on GPIIb-IIIa, essentially blocked all aggregation at the shear rates tested. We conclude that vWF, expressed on ADP-activated platelets, is at least the predominant cross-bridging molecule mediating aggregation at moderate shear stress. There is an absolute requirement for free activated GPIIb-IIIa receptors, postulated to interact with platelet-secreted, surface bound vWF. The GPIb-vWF cross-bridging reaction plays a facilitative role becoming increasingly important with increasing shear stress. Since aurin tricarboxylic acid, which blocks the GPIb binding domain on vWF, was also found to completely block aggregation in Poiseuille flow, we conclude that it too affects the GPIIb-IIIa interaction.

scholarly journals Shear-stress-induced von Willebrand factor binding to platelets causes the activation of tyrosine kinase(s)

1994 ◽  
Vol 302 (3) ◽  
pp. 681-686 ◽  
Author(s):  
K Razdan ◽  
J D Hellums ◽  
M H Kroll
Keyword(s):  
Shear Stress ◽  
Platelet Aggregation ◽  
Tyrosine Phosphorylation ◽  
Von Willebrand Factor ◽  
Arterial Blood Flow ◽  
Shear Stresses ◽  
Arterial Blood ◽  
Stress Dependent ◽  
Von Willebrand ◽  
Willebrand Factor

Pathological arterial blood flow generates fluid shear stresses that directly cause platelet aggregation. The mechanism of shear-induced platelet aggregation is incompletely understood, but involves von Willebrand factor (vWF) binding to platelet glycoprotein (GP) Ib and GP IIb-IIIa, leading to the transmembrane influx of Ca2+ and the activation of protein kinase C. To investigate this further, shear-stress-induced protein tyrosine phosphorylation (PTP) of washed platelets was studied in a cone-plate viscometer. A time- and shear-stress-dependent tyrosine phosphorylation of substrates with approx. M(r) 29,000-31,000, 36,000, 50,000, 58,000, 64,000, 76,000, 85,000 and 105,000 was observed. PTP in response to a threshold shear stress of 0.3 mN/cm2 (30 dyn/cm2) was enhanced in most cases by exogenous purified human vWF, and PTP in response to a pathological shear stress of 0.9 mN/cm2 (90 dyn/cm2) was inhibited in some cases by inhibiting vWF binding to GP Ib or GP IIb-IIIa, or by inhibiting Ca2+ responses with extracellular EGTA. Shear-induced PTP of a substrate of M(r) approximately 31,000 appeared to be independent of GP Ib, and PTP of a substrate(s) of M(r) approximately 29,000 was shear-stress-dependent but independent of extracellular Ca2+. Cytochalasin D, which inhibits GP Ib-cytoskeleton interactions, inhibits the PTP of a substrate of M(r) approximately 76,000. These results suggest that tyrosine phosphorylation may be involved in transmembrane signalling that mediates platelet adhesion and aggregation in response to pathological shear stresses generated at sites of arterial vaso-occlusion.

scholarly journals Platelet-collagen interaction: inhibition by ristocetin and enhancement by von Willebrand factor-platelet binding

Blood ◽  
1986 ◽  
Vol 68 (4) ◽  
pp. 927-937 ◽  
Author(s):  
FM LaDuca ◽  
RE Bettigole ◽  
WR Bell ◽  
EB Robson
Keyword(s):  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Platelet Rich Plasma ◽  
Platelet Membrane ◽  
Type I ◽  
Membrane Glycoproteins ◽  
Platelet Binding ◽  
Von Willebrand ◽  
Willebrand Factor

Abstract The contribution of von Willebrand factor (vWF)-platelet binding to platelet-collagen interaction was examined in vitro. The binding of vWF to platelets was mediated and regulated by ristocetin. Subthreshold concentrations of ristocetin (less than or equal to 1 mg/mL), insufficient to cause ristocetin-induced platelet aggregation (RIPA), were added to platelet-rich plasma (PRP) prior to the addition of collagen. The collagen-induced platelet aggregation (CIPA) was modified by ristocetin and the degree of alteration was dependent on the ristocetin concentration. Response as a function of ristocetin concentration was designated the Collagen-Platelet Aggregation Response (CoI-PAR). In normal PRP the CoI-PAR was a progressive inhibition followed by decreasing inhibition and then an enhanced response. The enhanced response occurred over a narrow range of ristocetin concentrations (0.8 to 1.0 mg/mL). In the absence of vWF (severe von Willebrand's disease, Type I, vWF less than 1%) the CoI-PAR was a progressive, eventually complete inhibition with no enhanced response (with ristocetin concentrations up to 3.0 mg/mL). With addition of vWF to this PRP an enhanced response was observed at a ristocetin concentration inversely proportional to the vWF level. PRP from a patient with severe Hemophilia A showed a response within the normal range. Subthreshold ristocetin did not cause plasma protein precipitation or platelet release of 3H-serotonin, nor induce micro platelet aggregate formation. Digestion of platelet membrane glycoproteins (GP(s] with chymotrypsin demonstrated that upon removal of GPI, RIPA was absent, CIPA retained and the CoI-PAR was progressive inhibition, with no enhancement. With removal of GPs I, II, and III, RIPA, CIPA, and the CoI-PAR were absent. A dose-response 125I-vWF- platelet binding occurred with increasing ristocetin concentrations which was unchanged by the addition of collagen. These results demonstrated that ristocetin-platelet association inhibited CIPA, and vWF-platelet binding enhanced platelet-collagen adhesion and platelet aggregation. The in vitro-enhanced CIPA represents a vWF-dependent aggregation of sufficient magnitude to overcome the inhibitory effect of ristocetin. These studies demonstrate an influential interaction of ristocetin, vWF, and collagen with the platelet membrane and imply an important hemostatic contribution of vWF-platelet binding in platelet- collagen interaction.

scholarly journals Shear stress-induced von Willebrand factor binding to platelet glycoprotein Ib initiates calcium influx associated with aggregation

Blood ◽  
1992 ◽  
Vol 80 (1) ◽  
pp. 113-120 ◽  
Author(s):  
TW Chow ◽  
JD Hellums ◽  
JL Moake ◽  
MH Kroll
Keyword(s):  
Monoclonal Antibody ◽  
Shear Stress ◽  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Fluid Shear Stress ◽  
Platelet Glycoprotein ◽  
Platelet Surface ◽  
Von Willebrand ◽  
Induced Aggregation ◽  
Willebrand Factor

Abstract Platelets subjected to elevated levels of fluid shear stress in the absence of exogenous agonists will aggregate. Shear stress-induced aggregation requires von Willebrand factor (vWF) multimers, extracellular calcium (Ca2+), adenosine diphosphate (ADP), and platelet membrane glycoprotein (GP)Ib and GPIIb-IIIa. The sequence of interaction of vWF multimers with platelet surface receptors and the effect of these interactions on platelet activation have not been determined. To elucidate the mechanism of shear stress-induced platelet aggregation, suspensions of washed platelets were subjected to different levels of uniform shear stress (15 to 120 dyne/cm2) in an optically modified cone and plate viscometer. Cytoplasmic ionized calcium ([Ca2+]i) and aggregation of platelets were monitored simultaneously during the application of shear stress; [Ca2+]i was measured using indo-1 loaded platelets and aggregation was measured as changes in light transmission. Basal [Ca2+]i was approximately 60 to 100 nmol/L. An increase of [Ca2+]i (up to greater than 1,000 nmol/L) was accompanied by synchronous aggregation, and both responses were dependent on the shear force and the presence of vWF multimers. EGTA chelation of extracellular Ca2+ completely inhibited vWF-mediated [Ca2+]i and aggregation responses to shear stress. Aurin tricarboxylic acid, which blocks the GPIb recognition site on the vWF monomer, and 6D1, a monoclonal antibody to GPIb, also completely inhibited platelet responses to shear stress. The tetrapeptide RGDS and the monoclonal antibody 10E5, which inhibit vWF binding to GPIIb-IIIa, partially inhibited shear stress-induced [Ca2+]i and aggregation responses. The combination of creatine phosphate/creatine phosphokinase, which converts ADP to adenosine triphosphate and blocks the effect of ADP released from stimulated platelets, inhibited shear stress-induced platelet aggregation without affecting the increase of [Ca2+]i. Neither the [Ca2+]i nor aggregation response to shear stress was inhibited by blocking platelet cyclooxygenase metabolism with acetylsalicylic acid. These results indicate that GPIb and extracellular Ca2+ are absolutely required for vWF-mediated [Ca2+]i and aggregation responses to imposed shear stress, and that the interaction of vWF multimers with GPIIb-IIIa potentiates these responses. Shear stress-induced elevation of platelet [Ca2+]i, but not aggregation, is independent of the effects of release ADP, and both responses occur independently of platelet cyclooxygenase metabolism. These results suggest that shear stress induces the binding of vWF multimers to platelet GPIb and this vWF-GPIb interaction causes an increase of [Ca2+]i and platelet aggregation, both of which are potentiated by vWF binding to the platelet GPIIb-IIIa complex.

scholarly journals Aurin tricarboxylic acid: a novel inhibitor of the association of von Willebrand factor and platelets

Blood ◽  
1988 ◽  
Vol 72 (6) ◽  
pp. 1898-1903 ◽  
Author(s):  
MD Phillips ◽  
JL Moake ◽  
L Nolasco ◽  
N Turner
Keyword(s):  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Competitive Inhibition ◽  
Platelet Rich Plasma ◽  
Tricarboxylic Acid ◽  
Platelet Glycoprotein ◽  
Dependent Manner ◽  
Von Willebrand ◽  
Induced Aggregation ◽  
Willebrand Factor

Abstract Shear stress activated platelets undergo aggregation in the presence of large or unusually large von Willebrand factor (vWF) multimers without the addition of ristocetin or any other exogenous chemical. This phenomenon may be analogous to the platelet aggregation that leads to thrombosis in the narrowed arteries and arterioles of patients with atherosclerosis or vasospasm. A triphenyl-methyl compound, aurin tricarboxylic acid (ATA), inhibits shear-induced, vWF-mediated platelet aggregation in platelet-rich plasma (PRP) in concentrations above 200 mumol/L and in buffer suspensions of washed platelets at a concentration of 0.1 mumol/L. In a concentration-dependent manner, ATA also inhibits ristocetin-induced, vWF-mediated platelet clumping in both fresh and formaldehyde-fixed platelet suspensions. This inhibition can be overcome by increasing the concentration of vWF, following the kinetics of first order competitive inhibition. ATA prevents the attachment to platelets of the largest vWF multimeric forms found in normal plasma and of the unusually large vWF multimers derived from endothelial cells. The rate of aggregation and degree of inhibition by ATA is not accounted for by the binding of ristocetin or calcium. Arachidonic acid- and adenosine diphosphate (ADP)-induced aggregation are not inhibited by ATA. Platelets incubated with ATA can be easily separated from the compound. However, ATA binds to large vWF multimeric forms and inhibits their ristocetin-induced interaction with platelet glycoprotein Ib. Because ATA also inhibits shear-induced, vWF-mediated platelet aggregation in vitro in the absence of ristocetin, it may be a useful prototype compound to impede the development of arterial thrombosis in vivo.

scholarly journals Aurin tricarboxylic acid: a novel inhibitor of the association of von Willebrand factor and platelets

Blood ◽  
1988 ◽  
Vol 72 (6) ◽  
pp. 1898-1903 ◽  
Author(s):  
MD Phillips ◽  
JL Moake ◽  
L Nolasco ◽  
N Turner
Keyword(s):  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Competitive Inhibition ◽  
Platelet Rich Plasma ◽  
Tricarboxylic Acid ◽  
Platelet Glycoprotein ◽  
Dependent Manner ◽  
Von Willebrand ◽  
Induced Aggregation ◽  
Willebrand Factor

Shear stress activated platelets undergo aggregation in the presence of large or unusually large von Willebrand factor (vWF) multimers without the addition of ristocetin or any other exogenous chemical. This phenomenon may be analogous to the platelet aggregation that leads to thrombosis in the narrowed arteries and arterioles of patients with atherosclerosis or vasospasm. A triphenyl-methyl compound, aurin tricarboxylic acid (ATA), inhibits shear-induced, vWF-mediated platelet aggregation in platelet-rich plasma (PRP) in concentrations above 200 mumol/L and in buffer suspensions of washed platelets at a concentration of 0.1 mumol/L. In a concentration-dependent manner, ATA also inhibits ristocetin-induced, vWF-mediated platelet clumping in both fresh and formaldehyde-fixed platelet suspensions. This inhibition can be overcome by increasing the concentration of vWF, following the kinetics of first order competitive inhibition. ATA prevents the attachment to platelets of the largest vWF multimeric forms found in normal plasma and of the unusually large vWF multimers derived from endothelial cells. The rate of aggregation and degree of inhibition by ATA is not accounted for by the binding of ristocetin or calcium. Arachidonic acid- and adenosine diphosphate (ADP)-induced aggregation are not inhibited by ATA. Platelets incubated with ATA can be easily separated from the compound. However, ATA binds to large vWF multimeric forms and inhibits their ristocetin-induced interaction with platelet glycoprotein Ib. Because ATA also inhibits shear-induced, vWF-mediated platelet aggregation in vitro in the absence of ristocetin, it may be a useful prototype compound to impede the development of arterial thrombosis in vivo.

Glycoprotein Ib Has a Partial Role in Platelet-von Willebrand Factor Collagen Interaction

1988 ◽  
Vol 60 (02) ◽  
pp. 182-187 ◽  
Author(s):  
Morio Aihara ◽  
Ken Tamura ◽  
Ryuko Kawarada ◽  
Keizou Okawa ◽  
Yutaka Yoshida
Keyword(s):  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Ricinus Communis ◽  
Protein S ◽  
Platelet Membrane ◽  
Membrane Glycoprotein ◽  
Normal Plasma ◽  
Ricinus Communis Agglutinin ◽  
Von Willebrand ◽  
Willebrand Factor

SummaryThe adhesion of human fixed washed platelets (FWP) to collagen was decreased after treatment with Serratia marcescens protease (SP), which removed 95% of the glycocalicin from platelet membrane glycoprotein (GP) lb. However, the diminished adhesion of SP treated FWP to collagen could still be increased in the presence of purified von Willebrand factor (vWF). This ability of vWF to increase FWP adhesion to collagen is defined as collagen cofactor (CCo). The adhesion of FWP to collagen was not affected by a monoclonal antibody (MAb) to GP Ilb/IIIa (10E5), that inhibits ADP and collagen induced platelet aggregation. On the other hand, it was decreased by 50% by a MAb to GP lb (6D1), that inhibits ristocetin induced platelet aggregation. Adhesion of FWP in buffer to collagen was completely inhibited by Ricinus communis agglutinin I or concanavalin A, while Lens culinalis agglutinin and wheat germ agglutinin showed 50% inhibition. The FWP adhesion to collagen in the presence of vWF (normal plasma) was unaffected by MAbs to GP Ilb/IIIa (10E5, P2, HPL1) but was decreased to 32-38% by MAbs to GP lb (6D1, AN51, HPL11). A MAb to vWF (CLB-RAg 35), that inhibits ristocetin induced binding of vWF to platelets, decreased the CCo of normal plasma by 70%. The MAb, CLB-RAg 201, that inhibits the binding of vWF to collagen, completely inhibited the CCo of normal plasma. In conclusion, our data suggest that (1) GP lb has a partial role in FWP adhesion to collagen; (2) the binding of vWF to collagen is required for the expression of CCo; (3) CCo is partly mediated through GP lb; but (4) other platelet membrane protein(s) besides GP lb or GP Ilb/IIIa must also be involved in FWP-vWF-collagen interactions.

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