Functional Involvement of Thrombospondin in Platelet Aggregation Induced by Low Versus High Concentrations of Thrombin

1986 ◽  
Vol 55 (01) ◽  
pp. 136-142 ◽  
Author(s):  
K J Kao ◽  
David M Shaut ◽  
Paul A Klein
Keyword(s):  
Platelet Aggregation ◽  
Binding Sites ◽  
Inhibitory Effect ◽  
Activated Platelets ◽  
Low Concentrations ◽  
Platelet Binding ◽  
Functional Involvement ◽  
Thrombin Activation ◽  
Platelet Aggregates ◽  
High Concentrations

SummaryThrombospondin (TSP) is a major platelet secretory glycoprotein. Earlier studies of various investigators demonstrated that TSP is the endogenous platelet lectin and is responsible for the hemagglutinating activity expressed on formaldehyde-fixed thrombin-treated platelets. The direct effect of highly purified TSP on thrombin-induced platelet aggregation was studied. It was observed that aggregation of gel-filtered platelets induced by low concentrations of thrombin (≤0.05 U/ml) was progressively inhibited by increasing concentrations of exogenous TSP (≥60 μg/ml). However, inhibition of platelet aggregation by TSP was not observed when higher than 0.1 U/ml thrombin was used to activate platelets. To exclude the possibility that TSP inhibits platelet aggregation by affecting thrombin activation of platelets, three different approaches were utilized. First, by using a chromogenic substrate assay it was shown that TSP does not inhibit the proteolytic activity of thrombin. Second, thromboxane B2 synthesis by thrombin-stimulated platelets was not affected by exogenous TSP. Finally, electron microscopy of thrombin-induced platelet aggregates showed that platelets were activated by thrombin regardless of the presence or absence of exogenous TSP. The results indicate that high concentrations of exogenous TSP (≥60 μg/ml) directly interfere with interplatelet recognition among thrombin-activated platelets. This inhibitory effect of TSP can be neutralized by anti-TSP Fab. In addition, anti-TSP Fab directly inhibits platelet aggregation induced by a low (0.02 U/ml) but not by a high (0.1 U/ml) concentration of thrombin. In conclusion, our findings demonstrate that TSP is functionally important for platelet aggregation induced by low (≤0.05 U/ml) but not high (≥0.1 U/ml) concentrations of thrombin. High concentrations of exogenous TSP may univalently saturate all its platelet binding sites consequently interfering with TSP-crosslinking of thrombin-activated platelets.

Ticlopidine Selectively Inhibits Human Platelet Responses to Adenosine Diphosphate

1991 ◽  
Vol 66 (06) ◽  
pp. 694-699 ◽  
Author(s):  
Marco Cattaneo ◽  
Benjaporn Akkawat ◽  
Anna Lecchi ◽  
Claudio Cimminiello ◽  
Anna M Capitanio ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Adenosine Diphosphate ◽  
Inhibitory Effect ◽  
Clot Retraction ◽  
Fibrinogen Binding ◽  
Low Concentrations ◽  
Binding Inhibition ◽  
High Concentrations ◽  
Formalin Fixed

SummaryPlatelet aggregation and fibrinogen binding were studied in 15 individuals before and 7 days after the oral administration of ticlopidine (250 mg b.i.d.). Ticlopidine significantly inhibited platelet aggregation induced by adenosine diphosphate (ADP), the endoperoxide analogue U46619, collagen or low concentrations of thrombin, but did not inhibit platelet aggregation induced by epinephrine or high concentrations of thrombin. Ticlopidine inhibited 125I-fibrinogen binding induced by ADP, U46619 or thrombin (1 U/ml). The ADP scavengers apyrase or CP/CPK, added in vitro to platelet suspensions obtained before ticlopidine, caused the same pattern of aggregation and 125I-fibrihogen binding inhibition as did ticlopidine. Ticlopidine did not inhibit further platelet aggregation and 125I-fibrinogen binding induced in the presence of ADP scavengers. After ticlopidine administration, thrombin or U46619, but not ADP, increased the binding rate of the anti-GPIIb/IIIa monoclonal antibody 7E3 to platelets. Ticlopidine inhibited clot retraction induced by reptilase plus ADP, but not that induced by thrombin or by reptilase plus epinephrine, and prevented the inhibitory effect of ADP, but not that of epinephrine, on the PGE1-induced increase in platelet cyclic AMP. The number of high- and low-affinity binding sites for 3H-ADP on formalin-fixed platelets and their K d were not modified by ticlopidine. These findings indicate that ticlopidine selectively inhibits platelet responses to ADP.

Requirement Of Fibrinogen And Calcium For Inter-Platelet Bridges In Platelet Aggregation: A Hypothesis

1981 ◽  
Author(s):  
Elizabeth Kornecki ◽  
Stefan Niewiarowski
Keyword(s):  
Platelet Aggregation ◽  
Binding Sites ◽  
Proteolytic Enzymes ◽  
Divalent Cations ◽  
Platelet Surface ◽  
Fibrinogen Binding ◽  
Platelet Aggregates ◽  
High Concentrations ◽  
Induced Aggregation ◽  
Aggregation Of Platelets

Fibrinogen and calcium are required for the aggregation of platelets stimulated by ADP or pre-treated with proteolytic enzymes. Specific platelet surface fibrinogen binding sites (receptors) are exposed after platelets are stimulated by ADP or pre-treated with Chymotrypsin or pronase. It has previously been shown in our laboratory that an intact, symmetrical fibrinogen molecule is essential for fibrinogen binding and fibrinogen-induced aggregation of both ADP-stimulated and proteolytically-treated platelets. Here we propose that the mechanism by which fibrinogen and calcium aggregate platelets is by forming inter-platelet bridges linking the fibrinogen receptors of adjacent platelets together. In support of this proposition are the following new lines of evidence: 1) The fibrinogen-induced aggregations of ADP-stfiliulated or proteolytically-treated platelets are inhibited by high concentrations of fibrinogen (Ki=2.6 and 8.5 × 10 5M, respectively). The fibrinogen binding sites on adjacent platelets, at these concentrations, would be saturated by fibrinogen and therefore no inter-platelet fibrinogen bridges could be formed to hold the platelets together. 2) ADP-stimulated or chymotrypsin-treated platelets aggregated by fibrinogen are deaggregated by Chymotrypsin or pronase and this deaggregation coincides with the loss of 125I-fibrinogen from the platelet surface. 3) Preincubation of platelets with EDTA results in inhibition of both platelet aggregation and 125I-fibrinogen binding. Following the aggregations of ADP-stimulated or of chymotrypsin-treated platelets by fibrinogen, the addition of EDTA to the platelet aggregates results in both their deaggregation and their loss of bound 125I-fibrinogen. Thus it appears that divalent cations, especially calcium, are essential for the formation of fibrinogen-linked platelet aggregates.

Potentiation of Adrenaline-Induced Platelet Aggregation by Angiotensin II

1985 ◽  
Vol 54 (03) ◽  
pp. 717-720 ◽  
Author(s):  
Yu-An Ding ◽  
D Euan MacIntyre ◽  
Christopher J Kenyon ◽  
Peter F Semple
Keyword(s):  
Platelet Aggregation ◽  
Angiotensin Ii ◽  
Human Platelet ◽  
Inhibitory Effect ◽  
Facilitatory Effect ◽  
Ang Ii ◽  
Human Platelet Aggregation ◽  
Low Concentrations ◽  
High Concentrations ◽  
Stimulation Of

SummaryThe effects of angiotensin II (ANG II) alone and in combination with other agonists on human platelet aggregation, thromboxane B2 (TxB2) and cytosolic [Ca2+]i were investigated. ANG II (10™11 - 10™7 M) alone had no direct effect on aggregation, TxB2 production or [Ca2+]i after short- (<2 min) or longterm (30 min) incubation. In contrast, low concentrations of ANG II (10™11 M) enhanced adrenaline-induced platelet aggregation but high concentrations (10™7 M) had an inhibitory effect. Moreover, ANG II (10™11 - 10™7 M) augmented platelet responses to the TxA2 mimetic, U44069. Pretreatment of platelets with flurbiprofen abolished this facilitatory effect of ANG II on adrenaline- but not on U44069-induced platelet aggregation. These results suggest that ANG II stimulation of agonist-induced platelet activation may be due to potentiation of the effects rather than the synthesis of TxA2

In Vitro Effects of Ethanol on Rabbit Platelet Aggregation, Secretion of Granule Contents, and Cyclic AMP Levels in the Presence of Prostacyclin

1989 ◽  
Vol 61 (02) ◽  
pp. 254-258 ◽  
Author(s):  
Margaret L Rand ◽  
Peter L Gross ◽  
Donna M Jakowec ◽  
Marian A Packham ◽  
J Fraser Mustard
Keyword(s):  
Cyclic Amp ◽  
Inhibitory Effect ◽  
Rabbit Platelet ◽  
Inhibitory Effects ◽  
Low Concentrations ◽  
Rabbit Platelets ◽  
High Concentrations ◽  
In Vitro Effects ◽  
Aggregation Of Platelets

SummaryEthanol, at physiologically tolerable concentrations, inhibits platelet responses to low concentrations of collagen or thrombin, but does not inhibit responses of washed rabbit platelets stimulated with high concentrations of ADP, collagen, or thrombin. However, when platelet responses to high concentrations of collagen or thrombin had been partially inhibited by prostacyclin (PGI2), ethanol had additional inhibitory effects on aggregation and secretion. These effects were also observed with aspirin- treated platelets stimulated with thrombin. Ethanol had no further inhibitory effect on aggregation of platelets stimulated with ADP, or the combination of ADP and epinephrine. Thus, the inhibitory effects of ethanol on platelet responses in the presence of PGI2 were very similar to its inhibitory effects in the absence of PGI2, when platelets were stimulated with lower concentrations of collagen or thrombin. Ethanol did not appear to exert its inhibitory effects by increasing cyclic AMP above basal levels and the additional inhibitory effects of ethanol in the presence of PGI2 did not appear to be brought about by further increases in platelet cyclic AMP levels.

Properties of Fibrinogen Cleaved by Jararhagin, a Metalloproteinase from the Venom of Bothrops jararaca

1994 ◽  
Vol 72 (02) ◽  
pp. 244-249 ◽  
Author(s):  
Aura S Kamiguti ◽  
Joseph R Slupsky ◽  
Mirko Zuzel ◽  
Charles R M Hay
Keyword(s):  
Platelet Aggregation ◽  
Platelet Function ◽  
Fibrin Clot ◽  
Clot Formation ◽  
Human Fibrinogen ◽  
Activated Platelets ◽  
Bothrops Jararaca ◽  
Platelet Binding ◽  
Fibrin Monomers ◽  
Fibrinogen Molecule

SummaryHaemorrhagic metalloproteinases from Bothrops jararaca and other venoms degrade vessel-wall and plasma proteins involved in platelet plug and fibrin clot formation. These enzymes also cause proteolytic digestion of fibrinogen which has been suggested to cause defective platelet function. Fibrinogen degradation by jararhagin, a metalloproteinase from B. jararaca, and the effect of jararhagin fibrinogenolysis on both platelet aggregation and fibrin clot formation were investigated. Jararhagin was found to cleave human fibrinogen in the C-terminal region of the Aα-chain giving rise to a 285-290 kDa fibrinogen molecule lacking the Aα-chain RGD 572-574 platelet-binding site. Platelet binding and aggregation of ADP-activated platelets is unaffected by this modification. This indicates that the lost site is not essential for platelet aggregation, and that the remaining platelet binding sites located in the N-terminal portion of Aα chains (RGD 95-97) and the C-terminal of γ chains (dodecapeptide 400-411) are unaffected by jararhagin-digestion of fibrinogen. Fibrin clot formation with thrombin of this remnant fibrinogen molecule was defective, with poor polymerization of fibrin monomers but normal release of FPA. The abnormal polymerization could be explained by the loss of one of the two complementary polymerization sites required for side-by-side association of fibrin protofibrils. Jararhagin-induced inhibition of platelet function, an important cause of haemorrhage in envenomed patients, is not caused by proteolysis of fibrinogen, as had been thought, and the mechanism remains to be elucidated.

The Effect of Collagen Mediated Platelet Release on Plasma Prekallikrein Activation

1984 ◽  
Vol 51 (01) ◽  
pp. 037-041 ◽  
Author(s):  
K M Weerasinghe ◽  
M F Scully ◽  
V V Kakkar
Keyword(s):  
Platelet Aggregation ◽  
Healthy Volunteers ◽  
Platelet Rich Plasma ◽  
Age Groups ◽  
Inhibitory Effect ◽  
Age Group ◽  
Platelet Factor ◽  
Activated Platelets ◽  
Platelet Release ◽  
Collagen Treatment

SummaryCollagen mediated platelet aggregation caused -5.6 ± 6.7% inhibition and +39.1 ± 15.2% potentiation of prekallikrein activation in plasma from normal healthy volunteers between 20–40 and 50–65 years of age, respectively (n = 15, p <0.01). The amouns of platelet factor-four (PF4) released in the two groups were not significantly different. Collagen treatment in the presence of indomethacin caused +11.5 ± 3.6% and +59.6 ± 19.5% potentiation in the 20–40 and 50–65 age groups respectively (p <0.02). Adrenaline mediated platelet aggregation caused -55.2 ± 7.1% and -35.2 ± 8.3% inhibition in the 20–40 and 50–65 age groups, respectively. Collagen treatment of platelet-deficient-plasma and platelet-rich-plasma in EDTA also caused potentiation of prekallikrein activation.The results indicate that the observed degree of prekallikrein activation after platelet aggregation is a net result of the inhibitory effect of PF4 and the potentiatory effect of activated platelets. The potentiatory effect was greater after collagen treatment as compared to adrenaline treatment, and in the 50–65 age group as compared to the 20–40 age group.

Inhibition of Platelet Function by Antiarrhythmic Drugs, Verapamil and Disopyramide

1982 ◽  
Vol 47 (02) ◽  
pp. 150-153 ◽  
Author(s):  
P Han ◽  
C Boatwright ◽  
N G Ardlie
Keyword(s):  
Platelet Aggregation ◽  
Platelet Function ◽  
Antiarrhythmic Drugs ◽  
Adenosine Diphosphate ◽  
Inhibitory Effect ◽  
Second Phase ◽  
Ionophore A23187 ◽  
High Concentrations ◽  
Artery Disease

SummaryVarious cardiovascular drugs such as nitrates and propranolol, used in the treatment of coronary artery disease have been shown to have an antiplatelet effect. We have studied the in vitro effects of two antiarrhythmic drugs, verapamil and disopyramide, and have shown their inhibitory effect on platelet function. Verapamil, a calcium channel blocker, inhibited the second phase of platelet aggregation induced by adenosine diphosphate (ADP) and inhibited aggregation induced by collagen. Disopyramide similarly inhibited the second phase of platelet aggregation caused by ADP and aggregation induced by collagen. Either drug in synergism with propranolol inhibited ADP or collagen-induced platelet aggregation. Disopyramide at high concentrations inhibited arachidonic add whereas verapamil was without effect. Verapamil, but not disopyramide, inhibited aggregation induced by the ionophore A23187.

Furosemide-sensitive thallium fluxes in smooth muscle of rabbit uterus

1983 ◽  
Vol 245 (6) ◽  
pp. F778-F783
Author(s):  
A. Johns ◽  
S. V. Cutshaw
Keyword(s):  
Smooth Muscle ◽  
Binding Sites ◽  
Rank Order ◽  
Chloride Concentration ◽  
Cation Binding ◽  
Exchange System ◽  
Total Uptake ◽  
Low Concentrations ◽  
Chloride Pump ◽  
High Concentrations

The furosemide-sensitive uptake of thallium represents approximately equal to 50% of the total uptake of thallium by rabbit uterus and requires Cl- and Na+. The furosemide-sensitive uptake of thallium is stimulated by other ions at low concentrations with the rank order Li+ greater than Tl+ greater than K+ = Rb+ greater than Cs+ and is inhibited by these ions at high concentrations with the rank order Tl+ greater than K+ = Rb+ greater than Cs+ greater than Li+, suggesting multiple cation binding sites on the carrier. Uptake of 36Cl- is inhibited by furosemide in the presence of ouabain. Thallium efflux and 36Cl efflux in the presence of ouabain is inhibited by furosemide. The chloride concentration regulates the proportion of thallium uptake that is ouabain sensitive and furosemide sensitive without altering the total uptake. It is suggested that the furosemide-sensitive uptake of thallium reflects a Na+-Cl- -K+ exchange system that could be classified as a cotransport or countertransport of any two of these ions and also could be the smooth muscle chloride pump.

scholarly journals Investigation of the mechanisms of monoclonal antibody-induced platelet activation

Blood ◽  
1991 ◽  
Vol 78 (4) ◽  
pp. 1019-1026 ◽  
Author(s):  
P Horsewood ◽  
CP Hayward ◽  
TE Warkentin ◽  
JG Kelton
Keyword(s):  
Platelet Aggregation ◽  
Platelet Activation ◽  
Binding Sites ◽  
Fc Receptors ◽  
Secondary Antibody ◽  
Igg Antibodies ◽  
Platelet Surface ◽  
Platelet Protein ◽  
Platelet Binding ◽  
Protein Components

Abstract Antiplatelet antibodies can activate platelets causing platelet aggregation and the release reaction. However, the pathway of activation by these antibodies is unknown and several potential mechanisms are possible. In this report, we describe studies investigating potential pathways of platelet activation by IgG antibodies. We tested 16 different IgG monoclonal antibodies (MoAbs) against a variety of platelet surface components and found that six antibodies were capable of causing platelet aggregation and release. These included MoAbs against glycoprotein (GP) IIb/IIIa, CD9, GPIV, and two other not well-characterized platelet components. There was no relationship between the number of platelet binding sites and the ability of an MoAb to activate the platelets. By adding intact and F(ab')2 preparations of the MoAb to control or Fc receptor-blocked platelets, we found that in all instances the MoAbs initiated platelet activation via interacting with the platelet Fc receptors. Clustering of the platelet protein components using a secondary antibody did not cause activation. Studies into the pathway of Fc-dependent activation demonstrated that the MoAbs were capable of activating platelets by occupying Fc receptors on adjacent platelets (interplatelet activation), as well as on the same platelet (intraplatelet activation).

Inhibitory Effect Of Exogenous Arachidonic Acid Or Linoleic Acid On Rabbit Platelet Aggregation And Release Reaction

1981 ◽  
Author(s):  
M Cattaneo ◽  
R L Kinlough-Rathbone ◽  
J F Mustard
Keyword(s):  
Arachidonic Acid ◽  
Linoleic Acid ◽  
Platelet Aggregation ◽  
Cell Membrane ◽  
Platelet Function ◽  
Unsaturated Fatty Acids ◽  
Inhibitory Effect ◽  
Rabbit Platelet ◽  
Lipoxygenase Pathway ◽  
High Concentrations

In contrast to other release-inducing agents (e.g. thrombin) arachidonic acid (AA) releases only 40-50% of amine storage granule contents and although low concentrations induce aggregation, high concentrations do not. Several theories have been proposed to explain these observations: 1) AA or its products inactivates the cyclo-oxygenase; 2) the products of AA increase platelet cAMP; 3) lipoxygenase products are inhibitory; 4) unsaturated fatty acids (UFA) perturb the cell membrane. Using washed rabbit platelets we examined the effect of AA on platelet function. In these experiments aspirin-treated platelets (ASA 5.5 mM) were exposed to AA (230 μM) for 15 min. and then to PGEj (10 μM) for 30 min. The platelets were then resuspended. These platelets did not aggregate to ADP (9 μM) and their response to thrombin (0.02-0.05 U/ml) was impaired in contrast to control, ASA-treated platelets not exposed to AA. Non-ASA-treated platelets exposed to AA (230 μM), deaggre- gated with PGE1, and then resuspended also did not aggregate in response to ADP (9 μM) collagen, AA (230 μM) or thrombin (0.02-0.05 U/ml). When platelets pretreated with ASA and AA were mixed 1:1 with normal platelets and the mixture stimulated with AA (230 μM), the AA-treated platelets did not release their granule contents whereas the normal platelets did. These results do not support the hypothesis- that the inhibitory effect of AA on platelet aggregation and release is primarily due to inhibition of cyclo-oxygenase or an increase in cAMP caused by AA products. It seems unlikely that inhibition by AA can be due to products of the lipoxygenase pathway, because the effect persists when the platelets are washed and resuspended. Similar results were obtained by incubating platelets with linoleic acid (230 μM). This evidence is compatible with the hypothesis that UFA can inhibit platelet function by perturbing the cell membrane. This effect may be related to changes in receptor availability.

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