scholarly journals Kinetics of ADP-induced human platelet shape change: apparent positive cooperativity

1980 ◽  
Vol 58 (1) ◽  
pp. 45-52 ◽  
Author(s):  
John G. Milton ◽  
W. Yung ◽  
C. Glushak ◽  
M. M. Frojmovic
Keyword(s):  
Light Transmission ◽  
Human Platelet ◽  
Platelet Rich Plasma ◽  
Shape Change ◽  
Hill Coefficient ◽  
A Value ◽  
The Hill ◽  
Kinetics Of ◽  
Type Response ◽  
Platelet Shape

The kinetics of ADP-induced human platelet shape change have been examined. Initial velocities of platelet shape change were estimated by two methods: (1) the slope of the initial decrease in light transmission through stirred, citrated platelet-rich plasma, and (2) direct examination of platelet morphologies by phase-contrast microscopy. In both cases, a value of the Hill coefficient, NH, significantly greater than 1 is obtained (2.0 ± 0.2 and 1.8 ± 0.2, respectively). The observed elevated value of NH is not due to a substantial fraction of the ADP being platelet bound, the presence of factors in the plasma, platelet heterogeneity, or the influence of the rate of platelet shape change reversion. Our observations suggest that ADP-induced platelet shape change may be a positively cooperative or "threshold" type response.

Altered Platelet Shape Change in Hereditary Gelsolin Asp187Asn-related Amyloidosis

2000 ◽  
Vol 83 (03) ◽  
pp. 491-495 ◽  
Author(s):  
Kaija Javela ◽  
Hannu Somer ◽  
Riitta Kekomäki ◽  
Sari Kiuru
Keyword(s):  
Factor Viii ◽  
Light Transmission ◽  
Platelet Rich Plasma ◽  
Shape Change ◽  
Coagulation Factor ◽  
Coagulation Factor Viii ◽  
Bleeding Tendency ◽  
Knock Out ◽  
Ristocetin Cofactor ◽  
Platelet Shape

SummaryHereditary gelsolin-related amyloidosis (AGel amyloidosis) is a systemic disorder caused by a G654A or G654T mutation in the gene coding for gelsolin, an actin-modulating protein. Altered platelet shape change has been demonstrated in gelsolin-deficient knock-out mice, but this has not been studied in humans with gelsolin deficiency. We measured platelet shape change, characterized by maximal decrease in light transmission (D) and reaction time (T), and aggregation, associated with stimulation of platelets with different agonists in platelet rich plasma, as well as coagulation factor VIII and ristocetin cofactor activities in 20 patients, 10 healthy sibs and 20 healthy control subjects. Statistically significant alterations of parameters describing platelet shape change (D, T) were observed after stimulation with adenosine diphosphate and collagen in patients when compared to healthy subjects, but not in maximal aggregation responses, platelet counts, coagulation factor VIII or ristocetin cofactor activity levels. Patients had more haemostatic derangements. Our results suggest that, in addition to amyloid deposition, the G654A gelsolin gene defect causes altered gelsolin-mediated cellular mechanisms, which may contribute, e. g., to bleeding tendency in AGel amyloidosis patients.

48740 RP INHIBITS PLATELET SHAPE CHANGE INDUCED BY PAF-ACETHER IN VITRO.

1987 ◽  
Author(s):  
G Jung ◽  
P Sedivy
Keyword(s):  
Sodium Citrate ◽  
Light Transmission ◽  
Platelet Rich Plasma ◽  
Shape Change ◽  
Maximum Amplitude ◽  
Maximal Velocity ◽  
Maximal Amplitude ◽  
Plasma Properties ◽  
Platelet Shape

Platelet shape change (PSC) is the first measurable physiological response to platelet pro-aggregant agonists such as PAF-acether (PAF) (1). The laser thromborheometer (2) was used to assess the PSC (detected as decrease in light scattering as 2 of maximal velocity) and the platelet aggrega tion (detected as increase in the light transmission as 2 of maximal velocity and maximal amplitude) in citrated platelet -rich plasma (cPRP) (1 volume 3.8 2 sodium citrate ± 9 volumes blood) from 12 volunteers of either sex. PAF concentrations ranging from 0.1 to 1 yM induced PSC (range of velocities : 13.2-69.8 2 of maximal velocity, n = 12) and platelet aggregation (range of velocities : 9.3-22.2 2 of maximal velocity and maximum amplitude of aggregation always superior to 20 2, n = 12). These effects were inhibited by 48740 R.P., 3-(3- pyridy1)-1H,3H pyrrolo [1 , 2-c] thiazo1e-7-carboxamide (100200 yM) a selective and competitive PAF-antagonist (3). For instance, 100 yM 48740 RP decreased by 76.4 ± 3.5 (mean ± S.E.M., n = 3) PSC evoked by 0.1 yM of PAF. Furthermore, 48740 RP was also able to reduce PSC in heparinized platelet - r ich plasma (hPRP). The antagonist effects of 46740 RP could be overcome by increasing PAF concentrations in the cPRP and hPRP. During this study, 6 volunteers were found, in whom even concentrations of PAF up to 10.5 pM failed to induce an amplitude of aggregation in cPRP greater than 20 2 whereas PSC was in the range of 19.1-79.4 2 of maximal velocity. These responses to PAF which were antagonized by 48740 RP were not due to an alteration in plasma properties ; thus, they are proposed to result from undetermined changes occuring at the level of the platelet (e.g.) decreased number of PAF-operationa1 receptors or alteration of the excitation - response pathways). In conclusion, 48740 RP is an antagonist of PAF-evoked aggregation and PSC in cPRP from volunteers responding either normally or poorly to PAF. (1) LAPETINA E.G. et al. J. Biol. Chem. 258, 7241 (1983). (2) JUNG G. et al. Nouv. Rev. Fr. H6matol. 27, 103 (1985). (3) SEDIVY P. et al. Thromb. Haemost. 54, 185 (1985).

scholarly journals The Effects of Two New Antithrombotic Agents (IM Idazoquinazoli Nones) on Platelet Shape and Aggregation

1977 ◽  
Author(s):  
S. S. Tang ◽  
M. M. Frojmovic
Keyword(s):  
Human Platelet ◽  
Platelet Rich Plasma ◽  
Shape Change ◽  
Inhibitory Effect ◽  
Antithrombotic Agents ◽  
Antithrombotic Agent ◽  
Agent Based ◽  
Platelet Shape

Recently, one member of a new series of compounds was reported as a potent, nontoxic and long lasting antithrombotic agent, based on in vitro and in vivo animal tests (Bristol Labs; Fleming et al (1975), J. Pharmacol. Exp. Ther. 194, 435).We here report on the effects of this compound, 6-methyl-l,2,3,5-tetrahydroimidazo [2,1-b]quinazolin-2-one hydrochloride monohydrate (BL-3459), and its metabol ical ly more stable 6,7-dichloro analogue (BL-4162) , on rabbit and human platelet shape change and aggregation, and compare them with other agents known to affect platelet adenosine 3′:5′-cyclic monophosphate (cAMP). In aggregometer studies with citrated (0.29%) platelet-rich plasma (PRP), both BL-compounds were found to inhibit platelet shape change and aggregation induced by ADP, thrombin, serotonin and adrenaline-serotonin. Typically for human PRP, aggregation induced by 10 μM ADP was inhibited by 90% with 10 μM BL-4162 or 0.1 μM prostaglandin E1 (PGE1), and by 60% with 10 μM BL-3459. In corresponding rabbit PRP tests, 60% inhibition was caused equally by 1 μM BL-3459 or BL-4162, and by 0.05 μM PGE1,Both BL-compounds, like methylxanthines, were found to potentiate the inhibitory effect of PGE1 on platelet aggregation but did not potentiate the action of methylxanthines. Moreover, they both slightly increased the basal level of rabbit cAMP and potentiated the elevation of cAMP by PGE1, These BL-compounds are potent inhibitors of human and rabbit shape change and aggregation and appear to act by a mechanism distinct from that of PGE1.

scholarly journals A study of the kinetics of ADP-triggered platelet shape change

Blood ◽  
1984 ◽  
Vol 64 (4) ◽  
pp. 896-906 ◽  
Author(s):  
RR Hantgan
Keyword(s):  
Light Scattering ◽  
Morphological Changes ◽  
Platelet Rich Plasma ◽  
Shape Change ◽  
Blood Platelets ◽  
Adenosine Diphosphate ◽  
Intensity Measurements ◽  
Kinetics Of ◽  
Rapid Transformation ◽  
Platelet Shape

Abstract The rapid transformation of human blood platelets from inert discoid cells to spheroechinocytes that is induced by adenosine diphosphate (ADP) has been followed by right-angle light scattering intensity measurements using a laser light source and a sensitive photomultiplier. Two steps have been observed, and their rate constants have been determined as a function of pH and [ADP] and in the presence and absence of calcium for both platelet-rich plasma and gel-filtered platelets. Both steps are significantly faster in the presence of physiologic levels of calcium. Platelets were fixed prior to and during activation, then examined by phase-contrast and scanning electron microscopy. The light scattering and morphological changes support a model in which, under physiologic conditions of pH, temperature, ionic strength, and calcium concentration, the initial rapid event in platelet shape change is the loss of discoid shape, with a decay time of two to three seconds, leading to an intermediate with short pseudopods. The slower extension of long pseudopods occurs next, with a time constant of approximately seven to eight seconds. These results may help to resolve the contradictory descriptions of the mechanism of platelet shape change that have recently appeared in the literature.

scholarly journals Importance of Human Platelet Echinocytes for Procoagulant Activity

1977 ◽  
Author(s):  
E. Toth ◽  
M.M. Frojmovic
Keyword(s):  
Light Transmission ◽  
Platelet Rich Plasma ◽  
Shape Change ◽  
Adenosine Diphosphate ◽  
Procoagulant Activity ◽  
Rate Limiting Step ◽  
Rate Limiting ◽  
Recalcification Time ◽  
Free Plasma ◽  
Platelet Shape

Various agents can be used to transform platelets from the disc-form (discocytes) into spherical shapes from which many pseudopodia project (echinocytes). This shape change normally precedes platelet aggregation and release. The relative importance of these changes for platelet procoagulant activity was investigated. Recalcification times of platelet-rich plasma were used to monitor procoagulant activity, and echinocytes were maintained by the addition of either thrombin, serotonin, adenosine diphosphate (ADP) or water. The amounts of these agents added were insufficient to cause aggregation and release, and had no effect on the recalcification times of platelet-free plasma. Platelet shape and extent of aggregation were assessed from the stirring dependent changes in light transmission in an aggregometer, and by direct observation under a phase contrast microscope. When more than 60% of the platelets were echinocytes, recalcificat ion times were shortened by at least 50%. Aggregates preformed with serotonin and ADP did not further shorten the reca1cifi cat ion times. The importance of the echinocyte for procoagulant activity is further supported by the observations that:1)aggregates of discocytes formed with adrenaline caused only 20% shortening of recalcification times,2)both echinocytes (for discocyte preparations) and their aggregates appeared only during the last 10% of the total recalcification time, and3) inhibition of the ADP-induced discocyte-echinocyte transformation by AMP prolonged recalcification times by 300%. These results suggest that platelet discocyte-echinocyte transformation is an important rate limiting step for platelet procoagulant activity in blood clotting.

A study of the kinetics of ADP-triggered platelet shape change

Blood ◽  
1984 ◽  
Vol 64 (4) ◽  
pp. 896-906
Author(s):  
RR Hantgan
Keyword(s):  
Light Scattering ◽  
Morphological Changes ◽  
Platelet Rich Plasma ◽  
Shape Change ◽  
Blood Platelets ◽  
Adenosine Diphosphate ◽  
Intensity Measurements ◽  
Kinetics Of ◽  
Rapid Transformation ◽  
Platelet Shape

The rapid transformation of human blood platelets from inert discoid cells to spheroechinocytes that is induced by adenosine diphosphate (ADP) has been followed by right-angle light scattering intensity measurements using a laser light source and a sensitive photomultiplier. Two steps have been observed, and their rate constants have been determined as a function of pH and [ADP] and in the presence and absence of calcium for both platelet-rich plasma and gel-filtered platelets. Both steps are significantly faster in the presence of physiologic levels of calcium. Platelets were fixed prior to and during activation, then examined by phase-contrast and scanning electron microscopy. The light scattering and morphological changes support a model in which, under physiologic conditions of pH, temperature, ionic strength, and calcium concentration, the initial rapid event in platelet shape change is the loss of discoid shape, with a decay time of two to three seconds, leading to an intermediate with short pseudopods. The slower extension of long pseudopods occurs next, with a time constant of approximately seven to eight seconds. These results may help to resolve the contradictory descriptions of the mechanism of platelet shape change that have recently appeared in the literature.

Platelet Hypersensitivity in Acute Malaria (Plasmodium falciparum) Infection in Man

1981 ◽  
Vol 46 (02) ◽  
pp. 547-549 ◽  
Author(s):  
E M Essien ◽  
M I Ebhota
Keyword(s):  
Plasmodium Falciparum ◽  
Malaria Infection ◽  
Light Transmission ◽  
Human Platelet ◽  
Platelet Rich Plasma ◽  
Wave Pattern ◽  
Falciparum Infection ◽  
Secondary Wave ◽  
Control Subjects ◽  
The Mean

SummaryDuring acute malaria infection, platelets in human platelet-rich plasma are hypersensitive to the addition of ADP between 1.0 uM and 5.0 uM, or adrenaline 0.11 uM as aggregating agents. The mean maximum aggregation amplitude (as % of light transmission) obtained from 8 subjects in response to added ADP (1.0 uM), 39.8 ± 27 (1SD), was significantly greater than the value in 6 controls (5.2±6.7 (1SD); t = 3, 51 P <0.005). A similar pattern of response was obtained with higher ADP concentrations (2.4,4.5 or 5.0 uM) in 22 patients and 20 control subjects (89.9±14.9% vs 77.8±16.5% (1SD) t = 2.45, P <0.02). Addition of 4.5 uM ADP to patient PRP usually evoked only a single aggregation wave (fused primary and secondary waves) while the typical primary and secondary wave pattern was usually obtained from controls.Mean plasma B-thromboglobulin (BTG) concentration in 7 patients (208.3 ± 15.6 ng/ml) was significantly higher than the value in 6 control subjects (59.2±15.7 ng/ml; t = 13.44, P <0.002).

Adenosine Diphosphate (ADP)-Induced ⍺-Granules Release from Platelets of Native Whole Blood Is Reduced by Ticlopidine but Not by Aspirin or Dipyridamole

1986 ◽  
Vol 56 (02) ◽  
pp. 147-150 ◽  
Author(s):  
V Pengo ◽  
M Boschello ◽  
A Marzari ◽  
M Baca ◽  
L Schivazappa ◽  
...  
Keyword(s):  
Whole Blood ◽  
Light Transmission ◽  
Ex Vivo ◽  
Early Stage ◽  
Shape Change ◽  
Adenosine Diphosphate ◽  
Dose Dependent ◽  
Plateletderived Growth Factor ◽  
Platelet Shape

SummaryA brief contact between native whole blood and ADP promotes a dose-dependent release of platelet a-granules without a fall in the platelet number. We assessed the “ex vivo” effect of three widely used antiplatelet drugs, aspirin dipyridamole and ticlopidine, on this system. Aspirin (a single 800 mg dose) and dipyridamole (300 mg/die for four days) had no effect, while ticlopidine (500 mg/die for four days) significantly reduced the a-granules release for an ADP stimulation of 0.4 (p <0.02), 1.2 (p <0.01) and 2 pM (p <0.01). No drug, however, completeley inhibits this early stage of platelet activation. The platelet release of α-granules may be related to platelet shape change of the light transmission aggregometer and may be important “in vivo” by enhancing platelet adhesiveness and by liberating the plateletderived growth factor.

Inhibition of ADP-Induced Responses in Human Platelets by Agents Elevating the Cyclic AMP Level: Comparison of Aggregation and Shape Change

1984 ◽  
Vol 52 (03) ◽  
pp. 333-335 ◽  
Author(s):  
Vider M Steen ◽  
Holm Holmsen
Keyword(s):  
Inhibitory Action ◽  
Human Platelet ◽  
Platelet Rich Plasma ◽  
Shape Change ◽  
Inhibitory Effect ◽  
Human Platelets ◽  
Inhibitory Effects ◽  
Early Step ◽  
Stimulus Response ◽  
Sequential Relationship

SummaryThe inhibitory effect of cAMP-elevating agents on shape change and aggregation in human platelets was studied to improve the understanding of the sequential relationship between these two responses.Human platelet-rich plasma was preincubated for 2 min at 37° C with prostaglandin E1 or adenosine, agents known to elevate the intracellular level of cAMP. Their inhibitory effects on ADP-induced shape change and aggregation were determined both separately and simultaneously. The dose-inhibition patterns for shape change and aggregation were similar for both PGE1 and adenosine. There was no distinct difference between the inhibitory action of these two inhibitors.These observations suggest that elevation of the intracellular concentration of cAMP interferes with an early step in the stimulus-response coupling that is common for aggregation and shape change.

scholarly journals Mitochondrial adenosine triphosphatase from human placenta--inhibition by free magnesium ions of ITP hydrolysis.

1994 ◽  
Vol 41 (1) ◽  
pp. 39-44 ◽  
Author(s):  
Z Aleksandrowicz
Keyword(s):  
Competitive Inhibition ◽  
Competitive Inhibitor ◽  
Hill Coefficient ◽  
Negative Cooperativity ◽  
Magnesium Ions ◽  
Beef Liver ◽  
Bicarbonate Ions ◽  
The Hill ◽  
Kinetics Of ◽  
Free Magnesium

The effects of Mg2+ and bicarbonate on the kinetics of ITP hydrolysis by soluble ATPase (F1) from human placental mitochondria were studied. Increasing amounts of Mg2+ at fixed ITP concentration, caused a marked activation of F1 followed by inhibition at higher Mg2+ concentration. The appropriate substrate for the mitochondrial F1 seems to be the MgITP complex as almost no ITP was hydrolysed in the absence of magnesium. Mg2+ behaved as a competitive inhibitor towards the MgITP complex. In this respect the human placental enzyme differ from that from other sources such as yeast, beef liver or rat liver. The linearity of the plot presenting competitive inhibition by free Mg2+ of MgITP hydrolysis (in the presence of activating bicarbonate anion) suggests that both Mg2+ and MgITP bind to the same catalytic site (Km(MgITP) = 0.46 mM, Ki(Mg) = 4 mM). When bicarbonate was absent in the ITPase assay, placental F1 exhibited apparent negative cooperativity in the presence of 5 mM Mg2+, just as it did with MgATP as a substrate under similar conditions. Bicarbonate ions eliminated the negative cooperativity with respect to ITP (as the Hill coefficient of 0.46 was brought to approx. 1), and thus limited inhibition by free Mg2+. The results presented suggest that the concentration of free magnesium ions may be an important regulatory factor of the human placental F1 activity.

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