Receptors for 5-Hydroxytryptamine on Rat Blood Platelets

1975 ◽  
Author(s):  
A. H. Drummond ◽  
J. L. Gordon
Keyword(s):  
Binding Sites ◽  
Platelet Rich Plasma ◽  
Shape Change ◽  
Blood Platelets ◽  
Close Correlation ◽  
Inhibitory Potency ◽  
Rat Blood ◽  
Active Uptake ◽  
Platelet Shape ◽  
Rat Platelets

When 5-hydroxytryptamine (5HT) or its analogue, 5-methoxy-α-methyltryptamine (5MOαMT) are added to rat citrated platelet-rich plasma (PRP), the platelets change in shape but do not aggregate. The response to both of these agents is inhibited by the 5HT antagonist, cinanserin (IC50 = 3 व 10-9 M). Cinanserin is at least 10,000 times less potent against the active uptake of 5HT (IC50 > 5 व 10-5 M). 5MOαMT is not actively transported by the platelet, although some instantaneous binding can be measured which is independent of temperature (4°-37°). 5MOαMT does not inhibit 5HT uptake over the concentration range at which it induces the shape change (10-8-10-5 M). Binding of (3H)-5HT to rat platelets at 4° indicates the presence of three binding sites, one of which is specifically blocked by cinanserin (IC50 = 2.8 × l0-9 M). Close correlation between the inhibitory potency of various drugs against (3H)-5HT binding and 5HT-induced shape change suggests that this site is the 5HT receptor on the platelet which initiates the shape change. Our results indicate that 5HT induces the platelet shape change by combination with a specific cinanserinsensitive 5HT receptor, which is unconnected with the uptake site.

scholarly journals Specific binding sites for 5-hydroxytryptamine on rat blood platelets

1975 ◽  
Vol 150 (1) ◽  
pp. 129-132 ◽  
Author(s):  
A H Drummond ◽  
J L Gordon
Keyword(s):  
Binding Sites ◽  
Specific Binding ◽  
Blood Platelets ◽  
Rat Blood ◽  
Active Uptake ◽  
Specific Binding Sites

5-Hydroxytryptamine changes the shape of rat blood platelets by combination with a cinanserin-sensitive receptor which is not associated with the active uptake of 5-hydroxytryptamine. Binding of 5-hydroxy[3H]tryptamine to platelets at 4°C demonstrates the presence of three saturable sites, and the highest-affinity site is apparently this 5-hydroxytryptamine receptor.

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.

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 Aggregation Caused by Dithiothreitol

1984 ◽  
Vol 51 (01) ◽  
pp. 119-124 ◽  
Author(s):  
M B Zucker ◽  
N C Masiello
Keyword(s):  
Shape Change ◽  
Blood Platelets ◽  
Dense Granule ◽  
Metabolic Inhibitors ◽  
Electrophoretic Patterns ◽  
Discernible Effect ◽  
Variable Extent ◽  
Triton X ◽  
Induced Aggregation ◽  
Platelet Shape

SummaryMacIntyre et al. showed that over 1 mM dithiothreitol (DTT) aggregates blood platelets in the presence of fibrinogen; aggregation is not inhibited by prostaglandin E1. We confirmed their data and found that 70 mM 2-mercaptoethanol was also active. DTT- induced aggregation was not associated with platelet shape change or secretion of dense granule contents, was not inhibited by tetracaine or metabolic inhibitors, was prevented at pH 6.5, and prevented, reversed, or arrested by EDTA, depending on when the EDTA was added. DTT did not cause aggregation of thrombasthenic, EDTA-treated, or cold (0° C) platelets, which also failed to aggregate with ADP. Platelets stimulated with DTT bound 125I-labeled fibrinogen. Thus DTT appears to “expose” the fibrinogen receptors. SDS gel electrophoresis of platelet fractions prepared by use of Triton X-114 showed that aggregating concentrations of DTT reduced proteins of apparent Mr 69,000 and 52,000 (probably platelet albumin) and, to a variable extent, glycoproteins Ib, IIb and III. Exposure of unlabeled or 125I- labeled platelets to ADP had no discernible effect on the electrophoretic patterns.

Properties of [3H]diazepam binding sites on rat blood platelets

Life Sciences ◽  
1980 ◽  
Vol 27 (20) ◽  
pp. 1881-1888 ◽  
Author(s):  
James K.T. Wang ◽  
Takashi Taniguchi ◽  
Sydney Spector
Keyword(s):  
Binding Sites ◽  
Blood Platelets ◽  
Rat Blood

ADP-induced inhibition of von Willebrand factor-mediated platelet agglutination

1976 ◽  
Vol 230 (5) ◽  
pp. 1406-1410 ◽  
Author(s):  
RA Grant ◽  
MB Zucker ◽  
J McPherson
Keyword(s):  
Human Plasma ◽  
Von Willebrand Factor ◽  
Prostaglandin E1 ◽  
Platelet Rich Plasma ◽  
Shape Change ◽  
Normal Human ◽  
Von Willebrand ◽  
Willebrand Factor ◽  
Formalin Fixed ◽  
Platelet Shape

Human plasma von Willebrand factor (vWF) plus the antibiotic ristocetin, or bovine or porcine vWF alone, agglutinates platelets in either normal human ethylenediaminetetraacetate (EDTA)-treated citrated platelet-rich plasma (PRP) or citrated PRP from patients with the congenital platelet defect thrombasthenia. The prior addition of 1-10 muM ADP, which causes platelet shape change but not aggregation under these conditions, inhibited vWF-mediated agglutination. Inhibition was prevented by 200 muM ATP. Addition of ADP caused prompt reversal of established vWF-mediated agglutination, which resumed when the ADP was enzymatically removed. EDTA-treated, Formalin-fixed, washed normal platelets also underwent vWF-mediated agglutination. ADP was inhibitory only when added before fixation. Epinephrine (40 muM), prostaglandin E1 (7 muM), or serotonin (2 muM) added before fixation caused slight to moderate inhibition but always less than ADP. Platelets from blood chilled before fixation were fully active. Platelets fixed in freshly prepared PRP did not agglutinate as well as those fixed after incubation of PRP, probably because centrifugation exposes the platelets to ADP. It concluded that ADP causes a reversible decrease in the accessibility of the membrane receptor to vWF.

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.

scholarly journals Mechanism of Action of Halofenate, A Platelet Inhibitor

1977 ◽  
Author(s):  
G. R. Favis ◽  
R. W. Colman
Keyword(s):  
Platelet Aggregation ◽  
Platelet Rich Plasma ◽  
Shape Change ◽  
Thiobarbituric Acid ◽  
Serotonin Release ◽  
Prostaglandin Synthesis ◽  
Second Phase ◽  
Change Curve ◽  
Cellulose Column ◽  
Platelet Shape

Halofenate (Hal) has previously been shown to inhibit epinephrine (Epi) and ADP induced platelet aggregation and C14-serotonin release. We further investigated the site of action of Hal by examining platelet shape change as a membrane event and malondialdehyde (MDA) formation as a measure of prostaglandin synthesis. Platelet-rich-plasma (PRP) with and without Hal wasdiluted in an EDTA buffer and examined in a spectrophotometer modified for stirring and maintained at 37°. ADP induced increase in absorbance was recorded and the velocity of the shape change curve was plotted against ADP concentration. MDA production was measured by the thiobarbituric acid assay and utilized a DEAE-52 cellulose column to concentrate the chromogen. Hal in pharmacologic concentrations (.96mM) had no effect on Epi induced primary aggregation or on ADP induced shape change. However, at higher than pharmacologic amounts (3.36mM), Hal did inhibit ADP induced shape change. Epi-induced MDA formation (.18μM-.33μM) normally occurs concomitant with the second phase of aggregation and serotonin release but was markedly decreased by Hal (.06μM-.085μM). This inhibition was not due to a direct effect on prostaglandin synthesis since sodium arachi-donate (1mM) caused secondary aggregation in PRP treated with Hal but not PRP treated with aspirin (4mM). Hal (.96mM) does not seem to inhibit platelet aggregation through an inhibition of ADP induced shape change or of Epi induced primary aggregation. Since Hal treated platelets respond to arachidonate, Hal must work at some earlier step than arachidonate induced prostaglandin synthesis. We suggest that this may be an alteration of the platelet membrane structure which makes ADP and Epi binding sites less accessible or which impairs arachidonic acid release by phospholipase. Decreased MDA formation and inhibition of aggregation would then be secondary to this membrane change.

Possible Differences In The Mode Of Action Of Ditazole And Non-Steroidal Anti-Inflammatory Drugs As Potential Antithrombotic Agents

1981 ◽  
Author(s):  
A K Sim ◽  
A P McCraw ◽  
L Caprino ◽  
F Antonetti ◽  
L Morelli
Keyword(s):  
Platelet Aggregation ◽  
Mode Of Action ◽  
Platelet Rich Plasma ◽  
Shape Change ◽  
Dose Range ◽  
Oral Drug ◽  
Inflammatory Drugs ◽  
Anti Inflammatory ◽  
Induced Aggregation ◽  
Platelet Shape

Ditazole (4,5-diphenyl-2-diethanolamino-oxazole), a weak anti-inflammatory drug, has been shown to be a potent inhibitor of platelet aggregation, adhesiveness and bleeding time. Acetylsalicylic acid (ASA), dipyridamole and a combination of these two drugs induced a platelet shape change which was much shorter lasting than their effect on platelet aggregation. Conversely, similar doses of ditazole induced a potent shape change but no effect on aggregation. Ditazole has now been shown to reversibly antagonise thromboxane A2 (TXA2)-induced contraction of rabbit aortic strips at an optimal concentration of 25 μm in the perfusate. Separately, over a dose range of 50-400 mg/kg/p.o., TXA2 production was inhibited between 39% and 85% in spontaneously clotted rabbit blood. In addition, we have shown that TXA2 formation following arachidonic acid-induced aggregation of platelet-rich plasma (PRP) is similarly inhibited. Ditazole however did not inhibit prostacyclin (PGI2) production in rabbit aortic rings following oral drug administration over a dose range of 50-400 mg/kg. At 1000 and 2000 mg/kg PGI2 production was inhibited by 23% and 41% respectively. TXA2 and PGI2 levels were measured by radioimmunoassay of their stable derivatives TXB2 and 6-keto-PGF1α. It is suggested that the mode of action of ditazole may be more specific than the cyclo-oxygenase/PG-synthetase blocking activity of most other non-steroidal anti-inflammatory drugs.

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.

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