Effect Of Prostacyclin (PGI2) On Human Platelet Aggregation And Secretion

1981 ◽  
Author(s):  
C M Chesney ◽  
D D Pifer
Keyword(s):  
Platelet Aggregation ◽  
Time Course ◽  
Platelet Rich Plasma ◽  
Dense Granule ◽  
Ionophore A23187 ◽  
Factor V ◽  
Platelet Factor ◽  
Dense Granule Secretion ◽  
Granule Secretion ◽  
Data Representative

PGI2,which increases platelet cAMP(Prostaglandins 13: 389,1977),is a potent inhibitor of aggregation and secretion .We stidued the time course of the same return of platelet function after exposure of platelets to PGI2.Sepharose 2B columns were equilibrated with Tyrode’s albumin buffer, pH7.5 (no Ca2+) containing PGI2 (534nM). Platelet rich plasma was applied and eluted with the same buffer. The filtered platelets(GFP) were then subsampled hourly after elution from the column. Fibrinogen was added to finel concentration of 1.7mg/ml. Platelet aggregation(PA) and release of 14C serotonin (5HT),platelet factor 4(PF4), and factor V (FV) were assayed after stimulation of the platelet by collagen(C), ADP,epinephrine(E), arachidonic acid(AA) and ionophore A23187(I). Data representative of 5 separate studies follow.I(20μg/ml) induced PA was 76%(Ohr),52%(1hr) and 61%(2hr and beyond). Release of 5HT, FV,and PF4 were 60%,1.89u,and 7.97 yg/10 pit, respectively, at time 0 and increased progressively, reaching a plateau at 2 hr. AA(500μg/ml) was 10%(0hr),30%(2hr),68%(3hr) and 8%(4hr). Release of 5HT paralleled PA but release of FV and PF4 remained suppressed for 4 hrs. In contrast α-granule (PF4 and FV)release by C(μg/ml)increased as PA increased while dense granule secretion remained suppressed. PA as well as a and dense granule secretion by ADP (10μM) were minimal during 4 hrs. PA and FV secretion by E (55μM) also remain inhibited for 4 hrs. In spite of this normal dense granule release occurred initially and declined progressively over 4 hours.

scholarly journals Thrombin and ionophore A23187-induced dense granule secretion in storage pool deficient platelets: evidence for impaired nucleotide storage as the primary dense granule defect

Blood ◽  
1983 ◽  
Vol 61 (1) ◽  
pp. 154-162 ◽  
Author(s):  
B Lages ◽  
H Holmsen ◽  
HJ Weiss ◽  
C Dangelmaier
Keyword(s):  
Platelet Rich Plasma ◽  
Adenine Nucleotides ◽  
Magnesium Content ◽  
Calcium Pyrophosphate ◽  
Dense Granule ◽  
Ionophore A23187 ◽  
Strongly Correlated ◽  
Storage Pool ◽  
Dense Granule Secretion ◽  
Granule Secretion

Abstract The secretion of the dense granule constituents ATP, ADP, calcium, pyrophosphate (PPi), and orthophosphate (Pi), and the release of magnesium induced by thrombin and the divalent cation ionophore A23187 have been quantitated directly in gel-filtered platelets from patients with storage pool deficiency (SPD). Both the contents and the maximal amounts of the dense granule constituents secretable by thrombin were decreased in all the patients studied, while the nonsecretable, retained amounts of these substances were identical in SPD and normal platelets. In response to both thrombin and A23187, the amounts of secretable ATP and ADP were strongly correlated in the platelets of individual patients; in contrast, secretable calcium showed no correlation with the nucleotides, and significant amounts of calcium were secreted in the total absence of nucleotide secretion in the platelets of several patients. The contents of magnesium were normal in all patients, and approximately 12% of platelet magnesium was liberated by thrombin in both SPD and normal platelets. A23187 induced the release of up to 70% of the magnesium content of normal platelets, but released significantly less (46%) magnesium from SPD platelets. Platelet aggregation induced by A23187 in platelet-rich plasma was also markedly decreased in SPD platelets. The correlations among secretable dense granule constituents suggest the presence in SPD platelets of abnormal dense granule structures that sequester calcium and other constituents but little or no adenine nucleotides, and are thus consistent with a hypothesis that impaired nucleotide transport and/or storage may be the primary dense granule defect in this disorder. In addition, these results demonstrate that certain responses to A23187 are impaired in SPD platelets.

scholarly journals Thrombin and ionophore A23187-induced dense granule secretion in storage pool deficient platelets: evidence for impaired nucleotide storage as the primary dense granule defect

Blood ◽  
1983 ◽  
Vol 61 (1) ◽  
pp. 154-162 ◽  
Author(s):  
B Lages ◽  
H Holmsen ◽  
HJ Weiss ◽  
C Dangelmaier
Keyword(s):  
Platelet Rich Plasma ◽  
Adenine Nucleotides ◽  
Magnesium Content ◽  
Calcium Pyrophosphate ◽  
Dense Granule ◽  
Ionophore A23187 ◽  
Strongly Correlated ◽  
Storage Pool ◽  
Dense Granule Secretion ◽  
Granule Secretion

The secretion of the dense granule constituents ATP, ADP, calcium, pyrophosphate (PPi), and orthophosphate (Pi), and the release of magnesium induced by thrombin and the divalent cation ionophore A23187 have been quantitated directly in gel-filtered platelets from patients with storage pool deficiency (SPD). Both the contents and the maximal amounts of the dense granule constituents secretable by thrombin were decreased in all the patients studied, while the nonsecretable, retained amounts of these substances were identical in SPD and normal platelets. In response to both thrombin and A23187, the amounts of secretable ATP and ADP were strongly correlated in the platelets of individual patients; in contrast, secretable calcium showed no correlation with the nucleotides, and significant amounts of calcium were secreted in the total absence of nucleotide secretion in the platelets of several patients. The contents of magnesium were normal in all patients, and approximately 12% of platelet magnesium was liberated by thrombin in both SPD and normal platelets. A23187 induced the release of up to 70% of the magnesium content of normal platelets, but released significantly less (46%) magnesium from SPD platelets. Platelet aggregation induced by A23187 in platelet-rich plasma was also markedly decreased in SPD platelets. The correlations among secretable dense granule constituents suggest the presence in SPD platelets of abnormal dense granule structures that sequester calcium and other constituents but little or no adenine nucleotides, and are thus consistent with a hypothesis that impaired nucleotide transport and/or storage may be the primary dense granule defect in this disorder. In addition, these results demonstrate that certain responses to A23187 are impaired in SPD platelets.

scholarly journals Loss of the exocyst complex component EXOC3 promotes hemostasis and accelerates arterial thrombosis

2021 ◽  
Vol 5 (3) ◽  
pp. 674-686
Author(s):  
Tony G. Walsh ◽  
Yong Li ◽  
Christopher M. Williams ◽  
Elizabeth W. Aitken ◽  
Robert K. Andrews ◽  
...  
Keyword(s):  
Arterial Thrombosis ◽  
Surface Expression ◽  
Dense Granule ◽  
Conditional Knockout ◽  
Integrin Activation ◽  
Platelet Factor ◽  
Glycoprotein Vi ◽  
Exocyst Complex ◽  
Dense Granule Secretion ◽  
Granule Secretion

Abstract The exocyst is an octameric complex comprising 8 distinct protein subunits, exocyst complex components (EXOC) 1 to 8. It has an established role in tethering secretory vesicles to the plasma membrane, but its relevance to platelet granule secretion and function remains to be determined. Here, EXOC3 conditional knockout (KO) mice in the megakaryocyte/platelet lineage were generated to assess exocyst function in platelets. Significant defects in platelet aggregation, integrin activation, α-granule (P-selectin and platelet factor 4), dense granule, and lysosomal granule secretion were detected in EXOC3 KO platelets after treatment with a glycoprotein VI (GPVI)-selective agonist, collagen-related peptide (CRP). Except for P-selectin exposure, these defects were completely recovered by maximal CRP concentrations. GPVI surface levels were also significantly decreased by 14.5% in KO platelets, whereas defects in proximal GPVI signaling responses, Syk and LAT phosphorylation, and calcium mobilization were also detected, implying an indirect mechanism for these recoverable defects due to decreased surface GPVI. Paradoxically, dense granule secretion, integrin activation, and changes in surface expression of integrin αIIb (CD41) were significantly increased in KO platelets after protease-activated receptor 4 activation, but calcium responses were unaltered. Elevated integrin activation responses were completely suppressed with a P2Y12 receptor antagonist, suggesting enhanced dense granule secretion of adenosine 5′-diphosphate as a critical mediator of these responses. Finally, arterial thrombosis was significantly accelerated in KO mice, which also displayed improved hemostasis determined by reduced tail bleeding times. These findings reveal a regulatory role for the exocyst in controlling critical aspects of platelet function pertinent to thrombosis and hemostasis.

nPKC Epsilon Negatively Regulates Platelet Functional Responses

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 2855-2855
Author(s):  
Yamini Saraswathy Bynagari ◽  
Bela Nagy ◽  
Kamala Bhavaraju ◽  
Donna Woulfe ◽  
Soochong Kim ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Ex Vivo ◽  
Dense Granule ◽  
Dependent Manner ◽  
P2y1 Receptor ◽  
Wild Type ◽  
Functional Responses ◽  
Dense Granule Secretion ◽  
Granule Secretion

Abstract Protein Kinase C (PKC) are family of serine threonine kinases, known to regulate various platelet functional responses. Among them novel class of PKC isoforms (nPKC) including delta(δ), theta(𝛉), eta(η), and epsilon(ε) are expressed in platelets. Although, the role of nPKC ε and η in platelets is fairly understood, not much is known about nPKC ε and η in platelets. In this study, we investigated the role of nPKC ε in platelet functional responses using ADP-induced signaling as our stereotype. ADP causes platelet activation via Gq-coupled P2Y1 receptor and Gi-coupled P2Y12 receptor. Thus, we primarily studied the role of P2Y1 receptor in nPKC ε activation. ADP activated nPKC ε in time- and concentration- dependent manner. In the presence of P2Y1 receptor antagonist MRS-2179 and in P2Y1 knockout (KO) murine platelets ADP failed to activate nPKC ε, suggesting that ADP activates nPKC ε via P2Y1 receptor. We further investigated the functional role of nPKC ε using specific nPKC ε inhibitory RACK peptide (ε V1-2). ε V1-2 is a peptide designed to compete with native nPKC ε to bind ε-Receptors for activated C Kinase (ε-RACK) and thereby inhibits nPKC ε catalytic activity due to decreased substrate accessibility. ADP-induced thromboxane generation in human platelets pretreated with ε V1-2 peptide was more compared to the platelets pretreated with control peptide. Similarly, ADP-induced thromboxane generation in platelets derived from nPKC ε KO mouse was more compared to the wild type (WT) littermates. However, ADP- induced alpha granule secretion and aggregation in aspirin treated platelets derived from PKC ε KO mice was not significantly different from platelets derived from wild type littermates. These data suggest that nPKC e regulates an unknown pathway, which primarily regulates thromboxane generation with minimal effects on aggregation and alpha granule secretion. Furthermore, we also investigated the role of nPKC ε in PAR- and GPVI- mediated platelet aggregation and dense granule secretion. Interestingly, in both aspirin-treated and non-aspirin-treated platelets PAR- and GPVI- mediated platelet aggregation and dense granule secretion were potentiated. Consistent with ex vivo studies, FeCl3-induced arterial thrombosis was enhanced in nPKC ε KO mice compared to WT littermates.

ELMO1 Is a Novel Negative Regulator of Glycoprotein VI Signaling in Platelets

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 2533-2533
Author(s):  
Akruti Patel ◽  
Soochong Kim ◽  
John Kostyak ◽  
Rachit Badolia ◽  
Carol Dangelmaier ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Thrombus Formation ◽  
Dense Granule ◽  
Negative Regulator ◽  
Related Protein ◽  
Rac1 Activity ◽  
Dense Granule Secretion ◽  
Granule Secretion ◽  
Deficient Mice

Abstract PI3-kinase (phosphoinositide 3-kinase) is an important signaling molecule that is activated downstream of various receptors upon platelet activation. PI3-kinase activation leads to the generation of PIP3 (Phosphatidylinositol (3,4,5)-trisphosphate) subsequently leading to the recruitment of PH (pleckstrin homology) domain containing proteins to the plasma membrane. Our laboratory screened for proteins that interacted with PIP3 (Phosphatidylinositol (3,4,5)-trisphosphate) using PIP3 beads. One of the proteins that interacted with PIP3 was ELMO1 (Engulfment and cell motility-1). ELMO1 is a scaffold protein with no catalytic activity and is well known to regulate actin cytoskeletal rearrangement via Rac1 in other cells. However, it is not known whether ELMO1 is expressed in platelets and if so, does it regulate platelet functional responses. Here, we show that ELMO1 is present in both human and murine platelets. We used ELMO1-deficient (ELMO1-/-) mice to study its role in platelets. ELMO1-/- murine platelets showed enhanced platelet aggregation and dense granule secretion in response to the GPVI agonist, CRP (Figure 1 A & B), compared to the wildtype controls although there was no difference in GPVI expression levels between the two. There was no difference observed in response to AYPGKF- or 2-MeSADP. These data suggest that ELMO1 plays a specific role downstream of GPVI pathway but GPCRs. Moreover, ELMO1-/- platelets exhibited enhanced clot retraction and spreading indicating its role in Glycoprotein IIb/IIa (GPIIb/IIIa) mediated outside-in signaling. Furthermore, whole blood from ELMO1-/- mice perfused over collagen under arterial shear conditions exhibited enhanced thrombus formation. In an in vivo pulmonary thromboembolism model, ELMO1-/- mice showed reduced survival compared to the wildtype control. ELMO1-/- mice also showed shorter time to occlusion and increased thrombus stability using the ferric-chloride injury model indicating the role of ELMO1 in thrombus formation in vivo. At the molecular level, Rac1 activity was enhanced in ELMO1-/- murine platelets compared to the wildtype control in response to CRP (Figure 1C). Together, these data suggest that ELMO1 regulates Rac1 activity upon GPVI-mediated thrombus formation and it may play a negative regulator role in both inside-out and outside-in signaling, which might involve Rac1. Figure 1 Representative figure of (A) platelet aggregation and (B) dense granule secretion. (C) Washed platelets were stimulated with CRP 1.25 μg/mL for the indicated times. GST-PAK-RBD was used to pull-down active Rac1 from platelet lysates and was detected using specific antibody to Rac1 by Western blot. WT = Wildtype mice. ELMO1-/- = ELMO1-deficient mice. CRP = collagen related protein. Figure 1. Representative figure of (A) platelet aggregation and (B) dense granule secretion. (C) Washed platelets were stimulated with CRP 1.25 μg/mL for the indicated times. GST-PAK-RBD was used to pull-down active Rac1 from platelet lysates and was detected using specific antibody to Rac1 by Western blot. WT = Wildtype mice. ELMO1-/- = ELMO1-deficient mice. CRP = collagen related protein. Disclosures No relevant conflicts of interest to declare.

Platelet aggregation and dense granule secretion in a colony of dogs with spontaneous hypertension

1992 ◽  
Vol 10 (12) ◽  
pp. 1493-1498 ◽  
Author(s):  
Jennifer S. Thomas ◽  
Mary F. McConnell ◽  
Thomas G. Bell ◽  
George A. Padgett
Keyword(s):  
Platelet Aggregation ◽  
Dense Granule ◽  
Spontaneous Hypertension ◽  
Dense Granule Secretion ◽  
Granule Secretion

An Optimized Assay for Assessing Platelet Dense Granule Secretion Using Diluted Whole Blood

2019 ◽  
Vol 152 (Supplement_1) ◽  
pp. S23-S23
Author(s):  
Joseph Cho ◽  
Krzysztof Mikrut ◽  
Jonathan Miller
Keyword(s):  
Whole Blood ◽  
Clinical Laboratory ◽  
Limit Of Detection ◽  
Platelet Rich Plasma ◽  
Atp Release ◽  
Dense Granule ◽  
Platelet Counts ◽  
Agonist Stimulation ◽  
Dense Granule Secretion ◽  
Granule Secretion

Abstract Assessment of dense granule secretion following agonist stimulation is an integral part of platelet function testing and can be performed in the clinical laboratory using lumi-aggregometry. A significant limitation of traditional lumi-aggregometry is the relatively large volume of blood required and the normal platelet counts needed to perform the assay, which often precludes usage of this test in pediatric and thrombocytopenic patients. By optimizing the luciferase-luciferin reaction with commercially available reagents and using a conventional lumi-aggregometer, we have developed a method that measures platelet dense granule secretion following agonist stimulation in diluted whole blood, at up to 10-fold dilutions. With the goal of developing a testing method independent of platelet count, the assay intentionally does not include specimen stirring. Direct comparison of the optimized reagents with the standard Chrono-lume reagent in 10-fold diluted whole blood showed an improved lower limit of detection for exogenously added ATP by at least one order of magnitude. We reproducibly observed dose-dependent responses in platelet ATP release using this assay upon stimulation with platelet agonists such as the thrombin receptor-activating peptide (TRAP) and the collagen receptor agonist convulxin. ATP release in 10-fold diluted whole blood, for example, was 168.6 ± 24.7 pmoles/107 platelets in response to 40 μM TRAP and 17.1 ± 2.9 pmoles/107 platelets in response to 1 nM convulxin (mean ± SEM, N = 6). Method comparisons of this assay were performed using 10-fold diluted whole blood without stirring, compared to standard methodology using undiluted platelet-rich plasma stirred at 1000 rpm. On concurrently run, matched specimens, ATP release in response to a series of agonists of varying stimulus intensity showed overall moderate concordance, with an r2 = 0.722. Based on ATP standard curves and the observed agonist responses to date, we are hopeful that this assay may prove capable of assessing platelet dense granule release in patient blood with platelet counts as low as 20,000/μL. Additionally, the assay requires less than 60 μL of whole blood per agonist with testing performed at two different agonist concentrations. The extended analytical range and robustness of the assay, with no need for centrifugation, offer promise that it may be useful for the assessment of platelet dense granule secretion in pediatric or thrombocytopenic patients who require assays amenable to limited blood volumes and low platelet counts.

Platelet 12-Lipoxygenase Is Required for Dense Granule Secretion and Platelet Aggregation: Role of 12-hLO In Platelet Hemostasis and Thrombosis

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 3203-3203
Author(s):  
Patrick Apopa ◽  
Megha Patel ◽  
Olivier Boutaud ◽  
Michael Holinstat
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Platelet Activation ◽  
Platelet Reactivity ◽  
Dense Granule ◽  
Clot Formation ◽  
Dense Granule Secretion ◽  
Granule Secretion ◽  
12 Lipoxygenase

Abstract Abstract 3203 Platelet activation plays a central role in regulating hemostasis. Uncontrolled activation of circulating platelets can result in the formation of occlusive thrombi and stroke. Following activation, metabolism of arachidonic acid by 12-lipoxygenase (12-hLO) may play a significant role in regulating the degree and stability of platelet reactivity. Using specific inhibitors for 12-hLO which do not interact with other lipoxygenases or enzymes in the COX-1 pathway, we were able for the first time to asses the involvement of 12-hLO in platelet reactivity. In order to assess the role of 12-hLO in platelet activation and thrombosis, dense granule secretion, platelet aggregation, alpha granule secretion, and platelet adhesion and clot formation under flow were measured. Inhibiting 12-hLO results in a complete inhibition of dense granule secretion with only a partial attenuation of alpha granule secretion indicating a novel regulatory scheme for modulating positive autocrine reinforcement of platelet reactivity and clot formation. Addition of the 12-hLO metabolite, 12-HETE (as low as 250 nM), resulted in a significant (25%) increase in PAR1-mediated dense granule secretion compare to agonist alone indicating that 12-HETE may be the crucial metabolite formed by 12-hLO metabolism of arachidonic acid. Importantly, platelet aggregation and adhesion are also significantly attenuated in the absence of 12-hLO. In fact, collagen-mediated platelet aggregation was shifted over 25 fold to the right in the absence of 12-hLO. These studies support the role of 12-hLO in hemostasis and may be a good target for anti-platelet therapy. Disclosures: No relevant conflicts of interest to declare.

Platelet aggregation and dense granule secretion in schizophrenia

1994 ◽  
Vol 54 (1) ◽  
pp. 13-24 ◽  
Author(s):  
Jeffrey K. Yao ◽  
Daniel P. van Kammen ◽  
John Gurklis ◽  
Jeffrey L. Peters
Keyword(s):  
Platelet Aggregation ◽  
Dense Granule ◽  
Dense Granule Secretion ◽  
Granule Secretion
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