Effect of the Rapid Shape Change of Platelets on the Transmission and Scattering of Light through Plasma

Michal, F; Born, G. V. R.

doi:10.1038/newbio231220a0

Cited by 98 publications

(44 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…PRP was then treated with either vehicle, U46619, 8-iso-PGF 2α , ADP, TRAP-PAR1, or the specific agonist/agent. The effects of these agents on shape change and aggregation were measured using the turbidimetric method [19,20] with a model 400 aggregometer (Chrono-Log; Havertown, PA). For the inhibitor studies, PRP was incubated with a predetermined dose of the drug for 1 min prior to stimulation with 8-iso-PGF 2α or U46619.…”

Section: Platelet Preparation and Functional Assay-human Platelet-ricmentioning

confidence: 99%

Characterization of isoprostane signaling: Evidence for a unique coordination profile of 8-iso-PGF2α with the thromboxane A2 receptor, and activation of a separate cAMP-dependent inhibitory pathway in human platelets

Khasawneh

Huang

Mir

et al. 2008

Biochemical Pharmacology

View full text Add to dashboard Cite

Since isoprostanes are thought to participate in the pathogenesis of thrombosis, presumably through their interaction with thromboxane receptors (TPRs), we examined the ability of 8-iso-PGF 2α to bind/signal through TPRs. Using TPR expressing HEK cells, it was found that 8-iso-PGF 2α mobilized calcium and bound TPRs with a dissociation constant (K d ) of 57 nM. Interestingly, site-directed-mutagenesis revealed that 8-iso-PGF 2α has a unique coordination profile with TPRs. Thus, while Phe 184 and Asp 193 are shared by both 8-iso-PGF 2α and classical TPR ligands, Phe 196 was found to be required only for 8-iso-PGF 2α binding. Functional studies also revealed interesting results. Namely, that 8-iso-PGF 2α signals in human platelets through both a stimulatory (TPR-dependent) and an inhibitory (cAMP-dependent) pathway. Consistent with the existence of two signaling pathways, platelets were also found to possess two separate binding sites for 8-iso-PGF 2α . While the stimulatory site is represented by TPRs, the second cAMP inhibitory site is presently unidentified, but does not involve receptors for PGI 2 , PGD 2 or PGE 2 . In summary, these studies provide the first documentation that: (1) 8-iso-PGF 2α coordinates with Phe 184 , Asp 193 and Phe 196 on platelet TPRs; (2) Phe 196 serves as a unique TPR binding site for 8-iso-PGF 2α ; (3) 8-iso-PGF 2α signals through both stimulatory and inhibitory pathways in platelets; (4) 8-iso-PGF 2α inhibits human platelet activation through a cAMP-dependent mechanism; (5) 8-iso-PGF 2α interacts with platelets at two separate binding sites. Collectively, these results provide evidence for a novel isoprostane function in platelets which is mediated through a cAMP-coupled receptor.

show abstract

Section: Platelet Preparation and Functional Assay-human Platelet-ricmentioning

confidence: 99%

Characterization of isoprostane signaling: Evidence for a unique coordination profile of 8-iso-PGF2α with the thromboxane A2 receptor, and activation of a separate cAMP-dependent inhibitory pathway in human platelets

Khasawneh

Huang

Mir

et al. 2008

Biochemical Pharmacology

View full text Add to dashboard Cite

show abstract

“…Aggregation was quantified photometrically (Born, 1962;Michal & Born, 1971) as the maximal rate of change in light transmission (arbitrary units/min) through a sample (0.5 ml) of stirred PRP at 37°C on addition of a test solution (10 tL) containing an ADP analogue alone or an ADP analogue plus ATP (final ATP concentration 50 tM).…”

Section: Aggregation Studiesmentioning

confidence: 99%

Competitive Inhibition by Adenosine 5′‐triphosphate of the Actions on Human Platelets of 2‐chloroadenosine 5′‐diphosphate, 2‐azidoadenosine 5′‐diphosphate and 2‐methylthioadenosine 5′‐diphosphate

Cusack

Hourani

1982

British J Pharmacology

View full text Add to dashboard Cite

Adenosine 5′‐diphosphate (ADP) induces human platelet aggregation and noncompetitively inhibits stimulated human platelet adenylate cyclase; these two effects are mediated by the same ADP receptor, at which adenosine 5′‐triphosphate (ATP) is a competitive antagonist. Two ADP analogues, 2‐azidoadenosine 5′‐diphosphate (2‐azido‐ADP) and 2‐methylthioadenosine 5′‐diphosphate (2‐methylthio‐ADP) have been reported to be more potent as inhibitors of adenylate cyclase than they are as aggregating agents, but no evidence has been presented that these actions are mediated solely by the ADP receptor. We therefore tested the ability of ATP to inhibit the actions of these compounds and of another ADP analogue, 2‐chloroadenosine 5′‐diphosphate (2‐chloro‐ADP). 2‐Chloro‐ADP, 2‐azido‐ADP and 2‐methylthio‐ADP each induced aggregation and inhibited stimulated adenylate cyclase. Both of these actions were competitively inhibited by ATP (50 μm) with pA2 values similar to those previously found for inhibition by ATP of these effects of ADP. The reported greater potency of 2‐azido‐ADP and of 2‐methylthio‐ADP as inhibitors of adenylate cyclase than as aggregating agents is therefore due only to their greater efficacy for this effect, not to some extra actions elsewhere.

show abstract

“…The initial rapid change in shape of platelets exposed to 5-HT or analogues was also measured without inhibiting their subsequent aggregation by recording the changes in light scattered by the suspension of platelets (Michal & Born, 1971). Platelet-rich plasma was diluted with 0-154 M NaCl (0-5 ml PRP and 0 5 ml saline) in a siliconized glass cuvette and the changes caused by the addition of 5-HT were measured simultaneously by recording the changes in light transmitted through the suspension (aggregation) and light scattered at right angles to the incident beam (shape change).…”

Section: Platelet Aggregationmentioning

confidence: 99%

Relative activities on and uptake by human blood platelets of 5‐hydroxytryptamine and several analogues

Born

Juengjaroen

Michal

1972

British J Pharmacology

Self Cite

109

View full text Add to dashboard Cite

Summary1. The specificity of platelet receptor sites for 5-HT uptake and for the rapid morphological change and aggregaition was investigated with 5-hydroxytryptamine (5-HT) and seventeen analogues as well as with some antagonists of 5-HT.2. The analogues, with the exception of 5-hydroxy-N'N'-dibutyltryptamine, caused the rapid morphological change in platelets. In concentrations below those needed to produce the agonistic action (viz. 0-05-2-0 )L,M), these analogues themselves inhibited competitively the shape change caused by 5-HT. 3. The velocity of change in shape caused by 5-HT was reduced in low Na media. 4. Ten analogues produced platelet aggregation; three of these, viz. 5-methoxya-methyltryptamine, 5-hydroxy-a-methyltryptamine and 5-hydroxy-N'N'-diisopropyltryptamine), were approximately equipotent with 5-HT. Six analogues did not induce platelet aggregation. 5. All the analogues which prevented the initial change in shape of platelets caused by 5-HT also inhibited its aggregating effect, apparently competitively with low Ki values (0-02-1-6 juM).6. As with the inhibition of shape change, the inhibition of aggregation shows relatively low structural specificity of the receptor site. 7. Methysergide was a potent inhibitor of shape change and aggregation (Ki-0-03 /LM); imipramine was much less inhibitory (Ki-5-10,uM).8. Only one analogue (5-hydroxy-a-methyltryptamine) was taken up like 5-HT by platelets. All the other analogues inhibited the uptake of 5-HT by platelets (K=0-2-2-7 gum). 9. Methysergide was a weak inhibitor of 5-HT uptake (Ki-125 ,M) whereas imipramine was very effective (Ki~-0-3 uM).10. Our results show that the initial change in shape of platelets is required for and precedes aggregaition. The structural specificity of the platelet receptor concerned with shape change and aggregation caused by 5-HT appears low whereas the uptake mechanism is a highly specific one. The uptake probably proceeds through more than one step, the relationship between the steps is not yet clear.

show abstract

Effect of the Rapid Shape Change of Platelets on the Transmission and Scattering of Light through Plasma

Cited by 98 publications

References 9 publications

Characterization of isoprostane signaling: Evidence for a unique coordination profile of 8-iso-PGF2α with the thromboxane A2 receptor, and activation of a separate cAMP-dependent inhibitory pathway in human platelets

Characterization of isoprostane signaling: Evidence for a unique coordination profile of 8-iso-PGF2α with the thromboxane A2 receptor, and activation of a separate cAMP-dependent inhibitory pathway in human platelets

Competitive Inhibition by Adenosine 5′‐triphosphate of the Actions on Human Platelets of 2‐chloroadenosine 5′‐diphosphate, 2‐azidoadenosine 5′‐diphosphate and 2‐methylthioadenosine 5′‐diphosphate

Relative activities on and uptake by human blood platelets of 5‐hydroxytryptamine and several analogues

Contact Info

Product

Resources

About