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Table 4 Platelet surface glycoproteins (GP's) and agonists

From: Role of platelets in neuroinflammation: a wide-angle perspective

 

Main Platelet Agonists

     
 

Agonist

Receptor(s)

 

Integrin(s)

 

For GPCR's:

 

Strongest

Thrombin + collagen

      
 

A23187*

  

-

   

Strong

Thrombin

PAR1

PAR4

αIIbβ3

α2β1

  
 

Collagen

      
 

PAF

      

Medium

ADP

P2Y1

P2Y12

  

Gqα

 
 

TXA2.

TP-α, -ß

   

Gq

G12

Weak

Epinephrine

α2A AR

    
 

Arachidonate

      
 

Vasopressin

      
 

Serotonin

      

Damping

Prostacyclins

IP R

EP2 R

    
 

PACAP, VIP

VPAC R

   

Gsα

 

* A23187, calcium ionophore [non-physiological]; admits external calcium.

  1. Listing of the main primary platelet agonists in approximate order of potency, and their receptors types, e.g. PAR = Protease-Activated Receptor. Other abbreviations are listed below. By "primary" is meant having direct action. For example, fibrinogen and vWF (Table 1) do not bind or activate the normal resting platelet. The third column lists the integrin names and the last column indicates some which are known to be GPCR's (= G-Protein Coupled Receptor). Similar listings appear in many sources. The relative potency may be misleading since it is based on data in vitro whereas in vivo several of these agonists, especially the "weak" ones, can act synergistically to potentiate or "prime" responses to others [5]. For example, serotonin [266, 319]; and vWF-induced aggregation requires co-stimulation (including by ristocetin, an antibiotic used in laboratory studies) or conformation change of vWF. Information on the GPCR's is simplified from Ch. 107 of Hoffman et al [8] with terminology updated according to Van Geet et al [320]. The "damping" agonists shown at bottom inhibit activation by raising cAMP (cyclic AMP) levels, which is opposite the usual effect of cAMP elevation in other cells. These tables are for orientation only. Other abbreviations (see also Table 2): TXA2 = thromboxane A2; α2A AR = a2A-adrenergic receptor; PACAP = pituitary adenylyl cyclase activating peptide; VIP = vasointestinal peptide; prostacyclins refer to prostaglandins such as PGE1, PGI2.
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Journal of Neuroinflammation

ISSN: 1742-2094