Gradient-dependent inhibition of stimulatory signaling from platelet G protein-coupled receptors

Haematologica. 2019 Jul;104(7):1482-1492. doi: 10.3324/haematol.2018.205815. Epub 2019 Jan 10.


As platelet activation is an irreversible and potentially harmful event, platelet stimulatory signaling must be tightly regulated to ensure the filtering-out of inconsequential fluctuations of agonist concentrations in the vascular milieu. Herein, we show that platelet activation via G protein-coupled receptors is gradient-dependent, i.e., determined not only by agonist concentrations per se but also by how rapidly concentrations change over time. We demonstrate that gradient-dependent inhibition is a common feature of all major platelet stimulatory G protein-coupled receptors, while platelet activation via the non-G protein-coupled receptor glycoprotein VI is strictly concentration-dependent. By systematically characterizing the effects of variations in temporal agonist concentration gradients on different aspects of platelet activation, we demonstrate that gradient-dependent inhibition of protease-activated receptors exhibits different kinetics, with platelet activation occurring at lower agonist gradients for protease-activated receptor 4 than for protease-activated receptor 1, but shares a characteristic bimodal effect distribution, as gradient-dependent inhibition increases over a narrow range of gradients, below which aggregation and granule secretion is effectively shut off. In contrast, the effects of gradient-dependent inhibition on platelet activation via adenosine diphosphate and thromboxane receptors increase incrementally over a large range of gradients. Furthermore, depending on the affected activation pathway, gradient-dependent inhibition results in different degrees of refractoriness to subsequent autologous agonist stimulation. Mechanistically, our study identifies an important role for the cyclic adenosine monophosphate-dependent pathway in gradient-dependent inhibition. Together, our findings suggest that gradient-dependent inhibition may represent a new general mechanism for hemostatic regulation in platelets.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Diphosphate / pharmacology*
  • Adult
  • Blood Platelets / drug effects
  • Blood Platelets / metabolism*
  • Cyclic AMP / pharmacology*
  • Epoprostenol / pharmacology
  • Humans
  • Platelet Activation / drug effects
  • Platelet Activation / physiology*
  • Platelet Aggregation / drug effects
  • Platelet Aggregation Inhibitors / pharmacology
  • Receptor, PAR-1 / metabolism
  • Receptors, G-Protein-Coupled / metabolism*
  • Receptors, Thrombin / metabolism
  • Signal Transduction / drug effects*
  • Thrombin / metabolism
  • Thromboxane A2 / metabolism


  • Platelet Aggregation Inhibitors
  • Receptor, PAR-1
  • Receptors, G-Protein-Coupled
  • Receptors, Thrombin
  • Thromboxane A2
  • Adenosine Diphosphate
  • Epoprostenol
  • Cyclic AMP
  • Thrombin