ADP Receptor P2Y ₁₂ Is Expressed in Vascular Smooth Muscle Cells and Stimulates Contraction in Human Blood Vessels

Abstract

Objective-ADP plays an important role in platelet aggregation by activating P2Y 12 receptors. We assessed the hypothesis that P2Y 12 receptors are expressed in vascular smooth muscle cells (VSMC). Methods and Results-P2Y 12 receptor mRNA was found to have a high expression among the P2 receptors in human VSMC, significantly higher than the other 2 ADP receptors (P2Y 1 and P2Y 13 , real-time polymerase chain reaction). Western blots gave a band of 50 kD, similar to that in platelets. To unmask a P2Y 12 receptor-mediated vasoconstriction by simulating the in vivo situation, vessels were precontracted to a submaximal level. 2-MeSADP stimulated contractions in vessel segments from internal mammary artery (IM), IM branches and small veins (E max ϭ15Ϯ6% of 60mmol/L K ϩ contraction, pEC 50 ϭ5.6Ϯ0.6, E max ϭ21Ϯ1%, pEC 50 ϭ6.8Ϯ0.1, and E max ϭ48Ϯ9%, pEC 50 ϭ6.6Ϯ0.4). The selective P2Y 12 antagonist AR-C67085 blocked 2-MeSADP contractions. The contraction was not reduced in patients using clopidogrel, a drug inhibiting ADP-induced platelet aggregation by blocking the P2Y 12 receptor. This may be explained by the high instability of the active clopidogrel metabolite that never reaches the systemic circulation. Conclusion-ADP acting on P2Y 12 receptors not only is important for platelet activation but also stimulates vasoconstriction. Stable drugs with antagonistic effects on P2Y 12 receptors, affecting both platelets and VSMC, could be of double therapeutic benefit in their prevention of both thrombosis and vasospasm. Key Words: vasoconstriction Ⅲ P2Y receptors Ⅲ platelets Ⅲ ADP E xtracellular nucleotides such as adenosine triphosphate (ATP), adenosine diphosphate (ADP), uridine triphosphate, and uridine diphosphate are released from sympathetic nerves, platelets, and endothelial and inflammatory cells. 1 Nucleotides induce vasoconstriction-stimulating P2 receptors on vascular smooth muscle cells (VSMC), regulating vascular tone and blood pressure. 1,2 Furthermore, extracellular nucleotides have been shown to mediate growth stimulation and migration in VSMC. 3,4 P2 receptors can be divided into 2 classes on the basis of their signal transmission mechanisms and their characteristic molecular structures: ligand-gated intrinsic ion channels, P2X receptors, and G-protein-coupled P2Y receptors. The P2Y family is composed of 8 cloned and functionally defined subtypes. [5][6][7][8][9] ADP is stored in high concentrations in platelet granula and is released as a positive feedback mechanism in response to most platelet activators. After release, ADP augments platelet aggregation by stimulation of P2Y 12 and P2Y 1 receptors. 10 The first clinical application of P2 receptor antagonists has been the use of thienopyridines as platelet aggregation inhibitors. Clopidogrel and ticlopidine are prodrugs that are converted in the liver into irreversible antagonists against P2Y 12 receptors. Clopidogrel is more efficient than aspirin in reducing the composite end point myocardial infarction, stroke, and death in patients with vascular disease...

Purinergic receptor P2RY12-dependent microglial closure of the injured blood–brain barrier

“…Although most relevant studies have highlighted the relative specificity of brain P2RY12 expression to microglial cells, some controversy on the point exists, in that studies have variably reported that P2RY12 might also be expressed in brain endothelial cells (35), human smooth muscle vascular cells (36), and astrocytes (37). However, these reports have without exception been based on analysis of cultured cells or ex vivo preparations.…”

Platelets, inflammation and anti-inflammatory effects of antiplatelet drugs in ACS and CAD

“…Recent studies demonstrate that the P2Y12 receptor is expressed not only in platelets but also in other cell types, such as monocytes (122), VSMCs (123), dendritic cells (124), and lymphocytes (122). Therefore effects of ADP-antagonists are not only expected in platelets but also in the target cells mentioned above.…”

The effects of clopidogrel, acetyl salicylic acid and tirofiban on acetylcholine-induced dilation in rat thoracic aorta segments

“…[17,18] These receptors have also been found to exist in cells other than platelets, including the rat and human vascular smooth muscle cells. [19] Adenosine diphosphate has been shown to induce vasoconstriction via P2Y12 receptors; however, it is also believed to cause arterial relaxation by increasing the synthesis of endothelium-derived nitric oxide (NO). [19][20][21] Thus, the effect of ADP-mediated pathways on the endothelium is currently unclear.…”

“…[19] Adenosine diphosphate has been shown to induce vasoconstriction via P2Y12 receptors; however, it is also believed to cause arterial relaxation by increasing the synthesis of endothelium-derived nitric oxide (NO). [19][20][21] Thus, the effect of ADP-mediated pathways on the endothelium is currently unclear. [22] Clopidogrel has been reported to exhibit vasomodulatory activity [23] and direct endothelial effects independent from antiplatelet actions, [24] which are still not fully understood.…”