ADP Acting on P2Y ₁₃ Receptors Is a Negative Feedback Pathway for ATP Release From Human Red Blood Cells

Abstract

Abstract-Red blood cells may regulate tissue circulation and O 2 delivery by releasing the vasodilator ATP in response to hypoxia. When released extracellularly, ATP is rapidly degraded to ADP in the circulation by ectonucleotidases. In this study, we show that ADP acting on P2Y 13 receptors on red blood cells serves as a negative feedback pathway for the inhibition of ATP release. mRNA of the ADP receptor P2Y 13 was highly expressed in human red blood cells and reticulocytes. Key Words: ATP release Ⅲ cAMP Ⅲ P2 receptors Ⅲ microdialysis Ⅲ red blood cells I t has become increasingly clear that, in addition to functioning as an intracellular energy source, ATP and ADP can serve as important extracellular signaling molecules. 1,2 Extracellular ATP in the circulation is rapidly degraded into ADP, AMP, and adenosine by ectonucleotidases. 3 ATP and ADP activate P2 receptors on endothelium, platelets, 4,5 and other blood cells, 6 regulating several physiological responses including vascular tone, 7 platelet aggregation, and the release of endothelial factors. At least 15 nucleotide-activated cell surface receptors (7 of P2X and 8 of P2Y) have been found in man, with remarkably broad and varied physiological responses.The matching of oxygen supply with demand requires a mechanism that increases blood flow in response to decreased tissue oxygen levels. Several reports suggest that the red blood cell (RBC) acts as a sensor for hypoxia, and different mechanisms have been suggested by which the deoxygenated RBC stimulates vasodilatation. 7-10 RBCs contain millimolar amounts of ATP and possess the membrane-bound glycolytic enzymes necessary for its production. 11-13 ATP is released in response to reductions in oxygen tension and pH. 7,9 It has been shown in vitro that the vessels dilate in response to low O 2 levels only when blood vessels are perfused with RBCs. 14 Recently, in vivo studies in man demonstrated that ATP is released in working skeletal muscle circulation depending on the number of unoccupied hemoglobin O 2 binding sites. 7,9 The released ATP then binds to P2Y receptors on the endothelium and stimulates vasodilatation by the release of nitric oxide (NO), prostaglandins, 2 and endothelium-derived hyperpolarizing factor (EDHF). 15,16 Thus, the RBC functions as an O 2 sensor, contributing to the regulation of blood flow and O 2 delivery by releasing ATP depending on the oxygenation state of hemoglobin.Physiologically important signaling systems are usually regulated by negative feedback systems, for example, noradrenaline and ATP release from sympathetic nerves is inhibited by presynaptic ␣ 2 and P 1 (A1 subtype) receptors. 17 We hypothesized that ATP release from RBCs is regulated by a P2 receptor-mediated negative feedback pathway. Materials and MethodsThe studies were approved by the local Ethics Committee of the Lund University and were conducted according to the principles of the Declaration of Helsinki. All participants gave written consent for the study. Preparation of RBCs and ReticulocytesHuman RBCs were...

Hemolysis in human erythrocytes by Clostridium perfringens epsilon toxin requires activation of P2 receptors

“…We tested whether these receptors were responsible for ETX-induced hemolysis using various antagonists of the receptors (Table 1). As there are no specific antagonists for P2Y2 receptor and P2X2 receptor and low predicted expression levels of P2Y2 receptor on human erythrocytes [16,21], the effect of P2Y2 and P2X2 receptors were not examined.…”

“…Functional P2Y13 is present on RBCs, where it negatively regulates ATP release from these cells [21]. Activation of this receptor by ADP impairs the release of ATP from human RBCs.…”

Adenosine Contributes to Blood Flow Regulation in the Exercising Human Leg by Increasing Prostaglandin and Nitric Oxide Formation

“…23 Furthermore, plasma ATP increases during exercise, 31 but adenosine does not play a role in ATP-induced vasodilation, 25,29 and the breakdown products of ATP are, therefore, likely to be rapidly taken up by erythrocytes. 32 A methodological limitation may be that the rapid uptake and degradation of adenosine require sampling from veins closer to the active muscle.…”

P2X7 receptor activation induces reactive oxygen species formation in erythroid cells

“…P2X7 is present on mature red blood cells (erythrocytes) [13,14] where it participates in cation fluxes [13,[15][16][17], cell death [16,[18][19][20] and the release of lipid-derived mediators [21]. P2X7 is also present on erythroid precursors including murine erythroleukaemia (MEL) cells [22,23].…”