Canine erythrocytes express the P2X₇receptor: greatly increased function compared with human erythrocytes

Abstract

Over three decades ago, Parker and Snow (Am J Physiol 223: 888-893, 1972) demonstrated that canine erythrocytes undergo an increase in cation permeability when incubated with extracellular ATP. In this study we examined the expression and function of the channel/pore-forming P2X(7) receptor on canine erythrocytes. P2X(7) receptors were detected on canine erythrocytes by immunocytochemistry and immunoblotting. Extracellular ATP induced (86)Rb(+) (K(+)) efflux from canine erythrocytes that was 20 times greater than that from human erythrocytes. The P2X(7) agonist 2'(3')-O-(4-benzoylbenzoyl)adenosine 5'-trisphosphate (BzATP) was more potent than ATP, and both stimulated (86)Rb(+) efflux from erythrocytes in a dose-dependent fashion with EC(50) values of approximately 7 and approximately 309 microM, respectively. 2-Methylthioadenosine 5'-triphosphate and adenosine 5'-O-(3-thiotriphosphate) induced a smaller (86)Rb(+) efflux from erythrocytes, whereas ADP, AMP, UTP, or adenosine had no effect. ATP-induced (86)Rb(+) efflux from erythrocytes was inhibited by oxidized ATP, KN-62, and Brilliant blue G, known P2X(7) antagonists. ATP also induced uptake of choline(+) into canine erythrocytes that was 60 times greater than that into human erythrocytes. Overnight incubation of canine erythrocytes with ATP and BzATP induced phosphatidylserine exposure in >80% of cells and caused up to 20% hemolysis. In contrast, <30% of human erythrocytes showed phosphatidylserine exposure after overnight incubation with ATP and BzATP, and hemolysis was negligible. Flow cytometric measurements of ATP-induced ethidium(+) uptake showed that P2X(7) function was three times lower in canine monocytes than in human monocytes. These data show that the massive cation permeability increase induced by extracellular ATP in canine erythrocytes results from activation and opening of the P2X(7) receptor channel/pore.

The P2X7 receptor mediates the uptake of organic cations in canine erythrocytes and mononuclear leukocytes: comparison to equivalent human cell types

“…Similar studies in other species and comparisons between equivalent cell types from different species are limited. Recently, we have observed that canine erythrocytes express the P2X 7 and that the relative function of this receptor is at least 40-fold greater than that of human erythrocytes [17]. This difference in receptor function corresponded to increased amounts of P2X 7 present on the plasma membrane of canine erythrocytes compared to human erythrocytes [17].…”

“…Recently, we have observed that canine erythrocytes express the P2X 7 and that the relative function of this receptor is at least 40-fold greater than that of human erythrocytes [17]. This difference in receptor function corresponded to increased amounts of P2X 7 present on the plasma membrane of canine erythrocytes compared to human erythrocytes [17]. The pharmacological properties of canine P2X 7 however have only been partly characterised.…”

“…The pharmacological properties of canine P2X 7 however have only been partly characterised. Canine P2X 7 is activated by BzATP and ATP, and to a lesser extent 2-methylthio-ATP and adenosine 5′-0-(3-thiotriphosphate), but not adenosine 5′-diphosphate (ADP) nor uridine 5′-triphosphate [17]. Moreover, canine P2X 7 can be inhibited by KN-62, oxidised ATP, Brilliant blue G or a phthalazinamine derivative, termed compound 18, each applied at concentrations conventionally used to impair either human or rat P2X 7 [17,18].…”

“…Canine P2X 7 is activated by BzATP and ATP, and to a lesser extent 2-methylthio-ATP and adenosine 5′-0-(3-thiotriphosphate), but not adenosine 5′-diphosphate (ADP) nor uridine 5′-triphosphate [17]. Moreover, canine P2X 7 can be inhibited by KN-62, oxidised ATP, Brilliant blue G or a phthalazinamine derivative, termed compound 18, each applied at concentrations conventionally used to impair either human or rat P2X 7 [17,18]. Whether canine P2X 7 can be impaired by ions such as Na + and Mg 2+ , as shown for other mammalian P2X 7 receptors [4], is unknown.…”

Identification and characterization of a novel variant of the human P2X7 receptor resulting in gain of function

“…P2X 7 receptors are predominantly expressed on cells from the hematopoietic lineages, such as erythrocytes, lymphocytes, neutrophils, eosinophils, mast cells, monocytes, and macrophages [9][10][11][12][13][14][15][16][17][18]. It has been reported recently that P2X 7 receptors are expressed in central and spinal cord neurons [19][20][21][22].…”