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 P2X7receptor on canine erythrocytes. P2X7receptors were detected on canine erythrocytes by immunocytochemistry and immunoblotting. Extracellular ATP induced86Rb+(K+) efflux from canine erythrocytes that was 20 times greater than that from human erythrocytes. The P2X7agonist 2′(3′)- O-(4-benzoylbenzoyl)adenosine 5′-trisphosphate (BzATP) was more potent than ATP, and both stimulated86Rb+efflux from erythrocytes in a dose-dependent fashion with EC50values of ∼7 and ∼309 μM, respectively. 2-Methylthioadenosine 5′-triphosphate and adenosine 5′- O-(3-thiotriphosphate) induced a smaller86Rb+efflux from erythrocytes, whereas ADP, AMP, UTP, or adenosine had no effect. ATP-induced86Rb+efflux from erythrocytes was inhibited by oxidized ATP, KN-62, and Brilliant blue G, known P2X7antagonists. 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 P2X7function 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 P2X7receptor channel/pore.