Extracellular ATP increases cation fluxes in human erythrocytes by activation of the P2X 7 receptor

Abstract

Canine erythrocytes are known to undergo a reversible increase in cation permeability when incubated with extracellular ATP. We have examined the expression and function of P2X receptors on human erythrocytes using confocal microscopy and a panel of anti-P2X 1-7 antibodies and have measured monovalent cation fluxes in the presence of various nucleotide agonists. Human erythrocytes expressed P2X 7 receptors on all cells examined from eight of eight subjects, as well as P2X 2 at a far lower staining intensity in six of eight subjects. ATP stimulated the efflux of 86Rb + (K +) from human erythrocytes in a dose-dependent fashion with an EC 50 of ∼95 μM. Other nucleotides also induced an efflux of 86Rb + from erythrocytes with an order of agonist potency of 2′-and 3′-O(4-benzoylbenzoyl) ATP (BzATP) 〉 ATP 〉 2-methylthio-ATP (2MeSATP) 〉 adenosine 5′-O-(3-thiotriphosphate) (ATPγS), whereas ADP or UTP had no effect. ATP-induced efflux of 86Rb + from erythrocytes was inhibited by extracellular Na + and oxidized ATP, as well as by KN-62, an antagonist specific for the human P2X 7 receptor. When erythrocytes were incubated in isotonic KCl medium, the addition of ATP stimulated an 86Rb + influx approximately equal in magnitude to ATP-stimulated 86Rb + efflux from the same cells. BzATP also stimulated the influx of 22Na + into erythrocytes incubated in isotonic NaCl medium. Both ATP-induced efflux and influx of 86Rb + and 22Na + were impaired in erythrocytes from subjects who had inherited loss-of-function polymorphisms in the P2X 7 receptor. These results suggest that the reversible permeabilization of erythrocytes by extracellular ATP is mediated by the P2X 7 receptor.