A Volume Regulatory Response Can Be Triggered by Nucleosides in Human Erythrocytes, a Perfect Osmometer No Longer

DIEGO E. PAFUNDO, CORA L. ALVAREZ, GERHARD KRUMSCHNABEL AND PABLO J. SCHWARZBAUM

JOURNAL OF BIOLOGICAL CHEMISTRY

AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC

Lugar: Bethesda, Maryland 20814 ; Año: 2010 vol. 285 p. 6134 - 6144

0021-9258

Human erythrocytes have been regarded as perfect osmometers,which swell or shrink as dictated by their osmotic environment.In contrast, in most other cells, swelling elicits a regulatoryvolume decrease (RVD) modulated by the activation ofpurinic and pyrimidinic receptors (P receptors). For humanerythrocytes this modulation has not been tested, and we thusinvestigated whether P receptor activation can induce RVD inthese cells. Further, because ectonucleotidases may scavengeATP or ADP or act as a source for extracellular adenosine andtherefore modulate P receptor activation and RVD, we alsodetermined their activity in intact erythrocytes. We foundrelatively low ectoATPase but significant ectoADPase andectoAMPase activities. When erythrocytes were exposed tohypotonic medium alone, they swelled as expected for an osmometricresponse and showed no RVD. Activation of P2 receptorsby exogenous ATP or ADP did not trigger RVD, whereas P1agonists adenosine and adenosine-5-N-ethylcarboxamideinduced significant RVD. The effect of adenosine-5-N-ethylcarboxamidewas dose-dependent (maximal RVD of 27%; apparentK1⁄2 of 1.6 1.7M). The RVD induced by adenosine was blocked80% with the non-selective P1 antagonist 8-(p-sulfophenyl theophylline)ortheP1-A2B inhibitorMRS1754,butnotbyinhibitorsofP1 subtypes A1, A2A, and A3. In addition, forskolin (an inducer ofintracellular cAMP formation) could mimic the effect of adenosine,supporting the idea of P1-A2B receptor activation. In conclusion,we report a novel P1-A2B receptor-mediated RVD activationin mature human erythrocytes and thus indicate that these longheld perfect osmometers are not so perfect after all.