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The oxygen required to meet metabolic needs of all tissues is delivered by the erythrocyte, a small, flexible cell, which, in mammals, is devoid of a nucleus and mitochondria. Despite its simple appearance, this cell has an important role in its own distribution, enabling the delivery of oxygen to precisely meet localized metabolic need. When an erythrocyte enters in a hypoxic area, a signalling pathway is activated within the cell resulting in the release of ATP in amounts adequate to activate purinergic receptors on vascular endothelium, which trigger secretion of nitric oxide and other factors resulting in vasodilatation. Among other mechanisms, binding of deoxyhemoglobin to the cytoplasmic domain of the anion-exchange protein band 3 is probably involved in this pathway. The present study investigates the effect of amyloid β peptide exposure on this molecular mechanism. We report that deoxygenated human erythrocytes fail to release ATP following 24 h exposure to amyloid β peptide. Concurrently, amyloid β peptide induces caspase 3 activation. Preincubation of amyloid β peptide treated erythrocytes with a specific inhibitor of caspase 3 prevents amyloid- induced caspase 3 activation and restores the erythrocyte's ability to release ATP under deoxygenated conditions. Since the activity of red cell phosphofructokinase, a key step in glycolytic flux, is not modified within the red cell following amyloid peptide exposure, it is likely that ATP release reduction is not dependent on glycolytic flux alterations. It has also been suggested that the heterotrimeric G protein, Gi, and adenylyl cyclase are downstream critical components of the pathway responsible for ATP release. We show that cAMP synthesis and ATP release are not failed in amyloid-peptide-treated erythrocytes in response to incubation with mastoparan 7 or forskolin plus 3-isobutyl-1-methyl xanthine, agents that stimulate cAMP synthesis. In conclusion, these results indicate that amyloid β peptide inhibits ATP release from deoxygenated erythrocytes by activating red cell caspase 3, suggesting a pathophysiologic role for vascular amyloid peptide in Alzheimer's disease. Key words: band 3, erythrocyte, caspase 3, amyloid β peptide, ATP, cAMP. L'oxygene requis pour combler les besoins metaboliques de tous les tissus est vehicule par les erythrocytes, une petite cellule flexible qui, chez les mammiferes, est depourvue de noyau et de mitochondries. Malgre son apparence simple, cette cellule jour un role important dans sa propre distribution, permettant la liberation d'oxygene pour combler precisement des besoins metaboliques localises. Lorsqu'un erythrocyte entre dans une region hypoxique, une voie de signalisation est activee dans la cellule pour induire la liberation d'ATP en quantite suffisante pour activer les recepteurs purinergiques de l'endothelium vasculaire qui amorcent la secretion d'oxyde nitrique et d'autres facteurs, resultant en une vasodilatation. Parmi d'autres mecanismes, la liaison de la deoxyhemoglobine au domaine cytoplasmique de la proteine de transport d'anions (bande 3) est probablement impliquee dans cette voie. Cette etude examine l'effet d'une exposition au peptide beta-amyloide sur ce mecanisme. Nous rapportons que les erythrocytes depourvus d'oxygene ne peuvent liberer de l'ATP apres une exposition de 24 h au peptide β-amyloide. En meme temps, le peptide β-amyloide induit l'activation de la caspase 3. La preincubation d'erythrocytes traites au peptide β-amyloide avec un inhibiteur specifique de la caspase 3 previent l'activation de la caspase 3 induite par l'amyloide et retablit la capacite de l'erythrocyte a liberer l'ATP en absence d'oxygene. Puisque l'activite de la phosphofructokinase du globule rouge, une enzyme cle de regulation de la glycolyse, n'est pas modifiee dans le globule rouge par une exposition au peptide amyloide, il est probable que la reduction de la liberation d'ATP ne depende pas de modifications de la regulation de la glycolyse. Il semble que la proteine G heterotrimerique Gi et l'adenylyl cyclase soient des composantes cles situees en aval du sentier, responsables de la liberation de l'ATP. Nous demontrons que la synthese d'AMPc et la liberation d'ATP ne sont pas affectees chez les erythrocytes traites au peptide amyloide en reponse a une incubation avec le mastoparan 7 et a la forskoline combinee au 3-isobutyl-1-methyl xanthine, des agents qui stimulent la synthese d'AMPc. En conclusion, ces resultats indiquent que le peptide betaamyloide inhibe la liberation d'ATP des erythrocytes prives d'oxygene en activant la caspase 3 du globule rouge, ce qui suggere que le peptide amyloide vasculaire joue un role pathophysiologique dans la maladie d'Alzheimer. Mots-cles : bande 3, erythrocyte, caspase 3, peptide β amyloide, ATP, AMPc. [Traduit par la Redaction], Introduction It has become increasingly clear that, in addition to functioning as an intracellular energy source, ATP can serve as an important extracellular signalling molecule (Gordon 1986). ATP activates P2 [...]

The importance of studying storage alterations in erythrocytes is highlighted by the need to understand changes that could potentially serve to optimize the storage system. With this aim, the non-equilibrium thermodynamic theory with internal variables was introduced, and perturbing the erythrocyte samples with a harmonic electric field some functions of the theory have been determined varying in the perturbation frequency. A frequency has been noted that acts as a separator element between two states showing a different entropy production above and below this frequency. In stored red blood cells compared to fresh ones, the increase in entropy production measured shows a greater state of disorder in the latter. Further alterations have been highlighted on the surface charge density of the stored erythrocyte membrane and on the speed of anionic kinetics. All these observations highlight the image of membrane structural and functional alterations of the stored erythrocytes and lead to the elaboration of a technique able to correlate a specific perturbation frequency with the aging time of red blood cells. [ABSTRACT FROM AUTHOR]