Abstract
Phagocytosis of phosphatidylserine (PS)–exposed erythrocytes by splenic macrophages determines the end of their 120–day lifespan. PS is usually maintained in the inner leaflet of plasma membranes by active transport from the outer leaflet via flippase (aminophospholipid translocase) using ATP. Since ATP is generated only through glycolysis in erythrocytes, the ATP content may reduce during storage because of decreased ATP production and consumption. Nevertheless, no obvious evidence exists for the correlation between intracellular ATP content and PS exposure, we therefore investigated this correlation in blood stored up to 120 days. PS–exposed erythrocytes increased by over 60- day storage while ATP content decreased to less than 0.2 mol/mL RBC, which corresponded to the michaelis constant (Km) for flippase. The adenine/inosine (A/I) treatment resulted in increased ATP content to normal level and significant decrease in PS–exposed cells. However, this treatment was not effective for PS exposure on erythrocytes stored over 75 days, despite the restoration of ATP content to ～ 0.5 mol/mL RBC, suggesting that flippase may be inactivated irreversibly in those cells. We suggest that ATP content less than 0.2 mol/mL RBC triggers PS exposure via inactivation of flippase and that A/I treatment enables to decrease PS–exposed erythrocytes stored for up to 60 days.
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