Erythrocytic ATP Release in the Presence of Modified Cell-Free Hemoglobin pp. 249-254
Authors: (Russell H. Cole, Transient Research, San Francisco, California, USA)
Abstract: The red blood cell (RBC) has gained acceptance as an intra-vascular O2 sensor through a link between the desaturation of membrane-bound intracellular hemoglobin (Hb) and the release of erythrocytic ATP, which diffuses to the vascular wall and causes vasodilation. The development of Hb-based O2 carriers (HBOCs) has been hampered by induced arteriolar vasoconstriction, which has been largely attributed to the high affinity of cell-free Hb for the endothelium-derived relaxing factor nitric oxide (NO). The involvement of ATP in vasomotion provides a potential mechanism for HBOC O2 affinity to couple with vascular flow regulation, since O2 release from HBOCs does not contribute to the intravascular ATP concentration. Furthermore, when HBOCs with low O2 affinity are mixed with RBCs, HBOC-O2 is preferentially released, as compared to RBC-O2, maintaining RBC O2 saturation and reducing ATP release. This phenomenon was demonstrated by an in vitro experiment, where RBCs were deoxygenated in the presence of two modified cell-free Hbs. Deoxygenation of human RBCs in the presence of human Hb intramolecularly cross-linked between subunits (Hb, p50 = 33 mmHg) resulted in the release of a larger amount of ATP than RBCs deoxygenated in the presence of Hb cross-linked between subunits ( Hb, p50 = 8 mmHg) . These results provide a potential mechanism for the O2 affinity of HBOCs to directly interfere with a vasodilatory signal.