Main Article from Howard Hughes Medical Institute
Jonathan Stamler's Laboratory investigates the mechanisms of Nitric Oxide siugnalling. Blood flow in the microcirculation is regulated by physiological O2 gradients that are coupled to vasodilation and vasoconstriction, but the mechanism underlying this fundamental vascular response (which controls O2 delivery to tissues) has remained a major unanswered question in vascular physiology. The discovery of a previously unknown S-nitrosothiol (SNO) derivative of hemoglobin that has potent vasodilatory activity has changed the picture. Most significantly, the affinity of cysteine β93 for NO is high in the R (or oxy) structure and low in the T (or deoxy) structure. Thus, deoxygenation is accompanied by an allosteric transition in SNO-hemoglobin (from R to T structure) that promotes release of the NO group. Moreover, the NO liberated upon deoxygenation is transferred to the red blood cell (RBC) membrane protein, anion exchanger AE1. NO transfer to AE1 plays a role in export of NO that subserves RBC-mediated vasodilation—a novel activity of RBCs. Emerging evidence that vasodilation by RBCs may be impaired in disorders characterized by impaired blood flow, including pulmonary hypertension, heart failure, and sickle cell disease, and that blood transfusions may be associated with NO insufficiency and increased mortality, suggests that defective RBC processing of NO is a contributing factor.