(Modified from the applicant): It is well established that nitric oxide (NO), is produced by endothelial cells and is capable of relaxing vascular smooth muscle. Alterations in shear stress have been suggested to be a major stimulus for NO release from the endothelium. A reappraisal of this viewpoint was required, however, when the investigators found that in the rabbit pulmonary circulation, in the absence of red blood cells (RBCs), alterations in shear stress alone did not evoke NO release. Therefore, it was concluded that, in the pulmonary circulation, an interaction, not related to shear stress, occurs between the RBC and the endothelium resulting in NO synthesis. In the present study it is hypothesized that the RBC releases a mediator that, in turn, stimulates NO synthesis, affecting, thereby, local hemodynamic changes. It is postulated that the mediator released is adenosine triphosphate (ATP) and that an important stimulus for the release of ATP is mechanical deformation of the RBC. In the present proposal the aims are to 1) characterize the contribution of the RBC and ATP to vascular caliber in the intact lung, 2) determine that mechanical deformation of the RBC is a stimulus for the release of ATP from that cell, 3) establish that RBC-derived ATP results in endothelial NO synthesis, 4) demonstrate that the mechanism by which ATP is released from the RBC in response to mechanical deformation is via the activity of the cystic fibrosis transmembrane conductance regulator and 5) establish that NO released into the vascular lumen alters RBC deformability leading to reduced ATP release. The thesis that mechanical deformation of RBCs leads to ATP release which, in turn, stimulates NO synthesis suggests a novel and important mechanism for the local control of vascular caliber. In this construct, the RBC is increasingly deformed by increments in blood flow through a vessel of constant or decreasing radius or by reductions in vascular caliber at constant or increasing flow. In response to deformation, ATP is released from the RBC which stimulates NO synthesis by endothelial cells. The abluminal release of NO results in relaxation of vascular smooth muscle leading, ultimately, to a decrease in the stimulus for RBC deformation, thereby, limiting the stimulus for ATP release and NO synthesis. In addition, NO released into the vascular lumen interacts with the RBC leading to increased deformablity and reduced ATP release, again limiting the stimulus for ATP release. This hypothesis is the logical progression of previous work and is consistent with a major focus of this group, namely identification and characterization of those mechanisms responsible for the control of vascular resistance.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
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Cardiovascular and Renal Study Section (CVB)
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Saint Louis University
Internal Medicine/Medicine
Schools of Medicine
Saint Louis
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Ellsworth, M L; Ellis, C G; Sprague, R S (2016) Role of erythrocyte-released ATP in the regulation of microvascular oxygen supply in skeletal muscle. Acta Physiol (Oxf) 216:265-76
Sprague, Randy S; Ellsworth, Mary L (2012) Erythrocyte-derived ATP and perfusion distribution: role of intracellular and intercellular communication. Microcirculation 19:430-9
Ellsworth, Mary L; Ellis, Christopher G; Goldman, Daniel et al. (2009) Erythrocytes: oxygen sensors and modulators of vascular tone. Physiology (Bethesda) 24:107-16
Sprague, Randy S; Stephenson, Alan H; Ellsworth, Mary L (2007) Red not dead: signaling in and from erythrocytes. Trends Endocrinol Metab 18:350-5
Moreland, K Trent; Procknow, Jesse D; Sprague, Randy S et al. (2007) Cyclooxygenase (COX)-1 and COX-2 participate in 5,6-epoxyeicosatrienoic acid-induced contraction of rabbit intralobar pulmonary arteries. J Pharmacol Exp Ther 321:446-54
Sprague, Randy; Stephenson, Alan; Bowles, Elizabeth et al. (2006) Expression of the heterotrimeric G protein Gi and ATP release are impaired in erythrocytes of humans with diabetes mellitus. Adv Exp Med Biol 588:207-16
Liang, Griffith; Stephenson, Alan H; Lonigro, Andrew J et al. (2005) Erythrocytes of humans with cystic fibrosis fail to stimulate nitric oxide synthesis in isolated rabbit lungs. Am J Physiol Heart Circ Physiol 288:H1580-5
Losapio, Jennifer L; Sprague, Randy S; Lonigro, Andrew J et al. (2005) 5,6-EET-induced contraction of intralobar pulmonary arteries depends on the activation of Rho-kinase. J Appl Physiol 99:1391-6
Olearczyk, Jeffrey J; Stephenson, Alan H; Lonigro, Andrew J et al. (2004) Heterotrimeric G protein Gi is involved in a signal transduction pathway for ATP release from erythrocytes. Am J Physiol Heart Circ Physiol 286:H940-5
Stephenson, Alan H; Sprague, Randy S; Losapio, Jennifer L et al. (2003) Differential effects of 5,6-EET on segmental pulmonary vasoactivity in the rabbit. Am J Physiol Heart Circ Physiol 284:H2153-61

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