Randy S. Sprague, M.D.
Pharmacological and Physiological Science
M.D., Saint Louis University, 1976
William Harvey Research Institute, London
A primary objective of our laboratory is to define a previously unrecognized role for the red blood cell (RBC) as a determinant of pulmonary vascular resistance. Recently, we reported that, in isolated perfused lungs, red blood cells were required for the stimulation of NO synthesis in response to increases in perfusate flow rate. RBCs contain millimolar amounts of adenosine triphosphate (ATP) which can activate P2y purinergic receptors present on the endothelial cell resulting in the synthesis of NO. The finding that NO synthesis was stimulated by flow solely in the presence of RBCs, coupled with the fact that RBCs contain millimolar amounts of ATP, permitted formulation of the novel hypothesis that RBC-derived ATP stimulates the synthesis of NO in the intact pulmonary circulation.
If RBC-derived ATP participates in the regulation of vascular resistance in the pulmonary circulation, it must be released in response to physiological stimuli. Previously it was reported that the RBC releases ATP in response to both severe hypoxia and acidosis. However, these conditions are not found in the pulmonary circulation of intact animals. Thus, another mechanism for the release of ATP from the RBC in the pulmonary circulation must be present. We hypothesize that mechanical deformation of the RBC that occurs as it traverses the pulmonary circulation is responsible for the release of ATP from the RBC. We have found that mechanical deformation of RBC of rabbits and healthy humans leads to release of ATP from the RBC. Moreover, the amount of ATP released increases as the stimulus for deformation increases.
The overall objective of this project is to demonstrate that, in the pulmonary circulation, as the RBC is deformed by increments in the velocity of blood flow through a vessel and/or by reductions in vascular caliber, the release of ATP from the RBC is increased. This RBC-derived ATP would, in turn, stimulate endothelial NO synthesis resulting in relaxation of vascular smooth muscle. The NO-induced increase in vascular caliber would be associated with a decrease in RBC deformation and ATP release leading, ultimately, to a decreased stimulus for NO synthesis.
Sprague, R.S., Bowles, E.A., Olearczyk, J.J., Stephenson, A.H. and Lonigro, A.J.: The role of G protein subunits in the Release of ATP from Human Erythrocytes. J. Physiol. and Pharmacol. 53:667-674, 2002
Sprague, R.S., Olearczyk, J.J., Spence, D.M., Stephenson, A.H., Sprung, R.W. and Lonigro, A.J.: Extracellular ATP Signaling in the Rabbit Lung: Erythrocytes as Determinants of Vascular Resistance. Am J Physiol. 285: H693 - 700, 2003.
Olearczyk, J.J., Stephenson, A.H., Lonigro, A.J. and Sprague, R.S.: Heterotrimeric G Protein Gi is Involved in a signal Transduction Pathway for ATP Release from Erythrocytes Am. J. Physiol 286:H940-H945, 2004.
Olearczyk, J.J., Ellsworth, M.L., Stephenson, A.H., Lonigro, A.J. and Sprague, R.S. Nitric Oxide Inhibits ATP Release from Erythrocytes. J Pharmacol. Exp. Ther. 309: 1079-1084, 2004.
Olearczyk, J.J., Stephenson, A.H., Lonigro, A.J. and Sprague, R.S.: NO Inhibits Signal Transduction Pathway for ATP Release from Erythrocytes via Its Action on Heterotrimeric G Protein Gi. Am. J. Physiol 287:H748-H754, 2004.
Liang, G., Stephenson, A.H., Lonigro, A.J. and Sprague, R.S.: Erythrocytes of Humans with Cystic Fibrosis Fail to Stimulate Nitric Oxide Synthesis in Isolated Rabbit Lungs. Am. J. Physiol 288:H1580-H1585, 2005.
Sprague, R.S., Bowles. E.A., Stumpf, M.S., Ricketts, G. Freidman, A., Hou, W.-H., Stephenson, A.H. and Lonigro, A.J.: Rabbit Erythrocytes possess Adenylyl Cyclase Type II that is Activated by the Heterotrimeric G Proteins Gs and Gi. Pharmacological Reports 57:222-228, 2005.
Sprague, R. S., Stephenson, A.H., Bowles, E.A., Stumpf, M.S., Rickets, G. and Lonigro, A.J.: Expression of the Heterotrimeric G Protein Gi and ATP Release are Impaired in Erythrocytes of Humans with Diabetes Mellitus. Hypoxia and Exercise, edited by R.C. Roach, et al. Springer, New York pp.207-216, 2006.
Sprague, R.S., Stephenson, A.H., Bowles, E.A., Stumpf, M.S. and Lonigro, A.J.: Reduced Expression of Gi in Erythrocytes of Humans with Diabetes Type 2 is Associated with Impairment of both cAMP Generation and ATP Release. Diabetes 55:3588-3593, 2006.
Thuet, KM, Bowles,EA, Sridharan, M, Adderley, SP, Ellsworth, ML, Sprague, RS, Stephenson, AH: The rho kinase inhibitor, Y27632, increases erythrocyte deformability and low oxygen tension-induced ATP release. Am. J. Physiol. (Heart and Circ). 301:H1891-6, 2011 (PMC3213963).
Sprague RS, Bowles, EA, Achilleus, D., Stephenson, AH, Ellis, CG, Ellsworth, ML: A selective phosphodiesterase 3 inhibitor rescues low PO2-induced ATP release from erythrocytes of humans with type 2 diabetes: Implication for vascular control, Am. J. Physiol. Physiol. 301:H2466-72, 2011. (PMC Journal – In Process)
Sridharan M, Bowles EA, Richards JP, Krantic M, Davis KL, Dietrich KA, Stephenson AH, Ellsworth ML, Sprague RS: Prostacyclin Receptor-Mediated ATP Release from Erythrocytes Requires the Voltage-Dependent Anion Channel VDAC). Am J Physiol Heart Circ Physiol. 2011 Dec 9. [Epub ahead of print].
Srague RS, Ellsworth ML: Erythrocyte-derived ATP and perfusion distribution: Role of intracellular and intercellular communication. Microcirculation (invited manuscript) (in press).
Sridharan, M, Bowles, EA, Richards, JP, Krantic M, Davis KL, Dietrich KA, Stephenson AH, Ellsworth ML, Sprague RS: Prostacyclin Receptor-Mediated ATP Release from Erythrocytes Requires the Voltage-Dependent Anion Channel (VDAC). Am. J. Physiol. (Heart and Circ) 302:H553-H559, 2012.
Sprague, RS, Ellsworth, ML: Erythrocyte-derived ATP and perfusion distribution: Role of intracellular and intercellular communication. Microcirculation 14:1-10, 2012.
Goldman, D, Fraser, GM, Sprague, RS, Ellsworth, ML, Ellis, CG, Stephenson, AH: Towards a multiscale description of microvascular flow regulation: the pathway for O2-dependent release of ATP from human erythrocytes and the distribution of ATP in capillary networks. Frontiers in Physiology, 3:article 246, 2012.
Ellsworth, ML and Sprague, RS: Regulation of blood flow distribution in skeletal muscle: Role of erythrocyte-released ATP. J. Physiol. 590:4985-4991, 2012.
Saint Louis University Presidential Grant
Dr. Sprague and Dr. Mary Ellsworth
Targeted Delivery of Phosphodiesterase Inhibitors to Erythrocytes: Implication for the Treatment of Vascular Disease in Type 2 Diabetes.
The central hypothesis of this project is that targeted delivery of existing pharmaceuticals into red blood cells (erythrocytes) can lead to an effective treatment of vascular disease associated with diabetes mellitus, type 2 (DM2) without causing side effects.