Our long-term goals center on defining the signaling events which coordinate the activity of endothelial cells (EC) and smooth muscle cells (SMC) in microvessels that control the delivery of oxygen and nutrients in accord with tissue metabolic demand. Our working hypothesis is that the local control of blood flow reflects the coordination of activity among EC and SMC of the feed arteries (FA) and arterioles which comprise microvascular resistance networks. Stimulating with acetylcholine (ACh) initiates complementary signals that propagate along the endothelium to relax consecutive SMC along vessel branches: (1) Hyperpolarization via activation of Ca2+-sensitive K+ channels (KCa), referred to as `rapid-conducted vasodilation'(RCVD;velocity >several mm/s) and mediated by electromechanical coupling, whereby intracellular Ca2+ ([Ca2+]i) and SMC (`myogenic') tone change with membrane potential (Vm);(2) A Ca2+ wave that releases nitric oxide, referred to as `slow-conducted conducted vasodilation'(SCVD;velocity, ~110 5m/s) and mediated through pharmacomechanical coupling (i.e., Ca2+ sensitization), whereby SMC tone changes independent of [Ca2+]i. This project is focused on understanding how SCVD is initiated, propagated and interacts with RCVD to control tissue blood flow. Experiments are performed using an established model of hamster FA with Ca2+ indicators in vitro complemented by in vivo studies using transgenic mice expressing a Ca2+ indicator protein (GCaMP2) in arteriolar EC. The source(s) of Ca2+ underlying endothelial Ca2+ waves is unknown.
Aim 1 will determine whether release of Ca2+ from internal stores is integral to SCVD by stimulating ryanodine and inositol 1,4,5- trisphosphate (IP3) receptors before and after store depletion. To test whether extracellular Ca2+ ([Ca2+]o) is integral to Ca2+ waves, [Ca2+]o is manipulated along with its entry into EC. In the absence of myogenic tone, Ca2+ waves travel <300 5m but propagate for ~1 mm when tone is present.
Aim 2 will determine why myogenic tone is required for effective propagation of EC Ca2+ waves by manipulating transmural pressure and SMC activation. We will evaluate whether (and if so, how) SMC tone affects EC [Ca2+]i and whether a threshold level of [Ca2+]i is required for EC to propagate Ca2+ waves. When hyperpolarization and RCVD are inhibited by KCa antagonists, the velocity of Ca2+ waves slows to ~20 5m/s.
Aim 3 will determine how RCVD interacts with SCVD by evaluating how changing Vm (with transmural pressure, adrenergic agonists, or by manipulating [K+]o) affects the propagation of Ca2+ waves along EC. Further, whereas KCa are activated at the site of ACh stimulation, we will explore why Ca2+ waves do not activate KCa at remote sites. Resolving the nature of Ca2+ waves and the interaction(s) between RCVD and SCVD will provide critical new insight for considering how respective signaling pathways may be affected during such pathophysiological conditions as diabetes, hypertension, and ischemia. We intend for this knowledge to facilitate the development of novel strategies for treating vascular disease and promoting the delivery of oxygen and nutrients to tissues throughout the body.

Public Health Relevance

The goal of this research project is to understand how electrical and chemical signals coordinate cells of the blood vessel wall to produce dilation and thereby increase blood flow and oxygen delivery to tissues throughout the body. We focus on the smallest of arterial (supply) vessels because these branches of the vascular network are the site of blood flow control. Understanding how vasodilator signals originate and are coordinated in vascular networks provides new insight for developing novel therapies for treating diseases associated with vascular complications and impaired tissue perfusion, e.g. diabetes and hypertension.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Method to Extend Research in Time (MERIT) Award (R37)
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Hypertension and Microcirculation Study Section (HM)
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OH, Youngsuk
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University of Missouri-Columbia
Schools of Medicine
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Sinkler, Shenghua Y; Fernando, Charmain A; Segal, Steven S (2016) Differential α-adrenergic modulation of rapid onset vasodilatation along resistance networks of skeletal muscle in old versus young mice. J Physiol 594:6987-7004
Boerman, Erika M; Segal, Steven S (2016) Depressed perivascular sensory innervation of mouse mesenteric arteries with advanced age. J Physiol 594:2323-38
Boerman, Erika M; Everhart, Jesse E; Segal, Steven S (2016) Advanced age decreases local calcium signaling in endothelium of mouse mesenteric arteries in vivo. Am J Physiol Heart Circ Physiol 310:H1091-6
Fernando, Charmain A; Liu, Yajun; Sowa, Grzegorz et al. (2016) Attenuated rapid onset vasodilation with greater force production in skeletal muscle of caveolin-2-/- mice. Am J Physiol Heart Circ Physiol 311:H415-25
Segal, Steven S (2015) Integration and Modulation of Intercellular Signaling Underlying Blood Flow Control. J Vasc Res 52:136-57
Nance, Michael E; Whitfield, Justin T; Zhu, Yi et al. (2015) Attenuated sarcomere lengthening of the aged murine left ventricle observed using two-photon fluorescence microscopy. Am J Physiol Heart Circ Physiol 309:H918-25
Behringer, Erik J; Segal, Steven S (2015) Membrane potential governs calcium influx into microvascular endothelium: integral role for muscarinic receptor activation. J Physiol 593:4531-48
Socha, Matthew J; Boerman, Erika M; Behringer, Erik J et al. (2015) Advanced age protects microvascular endothelium from aberrant Ca(2+) influx and cell death induced by hydrogen peroxide. J Physiol 593:2155-69
Segal, Steven S (2014) Blood flow restriction without sympathetic vasoconstriction in ageing skeletal muscle during exercise. J Physiol 592:4607-8
Domeier, Timothy L; Roberts, Cale J; Gibson, Anne K et al. (2014) Dantrolene suppresses spontaneous Ca2+ release without altering excitation-contraction coupling in cardiomyocytes of aged mice. Am J Physiol Heart Circ Physiol 307:H818-29

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