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Ghonaim NW, Fraser GM, Goldman D, Milkovich S, Yang J, Ellis CG. Evidence for role of capillaries in regulation of skeletal muscle oxygen supply. Microcirculation 2021; 28:e12699. [PMID: 33853202 DOI: 10.1111/micc.12699] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 02/23/2021] [Accepted: 03/22/2021] [Indexed: 11/30/2022]
Abstract
How oxygen (O2 ) supply to capillaries is regulated to match the tissue's demand is unknown. Erythrocytes have been proposed as sensors in this regulatory mechanism since they release ATP, a vasodilator, in an oxygen saturation (SO2 )-dependent manner. ATP causes hyperpolarization of endothelial cells resulting in conducted vasodilation to arterioles. OBJECTIVE We propose individual capillary units can regulate their own O2 supply by direct communication to upstream arterioles via electrically coupled endothelium. METHODS To test this hypothesis, we developed a transparent micro-exchange device for localized O2 exchange with surface capillaries of intact tissue. The device was fabricated with an O2 permeable micro-outlet 0.2 × 1.0 mm. Experiments were performed on rat extensor digitorum longus (EDL) muscle using dual wavelength video microscopy to measure capillary hemodynamics and erythrocyte SO2 . Responses to local O2 perturbations were measured with only capillaries positioned over the micro-outlet. RESULTS Step changes in the gas mixture %O2 caused physiological changes in erythrocyte SO2 , and appropriate changes in flow to offset the O2 challenge if at least 3-4 capillaries were stimulated. CONCLUSION These results support our hypothesis that individual capillary units play a role in regulating their erythrocyte supply in response to a changing O2 environment.
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Affiliation(s)
- Nour W Ghonaim
- Biomedical Engineering Graduate Program, The University of Western Ontario, London, ON, Canada
| | - Graham M Fraser
- Division of BioMedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, NL, Canada
| | - Daniel Goldman
- Biomedical Engineering Graduate Program, The University of Western Ontario, London, ON, Canada.,Department of Medical Biophysics, The University of Western Ontario, London, ON, Canada
| | - Stephanie Milkovich
- Department of Medical Biophysics, The University of Western Ontario, London, ON, Canada.,Schulich School of Medicine & Dentistry, Robarts Research Institute, The University of Western Ontario, London, ON, Canada
| | - Jun Yang
- Biomedical Engineering Graduate Program, The University of Western Ontario, London, ON, Canada.,Department of Mechanical and Materials Engineering, The University of Western Ontario, London, ON, Canada
| | - Christopher G Ellis
- Biomedical Engineering Graduate Program, The University of Western Ontario, London, ON, Canada.,Department of Medical Biophysics, The University of Western Ontario, London, ON, Canada.,Schulich School of Medicine & Dentistry, Robarts Research Institute, The University of Western Ontario, London, ON, Canada
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Ngo JP, Ow CP, Gardiner BS, Kar S, Pearson JT, Smith DW, Evans RG. Diffusive shunting of gases and other molecules in the renal vasculature: physiological and evolutionary significance. Am J Physiol Regul Integr Comp Physiol 2016; 311:R797-R810. [DOI: 10.1152/ajpregu.00246.2016] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Accepted: 07/27/2016] [Indexed: 01/22/2023]
Abstract
Countercurrent systems have evolved in a variety of biological systems that allow transfer of heat, gases, and solutes. For example, in the renal medulla, the countercurrent arrangement of vascular and tubular elements facilitates the trapping of urea and other solutes in the inner medulla, which in turn enables the formation of concentrated urine. Arteries and veins in the cortex are also arranged in a countercurrent fashion, as are descending and ascending vasa recta in the medulla. For countercurrent diffusion to occur, barriers to diffusion must be small. This appears to be characteristic of larger vessels in the renal cortex. There must also be gradients in the concentration of molecules between afferent and efferent vessels, with the transport of molecules possible in either direction. Such gradients exist for oxygen in both the cortex and medulla, but there is little evidence that large gradients exist for other molecules such as carbon dioxide, nitric oxide, superoxide, hydrogen sulfide, and ammonia. There is some experimental evidence for arterial-to-venous (AV) oxygen shunting. Mathematical models also provide evidence for oxygen shunting in both the cortex and medulla. However, the quantitative significance of AV oxygen shunting remains a matter of controversy. Thus, whereas the countercurrent arrangement of vasa recta in the medulla appears to have evolved as a consequence of the evolution of Henle’s loop, the evolutionary significance of the intimate countercurrent arrangement of blood vessels in the renal cortex remains an enigma.
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Affiliation(s)
- Jennifer P. Ngo
- Cardiovascular Disease Program, Biosciences Discovery Institute and Department of Physiology and
| | - Connie P.C. Ow
- Cardiovascular Disease Program, Biosciences Discovery Institute and Department of Physiology and
| | - Bruce S. Gardiner
- School of Engineering and Information Technology, Murdoch University, Perth, Western Australia
| | - Saptarshi Kar
- School of Computer Science and Software Engineering, The University of Western Australia, Perth, Australia; and
| | - James T. Pearson
- Cardiovascular Disease Program, Biosciences Discovery Institute and Department of Physiology and
- Monash Biomedical Imaging Facility, Monash University, Melbourne, Australia
- Department of Cardiac Physiology, National Cerebral and Cardiovascular Center Research Institute, Osaka, Japan
| | - David W. Smith
- School of Computer Science and Software Engineering, The University of Western Australia, Perth, Australia; and
| | - Roger G. Evans
- Cardiovascular Disease Program, Biosciences Discovery Institute and Department of Physiology and
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3
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Zimmermann H. Extracellular ATP and other nucleotides-ubiquitous triggers of intercellular messenger release. Purinergic Signal 2015; 12:25-57. [PMID: 26545760 DOI: 10.1007/s11302-015-9483-2] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Accepted: 10/29/2015] [Indexed: 12/21/2022] Open
Abstract
Extracellular nucleotides, and ATP in particular, are cellular signal substances involved in the control of numerous (patho)physiological mechanisms. They provoke nucleotide receptor-mediated mechanisms in select target cells. But nucleotides can considerably expand their range of action. They function as primary messengers in intercellular communication by stimulating the release of other extracellular messenger substances. These in turn activate additional cellular mechanisms through their own receptors. While this applies also to other extracellular messengers, its omnipresence in the vertebrate organism is an outstanding feature of nucleotide signaling. Intercellular messenger substances released by nucleotides include neurotransmitters, hormones, growth factors, a considerable variety of other proteins including enzymes, numerous cytokines, lipid mediators, nitric oxide, and reactive oxygen species. Moreover, nucleotides activate or co-activate growth factor receptors. In the case of hormone release, the initially paracrine or autocrine nucleotide-mediated signal spreads through to the entire organism. The examples highlighted in this commentary suggest that acting as ubiquitous triggers of intercellular messenger release is one of the major functional roles of extracellular nucleotides. While initiation of messenger release by nucleotides has been unraveled in many contexts, it may have been overlooked in others. It can be anticipated that additional nucleotide-driven messenger functions will be uncovered with relevance for both understanding physiology and development of therapy.
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Affiliation(s)
- Herbert Zimmermann
- Institute of Cell Biology and Neuroscience, Molecular and Cellular Neurobiology, Goethe University, Max-von-Laue-Str. 13, Frankfurt am Main, Germany.
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4
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Dominguez Rieg JA, Burt JM, Ruth P, Rieg T. P2Y₂ receptor activation decreases blood pressure via intermediate conductance potassium channels and connexin 37. Acta Physiol (Oxf) 2015; 213:628-41. [PMID: 25545736 PMCID: PMC4442688 DOI: 10.1111/apha.12446] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2014] [Revised: 10/14/2014] [Accepted: 12/17/2014] [Indexed: 02/06/2023]
Abstract
AIMS Nucleotides are important paracrine regulators of vascular tone. We previously demonstrated that activation of P2Y₂ receptors causes an acute, NO-independent decrease in blood pressure, indicating this signalling pathway requires an endothelial-derived hyperpolarization (EDH) response. To define the mechanisms by which activation of P2Y₂ receptors initiates EDH and vasodilation, we studied intermediate-conductance (KCa3.1, expressed in endothelial cells) and big-conductance potassium channels (KCa1.1, expressed in smooth muscle cells) as well as components of the myoendothelial gap junction, connexins 37 and 40 (Cx37, Cx40), all hypothesized to be part of the EDH response. METHODS We compared the effects of a P2Y₂/₄ receptor agonist in wild-type (WT) mice and in mice lacking KCa3.1, KCa1.1, Cx37 or Cx40 under anaesthesia, while monitoring intra-arterial blood pressure and heart rate. RESULTS Acute activation of P2Y₂/₄ receptors (0.01-3 mg kg(-1) body weight i.v.) caused a biphasic blood pressure response characterized by a dose-dependent and rapid decrease in blood pressure in WT (maximal response % of baseline at 3 mg kg(-1) : -38 ± 1%) followed by a consecutive increase in blood pressure (+44 ± 11%). The maximal responses in KCa3.1(-/-) and Cx37(-/-) were impaired (-13 ± 5, +17 ± 7 and -27 ± 1, +13 ± 3% respectively), whereas the maximal blood pressure decrease in response to acetylcholine at 3 μg kg(-1) was not significantly different (WT: -53 ± 3%; KCa3.1(-/-) : -52 ± 3; Cx37(-/-) : -53 ± 3%). KCa1.1(-/-) and Cx40(-/-) showed an identical biphasic response to P2Y2/4 receptor activation compared to WT. CONCLUSIONS The data suggest that the P2Y2/4 receptor activation elicits blood pressure responses via distinct mechanisms involving KCa3.1 and Cx37.
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MESH Headings
- Animals
- Blood Pressure/drug effects
- Connexins/deficiency
- Connexins/genetics
- Connexins/metabolism
- Dose-Response Relationship, Drug
- Endothelial Cells/drug effects
- Endothelial Cells/metabolism
- Heart Rate/drug effects
- Inosine/analogs & derivatives
- Inosine/pharmacology
- Intermediate-Conductance Calcium-Activated Potassium Channels/deficiency
- Intermediate-Conductance Calcium-Activated Potassium Channels/genetics
- Intermediate-Conductance Calcium-Activated Potassium Channels/metabolism
- Large-Conductance Calcium-Activated Potassium Channel alpha Subunits/genetics
- Large-Conductance Calcium-Activated Potassium Channel alpha Subunits/metabolism
- Male
- Mice, 129 Strain
- Mice, Inbred C57BL
- Mice, Knockout
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- Myocytes, Smooth Muscle/drug effects
- Myocytes, Smooth Muscle/metabolism
- Nitric Oxide Synthase Type III/genetics
- Nitric Oxide Synthase Type III/metabolism
- Purinergic P2Y Receptor Agonists
- Receptors, Purinergic P2Y2/drug effects
- Receptors, Purinergic P2Y2/metabolism
- Signal Transduction/drug effects
- Uridine Triphosphate/analogs & derivatives
- Uridine Triphosphate/pharmacology
- Vasodilation/drug effects
- Gap Junction alpha-4 Protein
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Affiliation(s)
- J. A. Dominguez Rieg
- Department of Basic Sciences, Bastyr University California, San Diego, CA, USA
- VA San Diego Healthcare System, San Diego, CA, USA
| | - J. M. Burt
- Department of Physiology, University of Arizona, Tucson, AZ, USA
| | - P. Ruth
- Department of Pharmacology, Toxicology and Clinical Pharmacy, University of Tübingen, Tübingen, Germany
| | - T. Rieg
- VA San Diego Healthcare System, San Diego, CA, USA
- Division of Nephrology-Hypertension, Department of Medicine, University of California San Diego, La Jolla, CA, USA
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Abstract
Purinergic signaling plays important roles in control of vascular tone and remodeling. There is dual control of vascular tone by ATP released as a cotransmitter with noradrenaline from perivascular sympathetic nerves to cause vasoconstriction via P2X1 receptors, whereas ATP released from endothelial cells in response to changes in blood flow (producing shear stress) or hypoxia acts on P2X and P2Y receptors on endothelial cells to produce nitric oxide and endothelium-derived hyperpolarizing factor, which dilates vessels. ATP is also released from sensory-motor nerves during antidromic reflex activity to produce relaxation of some blood vessels. In this review, we stress the differences in neural and endothelial factors in purinergic control of different blood vessels. The long-term (trophic) actions of purine and pyrimidine nucleosides and nucleotides in promoting migration and proliferation of both vascular smooth muscle and endothelial cells via P1 and P2Y receptors during angiogenesis and vessel remodeling during restenosis after angioplasty are described. The pathophysiology of blood vessels and therapeutic potential of purinergic agents in diseases, including hypertension, atherosclerosis, ischemia, thrombosis and stroke, diabetes, and migraine, is discussed.
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Affiliation(s)
- Geoffrey Burnstock
- Autonomic Neuroscience Centre, University College Medical School, Rowland Hill Street, London NW3 2PF, UK; and Department of Pharmacology, The University of Melbourne, Australia.
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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. Am J Physiol Heart Circ Physiol 2011; 302:H553-9. [PMID: 22159995 DOI: 10.1152/ajpheart.00998.2011] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Erythrocytes have been implicated as controllers of vascular caliber by virtue of their ability to release the vasodilator ATP in response to local physiological and pharmacological stimuli. The regulated release of ATP from erythrocytes requires activation of a signaling pathway involving G proteins (G(i) or G(s)), adenylyl cyclase, protein kinase A, and the cystic fibrosis transmembrane conductance regulator as well as a final conduit through which this highly charged anion exits the cell. Although pannexin 1 has been shown to be the final conduit for ATP release from human erythrocytes in response to reduced oxygen tension, it does not participate in transport of ATP following stimulation of the prostacyclin (IP) receptor in these cells, which suggests that an additional protein must be involved. Using antibodies directed against voltage-dependent anion channel (VDAC)1, we confirm that this protein is present in human erythrocyte membranes. To address the role of VDAC in ATP release, two structurally dissimilar VDAC inhibitors, Bcl-x(L) BH4(4-23) and TRO19622, were used. In response to the IP receptor agonists, iloprost and UT-15C, ATP release was inhibited by both VDAC inhibitors although neither iloprost-induced cAMP accumulation nor total intracellular ATP concentration were altered. Together, these findings support the hypothesis that VDAC is the ATP conduit in the IP receptor-mediated signaling pathway in human erythrocytes. In addition, neither the pannexin inhibitor carbenoxolone nor Bcl-x(L) BH4(4-23) attenuated ATP release in response to incubation of erythrocytes with the β-adrenergic receptor agonist isoproterenol, suggesting the presence of yet another channel for ATP release from human erythrocytes.
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Affiliation(s)
- Meera Sridharan
- Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, Saint Louis, Missouri, MO 63104, USA.
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7
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Sridharan M, Adderley SP, Bowles EA, Egan TM, Stephenson AH, Ellsworth ML, Sprague RS. Pannexin 1 is the conduit for low oxygen tension-induced ATP release from human erythrocytes. Am J Physiol Heart Circ Physiol 2010; 299:H1146-52. [PMID: 20622111 DOI: 10.1152/ajpheart.00301.2010] [Citation(s) in RCA: 159] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Erythrocytes release ATP in response to exposure to the physiological stimulus of lowered oxygen (O(2)) tension as well as pharmacological activation of the prostacyclin receptor (IPR). ATP release in response to these stimuli requires activation of adenylyl cyclase, accumulation of cAMP, and activation of protein kinase A. The mechanism by which ATP, a highly charged anion, exits the erythrocyte in response to lowered O(2) tension or receptor-mediated IPR activation by iloprost is unknown. It was demonstrated previously that inhibiting pannexin 1 with carbenoxolone inhibits hypotonically induced ATP release from human erythrocytes. Here we demonstrate that three structurally dissimilar compounds known to inhibit pannexin 1 prevent ATP release in response to lowered O(2) tension but not to iloprost-induced ATP release. These results suggest that pannexin 1 is the conduit for ATP release from erythrocytes in response to lowered O(2) tension. However, the identity of the conduit for iloprost-induced ATP release remains unknown.
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Affiliation(s)
- Meera Sridharan
- Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, Saint Louis, MO 63104, USA.
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8
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Kavdia M, Popel AS. Venular endothelium-derived NO can affect paired arteriole: a computational model. Am J Physiol Heart Circ Physiol 2005; 290:H716-23. [PMID: 16155098 DOI: 10.1152/ajpheart.00776.2005] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Venular endothelial cells can release nitric oxide (NO) in response to intraluminal flow both in isolated venules and in vivo. Experimental studies suggest that venular endothelium-released NO causes dilation of the adjacent paired arteriole. In the vascular wall, NO stimulates its target hemoprotein, soluble guanylate cyclase (sGC), which relaxes smooth muscle cells. In this study, a computational model of NO transport for an arteriole and venule pair was developed to determine the importance of the venular endothelium-released NO and its transport to the adjacent arteriole in the tissue. The model predicts that the tissue NO levels are affected within a wide range of parameters, including NO-red blood cell reaction rate and NO production rate in the arteriole and venule. The results predict that changes in the venular NO production affected not only venular endothelial and smooth muscle NO concentration but also endothelial and smooth muscle NO concentration in the adjacent arteriole. This suggests that the anatomy of microvascular tissue can permit the transport of NO from arteriolar to venular side, and vice versa, and may provide a mechanism for dilation of proximal arterioles by venules. These results will have significant implications for our understanding of tissue NO levels in both physiological and pathophysiological conditions.
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Affiliation(s)
- Mahendra Kavdia
- Biomedical Engineering Program, College of Engineering, 203 Engineering Hall, Univ. of Arkansas, Fayetteville, AR 72701, USA.
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9
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Jiang H, Quilley J, Reddy LM, Falck JR, Wong PYK, McGiff JC. Red blood cells: reservoirs of cis- and trans-epoxyeicosatrienoic acids. Prostaglandins Other Lipid Mediat 2005; 75:65-78. [PMID: 15789616 DOI: 10.1016/j.prostaglandins.2004.10.003] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Epoxyeicosatrienoic acids (EETs) are candidate endothelium-derived hyperpolarizing factors that demonstrate a wide range of biological effects. The presence of both cis- and trans-EETs in rat plasma was identified with HPLC-electrospray ionization tandem mass spectrometry in this study. The total EETs in plasma are 38.2 ng/ml with cis-EETs representing 21.4 +/- 0.4 ng/ml and trans-EETs 16.8 +/- 0.4 ng/ml. EETs in RBCs were estimated to be 20.2 ng/10(9) RBCs, which corresponds to 200 ng in RBCs contained in 1 ml blood. RBC incubation with 10 mM tert-butyl hydroperoxide resulted in 4.4-fold increase of total cis-EETs (from 9.2 to 40.2 ng/10(9) RBCs) and 5.5-fold increase of total trans-EETs (from 11.0 to 60.8 ng/10(9) RBCs). EETs were released (2 ng/ml) from RBCs after incubation at 37 degrees C for 10 min even after being washed 3 times, indicating that RBCs are reservoirs of plasma EETs. The identification of cis- and trans-EETs in RBCs and in plasma as well as their release from RBCs suggest a vasoregulatory role of RBCs in view of their potent vasoactivity.
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MESH Headings
- 8,11,14-Eicosatrienoic Acid/analogs & derivatives
- 8,11,14-Eicosatrienoic Acid/blood
- 8,11,14-Eicosatrienoic Acid/chemistry
- Animals
- Chromatography, High Pressure Liquid
- Erythrocytes/chemistry
- Lipid Peroxidation
- Male
- Phospholipids/blood
- Phospholipids/isolation & purification
- Rats
- Rats, Sprague-Dawley
- Spectrometry, Mass, Electrospray Ionization
- Stereoisomerism
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Affiliation(s)
- Houli Jiang
- Department of Pharmacology, New York Medical College, Valhalla, NY 10595, USA.
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Ellis CG, Jagger J, Sharpe M. The microcirculation as a functional system. CRITICAL CARE : THE OFFICIAL JOURNAL OF THE CRITICAL CARE FORUM 2005; 9 Suppl 4:S3-8. [PMID: 16168072 PMCID: PMC3226163 DOI: 10.1186/cc3751] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
This review examines experimental evidence that the microvascular dysfunction that occurs early in sepsis is the critical first stage in tissue hypoxia and organ failure. A functional microvasculature maintains tissue oxygenation despite limitations on oxygen delivery from blood to tissue imposed by diffusion; the density of perfused (functional) capillaries is high enough to ensure appropriate diffusion distances, and arterioles regulate the distribution of oxygen within the organ precisely to where it is needed. Key components of this regulatory system are the endothelium, which communicates and integrates signals along the microvascular network, and the erythrocytes, which directly monitor and regulate oxygen delivery. During hypovolemic shock, a functional microvasculature responds to diminish the impact of a decrease in oxygen supply on tissue perfusion. However, within hours of the onset of sepsis, a dysfunctional microcirculation is, due to a loss of functional capillary density and impaired regulation of oxygen delivery, unable to maintain capillary oxygen saturation levels and prevent the rapid onset of tissue hypoxia despite adequate oxygen supply to the organ. The mechanism(s) responsible for this dysfunctional microvasculature must be understood in order to develop appropriate management strategies for sepsis.
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Affiliation(s)
- Christopher G Ellis
- Department of Medical Biophysics, University of Western Ontario, London, Ontario, Canada.
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Oike M, Droogmans G, Ito Y. [ATP release pathways in vascular endothelial cells]. Nihon Yakurigaku Zasshi 2004; 123:403-11. [PMID: 15170080 DOI: 10.1254/fpj.123.403] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Vascular endothelial cells regulate vascular tonus, growth, and angiogenesis in response to mechanical stresses. ATP release is one of well-known mechanosensitive responses in endothelial cells. Released ATP induces Ca(2+) responses and nitric oxide production in neighboring cells in an auto/paracrine manner. Mechanosensitive and agonist-induced ATP releases are also observed in other cell types, but the cellular mechanisms and pathways of ATP release are largely unknown. Reported candidates for ATP release pathways are ABC proteins including P-glycoprotein and CFTR, exocytosis of ATP-containing vesicles, and ATP-permeable anion channels. In vascular endothelium, vesicular exocytosis, volume-regulated anion channels (VRAC), and connexin hemichannels have been reported as candidates for ATP release pathways. We found that VRAC inhibitors suppressed hypotonic stress-induced ATP release in bovine aortic endothelial cells. Furthermore, extracellular ATP suppressed VRAC current in a voltage dependent manner, which could be fitted to the permeation-blocker model with a Kd(0) of 1 mM and delta value of 0.41. However, it should be noted that VRAC is probably not the only pathway for ATP release in the endothelium, because basal ATP release was not inhibited by VRAC inhibitors. Further investigations are definitely warranted to clarify the details and therapeutic significance of mechanosensitive ATP release in the endothelium.
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Affiliation(s)
- Masahiro Oike
- Department of Pharmacology, Graduate School of Medical Sciences, Kyushu University.
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