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van Helden DF, Laver DR, Holdsworth J, Imtiaz MS. Generation and propagation of gastric slow waves. Clin Exp Pharmacol Physiol 2009; 37:516-24. [PMID: 19930430 DOI: 10.1111/j.1440-1681.2009.05331.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
1. Mechanisms underlying the generation and propagation of gastrointestinal slow wave depolarizations have long been controversial. The present review aims to collate present knowledge on this subject with specific reference to slow waves in gastric smooth muscle. 2. At present, there is strong agreement that interstitial cells of Cajal (ICC) are the pacemaker cells that generate slow waves. What has been less clear is the relative role of primary types of ICC, including the network in the myenteric plexus (ICC-MY) and the intramuscular network (ICC-IM). It is concluded that both ICC-MY and ICC-IM are likely to serve a major role in slow wave generation and propagation. 3. There has been long-standing controversy as to how slow waves 'propagate' circumferentially and down the gastrointestinal tract. Two mechanisms have been proposed, one being action potential (AP)-like conduction and the other phase wave-based 'propagation' resulting from an interaction of coupled oscillators. Studies made on single bundle gastric strips indicate that both mechanisms apply with relative dominance depending on conditions; the phase wave mechanism is dominant under circumstances of rhythmically generating slow waves and the AP-like propagation is dominant when the system is perturbed. 4. The phase wave mechanism (termed Ca(2+) phase wave) uses cyclical Ca(2+) release as the oscillator, with coupling between oscillators mediated by several factors, including: (i) store-induced depolarization; (ii) resultant electrical current flow/depolarization through the pacemaker cell network; and (iii) depolarization-induced increase in excitability of downstream Ca(2+) stores. An analogy is provided by pendulums in an array coupled together by a network of springs. These, when randomly activated, entrain to swing at the same frequency but with a relative delay along the row giving the impression of a propagating wave. 5. The AP-like mechanism (termed voltage-accelerated Ca(2+) wave) propagates sequentially like a conducting AP. However, it is different in that it depends on regenerative store Ca(2+) release and resultant depolarization rather than regenerative activation of voltage-dependent channels in the cell membrane. 6. The applicability of these mechanisms to describing propagation in large intact gastrointestinal tissues, where voltage-dependent Ca(2+) entry is also likely to be functional, is discussed.
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Affiliation(s)
- Dirk F van Helden
- School of Biomedical Sciences, Faculty of Health, University of Newcastle, Callaghan, New South Wales, Australia.
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102
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Imtiaz MS, von der Weid PY, van Helden DF. Synchronization of Ca2+ oscillations: a coupled oscillator-based mechanism in smooth muscle. FEBS J 2009; 277:278-85. [PMID: 19895582 DOI: 10.1111/j.1742-4658.2009.07437.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Entrained oscillations in Ca(2+) underlie many biological pacemaking phenomena. In this article, we review a long-range signaling mechanism in smooth muscle that results in global outcomes of local interactions. Our results are derived from studies of the following: (a) slow-wave depolarizations that underlie rhythmic contractions of gastric smooth muscle; and (b) membrane depolarizations that drive rhythmic contractions of lymphatic smooth muscle. The main feature of this signaling mechanism is a coupled oscillator-based synchronization of Ca(2+) oscillations across cells that drives membrane potential changes and causes coordinated contractions. The key elements of this mechanism are as follows: (a) the Ca(2+) release-refill cycle of endoplasmic reticulum Ca(2+) stores; (b) Ca(2+)-dependent modulation of membrane currents; (c) voltage-dependent modulation of Ca(2+) store release; and (d) cell-cell coupling through gap junctions or other mechanisms. In this mechanism, Ca(2+) stores alter the frequency of adjacent stores through voltage-dependent modulation of store release. This electrochemical coupling is many orders of magnitude stronger than the coupling through diffusion of Ca(2+) or inositol 1,4,5-trisphosphate, and thus provides an effective means of long-range signaling.
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Affiliation(s)
- Mohammad S Imtiaz
- Department of Physiology and Pharmacology, University of Calgary, Alberta, Canada.
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103
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Fellner SK, Arendshorst WJ. Complex interactions of NO/cGMP/PKG systems on Ca2+ signaling in afferent arteriolar vascular smooth muscle. Am J Physiol Heart Circ Physiol 2009; 298:H144-51. [PMID: 19880669 DOI: 10.1152/ajpheart.00485.2009] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Little is known about the effects of nitric oxide (NO) and the cyclic GMP (cGMP)/protein kinase G (PKG) system on Ca(2+) signaling in vascular smooth muscle cells (VSMC) of resistance vessels in general and afferent arterioles in particular. We tested the hypotheses that cGMP-, Ca(2+)-dependent big potassium channels (BK(Ca(2+))) buffer the Ca(2+) response to depolarization by high extracellular KCl and that NO inhibits adenosine diphosphoribose (ADPR) cyclase, thereby reducing the Ca(2+)-induced Ca(2+) release. We isolated rat afferent arterioles, utilizing the magnetized microsphere method, and measured cytosolic Ca(2+) concentration ([Ca(2+)](i)) with fura-2, a preparation in which endothelial cells do not participate in [Ca(2+)](i) responses. KCl (50 mM)-induced depolarization causes an immediate increase in [Ca(2+)](i) of 151 nM. The blockers N(omega)-nitro-L-arginine methyl ester (of nitric oxide synthase), 1,2,4-oxodiazolo-[4,3-a]quinoxalin-1-one (ODQ, of guanylyl cyclase), KT-5823 (of PKG activation), and iberiotoxin (IBX, of BK(Ca(2+)) activity) do not alter the [Ca(2+)](i) response to KCl, suggesting no discernible endogenous NO production under basal conditions. The NO donor sodium nitroprusside (SNP) reduces the [Ca(2+)](i) response to 77 nM; IBX restores the response to control values. These data show that activation of BK(Ca(2+)) in the presence of NO/cGMP provides a brake on KCl-induced [Ca(2+)](i) responses. Experiments with the inhibitor of cyclic ADPR 8-bromo-cyclic ADPR (8-Br-cADPR) and SNP + downstream inhibitors of PKG and BK(Ca(2+)) suggest that NO inhibits ADPR cyclase in intact arterioles. When we pretreat afferent arterioles with 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP; 10 muM), the response to KCl is 143 nM. However, in the presence of both IBX and 8-Br-cGMP, we observe a surprising doubling of the [Ca(2+)](i) response to KCl. In summary, we present evidence for effects of the NO/cGMP/PKG system to reduce [Ca(2+)](i), via activation of BK(Ca(2+)) and possibly by inhibition of ADPR cyclase, and to increase [Ca(2+)](i), by a mechanism(s) yet to be defined.
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Affiliation(s)
- Susan K Fellner
- Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7545, USA.
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104
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Yuill KH, McNeish AJ, Kansui Y, Garland CJ, Dora KA. Nitric oxide suppresses cerebral vasomotion by sGC-independent effects on ryanodine receptors and voltage-gated calcium channels. J Vasc Res 2009; 47:93-107. [PMID: 19729956 PMCID: PMC4826747 DOI: 10.1159/000235964] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2008] [Accepted: 02/09/2009] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND/AIMS In cerebral arteries, nitric oxide (NO) release plays a key role in suppressing vasomotion. Our aim was to establish the pathways affected by NO in rat middle cerebral arteries. METHODS In isolated segments of artery, isometric tension and simultaneous measurements of either smooth muscle membrane potential or intracellular [Ca(2+)] ([Ca(2+)](SMC)) changes were recorded. RESULTS In the absence of L-NAME, asynchronous propagating Ca(2+) waves were recorded that were sensitive to block with ryanodine, but not nifedipine. L-NAME stimulated pronounced vasomotion and synchronous Ca(2+) oscillations with close temporal coupling between membrane potential, tone and [Ca(2+)](SMC). If nifedipine was applied together with L-NAME, [Ca(2+)](SMC) decreased and synchronous Ca(2+) oscillations were lost, but asynchronous propagating Ca(2+) waves persisted. Vasomotion was similarly evoked by either iberiotoxin, or by ryanodine, and to a lesser extent by ODQ. Exogenous application of NONOate stimulated endothelium-independent hyperpolarization and relaxation of either L-NAME-induced or spontaneous arterial tone. NO-evoked hyperpolarization involved activation of BK(Ca) channels via ryanodine receptors (RYRs), with little involvement of sGC. Further, in whole cell mode, NO inhibited current through L-type voltage-gated Ca(2+) channels (VGCC), which was independent of both voltage and sGC. CONCLUSION NO exerts sGC-independent actions at RYRs and at VGCC, both of which normally suppress cerebral artery myogenic tone.
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MESH Headings
- Animals
- Calcium/metabolism
- Calcium Channel Blockers/pharmacology
- Calcium Channels, L-Type/drug effects
- Calcium Channels, L-Type/metabolism
- Calcium Signaling/drug effects
- Dose-Response Relationship, Drug
- Endothelium, Vascular/metabolism
- Enzyme Inhibitors/pharmacology
- Guanylate Cyclase/antagonists & inhibitors
- Guanylate Cyclase/metabolism
- In Vitro Techniques
- Large-Conductance Calcium-Activated Potassium Channels/antagonists & inhibitors
- Large-Conductance Calcium-Activated Potassium Channels/metabolism
- Male
- Membrane Potentials
- Middle Cerebral Artery/enzymology
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/enzymology
- Nitric Oxide/metabolism
- Nitric Oxide Donors/pharmacology
- Nitric Oxide Synthase/antagonists & inhibitors
- Nitric Oxide Synthase/metabolism
- Potassium Channel Blockers/pharmacology
- Rats
- Receptors, Cytoplasmic and Nuclear/antagonists & inhibitors
- Receptors, Cytoplasmic and Nuclear/metabolism
- Ryanodine Receptor Calcium Release Channel/drug effects
- Ryanodine Receptor Calcium Release Channel/metabolism
- Soluble Guanylyl Cyclase
- Time Factors
- Vasoconstriction/drug effects
- Vasodilation/drug effects
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Affiliation(s)
- Kathryn H Yuill
- Department of Pharmacy and Pharmacology, University of Bath, Bath
| | | | - Yasuo Kansui
- Department of Pharmacy and Pharmacology, University of Bath, Bath
| | | | - Kim A Dora
- Department of Pharmacology, University of Oxford, Oxford, UK
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105
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Methven L, McBride M, Wallace GA, McGrath JC. The alpha 1B/D-adrenoceptor knockout mouse permits isolation of the vascular alpha 1A-adrenoceptor and elucidates its relationship to the other subtypes. Br J Pharmacol 2009; 158:209-24. [PMID: 19572943 PMCID: PMC2795267 DOI: 10.1111/j.1476-5381.2009.00269.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2008] [Revised: 01/30/2009] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND AND PURPOSE Mesenteric and carotid arteries from the alpha(1B/D)-adrenoceptor knockout (alpha(1B/D)-KO) were employed to isolate alpha(1A)-adrenoceptor pharmacology and location and to reveal these features in the wild-type (WT) mouse. EXPERIMENTAL APPROACH Functional pharmacology by wire myography and receptor localization by confocal microscopy, using the fluorescent alpha(1)-adrenoceptor ligand BODIPY FL-Prazosin (QAPB), on mesenteric (an 'alpha(1A)-adrenoceptor' tissue) and carotid (an 'alpha(1D)-adrenoceptor' tissue) arteries. KEY RESULTS Alpha(1B/D)-KO mesenteric arteries showed straightforward alpha(1A)-adrenoceptor agonist/antagonist pharmacology. WT had complex pharmacology with alpha(1A)- and alpha(1D)-adrenoceptor components. alpha(1B/D)-KO had a larger alpha(1A)-adrenoceptor response suggesting compensatory up-regulation: no increase in fluorescent ligand binding suggests up-regulation of signalling. alpha(1B/D)-KO carotid arteries had low efficacy alpha(1A)-adrenoceptor responses. WT had complex pharmacology consistent with co-activation of all three subtypes. Fluorescent binding had straightforward alpha(1A)-adrenoceptor characteristics in both arteries of alpha(1B/D)-KO. Fluorescent binding varied between cells in relative intracellular and surface distribution. Total fluorescence was reduced in the alpha(1B/D)-KO due to fewer smooth muscle cells showing fluorescent binding. WT binding was greater and sensitive to alpha(1A)- and alpha(1D)-adrenoceptor antagonists. CONCLUSIONS AND IMPLICATIONS The straightforward pharmacology and fluorescent binding in the alpha(1B/D)-KO was used to interpret the properties of the alpha(1A)-adrenoceptor in the WT. Reduced total fluorescence in alpha(1B/D)-KO arteries, despite a clear difference in the functionally dominant subtype, indicates that measurement of receptor protein is unlikely to correlate with function. Fewer cells bound QAPB in the alpha(1B/D)-KO suggesting different cellular phenotypes of alpha(1A)-adrenoceptor exist. The alpha(1B/D)-KO provides robust assays for the alpha(1A)-adrenoceptor and takes us closer to understanding multi-receptor subtype interactions.
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MESH Headings
- Adrenergic Agonists/pharmacology
- Adrenergic Antagonists/pharmacology
- Adrenergic alpha-1 Receptor Agonists
- Animals
- Carotid Arteries/drug effects
- Carotid Arteries/physiology
- Male
- Mesenteric Arteries/drug effects
- Mesenteric Arteries/physiology
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/physiology
- Protein Subunits/classification
- Protein Subunits/physiology
- Receptors, Adrenergic, alpha-1/classification
- Receptors, Adrenergic, alpha-1/deficiency
- Receptors, Adrenergic, alpha-1/physiology
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Affiliation(s)
- L Methven
- Integrative and Systems Biology, Faculty of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK.
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106
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Aletti F, Lanzarone E, Costantino ML, Baselli G. Simulation study of autoregulation responses of peripheral circulation to systemic pulsatility. NONLINEAR BIOMEDICAL PHYSICS 2009; 3:7. [PMID: 19630959 PMCID: PMC2722629 DOI: 10.1186/1753-4631-3-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/01/2009] [Accepted: 07/24/2009] [Indexed: 05/28/2023]
Abstract
BACKGROUND This simulation study investigated potential modulations of total peripheral resistance (TPR), due to distributed peripheral vascular activity, by means of a lumped model of the arterial tree and a non linear model of microcirculation, inclusive of local controls of blood flow and tissue-capillary fluid exchange. RESULTS Numerical simulations of circulation were carried out to compute TPR under different conditions of blood flow pulsatility, and to extract the pressure-flow characteristics of the cardiovascular system. Simulations showed that TPR seen by the large arteries was increased in absence of pulsatility, while it decreased with an augmented harmonic content. This is a typically non linear effect due to the contribution of active, non linear autoregulation of the peripheral microvascular beds, which also generated a nonlinear relationship between arterial blood pressure and cardiac output. CONCLUSION This simulation study, though focused on a simple effect attaining TPR modulation due to pulsatility, suggests that non-linear autoregulation mechanisms cannot be overlooked while studying the integrated behavior of the global cardiovascular system, including the arterial tree and the peripheral vascular bed.
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Affiliation(s)
- Federico Aletti
- Dipartimento di Bioingegneria, Politecnico di Milano, P.za Leonardo da Vinci, 32, 20133, Milan, Italy
| | - Ettore Lanzarone
- Dipartimento di Bioingegneria, Politecnico di Milano, P.za Leonardo da Vinci, 32, 20133, Milan, Italy
- Laboratorio di Meccanica delle Strutture Biologiche, Dipartimento di Ingegneria Strutturale, Politecnico di Milano, P.za Leonardo da Vinci, 32, 20133, Milan, Italy
| | - Maria Laura Costantino
- Laboratorio di Meccanica delle Strutture Biologiche, Dipartimento di Ingegneria Strutturale, Politecnico di Milano, P.za Leonardo da Vinci, 32, 20133, Milan, Italy
| | - Giuseppe Baselli
- Dipartimento di Bioingegneria, Politecnico di Milano, P.za Leonardo da Vinci, 32, 20133, Milan, Italy
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107
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108
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Syyong HT, Yang HHC, Trinh G, Cheung C, Kuo KH, van Breemen C. Mechanism of asynchronous Ca(2+) waves underlying agonist-induced contraction in the rat basilar artery. Br J Pharmacol 2009; 156:587-600. [PMID: 19154440 DOI: 10.1111/j.1476-5381.2008.00063.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND AND PURPOSE Uridine 5'-triphosphate (UTP) is a potent vasoconstrictor of cerebral arteries and induces Ca(2+) waves in vascular smooth muscle cells (VSMCs). This study aimed to determine the mechanisms underlying UTP-induced Ca(2+) waves in VSMCs of the rat basilar artery. EXPERIMENTAL APPROACH Isometric force and intracellular Ca(2+) ([Ca(2+)](i)) were measured in endothelium-denuded rat basilar artery using wire myography and confocal microscopy respectively. KEY RESULTS Uridine 5'-triphosphate (0.1-1000 micromol.L(-1)) concentration-dependently induced tonic contraction (pEC(50) = 4.34 +/- 0.13), associated with sustained repetitive oscillations in [Ca(2+)](i) propagating along the length of the VSMCs as asynchronized Ca(2+) waves. Inhibition of Ca(2+) reuptake in sarcoplasmic reticulum (SR) by cyclopiazonic acid abolished the Ca(2+) waves and resulted in a dramatic drop in tonic contraction. Nifedipine reduced the frequency of Ca(2+) waves by 40% and tonic contraction by 52%, and the nifedipine-insensitive component was abolished by SKF-96365, an inhibitor of receptor- and store-operated channels, and KB-R7943, an inhibitor of reverse-mode Na(+)/Ca(2+) exchange. Ongoing Ca(2+) waves and tonic contraction were also abolished after blockade of inositol-1,4,5-triphosphate-sensitive receptors by 2-aminoethoxydiphenylborate, but not by high concentrations of ryanodine or tetracaine. However, depletion of ryanodine-sensitive SR Ca(2+) stores prior to UTP stimulation prevented Ca(2+) waves. CONCLUSIONS AND IMPLICATIONS Uridine 5'-triphosphate-induced Ca(2+) waves may underlie tonic contraction and appear to be produced by repetitive cycles of regenerative Ca(2+) release from the SR through inositol-1,4,5-triphosphate-sensitive receptors. Maintenance of Ca(2+) waves requires SR Ca(2+) reuptake from Ca(2+) entry across the plasma membrane via L-type Ca(2+) channels, receptor- and store-operated channels, and reverse-mode Na(+)/Ca(2+) exchange.
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Affiliation(s)
- H T Syyong
- Department of Anesthesiology, Pharmacology & Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
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109
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Sosnovtseva O, Pavlov A, Pavlova O, Mosekilde E, Holstein-Rathlou NH. The effect of L-NAME on intra- and inter-nephron synchronization. Eur J Pharm Sci 2009; 36:39-50. [DOI: 10.1016/j.ejps.2008.10.019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2008] [Accepted: 09/08/2008] [Indexed: 10/21/2022]
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110
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Sandow SL, Haddock RE, Hill CE, Chadha PS, Kerr PM, Welsh DG, Plane F. WHAT'S WHERE AND WHY AT A VASCULAR MYOENDOTHELIAL MICRODOMAIN SIGNALLING COMPLEX. Clin Exp Pharmacol Physiol 2009; 36:67-76. [DOI: 10.1111/j.1440-1681.2008.05076.x] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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111
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Jacobsen JCB, Aalkjaer C, Matchkov VV, Nilsson H, Freiberg JJ, Holstein-Rathlou NH. Heterogeneity and weak coupling may explain the synchronization characteristics of cells in the arterial wall. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2008; 366:3483-3502. [PMID: 18632459 DOI: 10.1098/rsta.2008.0105] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Vascular smooth muscle cells (SMCs) exhibit different types of calcium dynamics. Static vascular tone is associated with unsynchronized calcium waves and the developed force depends on the number of recruited cells. Global calcium transients synchronized among a large number of cells cause rhythmic development of force known as vasomotion. We present experimental data showing a considerable heterogeneity in cellular calcium dynamics in the vascular wall. In stimulated vessels, some SMCs remain quiescent, whereas others display waves of variable frequency. At the onset of vasomotion, all SMCs are enrolled into synchronized oscillation. Simulations of coupled SMCs show that the experimentally observed cellular recruitment, the presence of quiescent cells and the variation in oscillation frequency may arise if the cell population is phenotypically heterogeneous. In this case, quiescent cells can be entrained at the onset of vasomotion by the collective driving force from the synchronized oscillations in the membrane potential of the surrounding cells. Partial synchronization arises with an increase in the concentration of cyclic guanosine monophosphate, but in a heterogeneous cell population complete synchronization also requires a high-conductance pathway that provides strong coupling between the cells.
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Affiliation(s)
- Jens Christian Brings Jacobsen
- The Danish National Research Foundation Centre for Cardiac Arrhythmias, Department of Biomedical Sciences, University of Copenhagen, 2200 Copenhagen N, Denmark.
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112
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Rossi M, Carpi A, Galetta F, Franzoni F, Santoro G. Skin vasomotion investigation: A useful tool for clinical evaluation of microvascular endothelial function? Biomed Pharmacother 2008; 62:541-5. [DOI: 10.1016/j.biopha.2008.07.085] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2008] [Accepted: 07/01/2008] [Indexed: 11/29/2022] Open
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113
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Abstract
Smooth muscle cell (SMC) contraction is controlled by the Ca2+ and Rho kinase signalling pathways. While the SMC Rho kinase system seems to be reasonably constant, there is enormous variation with regard to the mechanisms responsible for generating Ca2+ signals. One way of dealing with this diversity is to consider how this system has been adapted to control different SMC functions. Phasic SMCs (vas deferens, uterus and bladder) rely on membrane depolarization to drive Ca2+ influx across the plasma membrane. This depolarization can be induced by neurotransmitters or through the operation of a membrane oscillator. Many tonic SMCs (vascular, airway and corpus cavernosum) are driven by a cytosolic Ca2+ oscillator that generates periodic pulses of Ca2+. A similar oscillator is present in pacemaker cells such as the interstitial cells of Cajal (ICCs) and atypical SMCs that control other tonic SMCs (gastrointestinal, urethra, ureter). The changes in membrane potential induced by these cytosolic oscillators does not drive contraction directly but it functions to couple together individual oscillators to provide the synchronization that is a characteristic feature of many tonic SMCs.
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114
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Calcium dynamics and vasomotion in arteries subject to isometric, isobaric, and isotonic conditions. Biophys J 2008; 95:2728-38. [PMID: 18586845 DOI: 10.1529/biophysj.108.131136] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In vitro, different techniques are used to study the smooth muscle cells' calcium dynamics and contraction/relaxation mechanisms on arteries. Most experimental studies use either an isometric or an isobaric setup. However, in vivo, a blood vessel is neither isobaric nor isometric nor isotonic, as it is continuously submitted to intraluminal pressure variations arising from heart beat. We use a theoretical model of the smooth muscle calcium and arterial radius dynamics to determine whether results may be considerably different depending on the experimental conditions (isometric, isobaric, isotonic, or cyclic pressure variations). We show that isobaric conditions appear to be more realistic than isometric or isotonic situations, as the calcium dynamics is similar under cyclic intraluminal pressure variations (in vivo-like situation) and under a constant pressure (isobaric situation). The arterial contraction is less pronounced in isotonic than in isobaric conditions, and the vasoconstrictor sensitivity higher in isometric than isobaric or isotonic conditions, in agreement with experimental observations. Interestingly, the model predicts that isometric conditions may generate artifacts like the coexistence of multiple stable states. We have verified this model prediction experimentally using rat mesenteric arteries mounted on a wire myograph and stimulated with phenylephrine.
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115
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Vasomotion has chloride-dependency in rat mesenteric small arteries. Pflugers Arch 2008; 457:389-404. [DOI: 10.1007/s00424-008-0532-3] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2008] [Revised: 04/22/2008] [Accepted: 05/13/2008] [Indexed: 10/22/2022]
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116
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VanBavel E, van der Meulen ET, Spaan JAE. Vasomotion dynamics following calcium spiking depend on both cell signalling and limited constriction velocity in rat mesenteric small arteries. J Cell Mol Med 2008; 12:899-913. [PMID: 18494932 PMCID: PMC4401133 DOI: 10.1111/j.1582-4934.2008.00142.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
Vascular smooth muscle cell contraction depends on intracellular calcium. However, calcium-contraction coupling involves a complex array of intracellular processes. Quantitating the dynamical relation between calcium perturbations and resulting changes in tone may help identifying these processes. We hypothesized that in small arteries accurate quantitation can be achieved during rhythmic vasomotion, and questioned whether these dynamics depend on intracellular signalling or physical vasoconstriction. We studied calcium-constriction dynamics in cannulated and pressurized rat mesenteric small arteries (∼300 μm in diameter). Combined application of tetra-ethyl ammonium (TEA) and BayK8644 induced rhythmicity, consisting of regular and irregular calcium spiking and superposition of spikes. Calcium spikes induced delayed vasomotion cycles. Their dynamic relation could be fitted by a linear second-order model. The dirac impulse response of this model had an amplitude that was strongly reduced with increasing perfusion pressure between 17 and 98 mmHg, while time to peak and relaxation time were the largest at an intermediate pressure (57 mmHg: respectively 0.9 and 2.3 sec). To address to what extent these dynamics reside in intracellular signalling or vasoconstriction, we applied rhythmic increases in pressure counteracting the vasoconstriction. This revealed that calcium-activation coupling became faster when vasoconstriction was counteracted. During such compensation, a calcium impulse response remained that lasted 0.5 sec to peak activation, followed by a 1.0 sec relaxation time, attributable to signalling dynamics. In conclusion, this study demonstrates the feasibility of quantitating calcium-activation dynamics in vasomoting small arteries. These dynamics relate to both intracellular sig-nalling and actual vasoconstriction. Performing such analyses during pharmacological intervention and in genetic models provides a tool for unravelling calcium-contraction coupling in small arteries.
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Affiliation(s)
- Ed VanBavel
- Academic Medical Center, University of Amsterdam, Department of Medical Physics, Amsterdam, The Netherlands.
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117
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Sweeney M, Wareing M, Mills TA, Baker PN, Taggart MJ. Characterisation of tone oscillations in placental and myometrial arteries from normal pregnancies and those complicated by pre-eclampsia and growth restriction. Placenta 2008; 29:356-65. [PMID: 18336903 DOI: 10.1016/j.placenta.2008.01.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/30/2006] [Revised: 01/18/2008] [Accepted: 01/23/2008] [Indexed: 11/29/2022]
Abstract
Agonist-induced tone oscillations (rhythmic contractions and relaxations) occur in vascular beds to allow acute regulation of volume flow and thus the delivery of oxygen and nutrients to the tissue. Mechanisms responsible for the control of human placental vasomotor tone and blood flow are poorly characterized. This study aimed to characterise thromboxane-induced tone oscillations in human placental and myometrial arteries. Chorionic plate and myometrial arteries obtained from biopsies at term were mounted for isometric tension measurement. Tone oscillations were observed in chorionic arteries only when exposed to sub-maximal (<1 microM) concentrations of U46619. Slow (mean+/-SEM) frequency (2.6+/-0.5 per hour), large amplitude (39+/-7% of peak contraction) tone oscillations were elicited by 0.03 microM U46619 (n=18). In the presence of the nitric oxide synthase (NOS) inhibitor l-NNA (100 microM) the amplitude was significantly reduced (40+/-13% to 18+/-8%, P<0.05, n=6), frequency was unaltered and the bradykinin-dependent vasodilator response was reduced (68+/-13% to 40+/-19%, P<0.05, n=6). Myometrial arteries exposed to 1 microM U46619 developed tone oscillations within 10 min, which increased in amplitude over 30min occurring at relatively constant frequency. The mean amplitude of oscillations at 30 min (31+/-7%, n=16) was similar to that in chorionic arteries but the occurrence more frequent (42.8+/-9.7 per hour, P<0.001). Inhibition of NOS did not alter tone oscillations in myometrial arteries. Tone oscillations in chorionic arteries from pre-eclamptic and growth restricted (FGR) pregnancies were reduced in amplitude whereas those in myometrial arteries had increased frequency. Inhibition of NOS further reduced oscillation amplitude in chorionic arteries from FGR pregnancies. The alterations may contribute to the vasculopathology of these conditions, or, may represent compensatory mechanisms to maintain a matching of materno-placental blood flow.
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Affiliation(s)
- M Sweeney
- Institute of Cellular Medicine, School of Surgical & Reproductive Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, UK.
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118
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Aletti F, Baselli G, Bassani T, Lucini D, Pagani M. Modèle paramétrique multivarié pour l’identification des composantes de pressions diastolique et pulsée. Ing Rech Biomed 2008. [DOI: 10.1016/j.rbmret.2007.12.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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119
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120
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Rocha ML, Bendhack LM. Effects of K+ channel modulators on oscillatory contractions in sinoaortic denervated rat aortas. Biol Pharm Bull 2007; 30:2098-104. [PMID: 17978483 DOI: 10.1248/bpb.30.2098] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Sinoaortic denervated (SAD) rats present arterial pressure lability without sustained hypertension. We investigated the relation between sinoaortic denervation and the occurrence of oscillatory contractions in SAD rat aortas, as well as the effect of various K(+) channel modulators on these oscillations. Aortas were removed and concentration-effect curves to phenylephrine (0.01 to 10 muM) were constructed in arteries from SAD and Sham-operated rats in order to verify the occurrence of oscillations. We also evaluated the effects of various K(+) channel modulators on these oscillations. Only SAD rat aortas exhibited oscillatory contractions. Tetraethylammonium increased the frequency (28.5+/-3.5 to 41.5+/-4.5 counts/5 min) and amplitude (0.435+/-0.07 to 0.630+/-0.09 g) of the oscillations. Apamin and 4-aminopyridine did not alter the oscillations. Barium chloride converted the oscillatory contractions to a tonic contraction. Pinacidil rapidly blocked the oscillatory contractions and glibenclamide evoked reduction in amplitude from 0.410+/-0.07 to 0.180+/-0.06 g. Iberiotoxin increased the frequency of oscillatory contractions (from 28.0+/-3.5 to 51.5+/-7.5 counts/5 min) but decreased the amplitude (from 0.410+/-0.08 to 0.195+/-0.2 g). Our results demonstrate that SAD rat aortas exhibit oscillatory contractions and K(+) channels, mainly K(ATP) and BK(Ca), play a dominant role in these oscillations.
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Affiliation(s)
- Matheus Lavorenti Rocha
- Department of Pharmacology, Faculty of Medicine of Ribeirão Preto, University of Sao Paulo, Ribeirão Preto, SP, Brazil
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121
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Rahman A, Hughes A, Matchkov V, Nilsson H, Aalkjaer C. Antiphase oscillations of endothelium and smooth muscle [Ca2+]i in vasomotion of rat mesenteric small arteries. Cell Calcium 2007; 42:536-47. [PMID: 17524481 DOI: 10.1016/j.ceca.2007.01.007] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2006] [Revised: 12/23/2006] [Accepted: 01/22/2007] [Indexed: 11/20/2022]
Abstract
The mechanisms leading to vasomotion in the presence of noradrenaline and inhibitors of the sarcoplasmic/endoplasmic reticulum calcium ATPase were investigated in isolated rat mesenteric small arteries. Isobaric diameter and isometric force were measured together with membrane potential in endothelial cells and smooth muscle cells (SMC). Calcium in the endothelial cells and SMC was imaged with confocal microscopy. In the presence of noradrenaline and cyclopiazonic acid, ryanodine-insensitive oscillations in tone were produced. The frequency was about 1 min(-1) and amplitude about 70% of the maximal tone. The amplitude was reduced by indomethacin and increased with L-NAME. Vasomotion was inhibited by nifedipine and by 40 mM potassium. The frequency was increased and amplitude decreased by removal of the endothelium and by application of charybdotoxin and apamin. The vasomotion was associated with in-phase oscillations of membrane potential in endothelial cells and SMC and oscillations of [Ca2+]i that were in near anti-phase. We suggest a working model for the generation of oscillation based on a membrane oscillator where ion channels in both endothelial cells and SMC interact via a current running between the two cell types through myoendothelial gap junctions, which sets up a near anti-phase oscillation of [Ca2+]i in the two cell types.
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Affiliation(s)
- Awahan Rahman
- The Water and Salt Center, Institute of Physiology and Biophysics, University of Aarhus, Denmark
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122
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Meng F, To W, Kirkman-Brown J, Kumar P, Gu Y. Calcium oscillations induced by ATP in human umbilical cord smooth muscle cells. J Cell Physiol 2007; 213:79-87. [PMID: 17477379 DOI: 10.1002/jcp.21092] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Arterial smooth muscle cells exhibit vasomotion, related to oscillations in intracellular Ca(2+) concentration, but the origin and function of these has not yet been fully determined. We measured intracellular Ca(2+) using conventional fluorescent methods in primary cultured, human umbilical cord artery smooth muscle cells (HUCASMC). Spontaneous oscillations in Ca(2+) was found in only 1% of all cells but exogenous, micromolar concentrations of ATP could induce Ca(2+) oscillations in 70% of cells with the most common pattern being one of regular amplitude and frequency with a return to basal levels between each peak. The P2Y agonist, UTP, but not the P2X agonist alphabeta-methylene ATP, could also induce Ca(2+) oscillations. Once induced, these oscillations could not be blocked by G-protein, PLC, VGCC or TRP channel antagonists applied individually, but could be prevented when antagonists were applied together. In the presence of EGTA, micromolar concentrations of ATP induced an elevation in intracellular Ca(2+) but did not induce Ca(2+) oscillations. The oscillation frequency induced by ATP was affected by bath Ca(2+) concentration. Taken together, these data suggest that external Ca(2+) entry maintains the Ca(2+) oscillation induced by activation of P2Y receptors. Once induced, multiple mechanisms are involved to maintain the oscillation and the oscillation frequency is determined by the speed of Ca(2+) refilling. Chronic hypoxia enhanced the Ca(2+) response and altered the oscillation frequency. We suggest that these oscillations may play a role in the maintenance of umbilical blood flow during situations in which GPCR are activated.
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MESH Headings
- Adenosine Triphosphate/analogs & derivatives
- Adenosine Triphosphate/pharmacology
- Arachidonic Acid/pharmacology
- Calcium/pharmacology
- Calcium Channels/drug effects
- Calcium Channels/metabolism
- Calcium Signaling/drug effects
- Cell Hypoxia/drug effects
- Cell Hypoxia/physiology
- Cells, Cultured
- Humans
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- Myocytes, Smooth Muscle/drug effects
- Myocytes, Smooth Muscle/metabolism
- Purinergic P2 Receptor Agonists
- Receptors, Purinergic P2/classification
- Receptors, Purinergic P2/metabolism
- Uridine Triphosphate/pharmacology
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Affiliation(s)
- Fei Meng
- Department of Physiology, School of Medicine, University of Birmingham, Edgbaston, UK
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Schmiedel O, Schroeter ML, Harvey JN. Microalbuminuria in Type 2 diabetes indicates impaired microvascular vasomotion and perfusion. Am J Physiol Heart Circ Physiol 2007; 293:H3424-31. [PMID: 17933972 DOI: 10.1152/ajpheart.00558.2007] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Vascular oscillation (vasomotion) occurs in the microcirculation and is thought to be a significant contributor to tissue perfusion. Our aims were to assess the relationship of vasomotion to perfusion in the cutaneous microcirculation of diabetic patients, to determine the influence on it of endothelium-dependent and nonendothelium-dependent vasodilatory stimuli, and to assess the relationship to perfusion and vasomotion of various biochemical markers of vascular function (HbA1c, LDL- and HDL-cholesterol, triglycerides, insulin resistance, high sensitive C-reactive protein, L- and E-selectin, soluble ICAM, von Willebrand factor) and microalbuminuria. Perfusion and vasomotion (spectral density at low and very low frequencies) were measured by laser-Doppler flowmetry after local heat and iontophoresis of ACh and sodium nitroprusside. Perfusion responses to all stimuli were impaired in patients with Type 2 diabetes (heat: F = 28.0, P < 0.001; ACh: F = 7.11, P = 0.003; sodium nitroprusside: F = 4.0, P = 0.028). Responses to endothelium-dependent stimuli were further impaired in microalbuminuric patients (heat: P = 0.035; ACh: P = 0.034). Vasomotion responses at low frequencies after endothelium-dependent stimuli were impaired in diabetic patients compared with that shown in controls (heat: F = 5.62, P = 0.002; ACh: F = 4.32, P = 0.015). Multivariate modeling showed microalbuminuria to be the only consistent predictor of perfusion and vasomotion responses. The results suggest that microalbuminuria in Type 2 diabetes reflects a generalized disturbance of microvascular function related to endothelium-dependent mechanisms.
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Affiliation(s)
- Ole Schmiedel
- Diabetic Centre and Academic Unit, Maelor Hospital, University of Wales College of Medicine, Gladstone Centre, Wrexham, UK.
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124
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Landsverk SA, Kvandal P, Bernjak A, Stefanovska A, Kirkeboen KA. The Effects of General Anesthesia on Human Skin Microcirculation Evaluated by Wavelet Transform. Anesth Analg 2007; 105:1012-9, table of contents. [PMID: 17898381 DOI: 10.1213/01.ane.0000281932.09660.96] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
BACKGROUND Time-frequency analysis of the laser Doppler flowmetry signal, using wavelet transform, shows periodic oscillations at five characteristic frequencies related to the heart (0.6-2 Hz), respiration (0.15-0.6 Hz), myogenic activity in the vessel wall (0.052-0.15 Hz), sympathetic activity (0.021-0.052 Hz), and very slow oscillations (0.0095-0.021), which can be modulated by the endothelium-dependent vasodilator acetylcholine. We hypothesized that wavelet transform of laser Doppler flowmetry signals could detect changes in the microcirculation induced by general anesthesia, such as alterations in vasomotion and sympathetic activity. METHODS Eleven patients undergoing faciomaxillary surgery were included. Skin microcirculation was measured on the lower forearm with laser Doppler flowmetry and iontophoresis with acetylcholine and sodium nitroprusside before and during general anesthesia with propofol, fentanyl, and midazolam. The laser Doppler flowmetry signals were analyzed using wavelet transform. RESULTS There were significant reductions in spectral amplitudes in the 0.0095-0.021 (P < 0.01), the 0.021-0.052 (P < 0.001), and the 0.052-0.15 Hz frequency interval (P < 0.01) and a significant increase in the 0.15-0.6 Hz frequency interval. General anesthesia had no effect on the difference between acetylcholine and sodium nitroprusside on relative amplitudes in the 0.0095-0.021 Hz frequency interval (P < 0.001). CONCLUSION General anesthesia reduces the oscillatory components of the perfusion signal related to sympathetic, myogenic activity and the component modulated by the endothelium. However, the iontophoretic data did not reveal a specific effect on the endothelium. The increase in the 0.15-0.6 Hz interval is related to the effect of mechanical ventilation.
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125
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Rocha ML, Bendhack LM. SPONTANEOUS OSCILLATORY CONTRACTIONS IN AORTAS OF RATS WITH ARTERIAL PRESSURE LABILITY CAUSED BY SINOAORTIC DENERVATION. Clin Exp Pharmacol Physiol 2007; 34:708-13. [PMID: 17600545 DOI: 10.1111/j.1440-1681.2007.04612.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
1. The spontaneous variation of blood pressure is defined as arterial pressure lability. Sinoaortic denervation (SAD) is characterized by arterial pressure lability without sustained hypertension. 2. The phenomenon of spontaneous oscillatory contractions (SOCs) occurs more frequently in the vascular beds of hypertensive animals. In large arteries, such as the aorta, SOCs occur only occasionally or they can be initiated by application of chemical stimuli. 3. In the present study, we investigated whether the arterial pressure lability evoked by SAD could be related to the emergence of SOCs in the aorta of rats submitted to SAD compared with sham-operated rats (SO). Three days after surgery (SAD or SO), aortic rings were placed in an organ chamber and the incidence (percentage of rats presenting SOCs), frequency (number of SOCs in 10 min) and amplitude (mN) of SOCs were measured. The participation of external Ca(2+) and K(+) channels in the maintenance of SOCs was also verified. 4. The incidence and frequency of SOCs were higher in endothelium-denuded aortas from SAD rats (82% and 38 +/- 4 SOCs/10 min, respectively) than in aortas from SO rats (40% and 14 +/- 2 SOCs/10 min, respectively). In aortas from SAD rats, verapamil (0.2 micromol/L), pinacidil (0.3 micromol/L) and tetraethylammonium (TEA; 5 mmol/L) totally inhibited SOCs, whereas increasing the CaCl(2) concentration to 2.0 and 2.5 mmol/L increased the frequency of SOCs. Interestingly, increasing the concentration of CaCl(2) to 3.5 mmol/L inhibited these contractions in aortas from SAD rats. 5. These results show that although SAD rats did not become hypertensive, their aortas were capable of initiating SOCs without the application of any chemical stimuli. The SOCs seem to be dependent on Ca(2+) influx sensitive to verapamil and also involve K(+) channels sensitive to pinacidil and TEA.
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Affiliation(s)
- Matheus L Rocha
- Department of Physics and Chemistry, Faculty of Pharmaceutical Sciences of Ribeirão Preto, University of Sao Paulo, Ribeirão Preto, Brazil
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126
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Jacobsen JCB, Aalkjaer C, Nilsson H, Matchkov VV, Freiberg J, Holstein-Rathlou NH. A model of smooth muscle cell synchronization in the arterial wall. Am J Physiol Heart Circ Physiol 2007; 293:H229-37. [PMID: 17369467 DOI: 10.1152/ajpheart.00727.2006] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Vasomotion is a rhythmic variation in microvascular diameter. Although known for more than 150 years, the cellular processes underlying the initiation of vasomotion are not fully understood. In the present study a model of a single cell is extended by coupling a number of cells into a tube. The simulated results point to a permissive role of cGMP in establishing intercellular synchronization. In sufficient concentration, cGMP may activate a cGMP-sensitive calcium-dependent chloride channel, causing a tight spatiotemporal coupling between release of sarcoplasmic reticulum calcium, membrane depolarization, and influx of extracellular calcium. Low [cGMP] is associated only with unsynchronized waves. At intermediate concentrations, cells display either waves or whole cell oscillations, but these remain unsynchronized between cells. Whole cell oscillations are associated with rhythmic variation in membrane potential and flow of current through gap junctions. The amplitude of these oscillations in potential grows with increasing [cGMP], and, past a certain threshold, they become strong enough to entrain all cells in the vascular wall, thereby initiating sustained vasomotion. In this state there is a rhythmic flow of calcium through voltage-sensitive calcium channels into the cytoplasm, making the frequency of established vasomotion sensitive to membrane potential. It is concluded that electrical coupling through gap junctions is likely to be responsible for the rapid synchronization across a large number of cells. Gap-junctional current between cells is due to the appearance of oscillations in the membrane potential that again depends on the entrainment of sarcoplasmic reticulum and plasma membrane within the individual cell.
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Affiliation(s)
- Jens Christian Brings Jacobsen
- Biomedical Institute, Division of Renal and Vascular Physiology, The Panum Institute, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark.
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127
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Pradhan RK, Chakravarthy VS, Prabhakar A. Effect of chaotic vasomotion in skeletal muscle on tissue oxygenation. Microvasc Res 2007; 74:51-64. [PMID: 17418241 DOI: 10.1016/j.mvr.2007.02.004] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2006] [Revised: 02/02/2007] [Accepted: 02/13/2007] [Indexed: 11/27/2022]
Abstract
Vasomotion refers to spontaneous variations in the lumen size of small vessels, with a plausible role in regulation of various aspects of microcirculation. We propose a computational model of vasomotion in skeletal muscle in which the pattern of vasomotion is shown to critically determine the efficiency of oxygenation of a muscle fiber. In this model, precapillary sphincters are modeled as nonlinear oscillators. We hypothesize that these sphincters interact via exchange of vasoactive substances. As a consequence, vasomotion is described as a phenomenon associated with a network of nonlinear oscillators. As a specific instance, we model the vasomotion of precapillary sphincters surrounding an active fiber. The sphincters coordinate their rhythms so as to minimize oxygen deficit in the fiber. Our modeling studies indicate that efficient oxygenation of the fiber depends crucially on the mode of interaction among the vasomotions of individual sphincters. While chaotic forms of vasomotion enhanced oxygenation, regular patterns of vasomotion failed to meet the oxygenation demand accurately.
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Affiliation(s)
- Ranjan K Pradhan
- Department of Electrical Engineering, Indian Institute of Technology, Madras, Chennai-36, India
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128
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Parthimos D, Haddock RE, Hill CE, Griffith TM. Dynamics of a three-variable nonlinear model of vasomotion: comparison of theory and experiment. Biophys J 2007; 93:1534-56. [PMID: 17483163 PMCID: PMC1948040 DOI: 10.1529/biophysj.107.106278] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The effects of pharmacological interventions that modulate Ca(2+) homeodynamics and membrane potential in rat isolated cerebral vessels during vasomotion (i.e., rhythmic fluctuations in arterial diameter) were simulated by a third-order system of nonlinear differential equations. Independent control variables employed in the model were [Ca(2+)] in the cytosol, [Ca(2+)] in intracellular stores, and smooth muscle membrane potential. Interactions between ryanodine- and inositol 1,4,5-trisphosphate-sensitive intracellular Ca(2+) stores and transmembrane ion fluxes via K(+) channels, Cl(-) channels, and voltage-operated Ca(2+) channels were studied by comparing simulations of oscillatory behavior with experimental measurements of membrane potential, intracellular free [Ca(2+)] and vessel diameter during a range of pharmacological interventions. The main conclusion of the study is that a general model of vasomotion that predicts experimental data can be constructed by a low-order system that incorporates nonlinear interactions between dynamical control variables.
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Affiliation(s)
- D Parthimos
- Wales Heart Research Institute, Department of Diagnostic Radiology, Cardiff University, Cardiff, UK
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129
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Lamblin V, Favory R, Boulo M, Mathieu D. Microcirculatory alterations induced by sedation in intensive care patients. Effects of midazolam alone and in association with sufentanil. CRITICAL CARE : THE OFFICIAL JOURNAL OF THE CRITICAL CARE FORUM 2007; 10:R176. [PMID: 17173680 PMCID: PMC1794492 DOI: 10.1186/cc5128] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/16/2006] [Revised: 08/29/2006] [Accepted: 12/15/2006] [Indexed: 12/03/2022]
Abstract
Introduction Sedation is widely used in intensive care unit (ICU) patients to limit the risk of pulmonary barotrauma and to decrease oxygen needs. However, adverse effects of cc5128sedation have not been fully evaluated; in particular, effects of benzodiazepine and opiates on microcirculation have not been extensively studied. The aim of this study was to evaluate the microcirculatory effects of a sedation protocol commonly prescribed in the ICU. Methods Ten non-septic patients under controlled ventilation requiring sedation for therapeutic purposes were enrolled in a prospective observational study conducted in an ICU of a university hospital. Sedation was conducted in two successive steps: first, each patient received midazolam (0.1 mg/kg per hour after a bolus of 0.05 mg/kg, then adapted to reach a Ramsay score of between 3 and 5). Second, after one hour, sufentanil was added (0.1 μg/kg per hour after a bolus of 0.1 μg/kg). Arterial pressure, heart rate, cardiac output determined by transthoracic impedance, transcutaneous oxygen (tcPO2) and carbon dioxide (tcPCO2) pressures, and microcirculatory blood flow determined by laser Doppler flowmetry at rest and during a reactive hyperaemia challenge were measured before sedation (NS period), one hour after midazolam infusion (H period), and one hour after midazolam-sufentanil infusion (HS period). Results Arterial pressure decreased in both sedation periods, but heart rate, cardiac output, tcPO2, and tcPCO2 remained unchanged. In both sedation periods, microcirculatory changes occurred with an increase in cutaneous blood flow at rest (H period: 207 ± 25 perfusion units [PU] and HS period: 205 ± 25 PU versus NS period: 150 ± 22 PU, p < 0.05), decreased response to ischaemia (variation of blood flow to peak: H period: 97 ± 16 PU and HS period: 73 ± 9 PU versus NS period: 141 ± 14 PU, p < 0.05), and attenuation of vasomotion. Conclusion Sedation with midazolam or a combination of midazolam and sufentanil induces a deterioration of vasomotion and microvascular response to ischaemia, raising the question of whether this effect may further alter tissue perfusion when already compromised, as in septic patients.
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Affiliation(s)
- Veronique Lamblin
- Service d'Urgence Respiratoire et Réanimation Médicale et de Médecine Hyperbare, Hôpital Calmette, Centre Hospitalier Universitaire, Boulevard du Professeur Jules Leclercq, 59037 Lille Cedex, France
| | - Raphael Favory
- Service d'Urgence Respiratoire et Réanimation Médicale et de Médecine Hyperbare, Hôpital Calmette, Centre Hospitalier Universitaire, Boulevard du Professeur Jules Leclercq, 59037 Lille Cedex, France
| | - Marie Boulo
- Service d'Urgence Respiratoire et Réanimation Médicale et de Médecine Hyperbare, Hôpital Calmette, Centre Hospitalier Universitaire, Boulevard du Professeur Jules Leclercq, 59037 Lille Cedex, France
| | - Daniel Mathieu
- Service d'Urgence Respiratoire et Réanimation Médicale et de Médecine Hyperbare, Hôpital Calmette, Centre Hospitalier Universitaire, Boulevard du Professeur Jules Leclercq, 59037 Lille Cedex, France
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130
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Jacobsen JCB, Aalkjaer C, Nilsson H, Matchkov VV, Freiberg J, Holstein-Rathlou NH. Activation of a cGMP-sensitive calcium-dependent chloride channel may cause transition from calcium waves to whole cell oscillations in smooth muscle cells. Am J Physiol Heart Circ Physiol 2007; 293:H215-28. [PMID: 17369468 DOI: 10.1152/ajpheart.00726.2006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In vitro, alpha-adrenoreceptor stimulation of rat mesenteric small arteries often leads to a rhythmic change in wall tension, i.e., vasomotion. Within the individual smooth muscle cells of the vascular wall, vasomotion is often preceded by a period of asynchronous calcium waves. Abruptly, these low-frequency waves may transform into high-frequency whole cell calcium oscillations. Simultaneously, multiple cells synchronize, leading to rhythmic generation of tension. We present a mathematical model of vascular smooth muscle cells that aims at characterizing this sudden transition. Simulations show calcium waves sweeping through the cytoplasm when the sarcoplasmic reticulum (SR) is stimulated to release calcium. A rise in cGMP leads to the experimentally observed transition from waves to whole cell calcium oscillations. At the same time, membrane potential starts to oscillate and the frequency approximately doubles. In this transition, the simulated results point to a key role for a recently discovered cGMP-sensitive calcium-dependent chloride channel. This channel depolarizes the membrane in response to calcium released from the SR. In turn, depolarization causes a uniform opening of L-type calcium channels on the cell surface, stimulating a synchronized release of SR calcium and inducing the shift from waves to whole cell oscillations. The effect of the channel is therefore to couple the processes of the SR with those of the membrane. We hypothesize that the shift in oscillatory mode and the associated onset of oscillations in membrane potential within the individual cell may underlie sudden intercellular synchronization and the appearance of vasomotion.
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Affiliation(s)
- Jens Christian Brings Jacobsen
- Biomedical Institute, Division of Renal and Vascular Physiology, The Panum Institute, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark.
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131
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Imtiaz MS, Zhao J, Hosaka K, von der Weid PY, Crowe M, van Helden DF. Pacemaking through Ca2+ stores interacting as coupled oscillators via membrane depolarization. Biophys J 2007; 92:3843-61. [PMID: 17351003 PMCID: PMC1869001 DOI: 10.1529/biophysj.106.095687] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
This study presents an investigation of pacemaker mechanisms underlying lymphatic vasomotion. We tested the hypothesis that active inositol 1,4,5-trisphosphate receptor (IP(3)R)-operated Ca(2+) stores interact as coupled oscillators to produce near-synchronous Ca(2+) release events and associated pacemaker potentials, this driving action potentials and constrictions of lymphatic smooth muscle. Application of endothelin 1 (ET-1), an agonist known to enhance synthesis of IP(3), to quiescent lymphatic smooth muscle syncytia first enhanced spontaneous Ca(2+) transients and/or intracellular Ca(2+) waves. Larger near-synchronous Ca(2+) transients then occurred leading to global synchronous Ca(2+) transients associated with action potentials and resultant vasomotion. In contrast, blockade of L-type Ca(2+) channels with nifedipine prevented ET-1 from inducing near-synchronous Ca(2+) transients and resultant action potentials, leaving only asynchronous Ca(2+) transients and local Ca(2+) waves. These data were well simulated by a model of lymphatic smooth muscle with: 1), oscillatory Ca(2+) release from IP(3)R-operated Ca(2+) stores, which causes depolarization; 2), L-type Ca(2+) channels; and 3), gap junctions between cells. Stimulation of the stores caused global pacemaker activity through coupled oscillator-based entrainment of the stores. Membrane potential changes and positive feedback by L-type Ca(2+) channels to produce more store activity were fundamental to this process providing long-range electrochemical coupling between the Ca(2+) store oscillators. We conclude that lymphatic pacemaking is mediated by coupled oscillator-based interactions between active Ca(2+) stores. These are weakly coupled by inter- and intracellular diffusion of store activators and strongly coupled by membrane potential. Ca(2+) store-based pacemaking is predicted for cellular systems where: 1), oscillatory Ca(2+) release induces depolarization; 2), membrane depolarization provides positive feedback to induce further store Ca(2+) release; and 3), cells are interconnected. These conditions are met in a surprisingly large number of cellular systems including gastrointestinal, lymphatic, urethral, and vascular tissues, and in heart pacemaker cells.
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Affiliation(s)
- Mohammad S Imtiaz
- Neuroscience Group, School of Biomedical Sciences, Faculty of Health, The University of Newcastle, Newcastle, Australia.
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132
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Aletti F, Baselli G, Bassani T, Lucini D, Pagani M. Multivariate parametric model for the identification of diastolic pressure and pulse pressure components. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2007; 2007:287-290. [PMID: 18001946 DOI: 10.1109/iembs.2007.4352280] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Arterial pressure variability is a relatively unexplored topic among the various and detailed studies of cardiovascular variability. A deeper analysis of components and contributions carried by diastolic and pulse pressure may provide a unique insight on the potential systemic effects due to vasomotor activity and response at the level of microcirculation, whose dynamics are either driven by neural and vascular modulations. The aim of the present work is to develop a multivariate parametric model for the identification of the main components of diastolic and pulse pressure in order to investigate all the potential correlations between systemic arterial pressure variability and peripheral sources of oscillations and to analyze their interactions with the most known mechanisms of cardiovascular regulation.
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Affiliation(s)
- Federico Aletti
- Dipartimento di Bioingegneria, Politecnico di Milano, Milano, 20133 Italy.
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133
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Zacharia J, Zhang J, Wier WG. Ca2+ signaling in mouse mesenteric small arteries: myogenic tone and adrenergic vasoconstriction. Am J Physiol Heart Circ Physiol 2006; 292:H1523-32. [PMID: 17114244 DOI: 10.1152/ajpheart.00670.2006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Arteries that have developed myogenic tone (MT) are in a markedly different physiological state compared with those that have not, with higher cytosolic [Ca(2+)] and altered activity of several signal transduction pathways. In this study, we sought to determine whether alpha(1)-adrenoceptor-induced Ca(2+) signaling is different in pressurized arteries that have spontaneously developed MT (the presumptive physiological state) compared with those that have not (a common experimental state). At 32 degrees C and intraluminal pressure of 70 mmHg, cytoplasmic [Ca(2+)] was steady in most smooth muscle cells (SMCs). In a minority of cells (34%), however, at least one propagating Ca(2+) wave occurred. alpha(1)-Adrenoceptor activation (phenylephrine, PE; 0.1-10.0 microM) caused strong vasoconstriction and markedly increased the frequency of Ca(2+) waves (in virtually all cells). However, when cytosolic [Ca(2+)] was elevated experimentally in these arteries ([K(+)] 20 mM), PE failed to elicit Ca(2+) waves, although it did elevate [Ca(2+)] (F/F(0)) further and caused further vasoconstriction. During development of MT, the cytosolic [Ca(2+)] (F/F(0)) in individual SMCs increased, Ca(2+) waves disappeared (from SMCs that had them), and small Ca(2+) ripples (frequency approximately 0.05 Hz) appeared in approximately 13% of cells. PE elicited only spatially uniform increases in [Ca(2+)] and a smaller change in diameter (than in the absence of MT). Nevertheless, when cytosolic [Ca(2+)] and MT were decreased by nifedipine (1 microM), PE did elicit Ca(2+) waves. Thus alpha(1)-adrenoceptor-mediated Ca(2+) signaling is markedly different in arteries with and without MT, perhaps due to the elevated [Ca(2+)], and may have a different molecular basis. alpha(1)-Adrenoceptor-induced vasoconstriction may be supported either by Ca(2+) waves or by steady elevation of cytoplasmic [Ca(2+)], depending on the amount of MT.
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Affiliation(s)
- Joseph Zacharia
- Dept of Physiology, Univ of Maryland, Baltimore, MD 21201, USA
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134
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Bény JL, Koenigsberger M, Sauser R. Role of myoendothelial communication on arterial vasomotion. Am J Physiol Heart Circ Physiol 2006; 291:H2036-8. [PMID: 16877557 DOI: 10.1152/ajpheart.00709.2006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
MESH Headings
- Animals
- Arteries/cytology
- Arteries/physiology
- Arteries/ultrastructure
- Biological Factors/physiology
- Calcium Signaling
- Cell Communication/physiology
- Cerebral Cortex/blood supply
- Cerebral Cortex/ultrastructure
- Connexins/metabolism
- Connexins/ultrastructure
- Endothelium, Vascular/cytology
- Endothelium, Vascular/metabolism
- Endothelium, Vascular/ultrastructure
- Enzyme Inhibitors/pharmacology
- Gap Junctions/ultrastructure
- Male
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Models, Cardiovascular
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/metabolism
- Muscle, Smooth, Vascular/ultrastructure
- NG-Nitroarginine Methyl Ester/pharmacology
- Nitric Oxide Synthase/antagonists & inhibitors
- Rats
- Rats, Wistar
- Vasomotor System/physiology
- Vasomotor System/ultrastructure
- Gap Junction alpha-5 Protein
- Gap Junction alpha-4 Protein
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135
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Haddock RE, Grayson TH, Brackenbury TD, Meaney KR, Neylon CB, Sandow SL, Hill CE. Endothelial coordination of cerebral vasomotion via myoendothelial gap junctions containing connexins 37 and 40. Am J Physiol Heart Circ Physiol 2006; 291:H2047-56. [PMID: 16815985 DOI: 10.1152/ajpheart.00484.2006] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Control of cerebral vasculature differs from that of systemic vessels outside the blood-brain barrier. The hypothesis that the endothelium modulates vasomotion via direct myoendothelial coupling was investigated in a small vessel of the cerebral circulation. In the primary branch of the rat basilar artery, membrane potential, diameter, and calcium dynamics associated with vasomotion were examined using selective inhibitors of endothelial function in intact and endothelium-denuded arteries. Vessel anatomy, protein, and mRNA expression were studied using conventional electron microscopy high-resolution ultrastructural and confocal immunohistochemistry and quantitative PCR. Membrane potential oscillations were present in both endothelial cells and smooth muscle cells (SMCs), and these preceded rhythmical contractions during which adjacent SMC intracellular calcium concentration ([Ca(2+)](i)) waves were synchronized. Endothelium removal abolished vasomotion and desynchronized adjacent smooth muscle cell [Ca(2+)](i) waves. N(G)-nitro-l-arginine methyl ester (10 microM) did not mimic this effect, and dibutyryl cGMP (300 muM) failed to resynchronize [Ca(2+)](i) waves in endothelium-denuded arteries. Combined charybdotoxin and apamin abolished vasomotion and depolarized and constricted vessels, even in absence of endothelium. Separately, (37,43)Gap27 and (40)Gap27 abolished vasomotion. Extensive myoendothelial gap junctions (3 per endothelial cell) composed of connexins 37 and 40 connected the endothelial cell and SMC layers. Synchronized vasomotion in rat basilar artery is endothelium dependent, with [Ca(2+)](i) waves generated within SMCs being coordinated by electrical coupling via myoendothelial gap junctions.
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Affiliation(s)
- Rebecca E Haddock
- Div. of Neuroscience, John Curtin School of Medical Research, Australian National Univ., Canberra, 2601 ACT Australia
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136
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Sakurai T, Terui N. Effects of sympathetically induced vasomotion on tissue-capillary fluid exchange. Am J Physiol Heart Circ Physiol 2006; 291:H1761-7. [PMID: 16731646 DOI: 10.1152/ajpheart.00280.2006] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The spontaneous and rhythmic constriction of peripheral arterioles, which is not associated with the cardiac or respiratory cycles, is called vasomotion. Vasomotion is observed in various tissues of various species, but the physiological role of vasomotion has not been clarified because of the difficulty in controlling the appearance of vasomotion in in vivo preparations. We developed a method of controlling vasomotion in in vivo experiments. The electrical stimulation of the cervical sympathetic nerve could reproducibly evoke vasomotion in rabbit ear skin. The frequencies of the evoked vasomotion were 0.04–0.07 Hz, which corresponded to spontaneously occurring vasomotion that has been reported before. Vasomotion was always evoked between 25 and 35°C. At lower than 17°C or higher than 37°C, vasomotion was not evoked. With the use of this method of evoking vasomotion in vivo, the role of vasomotion in tissue perfusion was examined. A tracer (Cr-EDTA) was injected into the ear tissue, and tracer fading was then measured by using a camera. The rates of fading (clearance) of the tracer with vasomotion were significantly greater (1.7 to 8.1 times) than those without vasomotion. These results provided evidence that vasomotion enhanced tissue perfusion.
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Affiliation(s)
- Terumi Sakurai
- Dept. of Physiology, Institute of Basic Medical Sciences, Graduate School of Comprehensive Human Sciences, Univ. of Tsukuba,. 1-1-1 Tennodai, Tsukuba-shi, Ibaraki-ken 305-8575, Japan.
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137
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Valero M, Pereboom D, Garay RP, Alda JO. Role of chloride transport proteins in the vasorelaxant action of nitroprusside in isolated rat aorta. Eur J Pharmacol 2006; 553:205-8. [PMID: 17074318 DOI: 10.1016/j.ejphar.2006.09.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2006] [Revised: 09/07/2006] [Accepted: 09/08/2006] [Indexed: 11/21/2022]
Abstract
Chloride ions play a key role in smooth muscle contraction, but little is known concerning their role in smooth muscle relaxation. Here we investigated the effect of chloride transport inhibitors on the vasorelaxant responses to nitroprusside in isolated and endothelium-denuded rat aorta, precontracted with phenylephrine 1 muM. Incubation of aortic rings in NO(3)(-) media strongly potentiated the vasorelaxant responses to nitroprusside. Bumetanide, DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid) and acetazolamide strongly potentiated the vasorelaxant responses to nitroprusside (by 70-100%). EC(50) were 2.3+/-0.5 microM for bumetanide, 26+/-15 microM for DIDS and 510+/-118 microM for acetazolamide (n=6 for condition). Niflumic acid, a selective inhibitor of ClCa (calcium-activated chloride channels), potentiated nitroprusside relaxation to a similar extent as chloride transport inhibitors, in a non-additive manner. Zinc and nickel ions, both modestly potentiated nitroprusside vasorelaxation (by 20-30%). Cobaltum had negligible effect on nitroprusside vasorelaxation. CPA (p-chlorophenoxy-acetic acid), an inhibitor of volume-sensitive chloride channels (ClC), slightly potentiated nitroprusside vasorelaxation (by 15%), and the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel inhibitors CFTR(inh)172 (5-[(4-Carboxyphenyl)methylene]-2-thioxo-3-[(3-trifluoromethyl)phenyl-4-thiazolidinone), DPC (diphenylamine-2,2'-dicarboxylic acid) and glibenclamide were without significant effect. In conclusion, inhibition of chloride transport proteins strongly potentiates the vasorelaxant responses to nitroprusside in isolated rat aorta. This effect seems mediated by chloride depletion and inhibition of a chloride channel activated by both, calcium and cyclic GMP (cGMP).
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Affiliation(s)
- Marta Valero
- Department of Physiology and Pharmacology, School of Medicine, University of Zaragoza, Spain
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138
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Abstract
Smooth muscle and endothelial cells in the arterial wall are exposed to mechanical stress. Indeed blood flow induces intraluminal pressure variations and shear stress. An increase in pressure may induce a vessel contraction, a phenomenon known as the myogenic response. Many muscular vessels present vasomotion, i.e., rhythmic diameter oscillations caused by synchronous cytosolic calcium oscillations of the smooth muscle cells. Vasomotion has been shown to be modulated by pressure changes. To get a better understanding of the effect of stress and in particular pressure on vasomotion, we propose a model of a blood vessel describing the calcium dynamics in a coupled population of smooth muscle cells and endothelial cells and the consequent vessel diameter variations. We show that a rise in pressure increases the calcium concentration. This may either induce or abolish vasomotion, or increase its frequency depending on the initial conditions. In our model the myogenic response is less pronounced for large arteries than for small arteries and occurs at higher values of pressure if the wall thickness is increased. Our results are in agreement with experimental observations concerning a broad range of vessels.
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Affiliation(s)
- Michèle Koenigsberger
- Ecole Polytechnique Fédérale de Lausanne, Laboratory of Cell Biophysics, Lausanne, Switzerland.
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139
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Hessellund A, Aalkjaer C, Bek T. Effect of cyclic guanosine-monophosphate on porcine retinal vasomotion. ACTA ACUST UNITED AC 2006; 84:228-33. [PMID: 16637842 DOI: 10.1111/j.1600-0420.2006.00633.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
PURPOSE Vasomotion refers to periodic oscillations in vascular tone that ensure the intermittent supply of blood to adjacent microvascular units. Previous evidence from vessels outside the eye suggests that cyclic guanosine-monophosphate (cGMP) is involved in the regulation of vasomotion, but it is unknown whether this compound has an effect on vasomotion in retinal vessels. METHODS Retinal arterioles from porcine eyes were studied in a wire myograph. After initiation of vasomotion, the vessels were stimulated with increasing concentrations of the cGMP agonist 8-Br-cGMP (n = 6), the phosphodiesterase inhibitor zaprinast (n = 6) and the cGMP synthesis inhibitor L-NAME (n = 6). High concentrations of L-NAME blocked vasomotion, and control experiments (n = 20) using 8-Br-cGMP, S-nitroso-N-acetylpenicillamine (SNAP), adenosine and pinacidil were carried out to elucidate whether this effect was related to changes in the general tone of the vessel. Additionally, the relationship between oscillations in vascular tone and intracellular calcium concentration was studied. RESULTS Induction of cGMP agonistic activity with either 8-Br-cGMP or zaprinast lowered the vasomotion frequency significantly, whereas L-NAME-induced inhibition of cGMP increased this frequency. Neither of the agents affected the amplitude of the oscillations. The control experiments indicated that the effect of cGMP on vasomotion frequency was independent of the accompanying increase in tone. The oscillations in tone during vasomotion were accompanied by similar oscillations in intracellular calcium concentration. CONCLUSION Cyclic GMP lowers the frequency without affecting the amplitude of vasomotion in isolated porcine retinal arterioles.
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Affiliation(s)
- Anders Hessellund
- Department of Ophthalmology, Aarhus University Hospital, Aarhus, Denmark.
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140
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Matchkov VV, Rahman A, Bakker LM, Griffith TM, Nilsson H, Aalkjaer C. Analysis of effects of connexin-mimetic peptides in rat mesenteric small arteries. Am J Physiol Heart Circ Physiol 2006; 291:H357-67. [PMID: 16428342 DOI: 10.1152/ajpheart.00681.2005] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Synthetic peptides homologous to the extracellular loops of the major vascular connexins represent a novel class of gap junction blockers that have been used to assess the role of direct cellular communication in arteries and veins. However, the specificity of action of such peptides on the coupling between smooth muscle cells (SMCs) has not yet been fully characterized. Isolated third-order rat mesenteric arteries were therefore studied with respect to isometric tension (myography), intracellular Ca2+ concentration ([Ca2+]i) (Ca2+ -sensitive dyes), membrane potential, and input resistance (sharp intracellular glass electrodes). Confocal imaging was used for visualization of [Ca2+]i events in individual SMCs in the arterial wall and membrane currents (patch clamp) measured in individual SMCs isolated from the same arteries. A triple peptide combination (37,43Gap 27 + 40Gap 27 + 43Gap 26) increased intercellular resistance (measured as input resistance) in intact arterial segments without affecting the membrane conductance of individual cells and also interrupted electrical coupling between pairs of rat aortic A7r5 myocytes. In intact arterial segments, the peptides desynchronized [Ca2+]i transients in individual SMCs and abolished vasomotion without suppressing Ca2+ transients in individual cells. They also depolarized SMCs, increased [Ca2+]i, and attenuated acetylcholine-induced, endothelium-dependent smooth muscle hyperpolarization. Experiments with endothelium-denuded arteries suggested that the depolarization produced by the peptides under basal conditions was in part secondary to electrical uncoupling of the endothelium from SMCs with loss of a tonic hyperpolarizing effect of the endothelium. Taken together, the results indicate that connexin-mimetic peptides block electrical signaling in rat mesenteric small arteries without exerting major nonjunctional effects.
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Affiliation(s)
- Vladimir V Matchkov
- The Water and Salt Research Center, Institute of Physiology and Biophysics, University of Aarhus, Aarhus, Denmark.
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141
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Zhang DX, Gauthier KM, Campbell WB. Mechanisms of histamine-induced relaxation in bovine small adrenal cortical arteries. Am J Physiol Endocrinol Metab 2005; 289:E1058-63. [PMID: 16076876 DOI: 10.1152/ajpendo.00162.2005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Adrenal steroidogenesis is closely correlated with increases in adrenal blood flow. Many reports have studied the regulation of adrenal blood flow in vivo and in perfused glands, but until recently few studies have been conducted on isolated adrenal arteries. The present study examined vasomotor responses of isolated bovine small adrenal cortical arteries to histamine, an endogenous vasoactive compound, and its mechanism of action. In U-46619-precontracted arteries, histamine (10(-9)-5 x 10(-6) M) elicited concentration-dependent relaxations. The relaxations were blocked by the H(1) receptor antagonists diphenhydramine (10 microM) or mepyramine (1 microM) (maximal relaxations of 18 +/- 6 and 22 +/- 6%, respectively, vs. 55 +/- 5% of control) but only partially inhibited by the H(2) receptor antagonist cimetidine (10 microM) and the H(3) receptor antagonist thioperamide (1 microM). Histamine-induced relaxations were also blocked by the nitric oxide synthase inhibitor N-nitro-L-arginine (L-NA, 30 microM; maximal relaxation of 13 +/- 7%) and eliminated by endothelial removal or L-NA combined with the cyclooxgenase inhibitor indomethacin (10 microM). In the presence of adrenal zona glomerulosa (ZG) cells, histamine did not induce further relaxations compared with histamine alone. Histamine (10(-7)-10(-5) M) concentration-dependently increased aldosterone production by adrenal ZG cells. Compound 48/80 (10 microg/ml), a mast cell degranulator, induced significant relaxations (93 +/- 0.6%), which were blocked by L-NA plus indomethacin or endothelium removal, partially inhibited by the combination of the H(1), H(2), and H(3) receptor antagonists, but not affected by the mast cell stabilizer sodium cromoglycate (1 mM). These results demonstrate that histamine causes direct relaxation of small adrenal cortical arteries, which is largely mediated by endothelial NO and prostaglandins via H(1) receptors. The potential role of histamine in linking adrenal vascular events and steroid secretion requires further investigation.
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Affiliation(s)
- David X Zhang
- Department of Pharmacology and Toxicology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
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142
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Thorneloe KS, Nelson MT. Ion channels in smooth muscle: regulators of intracellular calcium and contractility. Can J Physiol Pharmacol 2005; 83:215-42. [PMID: 15870837 DOI: 10.1139/y05-016] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Smooth muscle (SM) is essential to all aspects of human physiology and, therefore, key to the maintenance of life. Ion channels expressed within SM cells regulate the membrane potential, intracellular Ca2+ concentration, and contractility of SM. Excitatory ion channels function to depolarize the membrane potential. These include nonselective cation channels that allow Na+ and Ca2+ to permeate into SM cells. The nonselective cation channel family includes tonically active channels (Icat), as well as channels activated by agonists, pressure-stretch, and intracellular Ca2+ store depletion. Cl--selective channels, activated by intracellular Ca2+ or stretch, also mediate SM depolarization. Plasma membrane depolarization in SM activates voltage-dependent Ca2+ channels that demonstrate a high Ca2+ selectivity and provide influx of contractile Ca2+. Ca2+ is also released from SM intracellular Ca2+ stores of the sarcoplasmic reticulum (SR) through ryanodine and inositol trisphosphate receptor Ca2+ channels. This is part of a negative feedback mechanism limiting contraction that occurs by the Ca2+-dependent activation of large-conductance K+ channels, which hyper polarize the plasma membrane. Unlike the well-defined contractile role of SR-released Ca2+ in skeletal and cardiac muscle, the literature suggests that in SM Ca2+ released from the SR functions to limit contractility. Depolarization-activated K+ chan nels, ATP-sensitive K+ channels, and inward rectifier K+ channels also hyperpolarize SM, favouring relaxation. The expression pattern, density, and biophysical properties of ion channels vary among SM types and are key determinants of electrical activity, contractility, and SM function.
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Affiliation(s)
- Kevin S Thorneloe
- Department of Pharmacology, College of Medicine, University of Vermont, Burlington 05405, USA.
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143
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Haddock RE, Hill CE. Rhythmicity in arterial smooth muscle. J Physiol 2005; 566:645-56. [PMID: 15905215 PMCID: PMC1464779 DOI: 10.1113/jphysiol.2005.086405] [Citation(s) in RCA: 122] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2005] [Accepted: 05/13/2005] [Indexed: 12/21/2022] Open
Abstract
Many arteries and arterioles exhibit rhythmical contractions which are synchronous over considerable distances. This vasomotion is likely to assist in tissue perfusion especially during periods of altered metabolism or perfusion pressure. While the mechanism underlying vascular rhythmicity has been investigated for many years, it has only been recently, with the advent of imaging techniques for visualizing intracellular calcium release, that significant advances have been made. These methods, when combined with mechanical and electrophysiological recordings, have demonstrated that the rhythm depends critically on calcium released from intracellular stores within the smooth muscle cells and on cell coupling via gap junctions to synchronize oscillations in calcium release amongst adjacent cells. While these factors are common to all vessels studied to date, the contribution of voltage-dependent channels and the endothelium varies amongst different vessels. The basic mechanism for rhythmical activity in arteries thus differs from its counterpart in non-vascular smooth muscle, where specific networks of pacemaker cells generate electrical potentials which drive activity within the otherwise quiescent muscle cells.
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Affiliation(s)
- Rebecca E Haddock
- Division of Neuroscience, John Curtin School of Medical Research, GPO Box 334, Canberra, ACT, 2601, Australia.
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144
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Lee CH, Kuo KH, Dai J, van Breemen C. Asynchronous calcium waves in smooth muscle cells. Can J Physiol Pharmacol 2005; 83:733-41. [PMID: 16333375 DOI: 10.1139/y05-083] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Asynchronous Ca2+ waves or wave-like [Ca2+]i oscillations constitute a specialized form of agonist-induced Ca2+ signaling that is observed in a variety of smooth muscle cell types. Functionally, it is involved in the contractile regulation of the smooth muscle cells as it signals for tonic contraction in certain smooth muscle cells while causing relaxation in others. Mechanistically, repetitive Ca2+ waves are produced by repetitive cycles of sarcoplasmic reticulum Ca2+ release followed by Ca2+ uptake. Plasmalemmal Ca2+ entry mechanisms are important for providing the additional Ca2+ necessary to maintain proper refilling of the sarcoplasmic reticulum Ca2+ store and support ongoing Ca2+ waves. In this paper, we will review the phenomenon of asynchronous Ca2+ waves in smooth muscle and discuss the scientific and clinical significance of this new understanding.Key words: excitation-contraction coupling, confocal fluoresence microscopy, calcium signaling.
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Affiliation(s)
- Cheng-Han Lee
- The James Hogg iCAPTURE Centre for Cardiovascular and Pulmonary Research, University of British Columbia, St. Paul's Hospital, Vancouver, BC, Canada
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145
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Laporte R, Hui A, Laher I. Pharmacological modulation of sarcoplasmic reticulum function in smooth muscle. Pharmacol Rev 2005; 56:439-513. [PMID: 15602008 DOI: 10.1124/pr.56.4.1] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The sarco/endoplasmic reticulum (SR/ER) is the primary storage and release site of intracellular calcium (Ca2+) in many excitable cells. The SR is a tubular network, which in smooth muscle (SM) cells distributes close to cellular periphery (superficial SR) and in deeper aspects of the cell (deep SR). Recent attention has focused on the regulation of cell function by the superficial SR, which can act as a buffer and also as a regulator of membrane channels and transporters. Ca2+ is released from the SR via two types of ionic channels [ryanodine- and inositol 1,4,5-trisphosphate-gated], whereas accumulation from thecytoplasm occurs exclusively by an energy-dependent sarco-endoplasmic reticulum Ca2+-ATPase pump (SERCA). Within the SR, Ca2+ is bound to various storage proteins. Emerging evidence also suggests that the perinuclear portion of the SR may play an important role in nuclear transcription. In this review, we detail the pharmacology of agents that alter the functions of Ca2+ release channels and of SERCA. We describe their use and selectivity and indicate the concentrations used in investigating various SM preparations. Important aspects of cell regulation and excitation-contractile activity coupling in SM have been uncovered through the use of such activators and inhibitors of processes that determine SR function. Likewise, they were instrumental in the recent finding of an interaction of the SR with other cellular organelles such as mitochondria. Thus, an appreciation of the pharmacology and selectivity of agents that interfere with SR function in SM has greatly assisted in unveiling the multifaceted nature of the SR.
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Affiliation(s)
- Régent Laporte
- Ferring Research Institute, Inc., Ferring Pharmaceuticals, San Diego, California, USA
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146
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Sweeney M, Jones CJP, Greenwood SL, Baker PN, Taggart MJ. Ultrastructural features of smooth muscle and endothelial cells of isolated isobaric human placental and maternal arteries. Placenta 2005; 27:635-47. [PMID: 16029888 DOI: 10.1016/j.placenta.2005.05.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/04/2005] [Revised: 05/13/2005] [Accepted: 05/14/2005] [Indexed: 11/18/2022]
Abstract
The ability of a blood vessel to develop tone is dependent upon morphological parameters of the smooth muscle cells (SMC), including density, relationship with the endothelium and subcellular distribution of myofilaments and intracellular organelles. Consequently, wall ultrastructure of isolated human placental chorionic plate arteries (n=12), fixed when pressurised to mimic their in vivo geometry, was examined qualitatively using electron microscopy, and compared with maternal arteries (omental, n=10, myometrial, n=6). Arteries from women with uncomplicated pregnancy were tested for contractile viability before fixing, with some vessels post-fixed in osmium-ferricyanide for sarcoplasmic reticulum (SR) identification. In contrast to maternal arteries, placental arteries had no internal elastic lamina but exhibited considerable extracellular matrix separating circularly orientated SMC. Human SMC contained tightly packed arrays of myofilaments running parallel to the plasma membrane, enveloping cellular organelles. Synthetic SMC, with few myofilaments and much rough SR, were observed in placental arteries only. SR in SMC from maternal arteries was located centrally, often encircling mitochondria, and also near the plasma membrane associated with caveolae. Positive SR staining was rarely observed in SMC of placental arteries. This study highlights ultrastructural differences between placental and maternal arteries that may underlie specialised mechanisms of regulating vascular tone in the placenta.
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MESH Headings
- Adult
- Chorion/blood supply
- Chorion/physiology
- Electromyography/methods
- Endothelium, Vascular/physiology
- Endothelium, Vascular/ultrastructure
- Female
- Humans
- Microscopy, Electron, Transmission
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/physiology
- Muscle, Smooth, Vascular/ultrastructure
- Myometrium/blood supply
- Myometrium/physiology
- Omentum/blood supply
- Omentum/physiology
- Placental Circulation/drug effects
- Placental Circulation/physiology
- Pregnancy
- Pressure
- Sarcoplasmic Reticulum/ultrastructure
- Umbilical Arteries/physiology
- Umbilical Arteries/ultrastructure
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Affiliation(s)
- M Sweeney
- Maternal and Fetal Health Research Centre, Division of Human Development, University of Manchester, 1st Floor St. Mary's Hospital, Whitworth Park, Manchester M13 0JH, UK.
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147
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Matchkov VV, Aalkjaer C, Nilsson H. Distribution of cGMP-dependent and cGMP-independent Ca(2+)-activated Cl(-) conductances in smooth muscle cells from different vascular beds and colon. Pflugers Arch 2005; 451:371-9. [PMID: 16075241 DOI: 10.1007/s00424-005-1472-9] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2005] [Accepted: 05/13/2005] [Indexed: 12/22/2022]
Abstract
In the present patch-clamp study we have, for the first time, shown the tissue distribution of a recently characterized cGMP-dependent Ca(2+)-activated Cl(-) conductance [18] in smooth muscle cells freshly isolated from different regions: aorta, pulmonary artery, tail artery, femoral artery, femoral vein, middle cerebral artery, renal artery, portal vein, superior mesenteric artery, mesenteric small artery and colon. The cGMP-dependent Cl(-) conductance has properties distinct from those of the 'classical' Ca(2+)-activated Cl(-) conductances; their different sensitivities to niflumic acid and zinc were here utilized to distinguish them. They were found to be co-expressed in different patterns in smooth muscle cells of different origins. The cGMP-dependent conductance was greater in myocytes from cerebral artery and femoral vein and was greater in the renal artery, aorta, mesenteric small artery, femoral artery and the superior mesenteric artery. The presence of the cGMP-dependent Ca(2+)-activated Cl(-) current in smooth muscle cells isolated from the colon demonstrates that this conductance is not limited to the vasculature. The 'classical' Ca(2+)-activated Cl(-) conductance was strongly expressed in smooth muscle cells from the portal vein and the tail artery, and noticeably higher in the pulmonary artery.
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Affiliation(s)
- Vladimir V Matchkov
- The Water and Salt Research Center, Institute of Physiology and Biophysics, Department of Physiology, University of Aarhus, Building 160, Universitetsparken, 8000 Aarhus, Denmark.
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148
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Rahman A, Matchkov V, Nilsson H, Aalkjaer C. Effects of cGMP on coordination of vascular smooth muscle cells of rat mesenteric small arteries. J Vasc Res 2005; 42:301-11. [PMID: 15925896 DOI: 10.1159/000086002] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2004] [Accepted: 03/04/2005] [Indexed: 11/19/2022] Open
Abstract
OBJECTIVE We tested the hypothesis that cGMP can induce a state of only partial coordination of vascular smooth muscle cells (VSMC). METHODS This was done by studying the concentration-dependent effect of 8Br-cGMP on isometric and isobaric force development of noradrenaline-activated segments of rat mesenteric small arteries in which the endothelium was removed. We further measured the concentration-dependent effect of 8Br-cGMP on VSMC membrane potential, spatially resolved [Ca(2+)](i) and VSMC membrane conductance. RESULTS With 300 microM 8Br-cGMP, coordinated [Ca(2+)](i) activity and vasomotion were seen as previously reported. At 10-30 microM 8Br-cGMP, beating isometric tension oscillations were seen. Isobaric recordings revealed oscillations with different frequencies in different parts of the arteries. At these (10-30 microM) 8Br-cGMP concentrations, membrane potential oscillations did not always concur with isometric tension oscillations, and [Ca(2+)](i) oscillations were only synchronized locally within groups of cells. 8Br-cGMP concentration-dependently decreased the frequency of vasomotion and, in unsynchronized hyperpolarized VSMC, the frequency of [Ca(2+)](i) waves. CONCLUSION Our results demonstrated that cGMP can cause a partial coordination of the VSMC in the vascular wall (and at high concentrations near complete coordination). Furthermore, the cGMP concentration-dependent decrease of Ca(2+) wave frequency and of vasomotion frequency suggests that cGMP modifies oscillatory Ca(2+) release from the sarcoplasmic reticulum and supports the suggestion that this oscillatory release paces vasomotion.
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MESH Headings
- Animals
- Calcium/metabolism
- Cyclic GMP/analogs & derivatives
- Cyclic GMP/pharmacology
- Dose-Response Relationship, Drug
- Male
- Membrane Potentials/drug effects
- Mesenteric Arteries/cytology
- Mesenteric Arteries/drug effects
- Mesenteric Arteries/physiology
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/physiology
- Myocytes, Smooth Muscle/drug effects
- Myocytes, Smooth Muscle/physiology
- Rats
- Rats, Wistar
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Affiliation(s)
- Awahan Rahman
- The Water and Salt Center, Institute of Physiology and Biophysics, University of Aarhus, Denmark
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149
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Borovik A, Golubinskaya V, Tarasova O, Aalkjaer C, Nilsson H. Phase Resetting of Arterial Vasomotion by Burst Stimulation of Perivascular Nerves. J Vasc Res 2005; 42:165-73. [PMID: 15767763 DOI: 10.1159/000084405] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2004] [Accepted: 12/29/2004] [Indexed: 11/19/2022] Open
Abstract
Arteries display cyclic diameter variations, vasomotion. In vivo, these rhythmic contractions are modulated by the influence of sympathetic nerves. In this study, we investigated the effect of burst stimulation of intramural nerves in vitro on the vasomotion of rat mesenteric small arteries. Vessels were mounted for isometric force measurement. After initiation of vasomotion with noradrenaline (0.5-2 microM), periarterial sympathetic nerves were stimulated electrically (10 impulses at 20 Hz) at approximately half-minute intervals. With a delay of 2-3 s, a neurogenic burst caused a brief contraction of the vascular smooth muscle and altered the period of the current vasomotion cycle. The effect on amplitude decayed rapidly and was practically not apparent in the next vasomotion cycle after the burst. With respect to period, stimulation at increasing intervals from the trough in force of vasomotion caused gradual prolongation of the cycle until a critical interval was reached, after which cycle duration was reduced instead. Since subsequent cycles were not affected, a change in phase remained. When two segments of oscillating arteries were mounted in a two-vessel myograph, simultaneously applied bursts of impulses synchronized their oscillation. The data suggest that changes in neural activity are able to make different vessels oscillate in phase, thereby coordinating vasomotion in different parts of the vascular tree, possibly explaining the synchronicity of vasomotion in different vascular beds that can be observed in vivo.
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Affiliation(s)
- Anatoly Borovik
- Laboratory of Biocybernetics, A.V. Vishnevsky Surgery Institute, M.V. Lomonosov Moscow State University, Moscow, Russia
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150
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Abstract
Four connexin (Cx) molecules, namely Cx37, Cx40, Cx43 and Cx45, are expressed in the gap junctions that exist within and between the cellular layers of arteries. Endothelial cells are well coupled by large gap junctions expressing Cx37, Cx40 and, to a lesser extent, Cx43, whose expression may be more subject to regulation by physical factors. Smooth muscle cells are more heterogeneously coupled by gap junctions that are small and rare. The identity of the Cx expressed in the media may vary among different arteries. Myoendothelial gap junctions are small and more common in resistance arteries with fewer layers of smooth muscle cells. Given the small size of these gap junctions and the rapid turnover rate of Cxs, homocellular coupling in the media and heterocellular coupling between the cell layers may be subject to more dynamic control than coupling in the endothelium. Vascular gap junctions have been implicated in a number of vasomotor responses that may regulate vascular tone and blood pressure. These include the mechanism of action of the vasodilator, endothelium-derived hyperpolarizing factor (EDHF), the myogenic constriction to intramural pressure increase, the spontaneous or agonist-induced vasomotion of arteries and arterioles and the spreading vasodilation and constriction observed in microcirculatory networks. Few data are available on Cx expression in the media of resistance arteries during hypertension. Changes in the expression of Cx43 described in the media of the aorta of hypertensive rats vary with the hypertensive model studied and are likely to represent adaptations to structural changes in the vascular wall. In contrast, in the endothelium of the caudal and mesenteric arteries of spontaneously hypertensive rats, expression of Cxs is significantly decreased compared with arteries from normotensive rats and this decrease is reversed by inhibitors of the renin-angiotensin system. During hypertension, the activity of EDHF is decreased in the mesenteric artery, but this occurs much later than the initial increase in blood pressure and the decrease in endothelial Cxs, suggesting that changes in EDHF may not be causally related to hypertension or to the changes in endothelial Cxs. Upregulation of the myogenic response and the incidence of vasomotion has been reported in hypertension. Little is currently known of the effects of hypertension on spreading vasomotor responses. Deletion of specific Cxs in genetically modified mice is complicated by neonatal lethality or coordinate regulation and compensatory changes in the remaining Cxs. Nevertheless, mice in which Cx40 has been deleted are hypertensive and spreading vasodilatory responses are significantly impaired. Determination of a role for specific Cxs in the control of blood pressure must await the development of animals in which Cx expression can be modulated in a more complex temporal and tissue-specific manner.
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Affiliation(s)
- Nicole M Rummery
- John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory, Australia
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