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Solár P, Zamani A, Lakatosová K, Joukal M. The blood-brain barrier and the neurovascular unit in subarachnoid hemorrhage: molecular events and potential treatments. Fluids Barriers CNS 2022; 19:29. [PMID: 35410231 PMCID: PMC8996682 DOI: 10.1186/s12987-022-00312-4] [Citation(s) in RCA: 41] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Accepted: 01/24/2022] [Indexed: 12/12/2022] Open
Abstract
The response of the blood-brain barrier (BBB) following a stroke, including subarachnoid hemorrhage (SAH), has been studied extensively. The main components of this reaction are endothelial cells, pericytes, and astrocytes that affect microglia, neurons, and vascular smooth muscle cells. SAH induces alterations in individual BBB cells, leading to brain homeostasis disruption. Recent experiments have uncovered many pathophysiological cascades affecting the BBB following SAH. Targeting some of these pathways is important for restoring brain function following SAH. BBB injury occurs immediately after SAH and has long-lasting consequences, but most changes in the pathophysiological cascades occur in the first few days following SAH. These changes determine the development of early brain injury as well as delayed cerebral ischemia. SAH-induced neuroprotection also plays an important role and weakens the negative impact of SAH. Supporting some of these beneficial cascades while attenuating the major pathophysiological pathways might be decisive in inhibiting the negative impact of bleeding in the subarachnoid space. In this review, we attempt a comprehensive overview of the current knowledge on the molecular and cellular changes in the BBB following SAH and their possible modulation by various drugs and substances.
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Affiliation(s)
- Peter Solár
- Department of Anatomy, Cellular and Molecular Neurobiology Research Group, Faculty of Medicine, Masaryk University, 625 00, Brno, Czech Republic
- Department of Neurosurgery, Faculty of Medicine, Masaryk University and St. Anne's University Hospital Brno, Pekařská 53, 656 91, Brno, Czech Republic
| | - Alemeh Zamani
- Department of Anatomy, Cellular and Molecular Neurobiology Research Group, Faculty of Medicine, Masaryk University, 625 00, Brno, Czech Republic
| | - Klaudia Lakatosová
- Department of Anatomy, Cellular and Molecular Neurobiology Research Group, Faculty of Medicine, Masaryk University, 625 00, Brno, Czech Republic
| | - Marek Joukal
- Department of Anatomy, Cellular and Molecular Neurobiology Research Group, Faculty of Medicine, Masaryk University, 625 00, Brno, Czech Republic.
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Activating BK channels ameliorates vascular smooth muscle calcification through Akt signaling. Acta Pharmacol Sin 2022; 43:624-633. [PMID: 34163023 PMCID: PMC8888620 DOI: 10.1038/s41401-021-00704-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Accepted: 05/23/2021] [Indexed: 02/06/2023] Open
Abstract
Vascular calcification (VC) is characterized by pathological depositions of calcium and phosphate in the arteries and veins via an active cell-regulated process, in which vascular smooth muscle cells (VSMCs) transform into osteoblast/chondrocyte-like cells as in bone formation. VC is associated with significant morbidity and mortality in chronic kidney disease (CKD) and cardiovascular disease, but the underlying mechanisms remain unclear. In this study we investigated the role of large-conductance calcium-activated potassium (BK) channels in 3 experimental VC models. VC was induced in vascular smooth muscle cells (VSMCs) by β-glycerophosphate (β-GP), or in rats by subtotal nephrectomy, or in mice by high-dosage vitamin D3. We showed that the expression of BK channels in the artery of CKD rats with VC and in β-GP-treated VSMCs was significantly decreased, which was functionally confirmed by patch-clamp recording. In β-GP-treated VSMCs, BK channel opener NS1619 (20 μM) significantly alleviated VC by decreasing calcium content and alkaline phosphatase activity. Furthermore, NS1619 decreased mRNA expression of ostoegenic genes OCN and OPN, as well as Runx2 (a key transcription factor involved in preosteoblast to osteoblast differentiation), and increased the expression of α-SMA protein, whereas BK channel inhibitor paxilline (10 μM) caused the opposite effects. In primary cultured VSMCs from BK-/- mice, BK deficiency aggravated calcification as did BK channel inhibitor in normal VSMCs. Moreover, calcification was more severe in thoracic aorta rings of BK-/- mice than in those of wild-type littermates. Administration of BK channel activator BMS191011 (10 mg· kg-1 ·d-1) in high-dosage vitamin D3-treated mice significantly ameliorated calcification. Finally, co-treatment with Akt inhibitor MK2206 (1 μM) or FoxO1 inhibitor AS1842856 (3 μM) in calcified VSMCs abrogated the effects of BK channel opener NS1619. Taken together, activation of BK channels ameliorates VC via Akt/FoxO1 signaling pathways. Strategies to activate BK channels and/or enhance BK channel expression may offer therapeutic avenues to control VC.
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Lidington D, Wan H, Bolz SS. Cerebral Autoregulation in Subarachnoid Hemorrhage. Front Neurol 2021; 12:688362. [PMID: 34367053 PMCID: PMC8342764 DOI: 10.3389/fneur.2021.688362] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Accepted: 06/25/2021] [Indexed: 12/28/2022] Open
Abstract
Subarachnoid hemorrhage (SAH) is a devastating stroke subtype with a high rate of mortality and morbidity. The poor clinical outcome can be attributed to the biphasic course of the disease: even if the patient survives the initial bleeding emergency, delayed cerebral ischemia (DCI) frequently follows within 2 weeks time and levies additional serious brain injury. Current therapeutic interventions do not specifically target the microvascular dysfunction underlying the ischemic event and as a consequence, provide only modest improvement in clinical outcome. SAH perturbs an extensive number of microvascular processes, including the “automated” control of cerebral perfusion, termed “cerebral autoregulation.” Recent evidence suggests that disrupted cerebral autoregulation is an important aspect of SAH-induced brain injury. This review presents the key clinical aspects of cerebral autoregulation and its disruption in SAH: it provides a mechanistic overview of cerebral autoregulation, describes current clinical methods for measuring autoregulation in SAH patients and reviews current and emerging therapeutic options for SAH patients. Recent advancements should fuel optimism that microvascular dysfunction and cerebral autoregulation can be rectified in SAH patients.
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Affiliation(s)
- Darcy Lidington
- Department of Physiology, University of Toronto, Toronto, ON, Canada.,Toronto Centre for Microvascular Medicine at the Ted Rogers Centre for Heart Research Translational Biology and Engineering Program, University of Toronto, Toronto, ON, Canada
| | - Hoyee Wan
- Department of Physiology, University of Toronto, Toronto, ON, Canada.,Toronto Centre for Microvascular Medicine at the Ted Rogers Centre for Heart Research Translational Biology and Engineering Program, University of Toronto, Toronto, ON, Canada
| | - Steffen-Sebastian Bolz
- Department of Physiology, University of Toronto, Toronto, ON, Canada.,Toronto Centre for Microvascular Medicine at the Ted Rogers Centre for Heart Research Translational Biology and Engineering Program, University of Toronto, Toronto, ON, Canada.,Heart & Stroke/Richard Lewar Centre of Excellence for Cardiovascular Research, University of Toronto, Toronto, ON, Canada
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4
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Shi X, Zhen L, Ding H, Chen J, Zhang S, Fu Y. Role of ATP-sensitive potassium channels and inflammatory response of basilar artery smooth muscle cells in subarachnoid hemorrhage of rabbit and immune-modulation by shikonin. Food Chem Toxicol 2019; 134:110804. [PMID: 31505234 DOI: 10.1016/j.fct.2019.110804] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2019] [Revised: 08/17/2019] [Accepted: 09/04/2019] [Indexed: 02/02/2023]
Abstract
OBJECTIVE To investigate the role of inflammatory response, oxidative damage and changes of ATP-sensitive potassium channels (sKATP) in basilar artery (BA) smooth muscle cells (SMCS) of rabbits in subarachnoid hemorrhage (SAH) model. METHODS Time course studies on inflammatory response by real-time PCR, oxidative process and function of isolated basilar artery after SAH in New Zealand White rabbits were performed. Basilar artery smooth muscle cells (BASMCs) in each group were obtained and whole-cell patch-clamp technique was applied to record cell membrane capacitance and KATP currents. The morphologies of basal arteries were analyzed. Protective effect of shikonin were also determine by same parameters. RESULTS Inflammatory cytokines levels were highest at 24h compare to 72h after SAH whereas the oxidative damage and cell death marker were at highest peak at 72h. Oxidative damage peak coincided with significant alterations in cell membrane capacitance, KATP currents and morphological changes in basilar arteries. Shikokin pretreatment attenuated early inflammatory response at 24h and associated oxidative damage at 72h. Finally, shikonin attenuated morphological changes in basilar arteries and dysfunction. CONCLUSION Currents of ATP-sensitive potassium channels in basilar smooth muscle cells decreased after SAH by putative oxidative modification from immediate inflammatory response and can be protected by shikonin pretreatment.
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Affiliation(s)
- Xianqing Shi
- Intensive Care Unit, Guizhou Provincial People's Hospital, Guiyang, Guizhou Province, 550002, China.
| | - Lirong Zhen
- Intensive Care Unit, Guizhou Provincial People's Hospital, Guiyang, Guizhou Province, 550002, China
| | - Hao Ding
- Intensive Care Unit, Guizhou Provincial Orthopedics Hospital, Guiyang, Guizhou Province, 550007, China
| | - Jing Chen
- Intensive Care Unit, Guizhou Provincial People's Hospital, Guiyang, Guizhou Province, 550002, China
| | - Songsong Zhang
- Intensive Care Unit, Guizhou Provincial People's Hospital, Guiyang, Guizhou Province, 550002, China
| | - Yongjian Fu
- Intensive Care Unit, Guizhou Provincial People's Hospital, Guiyang, Guizhou Province, 550002, China
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5
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Jackson WF. K V channels and the regulation of vascular smooth muscle tone. Microcirculation 2018; 25. [PMID: 28985443 DOI: 10.1111/micc.12421] [Citation(s) in RCA: 89] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Accepted: 10/01/2017] [Indexed: 12/31/2022]
Abstract
VSMCs in resistance arteries and arterioles express a diverse array of KV channels with members of the KV 1, KV 2 and KV 7 families being particularly important. Members of the KV channel family: (i) are highly expressed in VSMCs; (ii) are active at the resting membrane potential of VSMCs in vivo (-45 to -30 mV); (iii) contribute to the negative feedback regulation of VSMC membrane potential and myogenic tone; (iv) are activated by cAMP-related vasodilators, hydrogen sulfide and hydrogen peroxide; (v) are inhibited by increases in intracellular Ca2+ and vasoconstrictors that signal through Gq -coupled receptors; (vi) are involved in the proliferative phenotype of VSMCs; and (vii) are modulated by diseases such as hypertension, obesity, the metabolic syndrome and diabetes. Thus, KV channels participate in every aspect of the regulation of VSMC function in both health and disease.
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Affiliation(s)
- William F Jackson
- Department of Pharmacology & Toxicology, Michigan State University, East Lansing, MI, USA
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Lidington D, Kroetsch JT, Bolz SS. Cerebral artery myogenic reactivity: The next frontier in developing effective interventions for subarachnoid hemorrhage. J Cereb Blood Flow Metab 2018; 38:17-37. [PMID: 29135346 PMCID: PMC5757446 DOI: 10.1177/0271678x17742548] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Aneurysmal subarachnoid hemorrhage (SAH) is a devastating cerebral event that kills or debilitates the majority of those afflicted. The blood that spills into the subarachnoid space stimulates profound cerebral artery vasoconstriction and consequently, cerebral ischemia. Thus, once the initial bleeding in SAH is appropriately managed, the clinical focus shifts to maintaining/improving cerebral perfusion. However, current therapeutic interventions largely fail to improve clinical outcome, because they do not effectively restore normal cerebral artery function. This review discusses emerging evidence that perturbed cerebrovascular "myogenic reactivity," a crucial microvascular process that potently dictates cerebral perfusion, is the critical element underlying cerebral ischemia in SAH. In fact, the myogenic mechanism could be the reason why many therapeutic interventions, including "Triple H" therapy, fail to deliver benefit to patients. Understanding the molecular basis for myogenic reactivity changes in SAH holds the key to develop more effective therapeutic interventions; indeed, promising recent advancements fuel optimism that vascular dysfunction in SAH can be corrected to improve outcome.
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Affiliation(s)
- Darcy Lidington
- 1 Department of Physiology, University of Toronto, Toronto, Canada.,2 Toronto Centre for Microvascular Medicine at TBEP, University of Toronto, Toronto, Canada
| | - Jeffrey T Kroetsch
- 1 Department of Physiology, University of Toronto, Toronto, Canada.,2 Toronto Centre for Microvascular Medicine at TBEP, University of Toronto, Toronto, Canada
| | - Steffen-Sebastian Bolz
- 1 Department of Physiology, University of Toronto, Toronto, Canada.,2 Toronto Centre for Microvascular Medicine at TBEP, University of Toronto, Toronto, Canada.,3 Heart & Stroke/Richard Lewar Centre of Excellence for Cardiovascular Research, University of Toronto, Toronto, Canada
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7
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Porras-González C, Ordóñez A, Castellano A, Ureña J. Regulation of RhoA/ROCK and sustained arterial contraction by low cytosolic Ca 2+ levels during prolonged depolarization of arterial smooth muscle. Vascul Pharmacol 2017; 93-95:33-41. [PMID: 28526517 DOI: 10.1016/j.vph.2017.05.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2017] [Revised: 05/15/2017] [Accepted: 05/16/2017] [Indexed: 11/19/2022]
Abstract
The role of L-type Ca2+ channels (LTCCs) and RhoA/Rho kinase (ROCK) on depolarization-induced sustained arterial contraction lasting several minutes is already known. However, in vivo, vascular smooth muscle cells can be depolarized for longer periods, inducing substantial inactivation of LTCCs and markedly reducing Ca2+ influx into the myocytes. We have examined, in femoral arterial rings, the role of LTCCs and RhoA/ROCK during long-lasting depolarization. Our results reveal a new vasoreactive response after 20-30min of depolarization in 2.5mM external Ca2+ that has not been identified previously with shorter stimuli. Prolonged depolarization-induced arterial contraction was permanently abolished when arterial rings were treated with 100nM external Ca2+ or 20nM nifedipine. However, when Ca2+ influx was restricted, applying ~7μM external Ca2+ solution or 3nM nifedipine, vasorelaxation was transient, and isometric force slowly increased after 30min and maintained its level until the end of the stimulus. Under these conditions, arterial contraction showed the same temporal course of RhoA activity and was sensitive to fasudil, nifedipine and cyclopiazonic acid. Ca2+-response curve in β-escin permeabilized arteries was also sensitive to ROCK inhibitors. Thus, although long-lasting depolarization inactivates LTCCs, the reduced Ca2+ entry can induce a detectable arterial contraction via RhoA/ROCK activation.
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Affiliation(s)
- Cristina Porras-González
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío, CSIC, Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, Spain
| | - Antonio Ordóñez
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío, CSIC, Universidad de Sevilla, CIBER CV, Spain
| | - Antonio Castellano
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío, CSIC, Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, Spain.
| | - Juan Ureña
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío, CSIC, Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, Spain.
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8
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Tykocki NR, Boerman EM, Jackson WF. Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles. Compr Physiol 2017; 7:485-581. [PMID: 28333380 DOI: 10.1002/cphy.c160011] [Citation(s) in RCA: 212] [Impact Index Per Article: 30.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.
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Affiliation(s)
- Nathan R Tykocki
- Department of Pharmacology, University of Vermont, Burlington, Vermont, USA
| | - Erika M Boerman
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri, USA
| | - William F Jackson
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan, USA
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9
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Kühl T, Imhof D. Regulatory Fe(II/III) heme: the reconstruction of a molecule's biography. Chembiochem 2014; 15:2024-35. [PMID: 25196849 DOI: 10.1002/cbic.201402218] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Indexed: 11/10/2022]
Abstract
More than 20 years of research on heme as a temporary effector molecule of proteins have revealed its widespread impact on virtually all primary functions in the human organism. As our understanding of this influence is still growing, a comprehensive overview of compiled data will give fresh impetus for creativity and developing new strategies in heme-related research. From known data concerning heme-regulated proteins and their involvement in the development of diseases, we provide concise information of Fe(II/III) heme as a regulator and the availability of "regulatory heme". The latter is dependent on the balance between free and bound Fe(II/III) heme, here termed "hemeostasis". Imbalance of this system can lead to the development of diseases that were not always attributed to this small molecule. Diseases such as cancer or Alzheimer's disease highlight the reawakened interest in heme, whose function was previously believed to be completely understood.
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Affiliation(s)
- Toni Kühl
- Pharmaceutical Chemistry I, Pharmaceutical Institute, University of Bonn, Brühler Strasse 7, 53119 Bonn (Germany).
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10
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Chen S, Feng H, Sherchan P, Klebe D, Zhao G, Sun X, Zhang J, Tang J, Zhang JH. Controversies and evolving new mechanisms in subarachnoid hemorrhage. Prog Neurobiol 2014; 115:64-91. [PMID: 24076160 PMCID: PMC3961493 DOI: 10.1016/j.pneurobio.2013.09.002] [Citation(s) in RCA: 270] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Revised: 09/07/2013] [Accepted: 09/12/2013] [Indexed: 12/13/2022]
Abstract
Despite decades of study, subarachnoid hemorrhage (SAH) continues to be a serious and significant health problem in the United States and worldwide. The mechanisms contributing to brain injury after SAH remain unclear. Traditionally, most in vivo research has heavily emphasized the basic mechanisms of SAH over the pathophysiological or morphological changes of delayed cerebral vasospasm after SAH. Unfortunately, the results of clinical trials based on this premise have mostly been disappointing, implicating some other pathophysiological factors, independent of vasospasm, as contributors to poor clinical outcomes. Delayed cerebral vasospasm is no longer the only culprit. In this review, we summarize recent data from both experimental and clinical studies of SAH and discuss the vast array of physiological dysfunctions following SAH that ultimately lead to cell death. Based on the progress in neurobiological understanding of SAH, the terms "early brain injury" and "delayed brain injury" are used according to the temporal progression of SAH-induced brain injury. Additionally, a new concept of the vasculo-neuronal-glia triad model for SAH study is highlighted and presents the challenges and opportunities of this model for future SAH applications.
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Affiliation(s)
- Sheng Chen
- Department of Neurosurgery, Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, China; Department of Physiology & Pharmacology, Loma Linda University, Loma Linda, CA, USA
| | - Hua Feng
- Department of Neurosurgery, Southwest Hospital, Third Military Medical University, Chongqing, China
| | - Prativa Sherchan
- Department of Physiology & Pharmacology, Loma Linda University, Loma Linda, CA, USA
| | - Damon Klebe
- Department of Physiology & Pharmacology, Loma Linda University, Loma Linda, CA, USA
| | - Gang Zhao
- Department of Neurology, Xijing Hospital, Fourth Military Medical University, Xi'an, Shanxi, China
| | - Xiaochuan Sun
- Department of Neurosurgery, First Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - Jianmin Zhang
- Department of Neurosurgery, Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, China
| | - Jiping Tang
- Department of Physiology & Pharmacology, Loma Linda University, Loma Linda, CA, USA
| | - John H Zhang
- Department of Physiology & Pharmacology, Loma Linda University, Loma Linda, CA, USA; Department of Neurosurgery, Loma Linda University, Loma Linda, CA, USA.
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11
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Shimamura N, Ohkuma H. Phenotypic transformation of smooth muscle in vasospasm after aneurysmal subarachnoid hemorrhage. Transl Stroke Res 2013; 5:357-64. [PMID: 24323729 DOI: 10.1007/s12975-013-0310-1] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2013] [Revised: 10/24/2013] [Accepted: 11/07/2013] [Indexed: 12/14/2022]
Abstract
Differentiated smooth muscle cells (SMC) control vasoconstriction and vasodilation, but they can undergo transformation, proliferate, secret cytokines, and migrate into the subendotherial layer with adverse consequences. In this review, we discuss the phenotypic transformation of SMC in cerebral vasospasm after subarachnoid hemorrhage. Phenotypic transformation starts with an insult as caused by aneurysm rupture: Elevation of intracranial and blood pressure, secretion of norepinephrine, and mechanical force on an artery are factors that can cause aneurysm. The phenotypic transformation of SMC is accelerated by inflammation, thrombin, and growth factors. A wide variety of cytokines (e.g., interleukin (IL)-1β, IL-33, matrix metalloproteinases, nitric oxidase synthases, endothelins, thromboxane A2, mitogen-activated protein kinase, platelet-derived vascular growth factors, and vascular endothelial factor) all play roles in cerebral vasospasm (CVS). We summarize the correlations between various factors and the phenotypic transformation of SMC. A new target of this study is the transient receptor potential channel in CVS. Statin together with fasdil prevents phenotypic transformation of SMC in an animal model. Clazosentan prevents CVS and improves outcome in aneurysmal subarachnoid hemorrhage in a dose-dependent manner. Clinical trials of cilostazol for the prevention of phenotypic transformation of SMC have been reported, along with requisite experimental evidence. To conquer CVS in its complexity, we will ultimately need to elucidate its general, underlying mechanism.
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Affiliation(s)
- Norihito Shimamura
- Department of Neurosurgery, Hirosaki University School of Medicine, 5-Zaihuchou, Hirosaki, Aomori Prefecture, 036-8562, Japan,
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12
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Yeung PKK, Shen J, Chung SSM, Chung SK. Targeted over-expression of endothelin-1 in astrocytes leads to more severe brain damage and vasospasm after subarachnoid hemorrhage. BMC Neurosci 2013; 14:131. [PMID: 24156724 PMCID: PMC3815232 DOI: 10.1186/1471-2202-14-131] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2013] [Accepted: 10/15/2013] [Indexed: 01/15/2023] Open
Abstract
Background Endothelin-1 (ET-1) is a potent vasoconstrictor, and astrocytic ET-1 is reported to play a role in the pathogenesis of cerebral ischemic injury and cytotoxic edema. However, it is still unknown whether astrocytic ET-1 also contributes to vasogenic edema and vasospasm during subarachnoid hemorrhage (SAH). In the present study, transgenic mice with astrocytic endothelin-1 over-expression (GET-1 mice) were used to investigate the pathophysiological role of ET-1 in SAH pathogenesis. Results The GET-1 mice experienced a higher mortality rate and significantly more severe neurological deficits, blood–brain barrier breakdown and vasogenic edema compared to the non-transgenic (Ntg) mice following SAH. Oral administration of vasopressin V1a receptor antagonist, SR 49059, significantly reduced the cerebral water content in the GET-1 mice. Furthermore, the GET-1 mice showed significantly more pronounced middle cerebral arterial (MCA) constriction after SAH. Immunocytochemical analysis showed that the calcium-activated potassium channels and the phospho-eNOS were significantly downregulated, whereas PKC-α expression was significantly upregulated in the MCA of the GET-1 mice when compared to Ntg mice after SAH. Administration of ABT-627 (ETA receptor antagonist) significantly down-regulated PKC-α expression in the MCA of the GET-1 mice following SAH. Conclusions The present study suggests that astrocytic ET-1 involves in SAH-induced cerebral injury, edema and vasospasm, through ETA receptor and PKC-mediated potassium channel dysfunction. Administration of ABT-627 (ETA receptor antagonist) and SR 49059 (vasopressin V1a receptor antagonist) resulted in amelioration of edema and vasospasm in mice following SAH. These data provide a strong rationale to investigate SR 49059 and ABT-627 as therapeutic drugs for the treatment of SAH patients.
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Affiliation(s)
| | | | | | - Sookja K Chung
- Department of Anatomy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China.
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13
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Influence of Experimental Subarachnoid Hemorrhage on Nicotine-induced Contraction of the Rat Basilar Artery in Relation to Nicotinic Acetylcholine Receptors, Calcium, and Potassium Channels. J Stroke Cerebrovasc Dis 2013; 22:371-7. [DOI: 10.1016/j.jstrokecerebrovasdis.2011.09.020] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2011] [Revised: 09/01/2011] [Accepted: 09/27/2011] [Indexed: 11/23/2022] Open
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14
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Kamp MA, Dibué M, Schneider T, Steiger HJ, Hänggi D. Calcium and potassium channels in experimental subarachnoid hemorrhage and transient global ischemia. Stroke Res Treat 2012; 2012:382146. [PMID: 23251831 PMCID: PMC3518967 DOI: 10.1155/2012/382146] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2012] [Accepted: 10/27/2012] [Indexed: 11/23/2022] Open
Abstract
Healthy cerebrovascular myocytes express members of several different ion channel families which regulate resting membrane potential, vascular diameter, and vascular tone and are involved in cerebral autoregulation. In animal models, in response to subarachnoid blood, a dynamic transition of ion channel expression and function is initiated, with acute and long-term effects differing from each other. Initial hypoperfusion after exposure of cerebral vessels to oxyhemoglobin correlates with a suppression of voltage-gated potassium channel activity, whereas delayed cerebral vasospasm involves changes in other potassium channel and voltage-gated calcium channels expression and function. Furthermore, expression patterns and function of ion channels appear to differ between main and small peripheral vessels, which may be key in understanding mechanisms behind subarachnoid hemorrhage-induced vasospasm. Here, changes in calcium and potassium channel expression and function in animal models of subarachnoid hemorrhage and transient global ischemia are systematically reviewed and their clinical significance discussed.
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Affiliation(s)
- Marcel A. Kamp
- Department for Neurosurgery, Medical Faculty, Heinrich Heine University, Moorenstraße 5, 40225 Düsseldorf, Germany
- Institute for Neurophysiology, University of Cologne, Robert-Koch-Straße 39, 50931 Cologne, Germany
| | - Maxine Dibué
- Department for Neurosurgery, Medical Faculty, Heinrich Heine University, Moorenstraße 5, 40225 Düsseldorf, Germany
- Institute for Neurophysiology, University of Cologne, Robert-Koch-Straße 39, 50931 Cologne, Germany
- Center of Molecular Medicine, Cologne, Germany
| | - Toni Schneider
- Institute for Neurophysiology, University of Cologne, Robert-Koch-Straße 39, 50931 Cologne, Germany
- Center of Molecular Medicine, Cologne, Germany
| | - Hans-Jakob Steiger
- Department for Neurosurgery, Medical Faculty, Heinrich Heine University, Moorenstraße 5, 40225 Düsseldorf, Germany
| | - Daniel Hänggi
- Department for Neurosurgery, Medical Faculty, Heinrich Heine University, Moorenstraße 5, 40225 Düsseldorf, Germany
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15
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Hu XQ, Zhang L. Function and regulation of large conductance Ca(2+)-activated K+ channel in vascular smooth muscle cells. Drug Discov Today 2012; 17:974-87. [PMID: 22521666 PMCID: PMC3414640 DOI: 10.1016/j.drudis.2012.04.002] [Citation(s) in RCA: 77] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Revised: 03/06/2012] [Accepted: 04/05/2012] [Indexed: 12/23/2022]
Abstract
Large conductance Ca(2+)-activated K(+) (BK(Ca)) channels are abundantly expressed in vascular smooth muscle cells. Activation of BK(Ca) channels leads to hyperpolarization of cell membrane, which in turn counteracts vasoconstriction. Therefore, BK(Ca) channels have an important role in regulation of vascular tone and blood pressure. The activity of BK(Ca) channels is subject to modulation by various factors. Furthermore, the function of BK(Ca) channels are altered in both physiological and pathophysiological conditions, such as pregnancy, hypertension and diabetes, which has dramatic impacts on vascular tone and hemodynamics. Consequently, compounds and genetic manipulation that alter activity and expression of the channel might be of therapeutic interest.
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Affiliation(s)
- Xiang-Qun Hu
- Center for Perinatal Biology, Division of Pharmacology, Department of Basic Sciences, Loma Linda University School of Medicine, Loma Linda, CA 92350, USA.
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16
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Potassium-Channel Openers KMUP-1 and Pinacidil Prevent Subarachnoid Hemorrhage–Induced Vasospasm by Restoring the BKCa-Channel Activity. Shock 2012; 38:203-12. [DOI: 10.1097/shk.0b013e31825b2d82] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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17
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Wang F, Yin YH, Jia F, Jiang JY. Antagonism of R-type calcium channels significantly improves cerebral blood flow after subarachnoid hemorrhage in rats. J Neurotrauma 2011; 27:1723-32. [PMID: 20568961 DOI: 10.1089/neu.2010.1276] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The effects of R-type calcium channels on cerebral blood flow (CBF) and vasospasm pathways following subarachnoid hemorrhage (SAH) have not been well studied. The aim of this study was to investigate the role of R-type calcium channels in vasospasm development and treatment. Sixty-five rats were randomly divided into four groups: sham (n = 14), SAH (n = 17), SAH + nimodipine (n = 17), and SAH + SNX-482 (n = 17). A prechiasmatic SAH model was constructed on day 0. Then 5 μg of nimodipine (an L-type calcium channel antagonist) or 0.1 μg of SNX-482 (an R-type calcium channel antagonist) was infused intracisternally on days 1 and 2. On day 3, neurological status was evaluated and CBF was determined using fluorescent microspheres. The extent of myosin light chain-2 (MLC2) phosphorylation was determined by urea-glycerol polyacrylamide gel electrophoresis, followed by immunoblotting. The relative presence of R-type calcium channels and calponin was determined by SDS polyacrylamide gel electrophoresis, followed by immunoblotting. Numbers of R-type calcium channels increased following SAH, and neurological deficit, CBF reduction, and enhancement of MLC2 phosphorylation as well as calponin degradation were all found to be present. There were no statistically significant differences in neurological scores among the SAH, SAH + nimodipine, and SAH + SNX-482 groups. Nimodipine had no significant effect on CBF reduction compared to the SAH group (p > 0.008), whereas SNX-482 significantly inhibited CBF reduction (p < 0.008). Both MLC2 phosphorylation and calponin degradation appeared to be inhibited by SNX-482, whereas the effects of nimodipine were relatively blunted. We concluded that an R-type calcium channel antagonist may improve CBF following SAH by partially inhibiting MLC2 phosphorylation and calponin degradation, and may exceed the potential of an L-type calcium channel antagonist, which suggests a more crucial role for R-type calcium channels in the development of SAH vasospasm and its treatment.
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Affiliation(s)
- Fei Wang
- Department of Neurosurgery, Renji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
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18
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Simard JM, Schreibman D, Aldrich EF, Stallmeyer B, Le B, James RF, Beaty N. Unfractionated heparin: multitargeted therapy for delayed neurological deficits induced by subarachnoid hemorrhage. Neurocrit Care 2011; 13:439-49. [PMID: 20809188 DOI: 10.1007/s12028-010-9435-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Aneurysmal subarachnoid hemorrhage (SAH) is associated with numerous "delayed neurological deficits" (DNDs) that have been attributed to multiple pathophysiological mechanisms, including ischemia, microthrombosis, free radical damage, inflammation, and vascular remodeling. To date, effective prophylactic therapy for SAH-induced DNDs has been elusive, due perhaps to the multiplicity of mechanisms involved that render typical, single-agent therapy seemingly futile. We hypothesized that heparin, which has multiple underappreciated salutary effects, might be useful as a multitargeted prophylactic agent against SAH-induced DNDs. We performed a comprehensive review of the literature to evaluate the potential utility of heparin in targeting the multiple pathophysiological mechanisms that have been identified as contributing to SAH-induced DNDs. Our literature review revealed that unfractionated heparin can potentially antagonize essentially all of the pathophysiological mechanisms known to be activated following SAH. Heparin binds >100 proteins, including plasma proteins, proteins released from platelets, cytokines, and chemokines. Also, heparin complexes with oxyhemoglobin, blocks the activity of free radicals including reactive oxygen species, antagonizes endothelin-mediated vasoconstriction, smooth muscle depolarization, and inflammatory, growth and fibrogenic responses. Our review suggests that the use of prophylactic heparin following SAH may warrant formal study.
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Affiliation(s)
- J Marc Simard
- Department of Neurosurgery, University of Maryland School of Medicine, 22 S. Greene St., Suite S12D, Baltimore, MD 21201-1595, USA.
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19
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Bilirubin oxidation end products directly alter K+ channels important in the regulation of vascular tone. J Cereb Blood Flow Metab 2011; 31:102-12. [PMID: 20424637 PMCID: PMC2970662 DOI: 10.1038/jcbfm.2010.54] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The exact etiology of delayed cerebral vasospasm following cerebral hemorrhage is not clear, but a family of compounds termed 'bilirubin oxidation end products (BOXes)' derived from heme has been implicated. As proper regulation of vascular smooth muscle tone involves large-conductance Ca(2+)- and voltage-dependent Slo1 K(+) (BK, maxiK, K(Ca)1.1) channels, we examined whether BOXes altered functional properties of the channel. Electrophysiological measurements of Slo1 channels heterologously expressed in a human cell line and of native mouse BK channels in isolated cerebral myocytes showed that BOXes markedly diminished open probability. Biophysically, BOXes specifically stabilized the conformations of the channel with its ion conduction gate closed. The results of chemical amino-acid modifications and molecular mutagenesis together suggest that two specific lysine residues in the structural element linking the transmembrane ion-permeation domain to the carboxyl cytosolic domain of the Slo1 channel are critical in determining the sensitivity of the channel to BOXes. Inhibition of Slo1 BK channels by BOXes may contribute to the development of delayed cerebral vasospasm following brain hemorrhage.
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20
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Nikitina E, Kawashima A, Takahashi M, Zhang ZD, Shang X, Ai J, Macdonald RL. Alteration in voltage-dependent calcium channels in dog basilar artery after subarachnoid hemorrhage. J Neurosurg 2010; 113:870-80. [DOI: 10.3171/2010.2.jns091038] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Object
The L-type Ca++ channel antagonists like nimodipine have limited efficacy against vasospasm after subarachnoid hemorrhage (SAH). The authors tested the hypothesis that this is because SAH alters these channels, rendering them less responsible for contraction.
Methods
Basilar artery smooth muscle cells were isolated 4, 7, and 21 days after SAH in dogs, and Ca++ channel currents were recorded in 10-mmol/L barium. Proteins for α1 subunits of L-type Ca++ channels were measured by immunoblotting and isometric tension recordings done on rings of the basilar artery.
Results
High voltage–activated (HVA) Ca++ channel currents were significantly decreased and low voltage–activated (LVA) currents increased during vasospasm 4, 7, and 21 days after SAH (p < 0.05). Vasospasm was associated with a significant decrease in the number of cells with negligible LVA current while the number of cells in which the LVA current formed greater than 50% of the maximal current increased (p < 0.01). Window currents through LVA and HVA channels were significantly reduced. All changes correlated with the severity of vasospasm. There was an increase in protein for Cav3.1 and Cav3.3 α1 subunits that comprise T-type Ca++ channels, a decrease in L-type (Cav1.2 and Cav1.3) and an increase in R-type (Cav2.3) Ca++ channel α1 subunits. Functionally, however, isometric tension studies showed vasospastic arteries still relaxed with nimodipine.
Conclusions
Voltage-dependent Ca++ channels are altered in cerebral arteries after SAH. While decreased L-type channels may account for the lack of efficacy of nimodipine clinically, there may be other reasons such as inadequate dose, effect of nimodipine on other cellular targets, and mechanisms of vasospasm other than smooth muscle contraction mediated by activation of L-type Ca++ channels.
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Affiliation(s)
- Elena Nikitina
- 1Department of Surgery, University of Chicago Medical Center and Pritzker School of Medicine, Chicago, Illinois; and
| | - Ayako Kawashima
- 2Division of Neurosurgery, Keenan Research Centre and the Li Ka Shing Knowledge Institute of St. Michael's Hospital and Department of Surgery, University of Toronto, Ontario, Canada
| | - Masataka Takahashi
- 1Department of Surgery, University of Chicago Medical Center and Pritzker School of Medicine, Chicago, Illinois; and
| | - Zhen-Du Zhang
- 1Department of Surgery, University of Chicago Medical Center and Pritzker School of Medicine, Chicago, Illinois; and
| | - Xueyuan Shang
- 2Division of Neurosurgery, Keenan Research Centre and the Li Ka Shing Knowledge Institute of St. Michael's Hospital and Department of Surgery, University of Toronto, Ontario, Canada
| | - Jinglu Ai
- 2Division of Neurosurgery, Keenan Research Centre and the Li Ka Shing Knowledge Institute of St. Michael's Hospital and Department of Surgery, University of Toronto, Ontario, Canada
| | - R. Loch Macdonald
- 2Division of Neurosurgery, Keenan Research Centre and the Li Ka Shing Knowledge Institute of St. Michael's Hospital and Department of Surgery, University of Toronto, Ontario, Canada
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Gürses L, Seçkin H, Simşek S, Senel OO, Yigitkanli K, Oztürk E, Beşalti O, Belen D, Bavbek M. Effects of raloxifene on cerebral vasospasm after experimental Subarachnoid Hemorrhage in rabbits. ACTA ACUST UNITED AC 2009; 72:490-4; discussion 494-5. [PMID: 19147193 DOI: 10.1016/j.surneu.2008.11.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2008] [Revised: 10/14/2008] [Accepted: 11/19/2008] [Indexed: 10/21/2022]
Abstract
BACKGROUND The aim of this study was to investigate the ability of a SERM, RLX, to prevent vasospasm in a rabbit model of SAH. METHODS Thirty-four New Zealand white rabbits were allocated into 3 groups randomly. Subarachnoid hemorrhage was induced by injecting autologous blood into the cisterna magna. The treatment groups were as follows: (1) sham operated (no SAH [n = 12]), (2) SAH only (n = 12), and (3) SAH plus RLX (n = 10). Basilar artery lumen areas and arterial wall thickness were measured to assess vasospams in all groups. RESULTS There was a statistically significant difference between the mean basilar artery cross-sectional areas and the mean arterial wall thickness measurements of the control and SAH-only groups (P < .05). The difference between the mean basilar artery cross-sectional areas and the mean arterial wall thickness measurements in the RLX-treated group was statistically significant (P < .05). The difference between the SAH group and the SAH + RLX group was also statistically significant (P < .05). CONCLUSIONS These findings demonstrate that RLX has marked vasodilatatory effect in an experimental model of SAH in rabbits. This observation may have clinical implications suggesting that this SERM drug could be used as possible anti-vasospastic agent in patients without major adverse effects.
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Affiliation(s)
- Levent Gürses
- Ministry of Health, Dişkapi Educational and Research Hospital, 2nd Neurosurgery Clinic, Ankara, Turkey
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22
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Molecular studies of BKCa channels in intracranial arteries: presence and localization. Cell Tissue Res 2008; 334:359-69. [DOI: 10.1007/s00441-008-0701-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2008] [Accepted: 09/16/2008] [Indexed: 01/17/2023]
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23
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Seçkin H, Yigitkanli K, Besalti O, Kosemehmetoglu K, Ozturk E, Simsek S, Belen D, Bavbek M. Lamotrigine attenuates cerebral vasospasm after experimental subarachnoid hemorrhage in rabbits. ACTA ACUST UNITED AC 2008; 70:344-51; discussion 351. [DOI: 10.1016/j.surneu.2007.07.052] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2007] [Accepted: 07/09/2007] [Indexed: 10/22/2022]
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24
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Induction of housekeeping gene expression after subarachnoid hemorrhage in dogs. J Neurosci Methods 2008; 172:1-7. [PMID: 18490059 DOI: 10.1016/j.jneumeth.2008.03.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2008] [Revised: 03/29/2008] [Accepted: 03/30/2008] [Indexed: 11/23/2022]
Abstract
Changes in gene expression are commonly assessed relative to the expression of housekeeping genes, which are assumed to remain unchanged. We tested this assumption in cerebral arteries obtained from dogs 4 and 7 days after subarachnoid hemorrhage (SAH) had been created using the double hemorrhage model. Basilar arteries were removed and examined for expression of messenger ribonucleic acid (mRNA) levels using quantitative real-time polymerase chain reaction. Cross-sections of basilar arteries were stained immunohistochemically for proliferating cell nuclear antigen (PCNA) and 4',6-diamidino-2-phenylindole (DAPI). Positively stained cells were counted and numbers obtained were normalized to the cross-sectional area. The results were compared to normal dog basilar arteries contracted pharmacologically in vitro. SAH resulted in significant vasospasm (P<0.001 for each, paired t-tests). There were significant increases in mRNA for beta-actin (441%, P=0.01), glyceraldehyde-3-phosphate dehydrogenase (566%, P=0.007) and 18S ribosomal RNA (320%, P=0.025) 7 days after SAH. Total mRNA was increased 7 days after SAH relative to genomic DNA (157%, P=0.009). There were significant increases in the number of cells in the tunica media and adventitia of arteries after SAH and a significant decrease in the media after contraction in vitro. Cells in the tunica media and adventitia labeled with PCNA were significantly increased at both times after SAH. Transcripts for housekeeping genes are increased after SAH, making standardization to them potentially invalid. The increase is due to proliferation of cells in the adventitia and increased total mRNA in the media and adventitia.
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25
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Jahromi BS, Aihara Y, Ai J, Zhang ZD, Weyer G, Nikitina E, Yassari R, Houamed KM, Macdonald RL. Temporal profile of potassium channel dysfunction in cerebrovascular smooth muscle after experimental subarachnoid haemorrhage. Neurosci Lett 2008; 440:81-6. [PMID: 18547725 DOI: 10.1016/j.neulet.2008.05.015] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2008] [Revised: 04/26/2008] [Accepted: 05/07/2008] [Indexed: 11/15/2022]
Abstract
The pathogenesis of cerebral vasospasm after subarachnoid haemorrhage (SAH) involves sustained contraction of arterial smooth muscle cells that is maximal 6-8 days after SAH. We reported that function of voltage-gated K+ (KV) channels was significantly decreased during vasospasm 7 days after SAH in dogs. Since arterial constriction is regulated by membrane potential that in turn is determined predominately by K+ conductance, the compromised K+ channel dysfunction may cause vasospasm. Additional support for this hypothesis would be demonstration that K+ channel dysfunction is temporally coincident with vasospasm. To test this hypothesis, SAH was created using the double haemorrhage model in dogs and smooth muscle cells from the basilar artery, which develops vasospasm, were isolated 4 days (early vasospasm), 7 days (during vasospasm) and 21 days (after vasospasm) after SAH and studied using patch-clamp electrophysiology. We investigated the two main K+ channels (KV and large-conductance voltage/Ca2+-activated (KCa) channels). Electrophysiologic function of KCa channels was preserved at all times after SAH. In contrast, function of KV channels was significantly decreased at all times after SAH. The decrease in cell size and degree of KV channel dysfunction was maximal 7 days after SAH. The results suggest that KV channel dysfunction either only partially contributes to vasospasm after SAH or that compensatory mechanisms develop that lead to resolution of vasospasm before KV channels recover their function.
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Affiliation(s)
- Babak S Jahromi
- Department of Surgery, University of Chicago Medical Center and Pritzker School of Medicine, Chicago 60637, USA
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26
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Voltage-gated K+ channel dysfunction in myocytes from a dog model of subarachnoid hemorrhage. J Cereb Blood Flow Metab 2008; 28:797-811. [PMID: 17987046 DOI: 10.1038/sj.jcbfm.9600577] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Delayed cerebral vasospasm after subarachnoid hemorrhage is primarily due to sustained contraction of arterial smooth muscle cells. Its pathogenesis remains unclear. The degree of arterial constriction is regulated by membrane potential that in turn is determined predominately by K+ conductance (GK). Here, we identified the main voltage-gated K+ (Kv) channels contributing to outward delayed rectifier currents in dog basilar artery smooth muscle as Kv2 class through a combination of electrophysiological and pharmacological methods. Kv2 current density was nearly halved in vasospastic myocytes after subarachnoid hemorrhage (SAH) in dogs, and Kv2.1 and Kv2.2 were downregulated in vasospastic myocytes when examined by quantitative mRNA, Western blotting, and immunohistochemistry. Vasospastic myocytes were depolarized and had a smaller contribution of GK toward maintenance of their membrane potential. Pharmacological block of Kv current in control myocytes mimicked the depolarization observed in vasospastic arteries. The degree of membrane depolarization was found to be compatible with the amount of vasoconstriction observed after SAH. We conclude that Kv2 dysfunction after SAH contributes to the pathogenesis of delayed cerebral vasospasm. This may confer a novel target for treatment of delayed cerebral vasospasm.
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27
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Wellman GC. Ion channels and calcium signaling in cerebral arteries following subarachnoid hemorrhage. Neurol Res 2007; 28:690-702. [PMID: 17164032 DOI: 10.1179/016164106x151972] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
Entry of Ca(2+) through voltage-dependent calcium channels (VDCCs) is critical to the regulation of intracellular free calcium concentration ([Ca(2+)](i)) in vascular smooth muscle and thus the control of cerebral artery diameter. Increased VDCC activity in cerebral artery myocytes may contribute to decreased cerebral blood flow and the accompanying neurological deficits associated with subarachnoid hemorrhage (SAH). This review will focus on the impact of SAH on VDCCs and K(+)-selective ion channels, two important classes of ion channels located in the plasma membrane of cerebral artery myocytes. SAH may act through a variety of direct and indirect mechanisms to increase the activity of VDCCs promoting cerebral artery constriction and reduced cerebral blood flow. Further, SAH may lead to suppression of K(+) channel activity to cause membrane potential depolarization to enhance VDCC activity. The ability of VDCC blockers or K(+) channel activators to alleviate SAH-induced vasospasm will also be examined.
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Affiliation(s)
- George C Wellman
- Department of Pharmacology, University of Vermont College of Medicine, Burlington, VT 05405-0068, USA.
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28
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Young JB, Jahromi BS, Zhang ZD, Macdonald RL. A novel device for in vitro isometric tension recordings of cylindrical artery segments. Med Eng Phys 2007; 29:169-74. [PMID: 16529973 DOI: 10.1016/j.medengphy.2006.02.003] [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: 08/22/2005] [Revised: 01/29/2006] [Accepted: 02/01/2006] [Indexed: 10/24/2022]
Abstract
There are few instruments specifically designed to measure circumferential force generated by ring segments of arteries in vitro. Typical limitations of some existing machines include poor isometry, large organ bath volume or difficult sample mounting. The authors designed, built and tested a device for isometric tension recording of force developed by rings of arteries in vitro. It is suitable for assessment of arteries from 0.3 to 3 mm in diameter and allows measurements of forces in the range 0-20 g on eight rings simultaneously. The organ baths are independently regulated in temperature, stirred, disposable and have a minimum useable volume of only 1.2 mL.
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Affiliation(s)
- Joseph B Young
- Section of Neurosurgery, MC3026, Department of Surgery, University of Chicago Medical Center and Pritzker School of Medicine, 5841 South Maryland Avenue, Chicago, IL 60637, USA
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29
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Ishiguro M, Morielli AD, Zvarova K, Tranmer BI, Penar PL, Wellman GC. Oxyhemoglobin-induced suppression of voltage-dependent K+ channels in cerebral arteries by enhanced tyrosine kinase activity. Circ Res 2006; 99:1252-60. [PMID: 17068294 DOI: 10.1161/01.res.0000250821.32324.e1] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Cerebral vasospasm following aneurysmal subarachnoid hemorrhage (SAH) has devastating consequences. Oxyhemoglobin (oxyhb) has been implicated in SAH-induced cerebral vasospasm as it causes cerebral artery constriction and increases tyrosine kinase activity. Voltage-dependent, Ca(2+)-selective and K(+)-selective ion channels play an important role in the regulation of cerebral artery diameter and represent potential targets of oxyhb. Here we provide novel evidence that oxyhb selectively decreases 4-aminopyridine sensitive, voltage-dependent K(+) channel (K(v)) currents by approximately 30% in myocytes isolated from rabbit cerebral arteries but did not directly alter the activity of voltage-dependent Ca(2+) channels or large conductance Ca(2+)-activated (BK) channels. A combination of tyrosine kinase inhibitors (tyrphostin AG1478, tyrphostin A23, tyrphostin A25, genistein) abolished both oxyhb-induced suppression of K(v) channel currents and oxyhb-induced constriction of isolated cerebral arteries. The K(v) channel blocker 4-aminopyridine also inhibited oxyhb-induced cerebral artery constriction. The observed oxyhb-induced decrease in K(v) channel activity could represent either channel block, or a decrease in K(v) channel density on the plasma membrane. To explore whether oxyhb altered trafficking of K(v) channels to the plasma membrane, we used an antibody generated against an extracellular epitope of K(v)1.5 channels. In the presence of oxyhb, staining of K(v)1.5 on the plasma membrane surface was markedly reduced. Furthermore, oxyhb caused a loss of spatial distinction between staining with K(v)1.5 and the general anti-phosphotyrosine antibody PY-102. We propose that oxyhb-induced suppression of K(v) currents occurs via a mechanism involving enhanced tyrosine kinase activity and channel endocytosis. This novel mechanism may contribute to oxyhb-induced cerebral artery constriction following SAH.
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Affiliation(s)
- Masanori Ishiguro
- Department of Pharmacology, Division of Neurological Surgery, University of Vermont College of Medicine, Burlington 05405-0068, USA
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30
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Ostrowski RP, Colohan AR, Zhang JH. Molecular mechanisms of early brain injury after subarachnoid hemorrhage. Neurol Res 2006; 28:399-414. [PMID: 16759443 DOI: 10.1179/016164106x115008] [Citation(s) in RCA: 204] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
OBJECTIVES Increasing body of experimental and clinical data indicates that early brain injury after initial bleeding largely contributes to unfavorable outcome after subarachnoid hemorrhage (SAH). This review presents molecular mechanisms underlying brain injury at its early stages after SAH. METHODS PubMed was searched using term 'subarachnoid hemorrhage' and key words referring to molecular and cellular pathomechanisms of SAH-induced early brain injury. RESULTS The authors reviewed intracranial phenomena and molecular agents that contribute to the early development of pathological sequelae of SAH in cerebral and vascular tissues, including cerebral ischemia and its interactions with injurious blood components, blood-brain barrier disruption, brain edema and apoptosis. DISCUSSION It is believed that detailed knowledge of molecular signaling pathways after SAH will serve to improve therapeutic interventions. The most promising approach is the protection of neurovascular unit including anti-apoptosis therapy.
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31
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Kiyoshi H, Yamazaki D, Ohya S, Kitsukawa M, Muraki K, Saito SY, Ohizumi Y, Imaizumi Y. Molecular and electrophysiological characteristics of K+ conductance sensitive to acidic pH in aortic smooth muscle cells of WKY and SHR. Am J Physiol Heart Circ Physiol 2006; 291:H2723-34. [PMID: 16815980 DOI: 10.1152/ajpheart.00894.2005] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Changes in K(+) conductances and their contribution to membrane depolarization in the setting of an acidic pH environment have been studied in myocytes from aortic smooth muscle cells of spontaneously hypertensive rats (SHR) compared with those from Wistar-Kyoto (WKY) rats. The resting membrane potential (RMP) of aortic smooth muscle at extracellular pH (pH(o)) of 7.4 was significantly more depolarized in SHR than in WKY rats. Acidification to pH(o) 6.5 made this difference in RMP between SHR and WKY rats more significant by further depolarizing the SHR myocytes. Large-conductance Ca(2+)-activated K(+) (BK) currents, which were markedly suppressed by acidification, were larger in aortic myocytes of SHR than in those of WKY rats. In contrast, acid-sensitive, non-BK currents were smaller in SHR. Western blot analyses showed that expression of BK-alpha- and -beta(1) subunits in SHR aortas was upregulated and comparable with those in WKY rats, respectively. Additional electrophysiological and molecular studies showed that pH- and halothane-sensitive two-pore domain weakly inward rectifying K(+) channel (TWIK)-like acid-sensitive K(+) (TASK) channel subtypes were functionally expressed in aortas, and TASK1 expression was significantly higher in WKY than in SHR. Although the background current through TASK channels at normal pH(o) (7.4) was small and may not contribute significantly to the regulation of RMP, TASK channel activation by halothane or alkalization (pH(o) 8.0) induced significant hyperpolarization in WKY but not in SHR. In conclusion, the larger depolarization and subsequent abnormal contractions after acidification in aortic myocytes in the setting of SHR hypertension are mainly attributable to the larger contribution of BK current to the total membrane conductance than in WKY aortas.
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MESH Headings
- Animals
- Aorta/metabolism
- Aorta/pathology
- Aorta/physiopathology
- Down-Regulation/physiology
- Electrophysiology
- Halothane/pharmacology
- Hydrogen-Ion Concentration
- Hypertension/pathology
- Hypertension/physiopathology
- Male
- Membrane Potentials/genetics
- Membrane Potentials/physiology
- Muscle, Smooth, Vascular/metabolism
- Muscle, Smooth, Vascular/pathology
- Muscle, Smooth, Vascular/physiopathology
- Myocardial Contraction/physiology
- Myocytes, Cardiac/metabolism
- Myocytes, Cardiac/pathology
- Nerve Tissue Proteins
- Potassium Channels, Calcium-Activated/genetics
- Potassium Channels, Calcium-Activated/metabolism
- Potassium Channels, Tandem Pore Domain/genetics
- Potassium Channels, Tandem Pore Domain/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Rats
- Rats, Inbred SHR
- Rats, Inbred WKY
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Affiliation(s)
- Hidekazu Kiyoshi
- Dept. of Molecular & Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Mizuhoku, Nagoya 467-8603, Japan
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32
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Macdonald RL, Zhang ZD, Takahashi M, Nikitina E, Young J, Xie A, Larkin L. Calcium sensitivity of vasospastic basilar artery after experimental subarachnoid hemorrhage. Am J Physiol Heart Circ Physiol 2006; 290:H2329-36. [PMID: 16399868 DOI: 10.1152/ajpheart.00911.2005] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [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 develop vasospasm after subarachnoid hemorrhage (SAH) may have altered contractility and compliance. Whether these changes are due to alterations in the smooth muscle cells or the arterial wall extracellular matrix is unknown. This study elucidated the location of such changes and determined the calcium sensitivity of vasospastic arteries. Dogs were placed under general anesthesia and underwent creation of SAH using the double-hemorrhage model. Vasospasm was assessed by angiography performed before and 4, 7, or 21 days after SAH. Basilar arteries were excised from SAH or control dogs ( n = 8–52 arterial rings from 2–9 dogs per measurement) and studied under isometric tension in vitro before and after permeabilization of smooth muscle with α-toxin. Endothelium was removed from all arteries. Vasospastic arteries demonstrated significantly reduced contractility to KCl with a shift in the EC50toward reduced sensitivity to KCl 4 and 7 days after SAH ( P < 0.05, ANOVA). There was reduced compliance that persisted after permeabilization ( P < 0.05, ANOVA). Calcium sensitivity was decreased during vasospasm 4 and 7 days after SAH, as assessed in permeabilized arteries and in those contracted with BAY K 8644 in the presence of different concentrations of extracellular calcium ( P < 0.05, ANOVA). Depolymerization of actin with cytochalasin D abolished contractions to KCl but failed to alter arterial compliance. In conclusion, it is shown for the first time that calcium sensitivity is decreased during vasospasm after SAH in dogs, suggesting that other mechanisms are involved in maintaining the contraction. Reduced compliance seems to be due to an alteration in the arterial wall extracellullar matrix rather than the smooth muscle cells themselves because it cannot be alleviated by depolymerization of smooth muscle actin.
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Affiliation(s)
- R Loch Macdonald
- Section of Neurosurgery (MC3026), University of Chicago Medical Center, 5841 S. Maryland Avenue, Chicago, IL 60637, USA.
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33
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del Valle-Rodríguez A, Calderón E, Ruiz M, Ordoñez A, López-Barneo J, Ureña J. Metabotropic Ca(2+) channel-induced Ca(2+) release and ATP-dependent facilitation of arterial myocyte contraction. Proc Natl Acad Sci U S A 2006; 103:4316-21. [PMID: 16537528 PMCID: PMC1449690 DOI: 10.1073/pnas.0508781103] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Voltage-gated Ca(2+) channels in arterial myocytes can mediate Ca(2+) release from the sarcoplasmic reticulum and, thus, induce contraction without the need of extracellular Ca(2+) influx. This metabotropic action of Ca(2+) channels (denoted as calcium-channel-induced calcium release or CCICR) involves activation of G proteins and the phospholipase C-inositol 1,4,5-trisphosphate pathway. Here, we show a form of vascular tone regulation by extracellular ATP that depends on the modulation of CCICR. In isolated arterial myocytes, ATP produced facilitation of Ca(2+)-channel activation and, subsequently, a strong potentiation of CCICR. The facilitation of L-type channel still occurred after full blockade of purinergic receptors and inhibition of G proteins with GDPbetaS, thus suggesting that ATP directly interacts with Ca(2+) channels. The effects of ATP appear to be highly selective, because they were not mimicked by other nucleotides (ADP or UTP) or vasoactive agents, such as norepinephrine, acetylcholine, or endothelin-1. We have also shown that CCICR can trigger arterial cerebral vasoconstriction in the absence of extracellular calcium and that this phenomenon is greatly facilitated by extracellular ATP. Although, at low concentrations, ATP does not induce arterial contraction per se, this agent markedly potentiates contractility of partially depolarized or primed arteries. Hence, the metabotropic action of L-type Ca(2+) channels could have a high impact on vascular pathophysiology, because, even in the absence of Ca(2+) channel opening, it might mediate elevations of cytosolic Ca(2+) and contraction in partially depolarized vascular smooth muscle cells exposed to small concentrations of agonists.
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Affiliation(s)
| | - Eva Calderón
- Unidad de Cirugía Cardiovascular, Hospital Universitario Virgen del Rocío, Universidad de Sevilla, E-41013, Seville, Spain
| | - Myriam Ruiz
- Unidad de Cirugía Cardiovascular, Hospital Universitario Virgen del Rocío, Universidad de Sevilla, E-41013, Seville, Spain
| | - Antonio Ordoñez
- Unidad de Cirugía Cardiovascular, Hospital Universitario Virgen del Rocío, Universidad de Sevilla, E-41013, Seville, Spain
| | | | - Juan Ureña
- *Laboratorio de Investigaciones Biomédicas and
- To whom correspondence should be addressed at:
Laboratorio de Investigaciones Biomédicas, Edificio de Laboratorios, 2nd Planta, Hospital Universitario Virgen del Rocío, Avenida Manuel Siurot s/n, E-41013, Seville, Spain. E-mail:
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34
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Weyer GW, Jahromi BS, Aihara Y, Agbaje-Williams M, Nikitina E, Zhang ZD, Macdonald RL. Expression and function of inwardly rectifying potassium channels after experimental subarachnoid hemorrhage. J Cereb Blood Flow Metab 2006; 26:382-91. [PMID: 16079788 DOI: 10.1038/sj.jcbfm.9600193] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Cerebral vasospasm after subarachnoid hemorrhage (SAH) is because of smooth muscle contraction, although the mechanism of this contraction remains unresolved. Membrane potential controls the contractile state of arterial myocytes by gating voltage-sensitive calcium channels and is in turn primarily controlled by K(+) ion conductance through several classes of K(+) channels. We characterized the role of inwardly rectifying K(+) (K(IR)) channels in vasospasm. Vasospasm was created in dogs using the double-hemorrhage model of SAH. Electrophysiological, real-time quantitative reverse-transcriptase polymerase chain reaction, Western blotting, immunohistochemistry, and isometric tension techniques were used to characterize the expression and function of K(IR) channels in normal and vasospastic basilar artery 7 days after SAH. Subarachnoid hemorrhage resulted in severe vasospasm of the basilar artery (mean of 61% +/- 5% reduction in diameter). Membrane potential of pressurized vasospastic basilar arteries was significantly depolarized compared with control arteries (-46 +/- 1.4 mV versus -29.8 +/- 1.8 mV, respectively, P < 0.01). In whole-cell patch clamp of enzymatically isolated basilar artery myocytes, average K(IR) conductance was 1.6 +/- 0.5 pS/pF in control cells and 9.2 +/- 2.2 pS/pF in SAH cells (P = 0.007). Blocking K(IR) channels with BaCl(2) (0.1 mmol/L) resulted in significantly greater membrane depolarization in vasospastic compared with normal myocytes. Expression of K(IR) 2.1 messenger ribonucleic acid (mRNA) was increased after SAH. Western blotting and immunohistochemistry also showed increased expression of K(IR) protein in vasospastic smooth muscle. Blockage of K(IR) channels in arteries under isometric tension produced a greater contraction in SAH than in control arteries. These results document increased expression of K(IR) 2.1 mRNA and protein during vasospasm after experimental SAH and suggest that this increase is a functionally significant adaptive response acting to reduce vasospasm.
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MESH Headings
- Animals
- Barium/pharmacology
- Basilar Artery/drug effects
- Basilar Artery/physiopathology
- Blood Pressure
- Cerebral Angiography
- Disease Models, Animal
- Dogs
- Female
- Membrane Potentials
- Muscle, Smooth/metabolism
- Muscle, Smooth/physiopathology
- Organ Culture Techniques
- Patch-Clamp Techniques
- Potassium/metabolism
- Potassium Channels, Inwardly Rectifying/genetics
- Potassium Channels, Inwardly Rectifying/metabolism
- RNA, Messenger/biosynthesis
- RNA, Messenger/genetics
- Subarachnoid Hemorrhage/complications
- Subarachnoid Hemorrhage/physiopathology
- Time Factors
- Vasospasm, Intracranial/diagnostic imaging
- Vasospasm, Intracranial/etiology
- Vasospasm, Intracranial/physiopathology
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Affiliation(s)
- George W Weyer
- Section of Neurosurgery, Department of Surgery and the Pritzker School of Medicine, University of Chicago, IL 60637, USA
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35
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Abstract
The elusive nature of events that sustain cerebral vasospasm after subarachnoid hemorrhage resulting from a ruptured aneurysm presents major challenges in designing effective therapies for this frequently devastating condition. Protracted cerebral artery constriction entails several dynamic components in intracellular signaling events initiated by endothelial factors, products of hemolysate, and numerous kinases, as well as increased intracellular Ca(2+). The rationale for potential treatment modalities and their efficacy are discussed in this brief review.
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Affiliation(s)
- Shigeru Nishizawa
- Department of Neurosurgery, Hamamatsu University School of Medicine, Hamamatsu, Japan
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Takeuchi K, Renic M, Bohman QC, Harder DR, Miyata N, Roman RJ. Reversal of delayed vasospasm by an inhibitor of the synthesis of 20-HETE. Am J Physiol Heart Circ Physiol 2005; 289:H2203-11. [PMID: 15964920 DOI: 10.1152/ajpheart.00556.2005] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study characterized the time course of changes in cerebral blood flow (CBF) and vascular diameter in a dual-hemorrhage model of subarachnoid hemorrhage (SAH) in rats and examined whether acute blockade of the synthesis of 20-hydroxyeicosatetraenoic acid (20-HETE) with N-(3-chloro-4-morpholin-4-yl)phenyl-N'-hydroxyimido formamide (TS-011) can reverse delayed vasospasm in this model. Rats received an intracisternal injection of blood (0.4 ml) on day 0 and a second injection 2 days later. CBF was sequentially measured using laser-Doppler flowmetry, and the diameters of the cerebral arteries were determined after filling the cerebral vasculature with a casting compound. CBF fell to 67% of control after the first intracisternal injection of blood but returned to a value near control 24 h later. CBF again fell to 63% of control after a second intracisternal injection of blood and remained 30% below control for 5 days. The fall in CBF after the second intracisternal injection of blood was associated with a sustained 30% reduction in the diameters of the middle cerebral, posterior communicating, and basilar arteries. Acute blockade of the synthesis of 20-HETE with TS-011 (0.1 mg/kg i.v.), 5 days after the second SAH, increased the diameters of the cerebral arteries, and CBF returned to control. These results indicate that the rats develop delayed vasospasm after induction of the dual-hemorrhage model of SAH and that blockade of the synthesis of 20-HETE fully reverses cerebral vasospasm in this model. They also implicate 20-HETE in the development and maintenance of delayed cerebral vasospasm.
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Affiliation(s)
- Kazuhiko Takeuchi
- Dept. of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226, USA
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37
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Abstract
Large conductance calcium-dependent (Slo1 BK) channels are allosterically activated by membrane depolarization and divalent cations, and possess a rich modulatory repertoire. Recently, intracellular heme has been identified as a potent regulator of Slo1 BK channels (Tang, X.D., R. Xu, M.F. Reynolds, M.L. Garcia, S.H. Heinemann, and T. Hoshi. 2003. Nature. 425:531-535). Here we investigated the mechanism of the regulatory action of heme on heterologously expressed Slo1 BK channels by separating the influences of voltage and divalent cations. In the absence of divalent cations, heme generally decreased ionic currents by shifting the channel's G-V curve toward more depolarized voltages and by rendering the curve less steep. In contrast, gating currents remained largely unaffected by heme. Simulations suggest that a decrease in the strength of allosteric coupling between the voltage sensor and the activation gate and a concomitant stabilization of the open state account for the essential features of the heme action in the absence of divalent ions. At saturating levels of divalent cations, heme remained similarly effective with its influence on the G-V simulated by weakening the coupling of both Ca(2+) binding and voltage sensor activation to channel opening. The results thus show that heme dampens the influence of allosteric activators on the activation gate of the Slo1 BK channel. To account for these effects, we consider the possibility that heme binding alters the structure of the RCK gating ring and thereby disrupts both Ca(2+)- and voltage-dependent gating as well as intrinsic stability of the open state.
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Affiliation(s)
- Frank T Horrigan
- Department of Physiology, School of Medecine, University of Pennsylvania, Philadelphia, PA 19104, USA
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