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Haji-Ghassemi O, Yuchi Z, Van Petegem F. The Cardiac Ryanodine Receptor Phosphorylation Hotspot Embraces PKA in a Phosphorylation-Dependent Manner. Mol Cell 2019; 75:39-52.e4. [PMID: 31078384 DOI: 10.1016/j.molcel.2019.04.019] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Revised: 03/05/2019] [Accepted: 04/11/2019] [Indexed: 12/22/2022]
Abstract
Ryanodine receptors (RyRs) are intracellular Ca2+ release channels controlling essential cellular functions. RyRs are targeted by cyclic AMP (cAMP)-dependent protein kinase A (PKA), a controversial regulation implicated in disorders ranging from heart failure to Alzheimer's. Using crystal structures, we show that the phosphorylation hotspot domain of RyR2 embraces the PKA catalytic subunit, with an extensive interface not seen in PKA complexes with peptides. We trapped an intermediary open-form PKA bound to the RyR2 domain and an ATP analog, showing that PKA can engage substrates in an open form. Phosphomimetics or prior phosphorylation at nearby sites in RyR2 either enhance or reduce the activity of PKA. Finally, we show that a phosphomimetic at S2813, a well-known target site for calmodulin-dependent kinase II, induces the formation of an alpha helix in the phosphorylation domain, resulting in increased interactions and PKA activity. This shows that the different phosphorylation sites in RyR2 are not independent.
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Affiliation(s)
- Omid Haji-Ghassemi
- Department of Biochemistry and Molecular Biology, Life Sciences Institute, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Zhiguang Yuchi
- Department of Biochemistry and Molecular Biology, Life Sciences Institute, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Filip Van Petegem
- Department of Biochemistry and Molecular Biology, Life Sciences Institute, University of British Columbia, Vancouver, BC V6T 1Z3, Canada.
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Hamilton S, Terentyev D. Proarrhythmic Remodeling of Calcium Homeostasis in Cardiac Disease; Implications for Diabetes and Obesity. Front Physiol 2018. [PMID: 30425651 DOI: 10.3389/fphys.2018.01517, 10.3389/fpls.2018.01517] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
A rapid growth in the incidence of diabetes and obesity has transpired to a major heath issue and economic burden in the postindustrial world, with more than 29 million patients affected in the United States alone. Cardiovascular defects have been established as the leading cause of mortality and morbidity of diabetic patients. Over the last decade, significant progress has been made in delineating mechanisms responsible for the diminished cardiac contractile function and enhanced propensity for malignant cardiac arrhythmias characteristic of diabetic disease. Rhythmic cardiac contractility relies upon the precise interplay between several cellular Ca2+ transport protein complexes including plasmalemmal L-type Ca2+ channels (LTCC), Na+-Ca2+ exchanger (NCX1), Sarco/endoplasmic Reticulum (SR) Ca2+-ATPase (SERCa2a) and ryanodine receptors (RyR2s), the SR Ca2+ release channels. Here we provide an overview of changes in Ca2+ homeostasis in diabetic ventricular myocytes and discuss the therapeutic potential of targeting Ca2+ handling proteins in the prevention of diabetes-associated cardiomyopathy and arrhythmogenesis.
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Affiliation(s)
- Shanna Hamilton
- Department of Medicine, The Warren Alpert Medical School of Brown University, Providence, RI, United States.,Cardiovascular Research Center, Rhode Island Hospital, Providence, RI, United States
| | - Dmitry Terentyev
- Department of Medicine, The Warren Alpert Medical School of Brown University, Providence, RI, United States.,Cardiovascular Research Center, Rhode Island Hospital, Providence, RI, United States
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Hamilton S, Terentyev D. Proarrhythmic Remodeling of Calcium Homeostasis in Cardiac Disease; Implications for Diabetes and Obesity. Front Physiol 2018; 9:1517. [PMID: 30425651 PMCID: PMC6218530 DOI: 10.3389/fphys.2018.01517] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Accepted: 10/09/2018] [Indexed: 12/28/2022] Open
Abstract
A rapid growth in the incidence of diabetes and obesity has transpired to a major heath issue and economic burden in the postindustrial world, with more than 29 million patients affected in the United States alone. Cardiovascular defects have been established as the leading cause of mortality and morbidity of diabetic patients. Over the last decade, significant progress has been made in delineating mechanisms responsible for the diminished cardiac contractile function and enhanced propensity for malignant cardiac arrhythmias characteristic of diabetic disease. Rhythmic cardiac contractility relies upon the precise interplay between several cellular Ca2+ transport protein complexes including plasmalemmal L-type Ca2+ channels (LTCC), Na+-Ca2+ exchanger (NCX1), Sarco/endoplasmic Reticulum (SR) Ca2+-ATPase (SERCa2a) and ryanodine receptors (RyR2s), the SR Ca2+ release channels. Here we provide an overview of changes in Ca2+ homeostasis in diabetic ventricular myocytes and discuss the therapeutic potential of targeting Ca2+ handling proteins in the prevention of diabetes-associated cardiomyopathy and arrhythmogenesis.
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Affiliation(s)
- Shanna Hamilton
- Department of Medicine, The Warren Alpert Medical School of Brown University, Providence, RI, United States.,Cardiovascular Research Center, Rhode Island Hospital, Providence, RI, United States
| | - Dmitry Terentyev
- Department of Medicine, The Warren Alpert Medical School of Brown University, Providence, RI, United States.,Cardiovascular Research Center, Rhode Island Hospital, Providence, RI, United States
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4
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Rebbeck RT, Willemse H, Groom L, Casarotto MG, Board PG, Beard NA, Dirksen RT, Dulhunty AF. Regions of ryanodine receptors that influence activation by the dihydropyridine receptor β1a subunit. Skelet Muscle 2015. [PMID: 26203350 PMCID: PMC4510890 DOI: 10.1186/s13395-015-0049-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Background Although excitation-contraction (EC) coupling in skeletal muscle relies on physical activation of the skeletal ryanodine receptor (RyR1) Ca2+ release channel by dihydropyridine receptors (DHPRs), the activation pathway between the DHPR and RyR1 remains unknown. However, the pathway includes the DHPR β1a subunit which is integral to EC coupling and activates RyR1. In this manuscript, we explore the isoform specificity of β1a activation of RyRs and the β1a binding site on RyR1. Methods We used lipid bilayers to measure single channel currents and whole cell patch clamp to measure L-type Ca2+ currents and Ca2+ transients in myotubes. Results We demonstrate that both skeletal RyR1 and cardiac RyR2 channels in phospholipid bilayers are activated by 10–100 nM of the β1a subunit. Activation of RyR2 by 10 nM β1a was less than that of RyR1, suggesting a reduced affinity of RyR2 for β1a. A reduction in activation was also observed when 10 nM β1a was added to the alternatively spliced (ASI(−)) isoform of RyR1, which lacks ASI residues (A3481-Q3485). It is notable that the equivalent region of RyR2 also lacks four of five ASI residues, suggesting that the absence of these residues may contribute to the reduced 10 nM β1a activation observed for both RyR2 and ASI(−)RyR1 compared to ASI(+)RyR1. We also investigated the influence of a polybasic motif (PBM) of RyR1 (K3495KKRRDGR3502) that is located immediately downstream from the ASI residues and has been implicated in EC coupling. We confirmed that neutralizing the basic residues in the PBM (RyR1 K-Q) results in an ~50 % reduction in Ca2+ transient amplitude following expression in RyR1-null (dyspedic) myotubes and that the PBM is also required for β1a subunit activation of RyR1 channels in lipid bilayers. These results suggest that the removal of β1a subunit interaction with the PBM in RyR1 could contribute directly to ~50 % of the Ca2+ release generated during skeletal EC coupling. Conclusions We conclude that the β1a subunit likely binds to a region that is largely conserved in RyR1 and RyR2 and that this region is influenced by the presence of the ASI residues and the PBM in RyR1. Electronic supplementary material The online version of this article (doi:10.1186/s13395-015-0049-3) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Robyn T Rebbeck
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN USA
| | - Hermia Willemse
- John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital, PO Box 334, Canberra, ACT 2601 Australia
| | - Linda Groom
- Department of Physiology and Pharmacology, University of Rochester Medical Center, Rochester, NY USA
| | - Marco G Casarotto
- John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital, PO Box 334, Canberra, ACT 2601 Australia
| | - Philip G Board
- John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital, PO Box 334, Canberra, ACT 2601 Australia
| | - Nicole A Beard
- Discipline of Biomedical Sciences, Centre for Research in Therapeutic Solutions, University of Canberra, Canberra, ACT 2601 Australia
| | - Robert T Dirksen
- Department of Physiology and Pharmacology, University of Rochester Medical Center, Rochester, NY USA
| | - Angela F Dulhunty
- John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital, PO Box 334, Canberra, ACT 2601 Australia
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Zamponi GW, Currie KPM. Regulation of Ca(V)2 calcium channels by G protein coupled receptors. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:1629-43. [PMID: 23063655 DOI: 10.1016/j.bbamem.2012.10.004] [Citation(s) in RCA: 141] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2012] [Revised: 10/02/2012] [Accepted: 10/04/2012] [Indexed: 12/29/2022]
Abstract
Voltage gated calcium channels (Ca²⁺ channels) are key mediators of depolarization induced calcium influx into excitable cells, and thereby play pivotal roles in a wide array of physiological responses. This review focuses on the inhibition of Ca(V)2 (N- and P/Q-type) Ca²⁺-channels by G protein coupled receptors (GPCRs), which exerts important autocrine/paracrine control over synaptic transmission and neuroendocrine secretion. Voltage-dependent inhibition is the most widespread mechanism, and involves direct binding of the G protein βγ dimer (Gβγ) to the α1 subunit of Ca(V)2 channels. GPCRs can also recruit several other distinct mechanisms including phosphorylation, lipid signaling pathways, and channel trafficking that result in voltage-independent inhibition. Current knowledge of Gβγ-mediated inhibition is reviewed, including the molecular interactions involved, determinants of voltage-dependence, and crosstalk with other cell signaling pathways. A summary of recent developments in understanding the voltage-independent mechanisms prominent in sympathetic and sensory neurons is also included. This article is part of a Special Issue entitled: Calcium channels.
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Affiliation(s)
- Gerald W Zamponi
- Department of Physiology & Pharmacology, Hotchkiss Brain Institute, University of Calgary, Canada
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Simms BA, Zamponi GW. Trafficking and stability of voltage-gated calcium channels. Cell Mol Life Sci 2012; 69:843-56. [PMID: 21964928 PMCID: PMC11115007 DOI: 10.1007/s00018-011-0843-y] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2011] [Revised: 09/15/2011] [Accepted: 09/19/2011] [Indexed: 02/07/2023]
Abstract
Voltage-gated calcium channels are important mediators of calcium influx into electrically excitable cells. The amount of calcium entering through this family of channel proteins is not only determined by the functional properties of channels embedded in the plasma membrane but also by the numbers of channels that are expressed at the cell surface. The trafficking of channels is controlled by numerous processes, including co-assembly with ancillary calcium channel subunits, ubiquitin ligases, and interactions with other membrane proteins such as G protein coupled receptors. Here we provide an overview about the current state of knowledge of calcium channel trafficking to the cell membrane, and of the mechanisms regulating the stability and internalization of this important ion channel family.
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Affiliation(s)
- Brett A. Simms
- Department of Physiology and Pharmacology, University of Calgary, 3330 Hospital Dr. NW, Calgary, T2N 4N1 Canada
| | - Gerald W. Zamponi
- Department of Physiology and Pharmacology, University of Calgary, 3330 Hospital Dr. NW, Calgary, T2N 4N1 Canada
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Zissimopoulos S, Seifan S, Maxwell C, Williams AJ, Lai FA. Disparities in the association of the ryanodine receptor and the FK506-binding proteins in mammalian heart. J Cell Sci 2012; 125:1759-69. [PMID: 22328519 DOI: 10.1242/jcs.098012] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The FK506-binding proteins (FKBP12 and FKBP12.6; also known as FKBP1A and FKBP1B, respectively) are accessory subunits of the ryanodine receptor (RyR) Ca(2+) release channel. Aberrant RyR2-FKBP12.6 interactions have been proposed to be the underlying cause of channel dysfunction in acquired and inherited cardiac disease. However, the stoichiometry of the RyR2 association with FKBP12 or FKBP12.6 in mammalian heart is currently unknown. Here, we describe detailed quantitative analysis of cardiac stoichiometry between RyR2 and FKBP12 or FKBP12.6 using immunoblotting and [(3)H]ryanodine-binding assays, revealing striking disparities between four mammalian species. In mouse and pig heart, RyR2 is found complexed with both FKBP12 and FKBP12.6, although the former is the most abundant isoform. In rat heart, RyR2 is predominantly associated with FKBP12.6, whereas in rabbit it is associated with FKBP12 only. Co-immunoprecipitation experiments demonstrate RyR2-specific interaction with both FKBP isoforms in native cardiac tissue. Assuming four FKBP-binding sites per RyR2 tetramer, only a small proportion of available sites are occupied by endogenous FKBP12.6. FKBP interactions with RyR2 are very strong and resistant to drug (FK506, rapamycin and cyclic ADPribose) and redox (H(2)O(2) and diamide) treatment. By contrast, the RyR1-FKBP12 association in skeletal muscle is readily disrupted under oxidative conditions. This is the first study to directly assess association of endogenous FKBP12 and FKBP12.6 with RyR2 in native cardiac tissue. Our results challenge the widespread perception that RyR2 associates exclusively with FKBP12.6 to near saturation, with important implications for the role of the FK506-binding proteins in RyR2 pathophysiology and cardiac disease.
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Affiliation(s)
- Spyros Zissimopoulos
- Wales Heart Research Institute, Department of Cardiology, Cardiff University School of Medicine, Cardiff, UK.
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Bannister RA, Beam KG. The cardiac alpha(1C) subunit can support excitation-triggered Ca2+ entry in dysgenic and dyspedic myotubes. Channels (Austin) 2009; 3:268-73. [PMID: 19625771 DOI: 10.4161/chan.3.4.9342] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Depolarization-induced entry of divalent ions into skeletal muscle has been attributed to a process termed Excitation-Coupled Ca(2+) Entry (ECCE), which is hypothesized to require the interaction of the ryanodine receptor (RyR1), the L-type Ca(2+) channel (DHPR) and another unidentified cation channel. Thus, ECCE is absent in myotubes lacking either the DHPR (dysgenic) or RyR1 (dyspedic). Furthermore, ECCE, as measured by Mn(2+) quench of Fura-2, is reconstituted by expression of a mutant DHPR alpha(1S) subunit (SkEIIIK) thought to be impermeable to divalent cations. Previously, we showed that the bulk of depolarization-induced Ca(2+) entry could be explained by the skeletal L-type current. Accordingly, one would predict that any Ca(2+) current similar to the endogenous current would restore such entry and that this entry would not require coupling to either the DHPR or RyR1. Here, we show that expression of the cardiac alpha(1C) subunit in either dysgenic or dyspedic myotubes does result in Ca(2+) entry similar to that ascribed to ECCE. We also demonstrate that, when potentiated by strong depolarization and Bay K 8644, SkEIIIK supports entry of Mn(2+). These results strongly support the idea that the L-type channel is the major route of Ca(2+) entry in response to repetitive or prolonged depolarization of skeletal muscle.
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Affiliation(s)
- Roger A Bannister
- Department of Physiology and Biophysics, School of Medicine, University of Colorado-Denver, Aurora, CO, USA
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Zhong J, Chen J, Cao T, Wang L, Zhang W, Liu D, Zhu Z. ADENOVIRUS-MEDIATED FKBP12.6 OVEREXPRESSION INDUCES HYPERTROPHY AND APOPTOSIS IN CULTURED NEONATAL CARDIOMYOCYTES. Clin Exp Pharmacol Physiol 2009; 36:135-40. [DOI: 10.1111/j.1440-1681.2008.05030.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Goddard CA, Ghais NS, Zhang Y, Williams AJ, Colledge WH, Grace AA, Huang CLH. Physiological consequences of the P2328S mutation in the ryanodine receptor (RyR2) gene in genetically modified murine hearts. Acta Physiol (Oxf) 2008; 194:123-40. [PMID: 18419777 PMCID: PMC2628439 DOI: 10.1111/j.1748-1716.2008.01865.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Aim To explore the physiological consequences of the ryanodine receptor (RyR2)-P2328S mutation associated with catecholaminergic polymorphic ventricular tachycardia (CPVT). Methods We generated heterozygotic (RyR2p/s) and homozygotic (RyR2s/s) transgenic mice and studied Ca2+ signals from regularly stimulated, Fluo-3-loaded, cardiac myocytes. Results were compared with monophasic action potentials (MAPs) in Langendorff-perfused hearts under both regular and programmed electrical stimulation (PES). Results Evoked Ca2+ transients from wild-type (WT), heterozygote (RyR2p/s) and homozygote (RyR2s/s) myocytes had indistinguishable peak amplitudes with RyR2s/s showing subsidiary events. Adding 100 nm isoproterenol produced both ectopic peaks and subsidiary events in WT but not RyR2p/s and ectopic peaks and reduced amplitudes of evoked peaks in RyR2s/s. Regularly stimulated WT, RyR2p/s and RyR2s/s hearts showed indistinguishable MAP durations and refractory periods. RyR2p/s hearts showed non-sustained ventricular tachycardias (nsVTs) only with PES. Both nsVTs and sustained VTs (sVTs) occurred with regular stimuli and PES with isoproterenol treatment. RyR2s/s hearts showed higher incidences of nsVTs before but mainly sVTs after introduction of isoproterenol with both regular stimuli and PES, particularly at higher pacing frequencies. Additionally, intrinsically beating RyR2s/s showed extrasystolic events often followed by spontaneous sVT. Conclusion The RyR2-P2328S mutation results in marked alterations in cellular Ca2+ homeostasis and arrhythmogenic properties resembling CPVT with greater effects in the homozygote than the heterozygote demonstrating an important gene dosage effect.
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Affiliation(s)
- C A Goddard
- Physiological Laboratory, University of Cambridge, Cambridge, UK
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Goonasekera SA, Beard NA, Groom L, Kimura T, Lyfenko AD, Rosenfeld A, Marty I, Dulhunty AF, Dirksen RT. Triadin binding to the C-terminal luminal loop of the ryanodine receptor is important for skeletal muscle excitation contraction coupling. ACTA ACUST UNITED AC 2007; 130:365-78. [PMID: 17846166 PMCID: PMC2151650 DOI: 10.1085/jgp.200709790] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ca2+ release from intracellular stores is controlled by complex interactions between multiple proteins. Triadin is a transmembrane glycoprotein of the junctional sarcoplasmic reticulum of striated muscle that interacts with both calsequestrin and the type 1 ryanodine receptor (RyR1) to communicate changes in luminal Ca2+ to the release machinery. However, the potential impact of the triadin association with RyR1 in skeletal muscle excitation–contraction coupling remains elusive. Here we show that triadin binding to RyR1 is critically important for rapid Ca2+ release during excitation–contraction coupling. To assess the functional impact of the triadin-RyR1 interaction, we expressed RyR1 mutants in which one or more of three negatively charged residues (D4878, D4907, and E4908) in the terminal RyR1 intraluminal loop were mutated to alanines in RyR1-null (dyspedic) myotubes. Coimmunoprecipitation revealed that triadin, but not junctin, binding to RyR1 was abolished in the triple (D4878A/D4907A/E4908A) mutant and one of the double (D4907A/E4908A) mutants, partially reduced in the D4878A/D4907A double mutant, but not affected by either individual (D4878A, D4907A, E4908A) mutations or the D4878A/E4908A double mutation. Functional studies revealed that the rate of voltage- and ligand-gated SR Ca2+ release were reduced in proportion to the degree of interruption in triadin binding. Ryanodine binding, single channel recording, and calcium release experiments conducted on WT and triple mutant channels in the absence of triadin demonstrated that the luminal loop mutations do not directly alter RyR1 function. These findings demonstrate that junctin and triadin bind to different sites on RyR1 and that triadin plays an important role in ensuring rapid Ca2+ release during excitation–contraction coupling in skeletal muscle.
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Affiliation(s)
- Sanjeewa A Goonasekera
- Department of Pharmacology and Physiology, University of Rochester, Rochester, NY 14642, USA
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Moreland KT, Procknow JD, Sprague RS, Iverson JL, Lonigro AJ, Stephenson AH. Cyclooxygenase (COX)-1 and COX-2 participate in 5,6-epoxyeicosatrienoic acid-induced contraction of rabbit intralobar pulmonary arteries. J Pharmacol Exp Ther 2007; 321:446-54. [PMID: 17267581 DOI: 10.1124/jpet.106.107904] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Epoxyeicosatrienoic acids (EETs) have been reported to contract intralobar pulmonary arteries (PA) of the rabbit in a cyclooxygenase (COX)-dependent manner. In the present study, we observed that COX-1 and COX-2 isoforms were expressed in freshly isolated PA of healthy rabbits. We examined the hypothesis that both COX isoforms participate in 5,6-EET-induced contraction of rabbit intralobar PA. Selective inhibition of COX-1 with 300 nM 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole (SC-560) prevented 5,6-EET (1x10(-8)-1x10(-5) M)-induced contractions of isolated intralobar rabbit PA rings in a manner similar to that observed with the nonselective cyclooxygenase inhibitor indomethacin at 10 microM. Selective inhibition of COX-2 with either 100 nM 5-bromo-2-(4-fluorophenyl)-3-(4-methylsulfonyl) thiophene (DUP-697) or 3 microM N-(2-cyclohexyloxy-4-nitrophenyl) methanesulfonamide (NS-398) shifted the EC50 value of 5,6-EET-induced PA contraction to the right but with considerably lower efficacy than SC-560. In rabbit PA, 5,6-EET-induced contraction was primarily dependent on COX-1 activity. Differential metabolism of 5,6-EET by COX-1 and COX-2 does not explain the primary dependence of PA contraction on COX-1 activity because 5,6-EET was metabolized similarly by both COX isoforms. COX-1 and -2 were expressed primarily in PA endothelium where COX-1 expression was dense and uniform, whereas COX-2 expression was sparse and nonuniform. 5,6-EET-induced PA contraction was endothelium-dependent. These results suggest that 5,6-EET-induced contraction is primarily dependent on COX-1 activity.
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Affiliation(s)
- K Trent Moreland
- Department of Pharmacological and Physiological Science, 1402 S. Grand Blvd., St. Louis, MO 63104, USA
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