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Elinder F, Liin SI. Actions and Mechanisms of Polyunsaturated Fatty Acids on Voltage-Gated Ion Channels. Front Physiol 2017; 8:43. [PMID: 28220076 PMCID: PMC5292575 DOI: 10.3389/fphys.2017.00043] [Citation(s) in RCA: 88] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Accepted: 01/16/2017] [Indexed: 01/29/2023] Open
Abstract
Polyunsaturated fatty acids (PUFAs) act on most ion channels, thereby having significant physiological and pharmacological effects. In this review we summarize data from numerous PUFAs on voltage-gated ion channels containing one or several voltage-sensor domains, such as voltage-gated sodium (NaV), potassium (KV), calcium (CaV), and proton (HV) channels, as well as calcium-activated potassium (KCa), and transient receptor potential (TRP) channels. Some effects of fatty acids appear to be channel specific, whereas others seem to be more general. Common features for the fatty acids to act on the ion channels are at least two double bonds in cis geometry and a charged carboxyl group. In total we identify and label five different sites for the PUFAs. PUFA site 1: The intracellular cavity. Binding of PUFA reduces the current, sometimes as a time-dependent block, inducing an apparent inactivation. PUFA site 2: The extracellular entrance to the pore. Binding leads to a block of the channel. PUFA site 3: The intracellular gate. Binding to this site can bend the gate open and increase the current. PUFA site 4: The interface between the extracellular leaflet of the lipid bilayer and the voltage-sensor domain. Binding to this site leads to an opening of the channel via an electrostatic attraction between the negatively charged PUFA and the positively charged voltage sensor. PUFA site 5: The interface between the extracellular leaflet of the lipid bilayer and the pore domain. Binding to this site affects slow inactivation. This mapping of functional PUFA sites can form the basis for physiological and pharmacological modifications of voltage-gated ion channels.
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Affiliation(s)
- Fredrik Elinder
- Department of Clinical and Experimental Medicine, Linköping University Linköping, Sweden
| | - Sara I Liin
- Department of Clinical and Experimental Medicine, Linköping University Linköping, Sweden
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Iglesias J, Lamontagne J, Erb H, Gezzar S, Zhao S, Joly E, Truong VL, Skorey K, Crane S, Madiraju SRM, Prentki M. Simplified assays of lipolysis enzymes for drug discovery and specificity assessment of known inhibitors. J Lipid Res 2015; 57:131-41. [PMID: 26423520 DOI: 10.1194/jlr.d058438] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2015] [Indexed: 12/25/2022] Open
Abstract
Lipids are used as cellular building blocks and condensed energy stores and also act as signaling molecules. The glycerolipid/ fatty acid cycle, encompassing lipolysis and lipogenesis, generates many lipid signals. Reliable procedures are not available for measuring activities of several lipolytic enzymes for the purposes of drug screening, and this resulted in questionable selectivity of various known lipase inhibitors. We now describe simple assays for lipolytic enzymes, including adipose triglyceride lipase (ATGL), hormone sensitive lipase (HSL), sn-1-diacylglycerol lipase (DAGL), monoacylglycerol lipase, α/β-hydrolase domain 6, and carboxylesterase 1 (CES1) using recombinant human and mouse enzymes either in cell extracts or using purified enzymes. We observed that many of the reported inhibitors lack specificity. Thus, Cay10499 (HSL inhibitor) and RHC20867 (DAGL inhibitor) also inhibit other lipases. Marked differences in the inhibitor sensitivities of human ATGL and HSL compared with the corresponding mouse enzymes was noticed. Thus, ATGListatin inhibited mouse ATGL but not human ATGL, and the HSL inhibitors WWL11 and Compound 13f were effective against mouse enzyme but much less potent against human enzyme. Many of these lipase inhibitors also inhibited human CES1. Results describe reliable assays for measuring lipase activities that are amenable for drug screening and also caution about the specificity of the many earlier described lipase inhibitors.
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Affiliation(s)
- Jose Iglesias
- Molecular Nutrition Unit and Montreal Diabetes Research Center, CRCHUM, Montréal, Québec, Canada H2X 0A9 Departments of Nutrition, Biochemistry, and Molecular Medicine, Université de Montréal, Montréal, Québec, Canada H2X 0A9
| | - Julien Lamontagne
- Molecular Nutrition Unit and Montreal Diabetes Research Center, CRCHUM, Montréal, Québec, Canada H2X 0A9 Departments of Nutrition, Biochemistry, and Molecular Medicine, Université de Montréal, Montréal, Québec, Canada H2X 0A9
| | - Heidi Erb
- Molecular Nutrition Unit and Montreal Diabetes Research Center, CRCHUM, Montréal, Québec, Canada H2X 0A9 Departments of Nutrition, Biochemistry, and Molecular Medicine, Université de Montréal, Montréal, Québec, Canada H2X 0A9
| | - Sari Gezzar
- Molecular Nutrition Unit and Montreal Diabetes Research Center, CRCHUM, Montréal, Québec, Canada H2X 0A9 Departments of Nutrition, Biochemistry, and Molecular Medicine, Université de Montréal, Montréal, Québec, Canada H2X 0A9
| | - Shangang Zhao
- Molecular Nutrition Unit and Montreal Diabetes Research Center, CRCHUM, Montréal, Québec, Canada H2X 0A9 Departments of Nutrition, Biochemistry, and Molecular Medicine, Université de Montréal, Montréal, Québec, Canada H2X 0A9
| | - Erik Joly
- Molecular Nutrition Unit and Montreal Diabetes Research Center, CRCHUM, Montréal, Québec, Canada H2X 0A9 Departments of Nutrition, Biochemistry, and Molecular Medicine, Université de Montréal, Montréal, Québec, Canada H2X 0A9
| | | | | | - Sheldon Crane
- NuChem Therapeutics, Montréal, Québec, Canada, H4P 2R2
| | - S R Murthy Madiraju
- Molecular Nutrition Unit and Montreal Diabetes Research Center, CRCHUM, Montréal, Québec, Canada H2X 0A9 Departments of Nutrition, Biochemistry, and Molecular Medicine, Université de Montréal, Montréal, Québec, Canada H2X 0A9
| | - Marc Prentki
- Molecular Nutrition Unit and Montreal Diabetes Research Center, CRCHUM, Montréal, Québec, Canada H2X 0A9 Departments of Nutrition, Biochemistry, and Molecular Medicine, Université de Montréal, Montréal, Québec, Canada H2X 0A9
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Glasgow SD, Chapman CA. Muscarinic depolarization of layer II neurons of the parasubiculum. PLoS One 2013; 8:e58901. [PMID: 23520542 PMCID: PMC3592838 DOI: 10.1371/journal.pone.0058901] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2012] [Accepted: 02/08/2013] [Indexed: 11/18/2022] Open
Abstract
The parasubiculum (PaS) is a component of the hippocampal formation that sends its major output to layer II of the entorhinal cortex. The PaS receives strong cholinergic innervation from the basal forebrain that is likely to modulate neuronal excitability and contribute to theta-frequency network activity. The present study used whole cell current- and voltage-clamp recordings to determine the effects of cholinergic receptor activation on layer II PaS neurons. Bath application of carbachol (CCh; 10–50 µM) resulted in a dose-dependent depolarization of morphologically-identified layer II stellate and pyramidal cells that was not prevented by blockade of excitatory and inhibitory synaptic inputs. Bath application of the M1 receptor antagonist pirenzepine (1 µM), but not the M2-preferring antagonist methoctramine (1 µM), blocked the depolarization, suggesting that it is dependent on M1 receptors. Voltage-clamp experiments using ramped voltage commands showed that CCh resulted in the gradual development of an inward current that was partially blocked by concurrent application of the selective Kv7.2/3 channel antagonist XE-991, which inhibits the muscarine-dependent K+ current IM. The remaining inward current also reversed near EK and was inhibited by the K+ channel blocker Ba2+, suggesting that M1 receptor activation attenuates both IM as well as an additional K+ current. The additional K+ current showed rectification at depolarized voltages, similar to K+ conductances mediated by Kir 2.3 channels. The cholinergic depolarization of layer II PaS neurons therefore appears to occur through M1-mediated effects on IM as well as an additional K+ conductance.
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Affiliation(s)
- Stephen D. Glasgow
- Center for Studies in Behavioral Neurobiology, Department of Psychology, Concordia University, Montréal, Québec, Canada
| | - C. Andrew Chapman
- Center for Studies in Behavioral Neurobiology, Department of Psychology, Concordia University, Montréal, Québec, Canada
- * E-mail:
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Reisenberg M, Singh PK, Williams G, Doherty P. The diacylglycerol lipases: structure, regulation and roles in and beyond endocannabinoid signalling. Philos Trans R Soc Lond B Biol Sci 2012; 367:3264-75. [PMID: 23108545 PMCID: PMC3481529 DOI: 10.1098/rstb.2011.0387] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The diacylglycerol lipases (DAGLs) hydrolyse diacylglycerol to generate 2-arachidonoylglycerol (2-AG), the most abundant ligand for the CB(1) and CB(2) cannabinoid receptors in the body. DAGL-dependent endocannabinoid signalling regulates axonal growth and guidance during development, and is required for the generation and migration of new neurons in the adult brain. At developed synapses, 2-AG released from postsynaptic terminals acts back on presynaptic CB(1) receptors to inhibit the secretion of both excitatory and inhibitory neurotransmitters, with this DAGL-dependent synaptic plasticity operating throughout the nervous system. Importantly, the DAGLs have functions that do not involve cannabinoid receptors. For example, 2-AG is the precursor of arachidonic acid in a pathway that maintains the level of this essential lipid in the brain and other organs. This pathway also drives the cyclooxygenase-dependent generation of inflammatory prostaglandins in the brain, which has recently been implicated in the degeneration of dopaminergic neurons in Parkinson's disease. Remarkably, we still know very little about the mechanisms that regulate DAGL activity-however, key insights can be gleaned by homology modelling against other α/β hydrolases and from a detailed examination of published proteomic studies and other databases. These identify a regulatory loop with a highly conserved signature motif, as well as phosphorylation and palmitoylation as post-translational mechanisms likely to regulate function.
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Affiliation(s)
| | | | - Gareth Williams
- Wolfson Centre for Age-Related Diseases, King's College London, SE1 9RT, UK
| | - Patrick Doherty
- Wolfson Centre for Age-Related Diseases, King's College London, SE1 9RT, UK
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Abstract
Voltage-gated M-type (KCNQ) K+ channels play critical roles in regulation of neuronal excitability. Previous work showed A-kinase-anchoring protein (AKAP)79/150-mediated protein kinase C (PKC) phosphorylation of M channels to be involved in M current (I(M)) suppression by muscarinic M1, but not bradykinin B2, receptors. In this study, we first explored whether purinergic and angiotensin suppression of I(M) in superior cervical ganglion (SCG) sympathetic neurons involves AKAP79/150. Transfection into rat SCG neurons of ΔA-AKAP79, which lacks the A domain necessary for PKC binding, or the absence of AKAP150 in AKAP150(-/-) mice, did not affect I(M) suppression by purinergic agonist or by bradykinin, but reduced I(M) suppression by muscarinic agonist and angiotensin II. Transfection of AKAP79, but not ΔA-AKAP79 or AKAP15, rescued suppression of I(M) by muscarinic receptors in AKAP150(-/-) neurons. We also tested association of AKAP79 with M(1), B(2), P2Y(6), and AT(1) receptors, and KCNQ2 and KCNQ3 channels, via Förster resonance energy transfer (FRET) on Chinese hamster ovary cells under total internal refection fluorescence microscopy, which revealed substantial FRET between AKAP79 and M1 or AT1 receptors, and with the channels, but only weak FRET with P2Y(6) or B2 receptors. The involvement of AKAP79/150 in G(q/11)-coupled muscarinic regulation of N- and L-type Ca2+) channels and by cAMP/protein kinase A was also studied. We found AKAP79/150 to not play a role in the former, but to be necessary for forskolin-induced upregulation of L-current. Thus, AKAP79/150 action correlates with the PIP(2) (phosphatidylinositol 4,5-bisphosphate)-depletion mode of I(M) suppression, but does not generalize to G(q/11)-mediated inhibition of N- or L-type Ca2+ channels.
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Zhao H, Kinch DC, Simasko SM. Pharmacological investigations of the cellular transduction pathways used by cholecystokinin to activate nodose neurons. Auton Neurosci 2011; 164:20-6. [PMID: 21664195 DOI: 10.1016/j.autneu.2011.05.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2010] [Revised: 05/18/2011] [Accepted: 05/19/2011] [Indexed: 11/25/2022]
Abstract
Cholecystokinin (CCK) directly activates vagal afferent neurons resulting in coordinated gastrointestinal functions and satiation. In vitro, the effects of CCK on dissociated vagal afferent neurons are mediated via activation of the vanilloid family of transient receptor potential (TRPV) cation channels leading to membrane depolarization and an increase in cytosolic calcium. However, the cellular transduction pathway(s) involved in this process between CCK receptors and channel opening have not been identified. To address this question, we monitored CCK-induced cytosolic calcium responses in dissociated nodose neurons from rat in the presence or absence of reagents that interact with various intracellular signaling pathways. We found that the phospholipase C (PLC) inhibitor U-73122 significantly attenuated CCK-induced responses, whereas the inactive analog U-73433 had no effect. Responses to CCK were also cross-desensitized by a brief pretreatment with m-3M3FBS, a PLC stimulator. Together these observations strongly support the participation of PLC in the effects of CCK on vagal afferent neurons. In contrast, pharmacological antagonism of phospholipase A(2), protein kinase A, and phosphatidylinositol 3-kinase revealed that they are not critical in the CCK-induced calcium response in nodose neurons. Further investigations of the cellular pathways downstream of PLC showed that neither protein kinase C (PKC) nor generation of diacylglycerol (DAG) or release of calcium from intracellular stores participates in the response to CCK. These results suggest that alteration of membrane phosphatidylinositol 4,5-bisphosphate (PIP(2)) content by PLC activity mediates CCK-induced calcium response and that this pathway may underlie the vagally-mediated actions of CCK to induce satiation and alter gastrointestinal functions.
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Affiliation(s)
- Huan Zhao
- Program in Neuroscience, Dept of Veterinary and Comparative Anatomy, Pharmacology, and Physiology, Washington State University, Pullman, WA 99164, USA.
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Zaika O, Zhang J, Shapiro MS. Combined phosphoinositide and Ca2+ signals mediating receptor specificity toward neuronal Ca2+ channels. J Biol Chem 2011; 286:830-41. [PMID: 21051544 PMCID: PMC3013042 DOI: 10.1074/jbc.m110.166033] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2010] [Revised: 10/08/2010] [Indexed: 01/17/2023] Open
Abstract
Phosphatidylinositol 4,5-bisphosphate (PIP(2)) regulates Ca(2+) (I(Ca)) and M-type K(+) currents in superior cervical ganglion sympathetic neurons. In those cells, M(1) muscarinic and AT(1) angiotensin types do not elicit Ca(2+)(i) signals and suppress both currents via depletion of PIP(2), whereas the B(2) bradykinin and P2Y purinergic types elicit robust IP(3)-mediated [Ca(2+)](i) rises and neither deplete PIP(2) nor inhibit I(Ca). We have suggested that this specificity arises from differential Ca(2+)(i) signals underlying receptor-specific stimulation of PIP(2) synthesis by phosphatidylinositol (PI) 4-kinase. Here, we investigate which PI 4-kinase isoform underlies this signal, whether stimulation of PI 4-phosphate 5-kinase is also required, and the origin of receptor-specific Ca(2+)(i) signals. Recordings of I(Ca) were used as a PIP(2) "biosensor." In control, stimulation of M(1), but not B(2) or P2Y, receptors robustly suppressed I(Ca). However, when PI 4-kinase IIIβ, diacylglycerol kinase, Rho, or Rho-kinase was blocked, agonists of all three receptors robustly suppressed I(Ca). Overexpression of exogenous M(1) receptors yielded large [Ca(2+)](i) rises by muscarinic agonist, and transfection of wild-type IRBIT decreased Ca(2+)(i) signals, whereas dominant negative IRBIT-S68A had little effect on B(2) or P2Y responses but greatly increased muscarinic responses. We conclude that overlaid on microdomain organization is IRBIT, setting a "threshold" for [IP(3)], assisting in fidelity of receptor specificity.
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Affiliation(s)
- Oleg Zaika
- From the Department of Physiology, University of Texas Health Science Center, San Antonio, Texas 78229
| | - Jie Zhang
- From the Department of Physiology, University of Texas Health Science Center, San Antonio, Texas 78229
| | - Mark S. Shapiro
- From the Department of Physiology, University of Texas Health Science Center, San Antonio, Texas 78229
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Abstract
Voltage-gated Ca(2+) channels translate the electrical inputs of excitable cells into biochemical outputs by controlling influx of the ubiquitous second messenger Ca(2+) . As such the channels play pivotal roles in many cellular functions including the triggering of neurotransmitter and hormone release by CaV2.1 (P/Q-type) and CaV2.2 (N-type) channels. It is well established that G protein coupled receptors (GPCRs) orchestrate precise regulation neurotransmitter and hormone release through inhibition of CaV2 channels. Although the GPCRs recruit a number of different pathways, perhaps the most prominent, and certainly most studied among these is the so-called voltage-dependent inhibition mediated by direct binding of Gβγ to the α1 subunit of CaV2 channels. This article will review the basics of Ca(2+) -channels and G protein signaling, and the functional impact of this now classical inhibitory mechanism on channel function. It will also provide an update on more recent developments in the field, both related to functional effects and crosstalk with other signaling pathways, and advances made toward understanding the molecular interactions that underlie binding of Gβγ to the channel and the voltage-dependence that is a signature characteristic of this mechanism.
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Affiliation(s)
- Kevin P M Currie
- Department of Anesthesiology, Pharmacology and Center for Molecular Neuroscience, Vanderbilt University School of Medicine, Nashville, TN, USA.
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Striessnig J. An oily competition: role of beta subunit palmitoylation for Ca2+ channel modulation by fatty acids. ACTA ACUST UNITED AC 2010; 134:363-7. [PMID: 19858356 PMCID: PMC2768802 DOI: 10.1085/jgp.200910330] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Jörg Striessnig
- Department of Pharmacology and Toxicology, Center for Molecular Biosciences, University of Innsbruck, A-6020 Innsbruck, Austria.
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Heneghan JF, Mitra-Ganguli T, Stanish LF, Liu L, Zhao R, Rittenhouse AR. The Ca2+ channel beta subunit determines whether stimulation of Gq-coupled receptors enhances or inhibits N current. ACTA ACUST UNITED AC 2010; 134:369-84. [PMID: 19858357 PMCID: PMC2768801 DOI: 10.1085/jgp.200910203] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
In superior cervical ganglion (SCG) neurons, stimulation of M1 receptors (M1Rs) produces a distinct pattern of modulation of N-type calcium (N-) channel activity, enhancing currents elicited with negative test potentials and inhibiting currents elicited with positive test potentials. Exogenously applied arachidonic acid (AA) reproduces this profile of modulation, suggesting AA functions as a downstream messenger of M1Rs. In addition, techniques that diminish AA's concentration during M1R stimulation minimize N-current modulation. However, other studies suggest depletion of phosphatidylinositol-4,5-bisphosphate during M1R stimulation suffices to elicit modulation. In this study, we used an expression system to examine the physiological mechanisms regulating modulation. We found the β subunit (CaVβ) acts as a molecular switch regulating whether modulation results in enhancement or inhibition. In human embryonic kidney 293 cells, stimulation of M1Rs or neurokinin-1 receptors (NK-1Rs) inhibited activity of N channels formed by CaV2.2 and coexpressed with CaVβ1b, CaVβ3, or CaVβ4 but enhanced activity of N channels containing CaVβ2a. Exogenously applied AA produced the same pattern of modulation. Coexpression of CaVβ2a, CaVβ3, and CaVβ4 recapitulated the modulatory response previously seen in SCG neurons, implying heterogeneous association of CaVβ with CaV2.2. Further experiments with mutated, chimeric CaVβ subunits and free palmitic acid revealed that palmitoylation of CaVβ2a is essential for loss of inhibition. The data presented here fit a model in which CaVβ2a blocks inhibition, thus unmasking enhancement. Our discovery that the presence or absence of palmitoylated CaVβ2a toggles M1R- or NK-1R–mediated modulation of N current between enhancement and inhibition identifies a novel role for palmitoylation. Moreover, these findings predict that at synapses, modulation of N-channel activity by M1Rs or NK-1Rs will fluctuate between enhancement and inhibition based on the presence of palmitoylated CaVβ2a.
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Affiliation(s)
- John F Heneghan
- Department of Physiology, University of Massachusetts Medical School, Worcester, MA 01655, USA
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Molecular reconstruction of mGluR5a-mediated endocannabinoid signaling cascade in single rat sympathetic neurons. J Neurosci 2009; 29:13603-12. [PMID: 19864572 DOI: 10.1523/jneurosci.2244-09.2009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Endocannabinoids (eCB) such as 2-arachidonylglycerol (2-AG) are lipid metabolites that are synthesized in a postsynaptic neurons and act upon CB(1) cannabinoid receptors (CB(1)R) in presynaptic nerve terminals. This retrograde transmission underlies several forms of short and long term synaptic plasticity within the CNS. Here, we constructed a model system based on isolated rat sympathetic neurons, in which an eCB signaling cascade could be studied in a reduced, spatially compact, and genetically malleable system. We constructed a complete eCB production/mobilization pathway by sequential addition of molecular components. Heterologous expression of four components was required for eCB production and detection: metabotropic glutamate receptor 5a (mGluR5a), Homer 2b, diacylglycerol lipase alpha, and CB(1)R. In these neurons, application of l-glutamate produced voltage-dependent modulation of N-type Ca(2+) channels mediated by activation of CB(1)R. Using both molecular dissection and pharmacological agents, we provide evidence that activation of mGluR5a results in rapid enzymatic production of 2-AG followed by activation of CB(1)R. These experiments define the critical elements required to recapitulate retrograde eCB production and signaling in a single peripheral neuron. Moreover, production/mobilization of eCB can be detected on a physiologically relevant time scale using electrophysiological techniques. The system provides a platform for testing candidate molecules underlying facilitation of eCB transport across the plasma membrane.
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Roberts-Crowley ML, Mitra-Ganguli T, Liu L, Rittenhouse AR. Regulation of voltage-gated Ca2+ channels by lipids. Cell Calcium 2009; 45:589-601. [PMID: 19419761 PMCID: PMC2964877 DOI: 10.1016/j.ceca.2009.03.015] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2009] [Revised: 03/23/2009] [Accepted: 03/24/2009] [Indexed: 11/23/2022]
Abstract
Great skepticism has surrounded the question of whether modulation of voltage-gated Ca(2+) channels (VGCCs) by the polyunsaturated free fatty acid arachidonic acid (AA) has any physiological basis. Here we synthesize findings from studies of both native and recombinant channels where micromolar concentrations of AA consistently inhibit both native and recombinant activity by stabilizing VGCCs in one or more closed states. Structural requirements for these inhibitory actions include a chain length of at least 18 carbons and multiple double bonds located near the fatty acid's carboxy terminus. Acting at a second site, AA increases the rate of VGCC activation kinetics, and in Ca(V)2.2 channels, increases current amplitude. We present evidence that phosphatidylinositol 4,5-bisphosphate (PIP(2)), a palmitoylated accessory subunit (beta(2a)) of VGCCs and AA appear to have overlapping sites of action giving rise to complex channel behavior. Their actions converge in a physiologically relevant manner during muscarinic modulation of VGCCs. We speculate that M(1) muscarinic receptors may stimulate multiple lipases to break down the PIP(2) associated with VGCCs and leave PIP(2)'s freed fatty acid tails bound to the channels to confer modulation. This unexpectedly simple scheme gives rise to unanticipated predictions and redirects thinking about lipid regulation of VGCCs.
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Affiliation(s)
- Mandy L. Roberts-Crowley
- Program in Neuroscience, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 USA
- Department of Physiology, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 USA
| | - Tora Mitra-Ganguli
- Program in Neuroscience, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 USA
- Department of Physiology, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 USA
| | - Liwang Liu
- Department of Physiology, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 USA
| | - Ann R. Rittenhouse
- Program in Neuroscience, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 USA
- Department of Physiology, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 USA
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Kubista H, Kosenburger K, Mahlknecht P, Drobny H, Boehm S. Inhibition of transmitter release from rat sympathetic neurons via presynaptic M(1) muscarinic acetylcholine receptors. Br J Pharmacol 2009; 156:1342-52. [PMID: 19309359 DOI: 10.1111/j.1476-5381.2009.00136.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND AND PURPOSE M(2), M(3) and/or M(4) muscarinic acetylcholine receptors have been reported to mediate presynaptic inhibition in sympathetic neurons. M(1) receptors mediate an inhibition of K(v)7, Ca(V)1 and Ca(V)2.2 channels. These effects cause increases and decreases in transmitter release, respectively, but presynaptic M(1) receptors are generally considered facilitatory. Here, we searched for inhibitory presynaptic M(1) receptors. EXPERIMENTAL APPROACH In primary cultures of rat superior cervical ganglion neurons, Ca(2+) currents were recorded via the perforated patch-clamp technique, and the release of [(3)H]-noradrenaline was determined. KEY RESULTS The muscarinic agonist oxotremorine M (OxoM) transiently enhanced (3)H outflow and reduced electrically evoked release, once the stimulant effect had faded. The stimulant effect was enhanced by pertussis toxin (PTX) and was abolished by blocking M(1) receptors, by opening K(v)7 channels and by preventing action potential propagation. The inhibitory effect was not altered by preventing action potentials or by opening K(v)7 channels, but was reduced by PTX and omega-conotoxin GVIA. The inhibition remaining after PTX treatment was abolished by blockage of M(1) receptors or inhibition of phospholipase C. When [(3)H]-noradrenaline release was triggered independently of voltage-activated Ca(2+) channels (VACCs), OxoM failed to cause any inhibition. The inhibition of Ca(2+) currents by OxoM was also reduced by omega-conotoxin and PTX and was abolished by M(1) antagonism in PTX-treated neurons. CONCLUSIONS AND IMPLICATIONS These results demonstrate that M(1), in addition to M(2), M(3) and M(4), receptors mediate presynaptic inhibition in sympathetic neurons using phospholipase C to close VACCs.
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Affiliation(s)
- H Kubista
- Centre of Biomolecular Medicine and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
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