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Tauber M, Ben-Chaim Y. Voltage Sensors Embedded in G Protein-Coupled Receptors. Int J Mol Sci 2024; 25:5295. [PMID: 38791333 PMCID: PMC11120775 DOI: 10.3390/ijms25105295] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2024] [Revised: 05/08/2024] [Accepted: 05/09/2024] [Indexed: 05/26/2024] Open
Abstract
Some signaling processes mediated by G protein-coupled receptors (GPCRs) are modulated by membrane potential. In recent years, increasing evidence that GPCRs are intrinsically voltage-dependent has accumulated. A recent publication challenged the view that voltage sensors are embedded in muscarinic receptors. Herein, we briefly discuss the evidence that supports the notion that GPCRs themselves are voltage-sensitive proteins and an alternative mechanism that suggests that voltage-gated sodium channels are the voltage-sensing molecules involved in such processes.
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Affiliation(s)
| | - Yair Ben-Chaim
- Department of Natural Sciences, The Open University of Israel, Ra’anana 4353701, Israel
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2
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Cohen-Armon M. Are Voltage Sensors Really Embedded in Muscarinic Receptors? Int J Mol Sci 2023; 24:ijms24087538. [PMID: 37108699 PMCID: PMC10142193 DOI: 10.3390/ijms24087538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2023] [Revised: 04/16/2023] [Accepted: 04/18/2023] [Indexed: 04/29/2023] Open
Abstract
Unexpectedly, the affinity of the seven-transmembrane muscarinic acetylcholine receptors for their agonists is modulated by membrane depolarization. Recent reports attribute this characteristic to an embedded charge movement in the muscarinic receptor, acting as a voltage sensor. However, this explanation is inconsistent with the results of experiments measuring acetylcholine binding to muscarinic receptors in brain synaptoneurosomes. According to these results, the gating of the voltage-dependent sodium channel (VDSC) acts as the voltage sensor, generating activation of Go-proteins in response to membrane depolarization, and this modulates the affinity of muscarinic receptors for their cholinergic agonists.
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Affiliation(s)
- Malka Cohen-Armon
- The Sackler School of Medicine, Department of Physiology and Pharmacology, and Sagol School of Neuroscience, Tel-Aviv University, Tel-Aviv 69978, Israel
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3
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Ben Chaim Y, Bochnik S, Parnas I, Parnas H. Voltage affects the dissociation rate constant of the m2 muscarinic receptor. PLoS One 2013; 8:e74354. [PMID: 24019965 PMCID: PMC3760861 DOI: 10.1371/journal.pone.0074354] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Accepted: 08/05/2013] [Indexed: 11/18/2022] Open
Abstract
G-protein coupled receptors (GPCRs) comprise the largest protein family and mediate the vast majority of signal transduction processes in the body. Until recently GPCRs were not considered to be voltage dependent. Newly it was shown for several GPCRs that the first step in GPCR activation, the binding of agonist to the receptor, is voltage sensitive: Voltage shifts the receptor between two states that differ in their binding affinity. Here we show that this shift involves the rate constant of dissociation. We used the m2 muscarinic receptor (m2R) a prototypical GPCR and measured directly the dissociation of [(3)H]ACh from m2R expressed Xenopus oocytes. We show, for the first time, that the voltage dependent change in affinity is implemented by voltage shifting the receptor between two states that differ in their rate constant of dissociation. Furthermore, we provide evidence that suggest that the above shift is achieved by voltage regulating the coupling of the GPCR to its G protein.
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Affiliation(s)
- Yair Ben Chaim
- Department of Natural and Life Sciences, The Open University of Israel, Ra’anana, Israel
| | - Shimrit Bochnik
- Department of Neurobiology, Institute of Life Sciences, The Hebrew University, Jerusalem, Israel
| | - Itzchak Parnas
- Department of Neurobiology, Institute of Life Sciences, The Hebrew University, Jerusalem, Israel
| | - Hanna Parnas
- Department of Neurobiology, Institute of Life Sciences, The Hebrew University, Jerusalem, Israel
- * E-mail:
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4
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The plasma membrane potential and the organization of the actin cytoskeleton of epithelial cells. Int J Cell Biol 2012; 2012:121424. [PMID: 22315611 PMCID: PMC3272338 DOI: 10.1155/2012/121424] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2011] [Accepted: 10/08/2011] [Indexed: 12/22/2022] Open
Abstract
The establishment and maintenance of the polarized epithelial phenotype require a characteristic organization of the cytoskeletal components. There are many cellular effectors involved in the regulation of the cytoskeleton of epithelial cells. Recently, modifications in the plasma membrane potential (PMP) have been suggested to participate in the modulation of the cytoskeletal organization of epithelia. Here, we review evidence showing that changes in the PMP of diverse epithelial cells promote characteristic modifications in the cytoskeletal organization, with a focus on the actin cytoskeleton. The molecular paths mediating these effects may include voltage-sensitive integral membrane proteins and/or peripheral proteins sensitive to surface potentials. The voltage dependence of the cytoskeletal organization seems to have implications in several physiological processes, including epithelial wound healing and apoptosis.
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5
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Parnas I, Parnas H. Control of neurotransmitter release: From Ca2+ to voltage dependent G-protein coupled receptors. Pflugers Arch 2010; 460:975-90. [PMID: 20811904 DOI: 10.1007/s00424-010-0872-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2010] [Revised: 08/08/2010] [Accepted: 08/09/2010] [Indexed: 11/28/2022]
Abstract
This review discusses two theories that try to explain mechanisms of control of neurotransmitter release in fast synapses: the Ca(2+) hypothesis and the Ca(2+) voltage hypothesis. The review summarizes experimental results that are incompatible with predictions from the Ca(2+) hypothesis and concludes that Ca(2+) is involved in the control of the amount of release but not in the control of the time course of evoked release, i.e., initiation and termination of evoked release. Results summarizing direct effects of changes in membrane potential on the release machinery are then presented. These changes in membrane potential affect the affinity (for the transmitter) of presynaptic autoinhibitory G-protein coupled receptors (GPCRs). The voltage dependence of these GPCRs and their pivotal role in determining the time course of evoked release is discussed.
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Affiliation(s)
- Itzchak Parnas
- Department of Neurobiology, Institute of life Science, The Hebrew University, Edmon Safra Campus, Jerusalem, Israel.
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6
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Mahaut-Smith MP, Martinez-Pinna J, Gurung IS. A role for membrane potential in regulating GPCRs? Trends Pharmacol Sci 2008; 29:421-9. [PMID: 18621424 DOI: 10.1016/j.tips.2008.05.007] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2007] [Revised: 05/16/2008] [Accepted: 05/28/2008] [Indexed: 10/21/2022]
Abstract
G-protein-coupled receptors (GPCRs) have ubiquitous roles in transducing extracellular signals into cellular responses. Therefore, the concept that members of this superfamily of surface proteins are directly modulated by changes in membrane voltage could have widespread consequences for cell signalling. Although several studies have indicated that GPCRs can be voltage dependent, particularly P2Y(1) receptors in the non-excitable megakaryocyte, the evidence has been mostly indirect. Recent work on muscarinic receptors has stimulated substantial interest in this field by reporting the first voltage-dependent charge movements for a GPCR. An underlying mechanism is proposed whereby a voltage-induced conformational change in the receptor alters its ability to couple to the G protein and thereby influences its affinity for an agonist. We discuss the strength of the evidence behind this hypothesis and include suggestions for future work. We also describe other examples in which direct voltage control of GPCRs can account for effects of membrane potential on downstream signals and highlight the possible physiological consequences of this phenomenon.
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Affiliation(s)
- Martyn P Mahaut-Smith
- Department of Cell Physiology and Pharmacology, University of Leicester, LE1 9HN, UK.
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7
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Ben-Chaim Y, Chanda B, Dascal N, Bezanilla F, Parnas I, Parnas H. Movement of 'gating charge' is coupled to ligand binding in a G-protein-coupled receptor. Nature 2006; 444:106-9. [PMID: 17065983 DOI: 10.1038/nature05259] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2006] [Accepted: 09/18/2006] [Indexed: 11/09/2022]
Abstract
Activation by agonist binding of G-protein-coupled receptors (GPCRs) controls most signal transduction processes. Although these receptors span the cell membrane, they are not considered to be voltage sensitive. Recently it was shown that both the activity of GPCRs and their affinity towards agonists are regulated by membrane potential. However, it remains unclear whether GPCRs intrinsically respond to changes in membrane potential. Here we show that two prototypical GPCRs, the m2 and m1 muscarinic receptors (m2R and m1R), display charge-movement-associated currents analogous to 'gating currents' of voltage-gated channels. The gating charge-voltage relationship of m2R correlates well with the voltage dependence of the affinity of the receptor for acetylcholine. The loop that couples m2R and m1R to their G protein has a crucial function in coupling voltage sensing to agonist-binding affinity. Our data strongly indicate that GPCRs serve as sensors for both transmembrane potential and external chemical signals.
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MESH Headings
- Acetylcholine/metabolism
- Animals
- Electric Conductivity
- Ion Channel Gating
- Ligands
- Membrane Potentials/physiology
- Movement
- Mutant Proteins/agonists
- Mutant Proteins/genetics
- Mutant Proteins/metabolism
- Mutation/genetics
- Oocytes/metabolism
- Protein Binding
- Receptor, Muscarinic M1/agonists
- Receptor, Muscarinic M1/genetics
- Receptor, Muscarinic M1/metabolism
- Receptor, Muscarinic M2/agonists
- Receptor, Muscarinic M2/genetics
- Receptor, Muscarinic M2/metabolism
- Receptors, G-Protein-Coupled/agonists
- Receptors, G-Protein-Coupled/chemistry
- Receptors, G-Protein-Coupled/genetics
- Receptors, G-Protein-Coupled/metabolism
- Signal Transduction
- Xenopus
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Affiliation(s)
- Yair Ben-Chaim
- Department of Neurobiology, The Hebrew University, Jerusalem, 91904, Israel
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8
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Eltit JM, García AA, Hidalgo J, Liberona JL, Chiong M, Lavandero S, Maldonado E, Jaimovich E. Membrane electrical activity elicits inositol 1,4,5-trisphosphate-dependent slow Ca2+ signals through a Gbetagamma/phosphatidylinositol 3-kinase gamma pathway in skeletal myotubes. J Biol Chem 2006; 281:12143-54. [PMID: 16513646 DOI: 10.1074/jbc.m511218200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Tetanic electrical stimulation of myotubes evokes a ryanodine receptor-related fast calcium signal, during the stimulation, followed by a phospholipase C/inositol 1,4,5-trisphosphate-dependent slow calcium signal few seconds after stimulus end. L-type calcium channels (Cav 1.1, dihydropyridine receptors) acting as voltage sensors activate an unknown signaling pathway involved in phospholipase C activation. We demonstrated that both G protein and phosphatidylinositol 3-kinase were activated by electrical stimulation, and both the inositol 1,4,5-trisphosphate rise and slow calcium signal induced by electrical stimulation were blocked by pertussis toxin, by a Gbetagamma scavenger peptide, and by phosphatidylinositol 3-kinase inhibitors. Immunofluorescence using anti-phosphatidylinositol 3-kinase gamma antibodies showed a clear location in striations within the cytoplasm, consistent with a position near the I band region of the sarcomere. The time course of phosphatidylinositol 3-kinase activation, monitored in single living cells using a pleckstrin homology domain fused to green fluorescent protein, was compatible with sequential phospholipase Cgamma1 activation as confirmed by phosphorylation assays for the enzyme. Co-transfection of a dominant negative form of phosphatidylinositol 3-kinase gamma inhibited the phosphatidylinositol 3-kinase activity as well as the slow calcium signal. We conclude that Gbetagamma/phosphatidylinositol 3-kinase gamma signaling pathway is involved in phospholipase C activation and the generation of the slow calcium signal induced by tetanic stimulation. We postulate that membrane potential fluctuations in skeletal muscle cells can activate a pertussis toxin-sensitive G protein, phosphatidylinositol 3-kinase, phospholipase C pathway toward modulation of long term, activity-dependent plastic changes.
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Affiliation(s)
- José M Eltit
- Centro de Estudios Moleculares de la Célula, Instituto de Ciencias Biomédicas, Facultades de Medicina y Ciencias Químicas y Farmacéuticas, Universidad de Chile, Independecia 1027, Santiago 7, Chile
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9
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Marcaggi P, Jeanne M, Coles JA. Neuron-glial trafficking of NH4+ and K+: separate routes of uptake into glial cells of bee retina. Eur J Neurosci 2004; 19:966-76. [PMID: 15009144 DOI: 10.1111/j.0953-816x.2004.03165.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Ammonium (NH4+ and/or NH3) and K+ are released from active neurons and taken up by glial cells, and can modify glial cell behaviour. Study of these fluxes is most advanced in the retina of the honeybee drone, which consists essentially of identical neurons (photoreceptors) and identical glial cells (outer pigment cells). In isolated bee retinal glial cells, ammonium crosses the membrane as NH4+ on a Cl- cotransporter. We have now investigated, in the more physiological conditions of a retinal slice, whether the NH4+-Cl- cotransporter can transport K+ and whether the major K+ conductance can transport NH4+. We increased [NH4+] or [K+] in the superfusate and monitored uptake by recording from the glial cell syncytium or from interstitial space with microelectrodes selective for H+ or K+. In normal superfusate solution, ammonium acidified the glial cells but, after 6 min superfusion in low [Cl-] solution, ammonium alkalinized them. In the same low [Cl-] conditions, the rise in intraglial [K+] induced by an increase in superfusate [K+] was unchanged, i.e. no K+ flux on the Cl- cotransporter was detected. Ba2+ (5 mm) abolished the glial depolarization induced by K+ released from photoreceptors but did not reduce NH4+uptake. We estimate that when extracellular [NH4+] is increased, 62-100% is taken up by the NH4+-Cl- cotransporter and that when K+ is increased, 77-100% is taken up by routes selective for K+. This separation makes it possible that the glial uptake of NH4+ and of K+, and hence their signalling roles, might be regulated separately.
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Affiliation(s)
- Païkan Marcaggi
- INSERM U394, Institut François Magendie, 33077 Bordeaux cedex, France
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10
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Nakahari T, Yoshida H, Imai Y, Fujiwara S, Ohnishi A, Shimamoto C, Katsu KI. Inhibition of Ca(2+) entry caused by depolarization in acetylcholine-stimulated antral mucous cells of guinea pig: G protein regulation of Ca(2+) permeable channels. THE JAPANESE JOURNAL OF PHYSIOLOGY 1999; 49:545-50. [PMID: 10603441 DOI: 10.2170/jjphysiol.49.545] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The effects of depolarizing conditions resulting from increasing extracellular K(+) concentration or nystatin treatment on intracellular Ca(2+) concentration ([Ca(2+)](i)) were studied in guinea pig antral mucous cells following acetylcholine (ACh) stimulation. ACh stimulation evoked a biphasic increase in [Ca(2+)](i), that is, an initial transient increase followed by a plateau. Depolarizing conditions reduced the [Ca(2+)](i) in the plateau phase during ACh stimulation. However, pertussis toxin (PTX, a G protein inhibitor) treatment caused [Ca(2+)](i) in the ACh-evoked plateau phase to increase under depolarizing conditions, while it had no effect on [Ca(2+)](i) under hyperpolarized conditions. Based on these observations, Ca(2+) permeable channels are regulated by a G protein which is activated by depolarized conditions and inhibited by hyperpolarized conditions and PTX; activation of the G protein (depolarization) causes Ca(2+) permeable channels to inhibit, and in turn, inhibition of the G protein (hyperpolarization) causes them to activate.
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Affiliation(s)
- T Nakahari
- Department of Physiology, Osaka Medical College, Takatsuki, 569-8686, Japan.
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11
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Anis Y, Nürnberg B, Visochek L, Reiss N, Naor Z, Cohen-Armon M. Activation of Go-proteins by membrane depolarization traced by in situ photoaffinity labeling of galphao-proteins with [alpha32P]GTP-azidoanilide. J Biol Chem 1999; 274:7431-40. [PMID: 10066808 DOI: 10.1074/jbc.274.11.7431] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Evidence for depolarization-induced activation of G-proteins in membranes of rat brain synaptoneurosomes has been previously reported (Cohen-Armon, M., and Sokolovsky, M. (1991) J. Biol. Chem. 266, 2595-2605; Cohen-Armon, M., and Sokolovsky, M. (1993) J. Biol. Chem. 268, 9824-9838). In the present work we identify the activated G-proteins as Go-proteins by tracing their depolarization-induced in situ photoaffinity labeling with [alpha32P]GTP-azidoanilide (GTPAA). Labeled GTPAA was introduced into transiently permeabilized rat brain-stem synaptoneurosomes. The resealed synaptoneurosomes, while being UV-irradiated, were depolarized. Relative to synaptoneurosomes at resting potential, the covalent binding of [alpha32P]GTPAA to Galphao1- and Galphao3-proteins, but not to Galphao2- isoforms, was enhanced by 5- to 7-fold in depolarized synaptoneurosomes, thereby implying an accelerated exchange of GDP for [alpha32P]GTPAA. Their depolarization-induced photoaffinity labeling was independent of stimulation of Go-protein-coupled receptors and could be reversed by membrane repolarization, thus excluding induction by transmitters release. It was, however, dependent on depolarization-induced activation of the voltage-gated sodium channels (VGSC), regardless of Na+ current. The alpha subunit of VGSC was cross-linked and co-immunoprecipitated with Galphao-proteins in depolarized brain-stem and cortical synaptoneurosomes. VGSC alpha subunit most efficiently cross-linked with guanosine 5'-O-2-thiodiphosphate-bound rather than to guanosine 5'-O-(3-thiotriphosphate)-bound Galphao-proteins in isolated synaptoneurosomal membranes. These findings support a possible involvement of VGSC in depolarization-induced activation of Go-proteins.
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Affiliation(s)
- Y Anis
- Department of Physiology and The Cardiac Research Institute, Sackler School of Medicine, Tel-Aviv University, 69978 Tel-Aviv, Israel
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12
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Gosling M, Harley SL, Turner RJ, Carey N, Powell JT. Human saphenous vein endothelial cells express a tetrodotoxin-resistant, voltage-gated sodium current. J Biol Chem 1998; 273:21084-90. [PMID: 9694861 DOI: 10.1074/jbc.273.33.21084] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Whole-cell patch-clamp electrophysiological investigation of endothelial cells cultured from human saphenous vein (HSVECs) has identified a voltage-gated Na+ current with a mean peak magnitude of -595 +/- 49 pA (n = 75). This current was inhibited by tetrodotoxin (TTX) in a concentration-dependent manner, with an IC50 value of 4.7 microM, suggesting that it was of the TTX-resistant subtype. An antibody directed against the highly conserved intracellular linker region between domains III and IV of known Na+ channel alpha-subunits was able to retard current inactivation when applied intracellularly. This antibody identified a 245-kDa protein from membrane lysates on Western blotting and positively immunolabeled both cultured HSVECs and intact venous endothelium. HSVECs were also shown by reverse transcription-polymerase chain reaction to contain transcripts of the hH1 sodium channel gene. The expression of Na+ channels by HSVECs was shown using electrophysiology and cell-based enzyme-linked immunosorbent assay to be dependent on the concentration and source of human serum. Together, these results suggest that TTX-resistant Na+ channels of the hH1 isoform are expressed in human saphenous vein endothelium and that the presence of these channels is controlled by a serum factor.
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Affiliation(s)
- M Gosling
- Department of Vascular Surgery, Imperial College School of Medicine at Charing Cross, Charing Cross Hospital, Fulham Palace Road, London W6 8RF, United Kingdom.
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13
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Wassarman PM, Florman HM. Cellular Mechanisms During Mammalian Fertilization. Compr Physiol 1997. [DOI: 10.1002/cphy.cp140124] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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14
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Nivarthi RN, Grant GJ, Turndorf H, Bansinath M. Effect of intrathecally administered local anesthetics on protein phosphorylation in the spinal cord. Biochem Pharmacol 1997; 53:979-86. [PMID: 9174111 DOI: 10.1016/s0006-2952(97)00119-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
To elucidate the biochemical mechanisms of spinal anesthesia, we studied the effects of procaine and tetracaine on protein phosphorylation in the mouse spinal cord. Mice were injected intrathecally with either procaine, tetracaine (67 mM/approximately 2%, 10 microL, N = 5/drug), or saline (N = 4/group). Five minutes after injection, animals were killed with a guillotine, and the spinal cord was removed. The caudal 3-cm cord segment was homogenized and centrifuged, and an aliquot of the supernatant was used for phosphorylation assays. Calcium-dependent phosphorylation was initiated by incubating the samples in buffer containing [gamma-32P]ATP at 37 degrees for 30 min. The proteins were electrophoresed using slab gel and two-dimensional electrophoresis, and phosphorylated proteins were visualized by autoradiography. The data demonstrated that spinal anesthesia changes the phosphorylation state of five endogenous substrate proteins with apparent molecular masses of 130 (protein-a), 105 (protein-b), 55 (protein-c), 47 (protein-d), and 33 (protein-e) kDa. In two-dimensional electrophoresis, protein-a resolved into two proteins (a1 and a2). Analysis of variance of the densitometric data suggested a significant effect for the treatment (F(2,16) 735, P < 0.00005). Post hoc comparisons with the saline-treated controls, using the Newman-Keuls test, indicated that local anesthetics significantly affected phosphoproteins (P < 0.05) except for protein-al in the tetracaine-treated group. Further characterization of these phosphoproteins should aid in determining their role in the signal transduction cascade affected by spinal anesthesia.
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Affiliation(s)
- R N Nivarthi
- Department of Anesthesiology, School of Medicine, New York University Medical Center, New York 10016, U.S.A
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15
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Cohen-Armon M, Hammel I, Anis Y, Homburg S, Dekel N. Evidence for endogenous ADP-ribosylation of GTP-binding proteins in neuronal cell nucleus. Possible induction by membrane depolarization. J Biol Chem 1996; 271:26200-8. [PMID: 8824268 DOI: 10.1074/jbc.271.42.26200] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
GTP-binding protein(s) recognized by antibodies against the alpha-subunits of Gi- and Go-proteins were detected in crude nuclei isolated from rat brain stem and cortex. Immunohistochemical staining indicated that in the cortex these proteins are perinuclear, or are embedded in the nuclear membrane. Evidence is presented for an endogenous ADP-ribosylation of these proteins, which competes with their PTX-catalyzed ADP-ribosylation. The endogenous reaction has the characteristics of nonenzymatic ADP-ribosylation of cysteine residues, known to involve NAD-glycohydrolase activity. In vitro experiments showed that the alpha-subunit of Go-proteins in the cell membrane also acts as a substrate of this endogenous ADP-ribosylation. The in situ effect of membrane depolarization on the nuclear GTP-binding proteins may be attributable to their depolarization-induced endogenous ADP-ribosylation, suggesting a novel signaling mechanism in neuronal cells in the central nervous system.
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Affiliation(s)
- M Cohen-Armon
- Department of Physiology and Pharmacology, Neufeld Cardiac Research Institute, Tel-Aviv University, 69978 Tel-Aviv, Israel
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16
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Spinal Anesthesia by Local Anesthetics Stimulates the Enzyme Protein Kinase C and Induces the Expression of an Immediate Early Oncogene, c-Fos. Anesth Analg 1996. [DOI: 10.1213/00000539-199609000-00018] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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17
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Nivarthi RN, Grant GJ, Turndorf H, Bansinath M. Spinal anesthesia by local anesthetics stimulates the enzyme protein kinase C and induces the expression of an immediate early oncogene, c-Fos. Anesth Analg 1996; 83:542-7. [PMID: 8780278 DOI: 10.1097/00000539-199609000-00018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
To understand the biochemical mechanisms involved in spinal anesthesia, we measured protein kinase C (PKC) activity and expression of immediate early oncogene protein, c-Fos, in the spinal cord. Spinal anesthesia was induced in mice using intrathecal injection of either 10 microL procaine or tetracaine (0.067 M/approximately 2%). Control groups were treated with either saline or ethanol. Animals were killed at 1, 5, and 15 min after the injection and the caudal 3 cm of the spinal cord was processed for biochemical analysis. PKC activity was measured by the transfer of a phosphate group from [gamma-32P]adenosine 5'-triphosphate to the threonine group on a synthetic peptide specific for PKC. Western blot analysis was used to detect changes in c-Fos protein expression. When compared to saline-treated controls, PKC activity was increased significantly (P < 0.0005) in procaine- and tetracaine-treated groups whereas ethanol decreased PKC activity. The less lipid-soluble procaine produced a larger increase in PKC activity than did the more lipid-soluble tetracaine. Moreover, parallel to the effect on PKC activity, procaine was more potent than tetracaine as a c-Fos inducer. These results implicate some role for a PKC- and c-Fos-dependent pathway in the mechanism of spinal anesthesia. However, these results also demonstrate a lack of correlation between an increase in PKC levels and either potency or lipid solubility of the anesthetics. The increased PKC activity may not be the sole mechanism for spinal anesthesia. These data on the effects of local anesthetics on PKC activity and c-Fos in vivo are of relevance for studies aimed at delineating the biochemical basis of spinal and epidural anesthesia.
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Affiliation(s)
- R N Nivarthi
- Department of Anesthesiology, School of Medicine, New York University Medical Center, NY 10016, USA
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18
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Sontheimer H, Black JA, Waxman SG. Voltage-gated Na+ channels in glia: properties and possible functions. Trends Neurosci 1996; 19:325-31. [PMID: 8843601 DOI: 10.1016/0166-2236(96)10039-4] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Glial cells are nervous-system cells that have classically been considered to be inexcitable. Despite their lack of electrical excitability, they can express voltage-activated Na+ channels with properties similar to the Na+ channels used by excitable cells to generate action potentials. The functional role that these voltage-activated Na+ channels play in glia is unclear. Three functions have been proposed: (1) glial cells might synthesize Na+ channels and donate them to adjacent neurons, thereby reducing the biosynthetic load of neurons; (2) Na+ channels might endow glial cells with the ability to sense electric activity of neighboring neurons, and might thus play a role in neuro-glial communication; and (3) Na+ influx through voltage-gated Na+ channels could be important to fuel the glial (Na+,K+)-ATPase, thereby facilitating and possibly modulating K+ uptake from the extracellular space.
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Affiliation(s)
- H Sontheimer
- Neurobiology Research Center, University of Alabama at Birmingham 35294-0021, USA
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Terenzi H, da Costa Maia J. Identification of a developmentally regulated Gα protein in Blastocladiella emersonii. FEMS Microbiol Lett 1996. [DOI: 10.1111/j.1574-6968.1996.tb08182.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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20
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Gordienko DV, Tsukahara H. Tetrodotoxin-blockable depolarization-activated Na+ currents in a cultured endothelial cell line derived from rat interlobar arter and human umbilical vein. Pflugers Arch 1994; 428:91-3. [PMID: 7971164 DOI: 10.1007/bf00374756] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Voltage-dependent Na+ current (INa) was identified in cultured endothelial cells derived from rat interlobar artery (RIAE cells) and human umbilical vein (HUVE cells). Tetrodotoxin (TTX) reduced INa in a dose-dependent manner with the apparent dissociation constant (Kd) of 1.4 microM. Low sensitivity of INa to TTX as well as its kinetics and voltage-dependent properties indicates that voltage-gated Na channels expressed in vascular endothelial cells belong to the so-called TTX-resistant type.
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Affiliation(s)
- D V Gordienko
- Department of Medicine, State University of New York at Stony Brook 11794-8152
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Chao TI, Skachkov SN, Eberhardt W, Reichenbach A. Na+ channels of Müller (glial) cells isolated from retinae of various mammalian species including man. Glia 1994; 10:173-85. [PMID: 8194860 DOI: 10.1002/glia.440100304] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Within the last few years, the expression of voltage-dependent, TTX-sensitive Na+ channels has been demonstrated in several types of neuroglial cells such as astrocytes and Schwann cells. Recently, we reported the occurrence of such Na+ currents in retinal Müller (glial) cells from dog and cat. This paper deals with the description of the properties of Na+ currents in Müller cells isolated from retinae of several mammalian species, as well as from human retinae. These Na+ currents were eliminated by TTX (1 microM), and by exposure to sodium-free extracellular solution; typically, they were demonstrable only after blocking most of the K+ conductance by Ba2+ (1 mM). Voltage-dependent activation and inactivation characteristics and time constants of the Na+ currents were similar to those of currents carried by neuronal Na+ channels. The estimated number of sodium channels per cell was low (about 1,500 channels per 7,500 microns 2), and the K+ conductance exceeded the peak Na+ conductance by an average factor of 5. Thus, the cells were incapable of generating action-potential-like responses under current clamp. Modelling estimations show that triggering of glial Na+ currents under physiological conditions, if any, can at best occur by emhaptic transmission at perinodal sites of optic axons. It is speculated that glial Na+ channels might be involved in neuroglial signalling events.
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Affiliation(s)
- T I Chao
- Carl Ludwig Institute of Physiology, Leipzig University, Germany
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