101
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Nirenberg MJ, Chan J, Liu Y, Edwards RH, Pickel VM. Vesicular monoamine transporter-2: immunogold localization in striatal axons and terminals. Synapse 1997; 26:194-8. [PMID: 9131778 DOI: 10.1002/(sici)1098-2396(199706)26:2<194::aid-syn10>3.0.co;2-y] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The vesicular monoamine transporter-2 (VMAT2) mediates the reserpine-sensitive neuronal uptake of monoamines into vesicles and other intracellular organelles. Accordingly, this transporter is expressed at high levels in regions that contain a dense monoamine innervation, such as the rat dorsolateral striatum. We used ultrastructural immunocytochemistry in this region to show that immunogold labeling for VMAT2 is present in varicose axonal processes, many of which also contain the catecholamine-synthesizing enzyme tyrosine-hydroxylase. Within these mainly dopaminergic processes, VMAT2 was associated with small synaptic vesicles (SSVs) and more rarely with large dense-core vesicles or tubulovesicles. These findings suggest that SSVs are the major organelles involved in the storage and release of dopamine in the dorsolateral striatum.
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Affiliation(s)
- M J Nirenberg
- Department of Neurology and Neuroscience, Cornell University Medical College, New York, New York 10021, USA.
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102
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Adamson CR, Emley TE, Herbig LJ, Near JA. Effects of nerve growth factor on dihydrotetrabenazine binding to PC12 cells. Neurochem Int 1997; 30:411-5. [PMID: 9106255 DOI: 10.1016/s0197-0186(96)00076-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Tetrabenazine and dihydrotetrabenzaine (TBZOH) are potent inhibitors of substrate transport by the predominant forms of the vesicular monoamine transporter (VMAT) present in bovine brain synaptic vesicles and bovine adrenal medullary chromaffin vesicles. Radiolabeled TBZOH binds to these preparations with apparent dissociation constants in the low nanomolar range. However, tetrabenazine is a much less potent inhibitor of transport by rVMAT1, a form of the transporter cloned from a rat pheochromocytoma (PC12) cDNA library and expressed in CHO cells. Reported attempts to observe binding of [3H]TBZOH to rVMAT1 have not been successful. We examined binding of [3H]TBZOH to a crude membrane fraction from PC12 cells. Computerized nonlinear least squares curve fitting revealed two classes of binding sites (Kd1 = 1.5 nM, R1 = 0.2 pmol/mg protein, Kd2 = 340 nM, R2 = 15.2 pmol/mg protein). While the identity of the higher affinity sites is not certain, their high affinity for TBZOH suggests that they may be associated with rVMAT2. The lower affinity sites are likely to be associated with rVMAT1 on the basis of their affinity for TBZOH and sensitivity to inhibition of TBZOH binding by transporter substrates and inhibitors. NGF-treated PC12 cells also exhibited two classes of sites (Kd1 = 1.9 nM, R1 = 0.18 pmol/mg protein; Kd2 = 370 nM, R2 = 23.7 pmol/mg protein). While there were no significant differences between control and NGF-treated cells in binding capacity of the higher affinity sites, nor in apparent dissociation constants for either class of sites, there was a highly significant increase in number of lower affinity binding sites in the NGF-treated cells (p = 0.001). These results provide direct evidence that the differential sensitivity of rat brain and adrenal catecholamine stores to depletion by tetrabenazine and its derivatives is due to a much lower affinity of rVMAT1 for these compounds, and that NGF treatment may increase levels of rVMAT1 expression in PC12 cells.
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Affiliation(s)
- C R Adamson
- Medical Sciences Program, Indiana University School of Medicine, Bloomington 47405, USA
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103
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Krantz DE, Peter D, Liu Y, Edwards RH. Phosphorylation of a vesicular monoamine transporter by casein kinase II. J Biol Chem 1997; 272:6752-9. [PMID: 9045708 DOI: 10.1074/jbc.272.10.6752] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The vesicular monoamine transporters (VMATs) package monoamine neurotransmitters into secretory vesicles for regulated exocytotic release. One isoform occurs in the adrenal gland (VMAT1) and another in the brain (VMAT2). To assess their potential for regulation, we have investigated the phosphorylation of the VMATs. Using heterologous expression in Chinese hamster ovary, PC12, and COS cells, we find that rat VMAT2, but not VMAT1, is constitutively phosphorylated. Phosphoamino acid analysis indicates that this phosphorylation occurs on serine residues, and the analysis of VMAT1-VMAT2 chimeras and site-directed mutagenesis localize the phosphorylation sites to serines 512 and 514 at the carboxyl terminus of VMAT2. Since these residues occur in an acidic region, we tested the ability of the acidotropic kinases casein kinase I (CKI) and casein kinase II (CKII) to phosphorylate bacterial fusion proteins containing the carboxyl terminus of VMAT2. Purified CKI and CKII phosphorylate the wild-type carboxyl terminus of VMAT2, but not a double mutant with both serines 512 and 514 replaced by alanine. The protein kinase inhibitor CKI-7 and unlabeled GTP both block in vitro phosphorylation by cell homogenates, indicating a role for CKII and possibly CKI in vivo. Both kinases phosphorylate the VMAT2 fusion protein to a much greater extent than a similar fusion protein containing the carboxyl terminus of VMAT1, consistent with differential phosphorylation of the two transporters observed in intact cells. These results provide the first demonstration of phosphorylation of a vesicular neurotransmitter transporter and a potential mechanism for differential regulation of the two VMATs.
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Affiliation(s)
- D E Krantz
- Department of Neurology, University of California School of Medicine, San Francisco, California 94143-0435, USA
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104
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Liu Y, Edwards RH. The role of vesicular transport proteins in synaptic transmission and neural degeneration. Annu Rev Neurosci 1997; 20:125-56. [PMID: 9056710 DOI: 10.1146/annurev.neuro.20.1.125] [Citation(s) in RCA: 217] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Classical neurotransmitters are synthesized in the cytoplasm, so they require transport into secretory vesicles for regulated exocytotic release. Previous work has identified distinct vesicular transport activities for the different classical transmitters, and all depend on the H+-electrochemical gradient across the vesicle membrane but differ in the extent to which they rely on the chemical and electrical components of this gradient. Drugs that interfere with vesicular amine transport have implicated this activity in psychiatric disease. Selection for a cDNA encoding vesicular amine transport in the neurotoxin MPP+ also implicates the activity in Parkinson's disease. Molecular cloning of vesicular monoamine transporters shows sequence similarity to bacterial antibiotic resistance proteins, supporting a role for transport in detoxification and defining a novel mammalian gene family that now also includes a transporter for acetylcholine. Current work focuses on the mechanism of transport and the role that regulation of activity and its subcellular localization have in transmitter release, behavior, and neural degeneration.
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Affiliation(s)
- Y Liu
- Department of Neurology, University of California San Francisco 94143-0435, USA
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105
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Pickel VM, Nirenberg MJ, Milner TA. Ultrastructural view of central catecholaminergic transmission: immunocytochemical localization of synthesizing enzymes, transporters and receptors. JOURNAL OF NEUROCYTOLOGY 1996; 25:843-856. [PMID: 9023729 DOI: 10.1007/bf02284846] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Affiliation(s)
- V M Pickel
- Department of Neurology and Neuroscience, Cornell University Medical College, New York, NY 10021, USA
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106
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Schweitzer ES, Jeng CJ, Tao-Cheng JH. Selective localization and regulated release of calcitonin gene-related peptide from dense-core vesicles in engineered PC12 cells. J Neurosci Res 1996; 46:519-30. [PMID: 8951664 DOI: 10.1002/(sici)1097-4547(19961201)46:5<519::aid-jnr1>3.0.co;2-m] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Introduction of the gene for calcitonin into the neuroendocrine PC12 cell line resulted in the expression of the neuronal-specific splice product, calcitonin gene-related peptide (CGRP). Expression of this neuropeptide did not require treatment of the PC12 cells with NGF. By all available criteria, including biochemical, immunological, and morphological analysis, we have determined that the CGRP in stably transfected PC12 cells is sorted selectively into the large, dense-core catecholamine-containing secretory vesicles. Conversely, the CGRP is excluded from the small, synaptophysin-rich vesicles present in the same cells. Stimulation conditions that trigger the release of catecholamines cause a parallel burst in the release of CGRP. In all these respects, the engineered PC12 cells process the foreign CGRP in a manner similar to that seen in spinal motor neurons in vivo. These results indicate that this small (37 amino acids) peptide contains sorting information sufficient for targeting to large, dense-core vesicles in heterologous cells, placing very narrow constraints on the possible location of sorting signals. In addition, this CGRP-expressing cell line opens the possibility of studying the physiological role of CGRP in the establishment and maintenance of neuromuscular contacts.
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Affiliation(s)
- E S Schweitzer
- Department of Neurobiology, University of California, Los Angeles Medical School, USA
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107
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Steiner-Mordoch S, Shirvan A, Schuldiner S. Modification of the pH profile and tetrabenazine sensitivity of rat VMAT1 by replacement of aspartate 404 with glutamate. J Biol Chem 1996; 271:13048-54. [PMID: 8662678 DOI: 10.1074/jbc.271.22.13048] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Vesicular monoamine transporters (VMAT) catalyze transport of serotonin, dopamine, epinephrine, and norepinephrine into subcellular storage organelles in a variety of cells. Accumulation of the neurotransmitter depends on the proton electrochemical gradient (Delta micro H+) across the organelle membrane and involves VMAT-mediated exchange of two lumenal protons with one cytoplasmic amine. Mutagenic analysis of the role of two conserved Asp residues located in transmembrane segments X and XI of rat VMAT type I reveals an important role of these two residues in catalysis. Replacement of Asp 431 with either Glu or Ser inhibits VMAT-mediated [3H]serotonin transport. The mutated proteins are unimpaired in ligand recognition as measured with the high affinity ligand [3H]reserpine or coupling to the proton electrochemical gradient as judged by its ability to accelerate [3H]reserpine binding. Therefore, the Asp residue is needed as such in this position and even a conservative replacement with Glu generates a protein that can catalyze only partial reactions but cannot complete the transport cycle. Replacement of Asp 404 with either Ser or Cys inhibits all VMAT-mediated reactions measured. However, replacement with Glu generated a protein that catalyzed [3H]serotonin transport with modified properties. Whereas the mutated protein binds [3H]reserpine to normal levels and the pH optimum of this reaction is only slightly affected, the optimum pH for transport activity shifted to the acid side and became very sharp; in addition the sensitivity to the inhibitor tetrabenazine increased significantly in this mutated protein. The results point to the need of a carboxyl moiety in position 404. A slight change in its relative location or in the environment around it has a significant effect on the pK of group(s) involved in steps after ligand recognition and coupling to the first H+.
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Affiliation(s)
- S Steiner-Mordoch
- Alexander Silberman Institute of Life Sciences, Hebrew University, Jerusalem, 91904 Israel
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108
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Weihe E, Tao-Cheng JH, Schäfer MK, Erickson JD, Eiden LE. Visualization of the vesicular acetylcholine transporter in cholinergic nerve terminals and its targeting to a specific population of small synaptic vesicles. Proc Natl Acad Sci U S A 1996; 93:3547-52. [PMID: 8622973 PMCID: PMC39647 DOI: 10.1073/pnas.93.8.3547] [Citation(s) in RCA: 241] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Immunohistochemical visualization of the rat vesicular acetylcholine transporter (VAChT) in cholinergic neurons and nerve terminals has been compared to that for choline acetyltransferase (ChAT), heretofore the most specific marker for cholinergic neurons. VAChT-positive cell bodies were visualized in cerebral cortex, basal forebrain, medial habenula, striatum, brain stem, and spinal cord by using a polyclonal anti-VAChT antiserum. VAChT-immuno-reactive fibers and terminals were also visualized in these regions and in hippocampus, at neuromuscular junctions within skeletal muscle, and in sympathetic and parasympathetic autonomic ganglia and target tissues. Cholinergic nerve terminals contain more VAChT than ChAT immunoreactivity after routine fixation, consistent with a concentration of VAChT within terminal neuronal arborizations in which secretory vesicles are clustered. These include VAChT-positive terminals of the median eminence or the hypothalamus, not observed with ChAT antiserum after routine fixation. Subcellular localization of VAChT in specific organelles in neuronal cells was examined by immunoelectron microscopy in a rat neuronal cell line (PC 12-c4) expressing VAChT as well as the endocrine and neuronal forms of the vesicular monoamine transporters (VMAT1 and VMAT2). VAChT is targeted to small synaptic vesicles, while VMAT1 is found mainly but not exclusively on large dense-core vesicles. VMAT2 is found on large dense-core vesicles but not on the small synaptic vesicles that contain VAChT in PC12-c4 cells, despite the presence of VMAT2 immunoreactivity in central and peripheral nerve terminals known to contain monoamines in small synaptic vesicles. Thus, VAChT and VMAT2 may be specific markers for "cholinergic" and "adrenergic" small synaptic vesicles, with the latter not expressed in nonstimulated neuronally differentiated PC12-c4 cells.
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Affiliation(s)
- E Weihe
- Department of Anatomy and Cell Biology, Philipps University, Marburg, Germany
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109
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Weber E, Jilling T, Kirk KL. Distinct functional properties of Rab3A and Rab3B in PC12 neuroendocrine cells. J Biol Chem 1996; 271:6963-71. [PMID: 8636125 DOI: 10.1074/jbc.271.12.6963] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Rab3A and Rab3B are highly homologous monomeric GTPases that are putative regulators of exocytosis in those tissues in which they are expressed. We have characterized and directly compared the targeting and functional properties of these isoforms in PC12 neuroendocrine cells. Rab3A and Rab3B both targeted to norepinephrine (NE)-containing large dense core vesicles (LDCVs) when stably expressed in PC12 cells, as determined by immunofluorescence and membrane fractionation. Both Rab3 isoforms also bound to recombinant rabphilin-3A in a GTP-dependent manner. The membrane association of rabphilin-3A was modestly enhanced in Rab3B-expressing PC12 cells relative to Rab3A-overexpressing cells. In addition, overexpression of Rab3A modestly inhibited Ca2+-evoked NE release, whereas Rab3B and a GTP binding mutant (Rab3B N135I) markedly stimulated the efficiency of [3H]NE secretion by PC12 cells (i.e. secretion normalized to total cell radioactivity). Expression of Rab3B and Rab3B N135I increased not only the efficiency of NE secretion but also the accumulation of [3H]NE into LDCVs (i.e. the secretory cargo available for secretion). Neither of these effects was attributable to changes in the numbers of LDCVs nor the docking of LDCVs at the plasma membrane. Our results indicate that Rab3A and Rab3B have similar membrane targeting properties and are capable of interacting with the same putative downstream effector; i.e. rabphilin-3A. However, these isoforms are functionally distinct monomeric GTPases with Rab3B stimulating a late step in Ca2+-evoked secretion when expressed in PC12 cells.
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Affiliation(s)
- E Weber
- Department of Physiology and Biophysics, Gregory Fleming James Cystic Fibrosis Research Center, University of Alabama at Birmingham, 35294, USA
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110
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Varoqui H, Meunier FM, Meunier FA, Molgo J, Berrard S, Cervini R, Mallet J, Israël M, Diebler MF. Expression of the vesicular acetylcholine transporter in mammalian cells. PROGRESS IN BRAIN RESEARCH 1996; 109:83-95. [PMID: 9009695 DOI: 10.1016/s0079-6123(08)62090-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- H Varoqui
- Laboratoire de Neurobiologie Cellulaire et Moléculaire, CNRS, Gif sur Yvette, France
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111
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Erickson JD, Weihe E, Schäfer MK, Neale E, Williamson L, Bonner TI, Tao-Cheng JH, Eiden LE. The VAChT/ChAT "cholinergic gene locus": new aspects of genetic and vesicular regulation of cholinergic function. PROGRESS IN BRAIN RESEARCH 1996; 109:69-82. [PMID: 9009694 DOI: 10.1016/s0079-6123(08)62089-0] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- J D Erickson
- Section on Molecular Neuroscience, NIMH, NIH, Bethesda, MD, USA
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112
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Liu Y, Peter D, Merickel A, Krantz D, Finn JP, Edwards RH. A molecular analysis of vesicular amine transport. Behav Brain Res 1995; 73:51-8. [PMID: 8788477 DOI: 10.1016/0166-4328(96)00069-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
To package classical neurotransmitters into vesicles so that their release can be regulated by activity, neuronal cells express a set of specific vesicular transport proteins. We have used selection in MPP+ to clone the cDNAs encoding two vesicular monoamine transporters, the first members of this novel gene family that now also includes the vesicular transporter for acetylcholine. The sequences show similarity to several bacterial antibiotic resistance proteins, further supporting a role in detoxification and possibly Parkinson's disease. The two vesicular amine transporters show differences in their affinity for substrates, their turnover number and their pharmacology. In particular, the proteins differ in their interactions with the potent inhibitor tetrabenazine and with amphetamines, accounting for several classic pharmacological observations. Since the subcellular localization of the transport proteins determines the site of monoamine storage and the site of monoamine storage appears to differ from other classical transmitters, we have also raised polyclonal antibodies to the transporters and used these to demonstrate localization in dense core vesicles rather than synaptic vesicles. In addition to the implications for monoamine release, these observations also indicate a vesicular amine transporter as the first integral membrane protein restricted to the regulated secretory pathway.
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Affiliation(s)
- Y Liu
- Department of Neurology, UCLA School of Medicine 90024-1769, USA
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113
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Gracy KN, Pickel VM. Comparative ultrastructural localization of the NMDAR1 glutamate receptor in the rat basolateral amygdala and bed nucleus of the stria terminalis. J Comp Neurol 1995; 362:71-85. [PMID: 8576429 DOI: 10.1002/cne.903620105] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The N-methyl-D-aspartate (NMDA)-type glutamate receptor in the basolateral amygdala (BLA) has been implicated in activity-dependent plasticity important for cortically evoked acquisition of fear-potentiated startle response. We examined the ultrastructural immunoperoxidase labeling of the R1 subunit of the NMDA receptor in the BLA of adult rats to determine the potential cellular and subcellular sites mediating the effects generated by NMDA activation. The localization was compared with that seen in the bed nucleus of the stria terminalis (BNST), the major efferent pathway from the central nucleus of the amygdala, which has a more pronounced involvement in autonomic function. Electron microscopy established that in the BLA, 68.4% (n = 177) of the profiles showing NMDAR1-like immunoreactivity (NMDAR1-LI) were dendrites, and 19.8% were distal tips of astrocytic processes. In contrast, profiles containing NMDAR1-LI (n = 262) in the BNST were more equally distributed between dendrites (37.4%) and axons (38.2%). The subcellular localization of NMDAR1 immunoreactivity was, however, similar in both regions. Our findings provide the first ultrastructural evidence that glutamate may prominently act through NMDAR1 receptors to elicit postsynaptic actions on intrinsic neurons in the BLA and BNST. The results also indicate that, in the BLA, the NMDAR1 receptor plays an important role in astrocytic function, whereas the receptor is more preferentially a presynaptic modulator in axons which terminate in or pass through the BNST.
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Affiliation(s)
- K N Gracy
- Department of Neurology and Neuroscience, Cornell University Medical College, New York, New York 10021, USA
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114
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Merickel A, Rosandich P, Peter D, Edwards RH. Identification of residues involved in substrate recognition by a vesicular monoamine transporter. J Biol Chem 1995; 270:25798-804. [PMID: 7592763 DOI: 10.1074/jbc.270.43.25798] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
To identify the residues involved in substrate recognition by recently cloned vesicular monoamine transporters (VMAT1 and VMAT2), we have mutagenized the conserved residues in a cytoplasmic loop between transmembrane domains two and three of VMAT2. Although studies of related bacterial antibiotic resistance proteins indicate an important functional role for this region, we found no effect of these mutations on VMAT2 activity. However, replacement of aspartate 33 in the first predicted transmembrane domain with an asparagine (D33N) eliminates transport. D33N shows normal levels of expression and normal binding at equilibrium to the potent inhibitor reserpine. However, in contrast to wild-type VMAT2, serotonin inhibits reserpine binding to D33N very poorly, indicating a specific defect in substrate recognition. Replacement of three serine residues in transmembrane domain three with alanine (Stmd3A) shows a similarly selective but even more profound defect in substrate recognition. The results suggest that by analogy to receptors and plasma membrane transporters for monoamines, the cationic amino group of the ligand interacts with an asparte in the first transmembrane domain of VMAT2 and hydroxyl groups on the catechol or indole ring interact with a group of serines in the third transmembrane domain. Importantly, D33N and Stmd3A retain coupling to the proton electrochemical gradient as measured by the delta microH(+)-induced acceleration of reserpine binding. This indicates that substrate recognition can be separated from coupling to the driving force.
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Affiliation(s)
- A Merickel
- Interdepartmental Program in Neuroscience, UCLA School of Medicine 90024-1769, USA
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115
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Tao-Cheng JH, Dosemeci A, Bressler JP, Brightman MW, Simpson DL. Characterization of synaptic vesicles and related neuronal features in nerve growth factor and ras oncogene differentiated PC12 cells. J Neurosci Res 1995; 42:323-34. [PMID: 8583500 DOI: 10.1002/jnr.490420306] [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: 01/31/2023]
Abstract
PC12 cells can differentiate into neuron-like cells after treatment with either nerve growth factor (NGF) or transduction with a retrovirus which expresses the K-ras oncogene. The concomitant treatment of NGF plus ras differentiates PC12 cells further than either agent alone with respect to neurite outgrowth, acetylcholinesterase levels, and most strikingly, the number of synaptic vesicle (SV) clusters. These SV clusters in PC12 cell neurites closely resemble those in the presynaptic terminals of neurons. Such SV clusters have not been described in cell lines previously. The SV clusters from all three differentiated groups (NGF, ras, and NGF plus ras) were similar in size, shape, and configuration, except that the ones in the doubly treated group occur in higher frequency and have more vesicles. The synaptic nature of these vesicle clusters was demonstrated by their regulated depletion after potassium stimulation. Furthermore, these vesicle clusters stained positively for two SV-associated proteins, synapsin I and synaptophysin, by EM immunocytochemistry (ICC). Such SV clusters in a cell line are very useful for characterizing the regulated release of SVs and the distribution of SV-related antigens in intact cells. Analysis by SDS-gel electrophoresis and immunoblotting indicated that synapsin I levels are higher in all three differentiated groups compared to untreated cells; whereas synaptophysin levels are lower in cells exposed to NGF alone or with NGF and ras double treatment. Possible convergence and/or divergence on the mechanisms of NGF and ras differentiation in PC12 cells are discussed.
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Affiliation(s)
- J H Tao-Cheng
- NINDS EM Facility, National Institutes of Health, Bethesda, MD 20892, USA
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116
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Nirenberg MJ, Liu Y, Peter D, Edwards RH, Pickel VM. The vesicular monoamine transporter 2 is present in small synaptic vesicles and preferentially localizes to large dense core vesicles in rat solitary tract nuclei. Proc Natl Acad Sci U S A 1995; 92:8773-7. [PMID: 7568015 PMCID: PMC41049 DOI: 10.1073/pnas.92.19.8773] [Citation(s) in RCA: 120] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
In central neurons, monamine neurotransmitters are taken up and stored within two distinct classes of regulated secretory vesicles: small synaptic vesicles and large dense core vesicles (DCVs). Biochemical and pharmacological evidence has shown that this uptake is mediated by specific vesicular monamine transporters (VMATs). Recent molecular cloning techniques have identified the vesicular monoamine transporter (VMAT2) that is expressed in brain. This transporter determines the sites of intracellular storage of monoamines and has been implicated in both the modulation of normal monoaminergic neurotransmission and the pathogenesis of related neuropsychiatric disease. We used an antiserum against VMAT2 to examine its ultrastructural distribution in rat solitary tract nuclei, a region that contains a dense and heterogeneous population of monoaminergic neurons. We find that both immunoperoxidase and immunogold labeling for VMAT2 localize to DCVs and small synaptic vesicles in axon terminals, the trans-Golgi network of neuronal perikarya, tubulovesicles of smooth endoplasmic reticulum, and potential sites of vesicular membrane recycling. In axon terminals, immunogold labeling for VMAT2 was preferentially associated with DCVs at sites distant from typical synaptic junctions. The results provide direct evidence that a single VMAT is expressed in two morphologically distinct types of regulated secretory vesicles in central monoaminergic neurons.
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Affiliation(s)
- M J Nirenberg
- Department of Neurology and Neuroscience, Cornell University Medical College, New York, NY 10021, USA
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117
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Borowsky B, Hoffman BJ. Neurotransmitter transporters: molecular biology, function, and regulation. INTERNATIONAL REVIEW OF NEUROBIOLOGY 1995; 38:139-99. [PMID: 8537200 DOI: 10.1016/s0074-7742(08)60526-7] [Citation(s) in RCA: 79] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- B Borowsky
- Unit on Molecular Pharmacology, National Institute of Mental Health, Bethesda, Maryland 20892-4090, USA
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