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At least 919 records · Page 51Linked to original sources
PubMed2006

Discrete residues in the c(2)b domain of synaptotagmin I independently specify endocytic rate and synaptic vesicle size.

It has been demonstrated that synapses lacking functional synaptotagmin I (Syt I) have a decreased rate of synaptic vesicle endocytosis. Beyond this, the function of Syt I during endocytosis remains undefined. Here, we demonstrate that a decreased rate of endocytosis in syt(null) mutants correlates with a stimulus-dependent perturbation of membrane internalization, assayed ultrastructurally. We then separate the mechanisms that control endocytic rate and vesicle size by mapping these processes to discrete residues in the Syt I C(2)B domain. Mutation of a poly-lysine motif alters vesicle size but not endocytic rate, whereas the mutation of calcium-coordinating aspartate residues (syt-D3,4N) alters endocytic rate but not vesicle size. Finally, slowed endocytic rate in the syt-D3,4N animals, but not syt(null) animals, can be rescued by elevating extracellular calcium concentration, supporting the conclusion that calcium coordination within the C(2)B domain contributes to the control of endocytic rate.

Adaptor Protein Complex alpha Subunits↗
PubMed1992

Linkage of the acetylcholine transporter-vesamicol receptor to proteoglycan in synaptic vesicles.

The relationship of the acetylcholine transporter-vesamicol receptor (AcChT-VR) to proteoglycan in Torpedo electric organ synaptic vesicles was investigated. The cholate-solubilized VR was immunoprecipitated by a monoclonal antibody directed against the SV1 epitope located in the glycosaminoglycan portion of the proteoglycan. AcChT that was photoaffinity-labeled with a tritiated high-affinity analogue of AcCh [cyclohexylmethyl cis-N-(4-azidophenacyl)-N-methylisonipecotate] and then denatured in sodium dodecyl sulfate also immunoprecipitated. The labeled AcChT exhibited a M(r) range of 100,000-200,000. Proteoglycan did not engage in detectable nonspecific reversible aggregation that might mask the presence of another subunit during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In vesicles permeabilized with cholate, the enzymes keratanase and testicular hyaluronidase inactivated binding of vesamicol and destroyed the SV1 epitope without detectable proteolysis. Other glycosaminoglycan-degrading enzymes were without effect. The results demonstrate that the AcChT-VR and proteoglycan are very strongly linked and that glycosaminoglycan-like polysaccharide controls the conformation of the VR. The unexpected linkage to proteoglycan suggests that AcChT-VR in intact terminals might communicate with extracellular matrix and participate in stabilization and operation of the synapse.

Acetylcholine↗
PubMed2004

Mobilization and fusion of a non-recycling pool of synaptic vesicles under conditions of endocytic blockade.

At vertebrate central synapses, it has been demonstrated that a resting pool of synaptic vesicles (SVs) exists that normally does not participate in SV release and recycling. It remains unclear whether SVs within the resting pool are capable of mobilization and fusion. Here, we combine live imaging of SV exo- and endocytosis using pH-sensitive GFP (synapto-pHluorins) with pharmacological and genetic manipulations of the SV cycle at the Drosophila NMJ. We demonstrate that a resting pool of SVs exists at this synapse that encompasses 30-41% of the total SV pool. Under conditions of endocytic blockade, using a temperature-sensitive dynamin mutation, the resting pool of SVs can be mobilized and released. We present a model for the presence of a resting pool of SVs that does not require molecular specification of a subpopulation of SVs.

Animals↗
PubMed2002

Non-polarized distribution of synaptotagmin IV in neurons: evidence that synaptotagmin IV is not a synaptic vesicle protein.

Synaptotagmin IV (Syt IV) expression is regulated by neuronal development and by depolarization in the brain and in neuronal cell cultures. In cultures, immunocytochemical analysis has shown that Syt IV is localized at the Golgi and at the tips of growing neurites, but little was known about associations between Syt IV and vesicles or organelles [J. Neurochem. 74 (2000) 518]. In this study we performed an electron microscopic (EM) analysis of developing mouse neocortex to determine the exact localization of Syt IV in native mouse tissues. In neurons of layer II/III, Syt IV was found to be localized in the dendrites and axons, and at the Golgi in the cell body. Some Syt IV signals were clearly associated with vesicles and/or organelles, but EM and cell fractionation studies showed no Syt IV signals at synaptic vesicles. Detection of fluorescence protein-tagged Syt IV (Syt IV-EGFP) in hippocampal neurons also showed the presence of Syt IV-EGFP vesicles or organelles in the axons and dendrites. These results suggest that Syt IV regulates non-polarized membrane trafficking in neurons, which may be involved in synaptic plasticity or neuronal development.

Animals↗
PubMed1995

Disassembly of the reconstituted synaptic vesicle membrane fusion complex in vitro.

The interaction of the presynaptic membrane proteins SNAP-25 and syntaxin with the synaptic vesicle protein synaptobrevin (VAMP) plays a key role in the regulated exocytosis of neurotransmitters. Clostridial neurotoxins, which proteolyze these polypeptides, are potent inhibitors of neurotransmission. The cytoplasmic domains of the three membrane proteins join into a tight SDS-resistant complex (Hayashi et al., 1994). Here, we show that this reconstituted complex, as well as heterodimers composed of syntaxin and SNAP-25, can be disassembled by the concerted action of the N-ethylmaleimide-sensitive factor, NSF, and the soluble NSF attachment protein, alpha-SNAP. alpha-SNAP binds to predicted alpha-helical coiled-coil regions of syntaxin and SNAP-25, shown previously to be engaged in their direct interaction. Synaptobrevin, although incapable of binding alpha-SNAP individually, induced a third alpha-SNAP binding site when associated with syntaxin and SNAP-25 into heterotrimers. NSF released prebound alpha-SNAP from full-length syntaxin but not from a syntaxin derivative truncated at the N-terminus. Disassembly of complexes containing this syntaxin mutant was impaired, indicating a critical role for the N-terminal domain in the alpha-SNAP/NSF-mediated dissociation process. Complexes containing C-terminally deleted SNAP-25 derivatives, as generated by botulinal toxins type A and E, were dissociated more efficiently. In contrast, the N-terminal fragment generated from synaptobrevin by botulinal toxin type F produced an SDS-sensitive complex that was poorly dissociated.

Bacterial Toxins↗
PubMed1999

The synaptic-vesicle-specific proteins rab3a and synaptophysin are reduced in thalamus and related cortical brain regions in schizophrenic brains.

Two synaptic-vesicle proteins, rab3a and synaptophysin, have been studied on post-mortem brain tissues of schizophrenics and healthy controls. We found significantly reduced levels of rab3a in thalamus (p<0.001); for both proteins in gyrus cinguli and hippocampus (p<0.0001); for rab3a in frontal and parietal cortex (p<0.05); and no differences in temporal cortex or cerebellum in schizophrenics compared with controls. Reduced synaptic density may be a prominent feature of the molecular neuropathology of schizophrenia.

Adult↗
PubMed1977

Energy utilization in the uptake of catecholamines by synaptic vesicles and adrenal chromaffin granules.

Several inhibitors of energy metabolism decreased the ATP-stimulated uptake of catecholamines by isolated synaptic vesicles from rat brain and by chromaffin granules from bovine adrenal medulla. Catecholamine uptake was inhibited by dinitrophenol, S-13 and oleic acid, which are known to block active transport by dissipating trans-membrane proton gradients. Thus a proton gradient appears to be involved in catecholamine transport. Both catecholamine uptake and vesicle-associated Ca2+/Mg2+-ATPase were inhibited by dicyclohexylcarbodiimide and tributyltin, which had previously been shown to inhibit the Ca2+/Mg2+-ATPase of mitochondria. However, mitochondrial ATPase was not involved in catecholamine uptake as oligomycin and aurovertin, more specific inhibitors of mitochondrial ATPase, did not affect catecholamine uptake. It is suggested that ATP stimulates catecholamine uptake by serving as a substrate for the ATPase. Activity of this enzyme causes translocation of protons across the vesicle membrane establishing a trans-membrane proton gradient. The proton gradient drives the transport of catecholamines.

Adenosine Triphosphate↗
PubMed1982

Identification of actin in highly purified synaptic vesicles from the electric organ of Torpedo marmorata.

Evidence has been obtained that actin is a major constituent of highly purified synaptic vesicles isolated from the electric organ of Torpedo marmorata. The mobility of a prominent spot in the polypeptide pattern of vesicles in high-resolution two-dimensional polyacrylamide gel electrophoresis is very similar to the mobility of the main component in the actin preparation purified from the whole electric organ by affinity chromatography on immobilized pancreatic deoxyribonuclease I. The comparison of tryptic peptide maps obtained from the putative vesicle actin and authentic actin from the electric organ, both purified by two-dimensional gel electrophoresis and labeled in situ with 125I, showed about 88% homology, thereby supporting the conclusion that the vesicle actin is indeed an actin isoform.

Actins↗
PubMed1982

Presynaptic plasma membranes and synaptic vesicles of cholinergic nerve endings demonstrated by means of specific antisera.

Antisera were raised to cholinergic presynaptic plasma membranes and synaptic vesicles isolated from the electric organ of Torpedo marmorata and tested by immunochemical and immunohistochemical methods. The antisera responded to many antigens not specific to nerve endings, but it was possible to eliminate these antibodies by means of simple absorption procedures with fractions containing the unwanted antigens. After absorption, staining of thin sections of electric organ by immunofluorescence was limited to the region of nerve endings in the tissue. The remaining antibodies responded in the case of the plasma membrane antisera predominantly to a 33,000 molecular-weight polypeptide and a chloroform/methanol-soluble antigen. In cross reactivity studies it was found that this antiserum not only stains cholinergic nerve endings in Torpedo but also those in mammalian tissue. The antigen responsible for the cross reactivity is restricted to the chloroform/methanol-soluble material. The vesicle antiserum labels cholinergic nerve endings in mammalian tissue as well; the relevant antigen in this case is different from the one described above and is likely to be a glycosaminoglycan. The antisera provide valuable markers for cholinergic nerve terminals. In addition, the vesicle antiserum may now be used to study axonal transport and the life cycle of this organelle in the cholinergic neurone.

Animals↗
PubMed1976

[Effect of several tropane derivatives on noradrenaline absorption by hypothalamic synaptic vesicles].

The influence of some tropan derivatives on the absorption of exogenous norepinephrine was studied in experiments on the isolated synaptic vesicles of the hypothalamus. LK II (beta-morpholinopropionic acid tropine ester dihydrochloride) at the concentration of 1. -5M decreased (like cocaine) the passive consumption of norephinephrine. The dependence of this effect on the transmitter concentration in the incubation medium was demonstrated.

Animals↗
PubMed1967

Synaptic vesicles of inhibitory and excitatory TERMINALS IN THE CEREBELLUM.

Populations of synaptic vesicles within cerebellar terminals considered excitatory or inhibitory on the basis of physiological evidence differ with respect to size and shape. Size rather than shape appears to be the main morphological difference between these populations. Elongation of vesicles is depenident on fixation with aldehyde fixatives, and both size and elongation change with age mainly during maturation.

Animals↗
PubMed1987

Position of the peptide linkage in glutamyl-taurine from calf brain synaptic vesicles.

To elucidate the position of the peptide bond in glutamyl-taurine this dipeptide was extracted from calf brain synaptic vesicles and subjected to paper electrophoresis. It was analyzed further in an automatic amino acid analyzer prior and subsequent to acid hydrolysis. Both alpha- and gamma-forms were found to be present in approximately equal amounts.

Animals↗
PubMed1999

Electrophysiology of synaptic vesicle cycling.

Patch-clamp capacitance measurements can monitor in real time the kinetics of exocytosis and endocytosis in living cells. We review the application of this technique to the giant presynaptic terminals of goldfish bipolar cells. These terminals secrete glutamate via the fusion of small, clear-core vesicles at specialized, active zones of release called synaptic ribbons. We compare the functional characteristics of transmitter release at ribbon-type and conventional synapses, both of which have a unique capacity for fast and focal vesicle fusion. Subsequent rapid retrieval and recycling of fused synaptic vesicle membrane allow presynaptic terminals to function independently of the cell soma and, thus, as autonomous computational units. Together with the mobilization of reserve vesicle pools, local cycling of synaptic vesicles may delay the onset of vesicle pool depletion and sustain neuronal output during high stimulation frequencies.

Animals↗
PubMed1992

The transport of neurotransmitters into synaptic vesicles.

As investigations identify additional plasma membrane neurotransmitter transporters, attention has focused on the molecular basis of neurotransmitter transport into synaptic vesicles. The transport of biogenic amines into chromaffin granules has served as the paradigm for understanding vesicular transport. Recent work now describes the vesicular transport of other classical neurotransmitters, which occur by distinct but related mechanisms. To determine their biochemical basis, several of the transporters have been functionally reconstituted in liposomes. The ability of vesicular amine transport to protect against the neurotoxin MPP+ has permitted the isolation of the first cDNA clone for a member of this family, and the sequence establishes a relationship with drug-resistance transporters in bacteria.

Animals↗
PubMed2003

Specific sorting of the a1 isoform of the V-H+ATPase a subunit to nerve terminals where it associates with both synaptic vesicles and the presynaptic plasma membrane.

Vacuolar H+ATPase (V-ATPase) accumulates protons inside various intracellular organelles, generating the electrochemical proton gradient required for many vital cellular processes. V-ATPase is a complex enzyme with many subunits that are organized into two domains. The membrane domain that translocates protons contains a proteolipid oligomer of several c subunits and a 100 kDa a subunit. Several a-subunit isoforms have been described that are important for tissue specificity and targeting to different membrane compartments, and could also result in the generation of V-ATPases with different functional properties. In the present report, we have cloned the Torpedo marmorata a1 isoform. This isoform was found to be addressed specifically to nerve endings, whereas VATPases in the neuron cell bodies contain a different a-subunit isoform. In nerve terminals, the V-ATPase membrane domain is present not only in synaptic vesicles but also in the presynaptic plasma membrane, where its density could reach 200 molecules microm(-2). This V-ATPase interacts with VAMP-2 and with the SNARE complexes involved in synaptic vesicle docking and exocytosis.

Amino Acid Sequence↗
PubMed1989

Shape and size of synaptic vesicles in different types of presynaptic profiles in the medial septal nucleus of the rat.

Long and short axis diameters of synaptic vesicles were obtained from 6 classes of presynaptic boutons found in the medial septal nucleus (MS) of the rat. The variability of vesicle size and shape was documented in diagrams and discussed with regard to their suitability as criteria of classification and their functional significance. The variability in shape, but not in size, of vesicles in synapses of Gray's type I is lower than of those in Gray's type II synapses.

Animals↗