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PubMed1979

[Interaction between actin like protein of the brain and isolated synaptic vesicles].

It was shown that Mg-ATP increased light diffusion in the suspension of synaptic vesicles (SV) of the rat brain in the presence of actinolike protein (ALP) of the bovine brain (the superprecipitation test). ALP enhanced the activity of the SV Mg-ATPase and increased endogenic moradrenaline release from the bovine hypothalamus SV, eliminated by cutochalazine B. Glycolipids (gengliosides and cerebrosides) inhibited the superprecipitation test. The results are considered from the standpoint of a contractile hypothesis on the mediator secretion.

Actins↗
PubMed1995

Synaptic vesicle proteins and regulated exocytosis.

The recent identification of novel proteins associated with the membranes of synaptic vesicles has ignited the field of molecular neurobiology to probe the function of these molecules. Evidence is mounting that the vesicle proteins vamp (synaptobrevin), rab3A, synaptophysin, synaptotagmin (p65) and SV2 play an important role in regulated exocytosis, by regulating neurotransmitter uptake, vesicle targeting and fusion with the presynaptic plasma membrane.

Animals↗
PubMed1992

Myosin II distribution in neurons is consistent with a role in growth cone motility but not synaptic vesicle mobilization.

We have generated a polyclonal antibody against myosin II from a neuronally derived cell line in order to assess potential roles for myosin II in growth cone movement and synaptic transmission. The distribution of neuronal myosin II, in isolated cells as well as in tissues of the adult rat brain and spinal cord, was examined at the light microscopic and ultrastructural levels. In isolated neuroblastoma cells and dorsal root ganglion neurons, myosin II was found at the leading edge of growth cones, within neuritic processes and cell soma, and adjacent to the plasma membrane. The subcellular distribution of myosin II overlapped significantly with that of both actin and single-headed myosin I. These results implicate both myosin I and myosin II as molecular motors required for neurite elongation and growth cone motility. An exclusive postsynaptic distribution of myosin II in neurons of the mature central nervous system suggests that myosin II cannot play a role in the mobilization of synaptic vesicles, but could participate in synaptic plasticity.

Animals↗
PubMed1988

A new method for electron microscopic observation of isolated synaptic vesicles labelled with monoclonal antibody.

The immunoreaction of a monoclonal antibody (Mab) and an isolated synaptic vesicle (SV) was processed on a grid mesh and the result could be easily observed with electron microscopy. The SV suspension was obtained and dispersed on the grid mesh where immunoreaction procedures were performed. The resulting immunoreaction was visualized by labelling with ferritin particle (FAD) or horseradish peroxidase (HRP) for the electron microscopic observation. The SV specimen was observed by electron microscopy after faint negative staining with 1% uranyl acetate. With this method, the positive immunoreaction of Mab 171B5 and the isolated SV could be easily identified by the formation of a halo of FAD or a cobweb of HRP surrounding the SV. In the control experiment, the SV specimen was incubated with normal mouse serum instead of the Mab while the other procedures were performed in the same way. The SV was not outlined by FAD in the control experiment. Thus, the positive immunoreaction of the Mab and SV was thought to be an immunologically specific one. It was also determined that the Mab reacted specifically with the SV but not with the small membrane fragments and other unknown material. The present method seems to be useful for observing the immunoreaction of subcellular structures and their antibodies under electron microscopy.

Animals↗
PubMed2005

Munc18-dependent regulation of synaptic vesicle exocytosis by syntaxin-1A in hippocampal neurons.

The fusion of secretory vesicles with the plasma membrane requires the formation of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes between the vesicle-SNARE vesicle-associated membrane protein present on the vesicular membrane and the target-SNAREs SNAP-25 and syntaxin-1A. Syntaxin-1A fluctuates between an open and closed form allowing it to selectively bind to different biological effectors in different conformations. In the open form, it can participate in SNARE complex formation, however, in the closed form it negatively regulates N- and P/Q-type voltage-dependent calcium channels, and is capable of inhibiting calcium influx. Thus paradoxically, syntaxin appears to have both positive and negative roles in controlling calcium-driven synaptic vesicle fusion at synaptic terminals. We show here that overexpression of syntaxin-1A inhibited exocytosis, in a manner that could be rescued by either elevating or reducing external calcium, or increasing action potential firing frequency. Elevating the level of Munc18 by coexpression with syntaxin-1A also abolished this inhibition, suggesting that Munc18 serves to limit the negative regulatory role of syntaxin by binding to, and thereby buffering, its closed form. Our results also indicate that syntaxin can control the frequency-response characteristics of the presynaptic fusion machinery.

Animals↗
PubMed1993

Synaptic vesicle proteins and regulated exocytosis.

The recent identification of novel proteins associated with the membranes of synaptic vesicles has ignited the field of molecular neurobiology to probe the function of these molecules. Evidence is mounting that the vesicle proteins vamp (synaptobrevin), rab3A, synaptophysin, synaptotagmin (p65) and SV2 play an important role in regulated exocytosis, by regulating neurotransmitter uptake, vesicle targeting and fusion with the presynaptic plasma membrane.

Animals↗
PubMed2005

Involvement of water channels in synaptic vesicle swelling.

Vesicle swelling is critical for secretion; however, the underlying mechanism of synaptic vesicle (SV) swelling is unknown. A G alphai3-phospholipase A2 (PLA2)-mediated involvement of the water channel aquaporin-1 (AQP1) in the regulation of secretory vesicle swelling in the exocrine pancreas has been previously reported. In the present study, the association and involvement of water channels in SV swelling was explored. Results from the study demonstrate that water channels AQP1 and AQP6, and the heterotrimeric Go protein are associated with SVs and participate in their swelling.

Animals↗
PubMed1994

Synaptic vesicles isolated from 32P-prelabeled synaptosomes contain a phosphoprotein of apparent M(r) 65,000 (pp65), a possible substrate for PKC.

In the present study, we have investigated the subcellular localization of pp65, a synaptosomal phosphoprotein of apparent M(r) 65,000. The results obtained strongly support that pp65 is localized to synaptic vesicles. The solubility properties of pp65, especially its partitioning into the detergent phase of Triton X-114, indicated that it is tightly associated with the membrane of synaptic vesicles. pp65 is multiply phosphorylated exclusively on serine. By studying the decay of labeled phosphate following incubation of 32P-prelabeled synaptosomes in the presence of cold inorganic phosphate, we have found that pp65 shows an unusually high turnover of phosphate. Exposure of synaptosomes to 1 microM phorbol 12-myristate 13-acetate prior to prelabeling with 32P(i) led to a reduction in the steady state phosphorylation of pp65, and tryptic/chymotryptic mapping was shown to selectively affect phosphopeptide 4. Identical results were obtained following incubation of synaptosomes with the protein kinase C (PKC) inhibitor, GF 109203 X. These results indicated that one of the protein kinases involved in steady state phosphorylation of pp65 is PKC-dependent or is PKC itself. Several characteristics of pp65 reported in the present study suggest a regulatory role in nerve terminal function.

Animals↗
PubMed1989

Regional distribution of gamma-aminobutyrate and L-glutamate uptake into synaptic vesicles isolated from rat brain.

The ATP-dependent uptake of GABA and L-glutamate into synaptic vesicles isolated from 4 different regions of the rat brain was studied. The regional distribution of the vesicular uptake was related to the Na+-dependent synaptosomal uptake, which, as a first approximation, corresponds to the distribution of GABAergic and glutamatergic terminals. The ratio found between the vesicular GABA and L-glutamate uptake varied between 1.3 and 6.2. This indicates that GABA and L-glutamate are taken up into different vesicle populations.

Animals↗
PubMed1985

Separation of recycling and reserve synaptic vesicles from cholinergic nerve terminals of the myenteric plexus of guinea pig ileum.

Acetylcholine-rich synaptic vesicles were isolated from myenteric plexus-longitudinal muscle strips derived from the guinea pig ileum by the method of Dowe, Kilbinger, and Whittaker [J. Neurochem. 35, 993-1003 (1980)] using either unstimulated preparations or preparations field-stimulated at 1 Hz for 10 min using pulses of 1 ms duration and 10 V . cm-1 intensity. The organ bath contained either tetradeuterated (d4) choline (50 microM) or [3H]acetate (2 muCi . ml-1); d4 acetylcholine was measured by gas chromatography-mass spectrometry. As with Torpedo electromotor cholinergic vesicle preparations made under similar conditions the distribution of newly synthesized (d4 or [3H]) acetylcholine in the zonal gradient from stimulated preparations was not identical with that of endogenous (d0, [1H]) acetylcholine, but corresponded to a subpopulation of denser vesicles (equivalent to the VP2 fraction from Torpedo) that had preferentially taken up newly synthesized transmitter. The density difference between the reserve (VP1) and recycling (VP2) vesicles was less than that observed in Torpedo but this smaller difference can be accounted for theoretically by the difference in size between the vesicles of the two tissues. At rest, a lesser incorporation of labelled acetylcholine into the vesicle fraction was observed, and the peaks of endogenous and newly synthesized acetylcholine coincided. Stimulation in the absence of label followed by addition of label did not lead to incorporation of labelled acetylcholine, suggesting that the synthesis and storage of acetylcholine in this preparation and its recovery from stimulation is much more rapid than in Torpedo.

Acetates↗
PubMed2006

Rat brain synaptic vesicles are devoid of Mg2+-ATPase activity and contain beta-amyloid precursor protein.

Rat brain synaptic vesicles (SVs) isolated by gel filtration on Sephacryl S-500 had little Mg2+(H+)-ATPase activity, though it was identified by Western blots with antibodies against the H+-ATPase A-subunit and other vesicle proteins. In contrast, tyrosine hydroxylase and dopa decarboxylase activities in the SVs were substantial, suggesting that the absence of Mg2+(H+)-ATPase activity was not due to inactivation during isolation but rather to the nature of the SVs. The vesicle component reactive to H+-ATPase antibody was also identified in the synaptosomal cytosol, so the antibody for the A-subunit seemed unnecessary to detect H+-ATPase. The SVs contained beta-amyloid precursor protein of approximately 100 kDa. Based on these observations, SVs without Mg2+(H+)-ATPase seemed to play a role(s) in the delivery of cytoplasmic and plasma membrane proteins to nerve terminals as well as in neurotransmission.

Amyloid beta-Protein Precursor↗
PubMed1985

Carboxypeptidase activity in synaptic vesicles isolated from striatum and cortex of calf brain.

A carboxypeptidase activity has been found in synaptic vesicles (secretory granules) isolated from the cortex and striatum of calf brain which removes amino acids from the carboxy terminus of enkephalin-containing (EC) peptides. The formed enkephalin molecules are not further degraded by this enzyme activity. The preparations were found to be free of cytoplasmic and lysosomal constituents as determined by marker enzyme activities. The vesicle preparations of both cortex and striatum showed differences in the degradation velocities of the various EC peptides depending on size and charge of the amino acid present at the carboxy terminus. The pH optimum of the release of Met-enkephalin from Met-enkephalin-Arg6 has been shown to be between pH 5 and 6. The enzyme activity is inhibited by thiol-blocking agents such as p-hydroxymercuribenzoate and copper ions, but only slightly by metal-chelating agents.

Animals↗
PubMed1986

Acetylcholine transport and drug inhibition kinetics in Torpedo synaptic vesicles.

Steady-state initial velocity uptake of [3H]acetylcholine ([3H]ACh) by purified Torpedo electric organ synaptic vesicles was studied. Transport specific activity decreased at higher vesicle concentration. Michaelis-Menten type kinetics describe [3H]ACh active transport at constant vesicle concentration with no evidence of cooperativity or transporter heterogeneity. The ACh dissociation constant is about 0.3 mM, transport has a maximal velocity of about 1.6 nmol/min/mg protein, and both are dependent on the vesicle preparation. Nonradioactive ACh was a competitive inhibitor with respect to [3H]ACh. The potent transport inhibitor dl-trans-2-(4-phenylpiperidino)cyclohexanol (AH5183) is a non-competitive inhibitor with respect to [3H]ACh, with an inhibition constant of 41 +/- 7 nM. Inhibition by AH5183 is reversible. The results suggest that AH5183 does not bind to the ACh transporter recognition site on the outside of the vesicle membrane, and thus it might inhibit allosterically.

Acetylcholine↗
PubMed2000

Drosophila endosomal proteins hook and deep orange regulate synapse size but not synaptic vesicle recycling.

To study the function of endosomes at synapses we analyzed the localization and function of two Drosophila endosomal proteins, Hook and Deep orange (Dor), at the larval neuromuscular junction. Hook, a negative regulator of endocytic trafficking, and Dor, a positive regulator of endocytic trafficking, are highly enriched at synapses, especially close to postsynaptic membranes. Mutations in hook (hk) and dor do not affect synaptic vesicle recycling, as assessed by electrophysiological analysis of synaptic transmission and behavioral studies of double mutants with shi(ts) mutations that alter vesicle recycling. However, hk and dor mutations alter the number of presynaptic varicosities (synapse size) in opposing ways. Synapse size is increased in hk(11) mutants and is decreased in dor(4) mutants. Double mutants for dor and hk show a dor-like phenotype. These effects on synapse size parallel known functions of Hook and Dor in endocytosis and strongly indicate a role for endocytic trafficking in the regulation of synapse size in vivo. Our observations suggest a model in which Hook and Dor function in later stages of endocytosis is essential for regulating synaptic plasma membrane composition but not synaptic vesicle recycling.

Animals↗
PubMed1982

Divalent cation, ATP-dependent [3H]leu-enkephalin uptake by synaptic vesicle fraction isolated from bovine caudate nucleus.

The mechanism of [3H]Leu-enkephalin uptake into synaptic vesicle fraction from bovine caudate nucleus was investigated. The simultaneous addition of 2 mM MgCl2, 2 mM CaCl2, and 2 mM ATP stimulated the uptake 22 times over the control, whereas the separate addition of these agents augmented the uptake 2.4 times at most. The addition of 2 mM MGCl2 plus 2 mM ATP and of 2 mM CaCl2 plus 2 mM ATP increased the uptake 6.6 times and 4.5 times, respectively. The cation, ATP-dependent uptake reached its half-maximal level within 10 min after the initiation of incubation at 25 degrees C, and little Leu-enkephalin was taken up at 0 degree C. The apparent Km for the uptake of [3H]Leu-enkephalin was 1.8 x 10(-7) M. Guanosine triphosphate stimulated the uptake as well as ATP, whereas CTP and ITP were only one-fourth effective of ATP. The cation, ATP-dependent uptake was inhibited by 25% and 20% in the presence of 0.1 mM colchicine and 1 microM reserpine, respectively.

Adenosine Triphosphate↗
PubMed1990

Energy dependence and functional reconstitution of the gamma-aminobutyric acid carrier from synaptic vesicles.

The energy dependence of gamma-aminobutyric acid (GABA) uptake was characterized in rat brain synaptic vesicles and in proteoliposomes reconstituted with a new procedure from vesicular detergent extracts. The proteoliposomes displayed high ATP-dependent GABA uptake activity with properties virtually identical to those of intact vesicles. GABA uptake was similar at chloride concentrations of 0 and 150 mM, i.e. conditions under which either the membrane potential (delta psi) or the pH difference (delta pH) predominates. Delta psi was gradually dissipated by increasing the concentration of SCN-. GABA uptake was reduced by 10 mM SCN-, showing less sensitivity to delta psi reduction than glutamate uptake but more than dopamine uptake. Dissipation of delta pH with NH+4 abolished GABA uptake at pH 7.3, whereas no significant inhibition occurred at pH 6.5. In contrast, dopamine uptake was inhibited more strongly, even at pH 6.5, and glutamate uptake was not reduced in either condition. We conclude that GABA uptake is driven by both components of the proton electrochemical gradient, delta pH and delta psi, and that this is different from the uptake of both dopamine and glutamate, which is more strongly dependent on delta pH and delta psi, respectively. Thus, our data suggest that GABA uptake is electrogenic and occurs in exchange for protons.

Adenosine Triphosphate↗