Adult rat brain synaptic vesicles. I. Isolation and characterization

Synaptosomes as a platform for loading nanoparticles into synaptic vesicles

Synaptosomes are intact, isolated nerve terminals that contain the necessary machinery to recycle synaptic vesicles via endocytosis and exocytosis upon stimulation. Here we use this property of synaptosomes to load quantum dots into synaptic vesicles. Vesicles are then isolated from the synaptosomes, providing a method to probe isolated, individual synaptic vesicles where each vesicle contains a single, encapsulated nanoparticle. This technique provided an encapsulation efficiency of ~16%, that is, ~16% of the vesicles contained a single quantum dot while the remaining vesicles were empty. The ability to load single nanoparticles into synaptic vesicles opens new opportunity for employing various nanoparticle-based sensors to study the dynamics of vesicular transporters.

Synthesis and translocation of gangliosides and glycoproteins during urethane anesthesia

In this work, we have studied (a) the contents of gangliosides, glycoproteins, and phospholipids of the vesicle and plasma membrane fractions from brains of anesthetized and control rats and chickens and (b) the labeling of gangliosides and glycoproteins in the retina ganglion cell layer and optic tectum of urethane-anesthetized and control chickens after intraocular injection of a labeled N-acetylneuraminic acid precursor and the distribution of the label after subcellular fractionation. We found an increase in the content of gangliosides relative to protein in the vesicle fraction of both anesthetized rats and chickens relative to their controls. Other values were not affected by anesthesia. These results do not reflect a faster synthesis of gangliosides stimulated by urethane, because their rate of labeling was diminished in anesthetized animals. During the 4-h period after the animals were injected intraocularly with the radioactive precursor, the highest values of ganglioside-specific radioactivity were found in the vesicle fraction of control and anesthetized animals; at longer intervals, the specific radioactivity of the vesicle and plasma membrane fractions became rather similar. These data are in accordance with previous studies from this laboratory suggesting that the synthesis of the carbohydrate chain of gangliosides is regulated by the physiological demands made by the neurotransmitting system.

A hemagglutinin specific for sialic acids in a rat brain synaptic vesicle-enriched fraction

A hemagglutinating activity was detected in a synaptic vesicle-enriched fraction prepared from adult rat brain, using trypsinized glutaraldehyde-fixed rabbit erythrocytes. The specific activity of the fraction, in two series of experiments, was 7.5 and 16-fold higher than in the other subcellular fractions. The activity was absent from the synaptosome cytosol. In a study using twenty-five different carbohydrates and glycoproteins, best inhibitors were N-acetylneuraminic acid and N-glycolylneuraminic acid, together with bovine submaxillary mucin and a glycopeptide fraction prepared from rabbit erythrocyte membranes. The activity was thermolabile and very sensitive to proteolytic enzymes (but insensitive to neuraminidase) indicating that a protein (agglutinin) is responsible for the activity. Experiments using detergents and high ionic strength showed that the agglutinin is tightly bound to membranes, inactivated by the so-called non denaturing detergents, and stable in diluted sodium dodecyl sulphate. Hypotheses are discussed on the possible function of the agglutinin.

A similar calmodulin-binding protein expressed in chromaffin, synaptic, and neurohypophyseal secretory vesicles

The presence of calmodulin-binding proteins in three neurosecretory vesicles (bovine adrenal chromaffin granules, bovine posterior pituitary secretory granules, and rat brain synaptic vesicles) was investigated. When detergent-solubilized membrane proteins from each type of secretory organelle were applied to calmodulin-affinity columns in the presence of calcium, several calmodulin-binding proteins were retained and these were eluted by EGTA from the columns. In all three membranes, a 65-kilodalton (63 kilodaltons in rat brain synaptic vesicles) and a 53-kilodalton protein were found consistently in the EGTA eluate. 125I-Calmodulin overlay tests on nitrocellulose sheets containing transferred chromaffin and posterior pituitary secretory granule membrane proteins showed a similarity in the protein bands labeled with radioactive calmodulin. In the presence of 10(-4) M calcium, eight major protein bands (240, 180, 145, 125, 65, 60, 53, and 49 kilodaltons) were labeled with 125I-calmodulin. The presence of 10 microM trifluoperazine (a calmodulin antagonist) significantly reduced this labeling, while no labeling was seen in the presence of 1 mM EGTA. Two monoclonal antibodies (mAb 30, mAb 48), previously shown to react with a cholinergic synaptic vesicle membrane protein of approximate molecular mass of 65 kilodaltons, were tested on total membrane proteins from the three different secretory vesicles and on calmodulin-binding proteins isolated from these membranes using calmodulin-affinity chromatography. Both monoclonal antibodies reacted with a 65-kilodalton protein present in membranes from chromaffin and posterior pituitary secretory granules and with a 63-kilodalton protein present in rat brain synaptic vesicle membranes. When the immunoblotting was repeated on secretory vesicle membrane calmodulin-binding proteins isolated by calmodulin-affinity chromatography, an identical staining pattern was obtained. These results clearly indicate that an immunologically identical calmodulin-binding protein is expressed in at least three different neurosecretory vesicle types, thus suggesting a common role for this protein in secretory vesicle function.

Protein organization of rat synaptic plasma membranes and synaptic vesicles: a one- and two-dimensional study

The protein organization of rat brain synaptic plasma membranes (SPM) and synaptic vesicles (SV) was investigated by surface iodination and one- and two-dimensional electrophoresis. Polypeptides of molecular weights (MWs, in Kilodaltons) 170 K, 135 K, 96-86 K, 68-64-61 K, 56 K, 52 K, 38 K, 35-33 K, and 18 K are predominantly or exclusively exposed on the extracellular side of synaptosomes. Several polypeptides of MW between 70 K and 40 K are exclusively exposed on the cytoplasmic side of SPM. The use of two-dimensional electrophoresis allowed to recognize that, for some classes of MW, there are polypeptides of nearly the same MW and different isoelectric points exposed on both sides of SPM. The synaptosomal membrane shows a predominance of acidic proteins on the extracellular side and more neutral and basic proteins on the cytoplasmic side. With respect to SPM, SV are particularly enriched with polypeptides of MW 71 K, 56 K, 39-38 K, 32 K, 16 K, and 15 K. One of them, a doublet of MW 39-38 K, is the most highly labeled species upon surface iodination and is similar, but not identical, with a doublet located on the cytoplasmic side of SPM.

Heterogeneous localization of some purine enzymes in subcellular fractions of rat brain and cerebellum

The activity of guanine deaminase (GAH, E.C.3.5.4.3) was lower in rat cerebellum soluble and microsomal fractions than in rat brain subfractions. Adenosine deaminase (ADA, E.C.3.5.4.4) activity was released in higher proportion than guanine deaminase, purine nucleoside phosphorylase (PNP, E.C.2.1.2.4), 5'-nucleotidase (5'N, E.C.3.1.3.5), and lactate (LDH, E.C. 1.1.1.27) and malate (MDH, E.C. 1.1.1.37) dehydrogenase in press-juices of rat brain. Furthermore, nerve ending-derived fractions (synaptosomes and synaptic vesicles) showed an enrichment of adenosine deaminase and also of 5'-nucleotidase. The action of deoxycholate over the subfractions did not increase the activity of either enzyme. The contrary occurred with the remaining enzymes studied. Thus, it is possible that one set of enzymes are located on the surface of the particulate vesicles, whereas another set are located inside these vesicles, suggesting a compartmentation of purine catabolic enzymes in different areas of the central nervous system.

Binding of concanavalin A to calf brain synaptic vesicles

Concanavalin A was employed as a tool to investigate the organization of synaptic vesicle glycoproteins. The lectin was incubated in the presence of both intact and Triton X-100 treated calf brain synaptic vesicles. Electrophoresis of treated membranes clearly demonstrated that the majority of Concanavalin A binding sites was not exposed in intact synaptic vesicles. The vesicles were isolated by the procedure of DeLorenzo and Freedman (DeLorenzo, R. J., and Freedman, S. D. (1978) Biochem. Biophys. Res. Commun. 80, 183-192). However, an extra centrifugation step at 55,000 g was required to obtain plain vesicles nearly free from coated vesicles and membrane fragments.

Cyclic AMP independent protein kinase activity in rat cerebral cortex synaptic vesicles--partial characterization

The intrinsic protein kinase activity of a highly purified synaptic vesicle preparation was characterized. The time-course of the reaction was found to be rapid and linear for about 1 min, but plateaued after 30 min by which time approximately 1 nmol of 32P per mg protein was incorporated into trichloroacetic acid precipitated vesicular protein. The enzyme was optimally active at pH 6.0 (37 degrees C), and had apparent Km values of 40 and 88 microM for ATP and GTP respectively. The enzyme was not stimulated by cAMP or cGMP. Mg2+ was required for maximal activity. The reaction was inhibited by free Ca2+, and non-selectively by Na+, K+, and NH4+.

Effect of indomethacin on Ca2+-stimulated adenosine triphosphatase in the synaptic vesicles of rat brain in vitro

1. Indomethacin inhibits calcium-stimulated adenosine triphosphatase (Ca2+-ATPase), calcium, magnesium-stimulated adenosine triphosphatase (Ca2+,Mg2+-ATPase) and magnesium-stimulated adenosine triphosphatase (Mg2+-ATPase) activities in rat brain synaptic vesicles in vitro. 2. The Ca2+-ATPase activity is most strongly affected by this drug all of the activities of ATPases tested. 3. The decrease of Ca2+-ATPase activity by addition of indomethacin is due to a decrease of Vmax. 4. The Ki values for this drug for ATP and Ca2+ in Ca2+-ATPase were 1.13 mM and 0.68 mM, respectively.

Surface potential and surface charge density of the cerebral-cortex synaptic vesicle and stability of vesicle suspension

Using a microelectrophoresis instrument employing the Lazer-Zee system, the electrophoretic mobility of synaptic vesicles isolated from Guinea-pig brain cortex was measured under conditions. The mobility was found to depend on both pH and ionic concentration of the solution. The surface of the synaptic vesicle was shown to be negatively charged under physiological conditions. The isoelectric point was observed at pH 4.0 in 0.01 M NaCl solution. Effects of divalent cations were examined and reversal of surface charge was observed in 0.1 M CaCl2 solution. Interaction of vesicles was also considered on the basis of the DLVO theory of colloid stability by using calculated values of surface charge density and surface potential of the synaptic vesicle.

Glycoproteins from adult rat brain synaptic vesicles. Fractionation on four immobilized lectins

Glycoproteins obtained from large amounts of highly purified synaptic vesicles isolated from adult rat brain were fractionated by sequential affinity chromatography in the presence of SDS on four different immobilized lectins: concanavalin A, Ulex europeus lectin, Ricinus sanguinis lectin and wheat germ agglutinin. 83% of the total protein-bound sugar of synaptic vesicles can be adsorbed on the lectins and separated from the bulk of carbohydrate free proteins. Nine fractions containing only glycoproteins and differing by their terminal sugars were separated by analysed for their carbohydrate composition and electrophoretic profiles. A considerable heterogeneity of the glycoprotein population was observed which cannot be explained solely by the microheterogeneity of the glycans of the synaptic vesicle glycoproteins.

Electrokinetic properties of synaptic vesicles and synaptosomal membranes

Using the technique of electrophoretic light scattering, we have measured the electrophoretic mobilities of synaptic vesicles and synaptosomal plasma membranes isolated from guinea-pig cerebral cortex. The electrophoretic mobility of synaptic vesicles is slightly greater than that of synaptosomal plasma membranes. Ca+2 and Mg+2 reduced the mobility of both species to the same extent at physiologically relevant concentrations (0-1 mM) and near-physiologic ionic strength. The extent of the reduction was not large (approximately 6% for synaptic vesicles in the presence of 100 mM KCl) at 1 mM divalent cation concentrations. At concentrations of approximately 2 mM and higher, Ca+2 reduced the mobility of synaptic vesicles more than did Mg/2. A similar but much smaller effect was observed in the case of synaptosomal plasma membranes. The addition of 1 mM Mg+2-ATP had no effect upon synaptic vesicle mobility either in the presence or absence of the ionophores nigericin or valinomycin. These data, together with earlier work (Siegel et al., 1978, Biophys. J. 22:341-346), demonstrate that substantial reduction of the average electrostatic surface charge density is not the most important role of divalent cations in promoting close approach of secretory granules and secretory cell membranes, and that it is certainly not the Ca+2-specific step in exocytosis.

Free amino acids in the synaptosome and synaptic vesicle fractions of different bovine brain areas

Free amino acids were quantitatively estimated in intact tissues and isolated synaptosome and synaptic vesicle fractions of the bovine brain regions with the aid of a sensitive amino acid analyzer. The brain areas studied were frontal, parietal and occipital cerebral cortices, cerebellar cortex, caudate and lenticular nuclei, superior colliculi, thalamus, pons and medulla. The most abundant amino acid in tissue samples and synaptosome fractions was glutamic acid, followed by glutamine, aspartic acid, GABA and taurine. The dominatating amino acid in all isolated synaptic vesicle fractions was taurine. The concentrations of glutamic acid, glutamine, GABA and aspartic acid were generally much lower. The 5 transmitter candidates, viz. GABA, glycine, glutamic acid, as particaid and taurine, comprised about one-half of the total amino acids in all samples. Taurine was the only amino acid highly enriched in the vesicle fractions. This enrichment was discernible in all brain areas. It is suggested therefore that taurine is rather a ubiquitous associate of synaptic membrane structures than a specific inhibitory transmitter.

Studies on synaptic vesicles in mammalian brain characterization of highly purified synaptic vesicles from bovine cerebral cortex

Synaptic vesicles have been isolated from bovine cerebral cortex by sequential differential and density gradient centrifugations followed by chromatography on a Sepharose 6B column. We have studied the morphology, enzymatic markers, neurotransmitter and ATP contents and protein composition of the vesicles. The specific contents of acetylcholine, gamma-aminobutyric acid, aspartate, glutamate and catecholamines were 4--8-fold higher in the vesicle fraction compared to the crude synaptosomal pellet. Electron micrographs of the vesicle preparation showed enrichment of vesicular material with an average diameter of 50 nm. The purity of the preparation was assessed by the very low activities of enzymatic markers of cellular membranes and cytosol components. Some Ca--Mg-activated ATPase activity was detected in the vesicle preparations, but its content relative to the neurotransmitters fell on chromatography, suggesting that this activity may be partially contributed by non-synaptic vesicle components, such as small microsomes. The isolated synaptic vesicles were solubilized with 1% sodium dodecyl sulfate and subjected to polyacrylamide gel electrophoresis. The major Coomassie blue stained bands observed with apparent molecular weights of 160,000 and 55,000 were enriched in parallel to the increase in purity of the preparation.

Amino acids in the synaptic vesicle fraction from calf brain: content, uptake and metabolism

A synaptic vesicle fraction was prepared from calf brain cortex, containing 10 identified amino acids and two unidentified ninhydrin-positive compounds, one of which is apparently a peptide. The most plentiful amino acids were taurine (1.8 nmol/g original tissue), glutamic acid (1.8), serine (0.9), aspartic acid (0.8) and GABA (0.8); the others identified were cysteic acid (or cysteinesulphinic acid), glutamine, alanine, glycine and lysine. The unknown peptide occurred in a high concentration (about 16 alanine equivalents/g), and contained mainly aspartic acid and serine. Cysteic acid (or cysteinesulphinic acid) also occurred in relatively high amounts, but its peak contained acid-labile impurities. The influx of [14C]glutamate into the vesicles took place by means of non-saturable migration, while two saturable systems having very similar properties were dominant only at low glutamate concentrations. Influx constants for these quantitatively low uptake systems were Km, 34 and 92 micrometer, and Vmax, 33 and 49 nmol/min/g obtained by v versus v/S plot. Almost the same values were also obtained by a 1/v versus 1/S plot. GAD and GABA-T activities in the vesicles were only 1/200th of those in the synaptosomes.

Membrane protein and glycoprotein composition of beef brain synaptic vesicles

Synaptic vesicles were isolated from adult bovine cortical gray matter by differential centrifugation and membrane filtration of a hypoosmotically lysed crude mitochondrial fraction. Vesicle preparations were analyzed for purity by electron microscopy and enzyme assays. Polyacrylamide gel electrophoresis of SDS-solubilized and 2-mercaptoethanol-reduced vesicle membrane proteins revealed 4 major proteins with molecular weights ranging from 17,000 to 60,000, and about 10 minor proteins with molecular weights up to 170,000. The protein profile of the Triton X-100-extracted vesicle membranes was less complex, with 1 major protein and 5 minor bands. The major protein of the Triton extract was identified as a glycoprotein with a molecular weight of 45,000. Two additional minor PAS-positive bands were seen, with molecular weights of 78,000 and 95,000.

A spin label study of rat brain membranes. Effects of temperature and divalent cations

Rat brain myelin, synaptosomal plasma membranes and synaptic vesicles were spin labelled with stearic acid nitroxide derivatives. Their electron spin resonance spectra were studied as a function of temperature and devalent ions (Ca2+ and Mg2+) concentrations. (1) Synaptosomal plasma membranes and synaptic vesicles show identical temperature variations of their order parameter (S = 0.58 at 35 degrees C and S = 0.72 AT 22 DEGREES C). Myelin appears more rigid (S = 0.66 at 35 degrees C and S = 0.76 at 22 degrees C). A discontinuity of the order parameter variation as a function of temperature, is observed between 14.5 degrees C and l9.5 degrees C with the three types of membranes. (2) The hydrophobic core of these membranes is very fluid. No transition temperature is observed. The measured values of the spin label rotation correlation times and rotational activation energies are 2.1 and 2.8 ns at 35 degrees C and 3.1 and 3.6 kcal/mol respectively for synaptosomal plasma membranes and myelin. (3) Ca2+ enhances the membrane rigidity (12+/-0.7% increase of the order parameter at 35 degrees C in the presence of 10(-3) M Ca2+) and increases the transition temperature. At a lower extend, similar effects are observed with Mg2+.

The preparation and characterization of synaptic vesicles of high purity

Very pure preparations of synaptic vesicles have been obtained from guinea pig cerebral cortex and from the electromotor synapses of Torpedo marmorata by density gradient centrifugation in a zonal rotor followed by chromatography on columns of glass beads of controlled pore size. Markers for soluble cytoplasm (lactate dehydrogenase), plasma and endoplasmic membranes membranes (Na-K-ATPase; acetylcholinesterase, NADPH-cytochrome c reductase], mitochondrial membranes [cytochrome oxidase] and lysosomes [acid phosphatase] were used to assess contamination and were undetectable. The only enzymes detected in the highly purified preparations from guinea pig cerebral cortex were Mg- and Ca-activated ATPases, but their content relative to acetylcholine fell on chromatography suggesting that they may be constituents of non-cholinergic vesicles. Lipids analyses of the highly purified vesicles confirmed earlier results and showed that glycolipids and lysolecithin are present in negligible amounts; this suggests that lysolecithin is not required for exocytosis of synaptic vesicles. A discussion of the probable limiting concentration of acetycholine in cerebral cortical vesicles derived solely from cholinergic terminals suggests that from 13 to 56% of the vesicles isolated are cholinergic, depending on the assumptions made.

Isolation and partial characterization of chick brain synaptic plasma membranes

An isolation procedure for synaptic plasma membranes from whole chick brain is reported that uses the combined flotation-sedimentation density gradient centrifugation procedure described by Jones and Matus (Jones, D. H. and Matus, A. I. (1974) Biochim. Biophys. Acta 356, 276-287) for rat brain. The particulate of the osmotically shocked and sonicated crude mitochondrial fraction was used for a flotation-sedimentation gradient step. Four fractions were recovered from the gradient after 30 min centrifugation. The fractions were identified and characterized by electron microscopy and by several markers for plasma membrane and other subcellular organelles. Fraction 2 was recovered from the 28.5-34% (w/v) sucrose interphase and contained the major part of the activities of the neuronal plasma membrane marker enzymes. The specific activities of the (Na+ +K+)-activated ATPase (EC 3.6.1.3), acetylcholinesterase (EC 3.1.1.7) and 5'-nucleotidase (EC 3.1.3.5) were, respectively, 4.5, 2.0 and 1.2 times higher than in the homogenate. However, Fraction 2 also contained considerable amounts of activities of putative lysosomal and microsomal markers in addition to lower amounts of mitochondrial and myelin markers. Although no prepurification of synaptosomes from the crude mitochondrial fraction was performed, the synaptic plasma membranes obtained showed many properties analogous to similar preparations from rat brain described in recent years.

Effects of Ischemia on the Mg + + Requiring Adenosine Triphosphatase Associated With Neuronal Synaptic Vesicles in Gerbil Brain

The Mg + + requiring adenosine triphosphatase (ATPase) associated with neuronal synaptic vesicles is extremely vulnerable to ischemia. After five minutes of ischemia both the maximum velocity and the substrate binding capacity of the enzyme were decreased. Results also indicate that these changes are related to the rapid intraneuronal lactic acidosis accompanying ischemia. Ischemia was simulated by 37°C incubation of gerbil brain after decapitation. According to a recent hypothesis this enzyme plays a key role in exocytotic neurotransmitter release. Therefore, any inhibition of the ability of this enzyme to function would result in a drastically reduced capacity for transsynaptic impulse propagation.