Synaptosomal proteins

Excitable tissue preparations were obtained fresh daily from live animals using the technique described by Dodd et al. (12). Protein was measured on each synapto-some preparation using the Coomassie Brilliant Blue dye technique described by Bradford (13) results were expressed as "toxin bound per mg synaptosome protein". 

Figure 4. Binding was measured in rat brain synaptosomes using a rapid centrifugation technique. Total ( ), and nonspecific ( ) binding of tritiated PbTx-3 were measured, their difference representing specific binding (A). Rosenthal analysis yields a of 2.6 nM and a B of 6.0 pmol toxin bound/mg protein.

Figure 6. Effect of brevetoxins on tritiated PbTx-3 binding to rat brain synaptosomes. Incubations, in the presence of 50 fig synaptosomal protein and 16 nM tritiated PbTx-3 with increasing amounts of unlabeled PbTx-1 ( ), PbTx-2 ( ), PbTx-3 ( ), PbTx-5 (A), PbTx-6 ( ), or PbTx-7 (o) were for 1 hr at 4 C. Each point represents the mean of three triplicate determinations.

ATP certainly fulfils the criteria for a NT. It is mostly synthesised by mitochondrial oxidative phosphorylation using glucose taken up by the nerve terminal. Much of that ATP is, of course, required to help maintain Na+/K+ ATPase activity and the resting membrane potential as well as a Ca +ATPase, protein kinases and the vesicular binding and release of various NTs. But that leaves some for release as a NT. This has been shown in many peripheral tissues and organs with sympathetic and parasympathetic innervation as well as in brain slices, synaptosomes and from in vivo studies with microdialysis and the cortical cup. There is also evidence that in sympathetically innervated tissue some extracellular ATP originates from the activated postsynaptic cell. While most of the released ATP comes from vesicles containing other NTs, some... 

Bagni, C., Mannucci, L., Dotti, C. G., and Amaldi, F. (2000). Chemical stimulation of synaptosomes modulates alpha —Ca2+/calmodulin-dependent protein kinase II mRNA association to polysomes. J. Neurosci. 20, RC76. 

Na+,H+ antiporters (NHE) occur in synaptosomes, glia and neuroblastoma cells [60] (Fig. 5-8B). They are relatively inactive at neutral pH but with a decrease in intracellular pH they produce an efflux of protons at the expense of the Na+ gradient. The NHE transport stoichiometry is 1 1. Activation by an internal pH decrement apparently results from protonation of a cytoplasmic site, which allosterically increases the affinity of the proton ionophoric site. In some cells, the NHE is under additional control by receptor mechanisms. Several growth factors and hormones produce transient cytoplasmic alkalinization, probably by mediating a protein kinase... 

The initial step after cellular uptake of T4 is metabolic transformation to 3,5,3, -tri-iodothyronine (T3) (Fig. 52-8), which interacts with cytosolic and nuclear receptors, as well as with synaptosomal membrane binding sites of unknown function [25], Cytosolic receptors are proteins of 70 kDa that do not appear to undergo translocation to cell nuclei, nor do they appear to be nuclear proteins that have leaked out of cell nuclei during cell rupture nuclear receptors are proteins of 50 70 kDa that have both DNA-and hormone-binding domains [25,26,28],... 

Some intracellular signal transduction molecules are reduced in schizophrenia. The release of neurotransmitters is regulated by a family of proteins that coordinate vesicular trafficking (see Ch. 9). Of these, the expression of complexin I and II appears to be decreased in prefrontal cortex and subfields of the hippocampal formation, and the ratio of complexin I to complexin II is elevated in the hippocampus [35], SNAP-25 (Synaptosomal Associated Protein, kDa 25) has inconsistently been found to be down-regulated in both these regions. Synapsin expression is also reduced, but more robust decrements have been observed in bipolar disorder (Ch. 55). 

All botulin neurotoxins act in a similar way. They only differ in the amino-acid sequence of some protein parts (Prabakaran et al., 2001). Botulism symptoms are provoked both by oral ingestion and parenteral injection. Botulin toxin is not inactivated by enzymes present in the gastrointestinal tracts. Foodborne BoNT penetrates the intestinal barrier, presumably due to transcytosis. It is then transported to neuromuscular junctions within the bloodstream and blocks the secretion of the neurotransmitter acetylcholine. This results in muscle limpness and palsy caused by selective hydrolysis of soluble A-ethylmalemide-sensitive factor activating (SNARE) proteins which participate in fusion of synaptic vesicles with presynaptic plasma membrane. SNARE proteins include vesicle-associated membrane protein (VAMP), synaptobrevin, syntaxin, and synaptosomal associated protein of 25 kDa (SNAP-25). Their degradation is responsible for neuromuscular palsy due to blocks in acetylcholine transmission from synaptic terminals. In humans, palsy caused by BoNT/A lasts four to six months. 

Schengrund, C.L., Ringler, N.J. and DasGupta, B.R., Adherence of botulinum and tetanus neurotoxins to synaptosomal proteins, Brain Res. Bull., 29, 917-924, 1991. 

F. Matsumura, sponsored by the National Institute of Environmental Health Sciences (NIEHS), plans to study the toxic effects of chlorinated and pyrethroid pesticides primarily on calcium and sodium regulating processes in the nervous system. To examine the interactions of the pesticides with calcium regulating processes, researchers will use synaptosomal preparations from the brains of rats and the central nervous systems of squid. To examine the interactions of the pesticides with sodium regulating processes, they will collect antibodies directed against sodium channel proteins. 

Plasma Membranes and Derived Transporters Measurement of transported calcium in synaptosomes, 174, 3 glutamate accumulation into synaptic vesicles, 174, 9 identification of bile acid transport protein in hepatocyte sinusoidal plasma membranes,... 

Rats exposed to 50 or 250ppmg-cymene 6 hours/day, 5 days/week for 4 weeks had a significantly decreased yield of synaptosomal protein in the brain, suggesting a decrease in the density and total number of synapses. ... 

It is universally accepted that the action of opioids is mediated by specific receptors. It is presumed that several types of opioid receptors exist p, k, 5, and a. A few of these are in turn subdivided into subtypes. It has been found that opioid receptors are seven transmembrane G-protein-coupled receptors that are localized in the membranous part of the synaptosomal head it has also been found that they are glycoproteins. They are prone to conformational changes in certain situations, which is essential for their selective binding with agonists or antagonists. 

Thompson PM, Rosenberger C, Holt S, Perrone-Bizzozero N1 (1998) Measuring synaptosomal associated protein-25 kDa in human cerebral spinal fluid. J Psychiatr Res 32 297-300... 

Schematic illustration of a generalized cholinergic junction (not to scale). Choline is transported into the presynaptic nerve terminal by a sodium-dependent choline transporter (CHT). This transporter can be inhibited by hemicholinium drugs. In the cytoplasm, acetylcholine is synthesized from choline and acetyl -A (AcCoA) by the enzyme choline acetyltransferase (ChAT). Acetylcholine is then transported into the storage vesicle by a second carrier, the vesicle-associated transporter (VAT), which can be inhibited by vesamicol. Peptides (P), adenosine triphosphate (ATP), and proteoglycan are also stored in the vesicle. Release of transmitter occurs when voltage-sensitive calcium channels in the terminal membrane are opened, allowing an influx of calcium. The resulting increase in intracellular calcium causes fusion of vesicles with the surface membrane and exocytotic expulsion of acetylcholine and cotransmitters into the junctional cleft (see text). This step can he blocked by botulinum toxin. Acetylcholine s action is terminated by metabolism by the enzyme acetylcholinesterase. Receptors on the presynaptic nerve ending modulate transmitter release. SNAPs, synaptosome-associated proteins VAMPs, vesicle-associated membrane proteins.

The toxin produced by the bacterium C. botulinum is a mixture of six large molecules and is one of the two most potent toxins known to humans. Each consists of two components, a heavy (100 kDa) and light (50 kDa) polypeptide chain. The toxin molecule is transported into nerve cells and destroys a synaptosomal protein, which prevents the release of the neurotransmitter acetylcholine. This blocks muscle contraction, causing paralysis. This can be fatal. 

Botulinum toxin is a mixture of six large molecules, each of which consist of two components, a heavy (lOOkDa) and light (50kDa) polypeptide chain. The heavy chain binds to the walls of nerve cells, which then allows the whole toxin molecule to be transported into the cell inside a vesicle via receptor-mediated endocytosis. Once inside, the light chain translocates into the cytosol and acting as a peptidase, destroys a synaptosomal protein. 

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