Brain membrane synaptosomes

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... 

Preliminary experiments to delineate the optimum conditions for [ H]MDA and [ HJMDMA binding to rat brain membranes indicated that the best signal-to-noise ratio was found using a crude synaptosomal preparation incubated at 4 °C. While most experiments employed 50 mM Tris-HCl (pH 7.1) as the incubation medium, we found that the addition of 0.27 M sucrose to the incubation medium increased the specific binding approximately fivefold. Subsequent experiments were carried out under both conditions. Other preliminary experiments suggested that [ H]MDA and... 

As stated earlier, the primary site of association of [ H]MDA with brain synaptosomes is with membrane components, not with the intrasynaptic space. While the phenolic ends of these compounds may enable them to interact with hydrophobic environments of brain membrane components, their polar side chains may inhibit the ability of these compounds to move freely across the membranes, thus inhibiting internalization. The pKa of... 

Another example is the perturbing effect of eight calcium channel blockers on membranes prepared from two different lipids [68]. The authors used total lipids from rat brain and synaptosomal membranes. The spin probe was l-palmitoyl-2-stearoyl-phosphatidyl-choline labeled at the doxyl group at the carbon-16 position (16-PC). The apparent order parameter, S, is calculated from the apparent outer (Amax) and inner (Amin) splittings which were directly taken from the ESR spectra. It is used to describe the relative efficiency of the dmgs in perturbing the lipid membrane. 

The aminopeptidase was obtained from either serum, rat brain, or synaptosomal membrane. 

Suzuki H, Manabe S, Wada O, Crawford MA. Rapid incorporation of docosahexaenoic acid from dietary sources into brain microsomal, synaptosomal and mitochondrial membranes in adult mice. Int J Vitam Nutr Res 1997 67 272-278. 

Sodium uptake assay. Assays using mouse brain synaptosomes were performed as described previously (6., ), except that insecticides were introduced to resuspended synaptosomes in 0.2-0.4 yl of ethanol rather than as a residue in the incubation tube. This amount of ethanol improved the delivery of insecticides, thereby increasing the reproducibility of the assay, and had no measurable effect on veratridine-dependent sodium channel activation. These methods were also used for assays with fish brain membranes, except that all buffers were augmented with sucrose to give osmolarities equivalent to the 0 7 M sucrose used for membrane isolation. 

Furthermore, the substitution of methyl groups at the T and 6 position of Tyr (Dmt) yielded Dmt-Tic- peptides (3) endowed with dramatically increased 8-affinity, comparable to the 8-affinity observed with deltorphins [59-63]. On the other hand, p-affinity of 3 rose 20-fold relative to 1 and 2, while k-affinity increased over 40-fold in guinea pig brain membranes, 20-fold in rat brain synaptosomes compared to 2 and approximately 40-fold for both membrane preparation relative to 1. Inclusion of the Tyr-D-Ala-Phe message domain (4) essentially eliminated opioid interaction with k-receptors, whereas 8- and p-affinities were only moderately altered in comparison to DYN (1-11) -NH2 (Table... 

Changes in the fatty acid composition of structural lipids in brain membranes have been reported to modify (Na+K)-ATPase in synaptosomes (Sun Sun, 1975) and n-6 and n-3 fatty acids are considered important for the activity of certain membrane-bound enzymes (Bernsohn Spitz, 1974). Modifications in learning... 

Batrachotoxinin-A 20a-p-pH] benzoate (pH]-BTX-B) has proven to be a satisfactory ligand for the investigation of batrachotoxin-binding sites in brain membranes and synaptosomes (45,46,66). The affinity constant for [3H]-BTX-B is approximately 50 nM in the presence of scorpion toxin and approximately 700 nM in the absence of a polypeptide. The density of sites... 

H]MDMA interacted with multiple sites in rat brain. A low affinity pH]MDA binding site (apparent Kd>1.0 mM) was found to be resistant to boiling of the synaptosomal preparation for 15 minutes. This site was saturable, as indicated by a 30 pereent inhibition of [ H]MDA binding to boiled synaptosomes by 1.0 mM MDA and a 56 pereent inhibition of the binding by 0.1 mM of the serotonin uptake bloeker paroxetine. The indication of a saturable, nonspecific binding site for [ H]MDA in boiled membranes necessitated that we use boiled tissue to assess nonspecific binding in all subsequent experiments. 

Krueger, B.K. Ratzlaff, R.W. Strichartz, G.R. and Blaustein, M.P. Saxitoxin binding to synaptosomes, membranes and solubilized binding sites from rat brain. J. Membr Biol 50 287-310,... 

Compounds 227 and 232 were tested in vitro for inhibition of [3H]-diazepam-specific binding to benzodiazepine receptors in membranes from synaptosomes of rat brain and in vivo for their effects on conditioned behavior in rats (89FES29). 

Mercuric chloride is thought to gain access to the intracellular compartment through Na + and Ca2 + channels in the membrane [ 100]. Sulphydryl reagents, including Hg2 +, could inhibit K +-stimulated uptake of Ca2+ into rat brain synaptosomes in vitro [101]. In muscle sarcoplasmic reticulum, Hg2+ causes inhibition of ATP-dependent Ca2 + uptake and loss of accumulated calcium [ 102,103]. However, HgCl2 has been found to inhibit ATP-dependent calcium uptake more strongly than it inhibits potassium-stimulated uptake [ 104],... 

Mehorta and coworkers (1989) observed that isolated fractions of brain and heart cells from rats orally administered 0.5-10 mg endrin/kg showed significant inhibition of Ca+2 pump activity and decreased levels of calmodulin, indicating disruption of membrane Ca+2 transport mechanisms exogenous addition of calmodulin restored Ca+2-ATPase activity. In vitro exposure of rat brain synaptosomes and heart sarcoplasmic reticuli decreased total and calmodulin-stimulated calcium ATPase activity with greater inhibition in brain preparations (Mehorta et al. 1989). However, endrin showed no inhibitory effects on the calmodulin-sensitive calcium ATPase activity when incubated with human erythrocyte membranes (Janik and Wolf 1992). In vitro exposure of rat brain synaptosomes to endrin had no effect on the activities of adenylate cyclase or 3, 5 -cyclic phosphodiesterase, two enzymes associated with synaptic cyclic AMP metabolism (Kodavanti et al. 1988). 

At the cellular level, chlordecone causes spontaneous neurotransmitter release (End et al. 1981) and increases in free intracellular calcium in synaptosomes (Bondy and Halsall 1988 Bondy and McKee 1990 Bondy et al. 1989 Komulainen and Bondy 1987). This appears to be due at least in part to increased permeability of the plasma membrane (Bondy and Halsall 1988 Bondy and McKee 1990 Bondy et al. 1989 Komulainen and Bondy 1987), activation of voltage-dependent calcium channels (Komulainen and Bondy 1987), and inhibition of brain mitochondrial calcium uptake (End et al. 1979, 1981). 

Evans, D., Williams, R.S., Shone, C.C., Hambleton, P., Melling, J. and Dolly, J.O., Botulinum neurotoxin type B. Its purification, radioiodination and interaction with rat-brain synaptosomal membranes, Eur. I. Biochem., 154, 409-416, 1986. 

As the name implies, these drugs have a high affinity for the serotonin transporter both on neuronal and also platelet membranes. There is abundant evidence that the SSRIs inhibit the reuptake of 3H-5-HT into platelets, brain slices and synaptosomal fractions, as illustrated in Table 7.10, but it is clear that there is no direct relationship between the potency of the drug to inhibit 5-HT reuptake in vitro and the dose necessary to relieve depression in the clinic. In experimental studies, it is clear that the increased release of 5-HT from the frontal cortex only occurs following the chronic (2 weeks or longer) administration of any of the SSRIs. Thus the inhibition of 5-HT reuptake may be a necessary condition for the antidepressant activity, but it is not sufficient in itself. 

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