Synaptosomal membrane examination

Figure 5. Electron microscopic examination of the "nerve ending fraction (X13,000) and of the synaptosomal membrane fraction (X.7150)...

Avermectin Bia has been shown to stimulate chloride ion uptake into cockroach muscle ( 140 and block transmission at the arthropod neuromuscular junction by increasing GABA-mediated chloride ion permeability (15), (16). To extend our understanding of ion channel types present in the surface membrane of the synaptosome we examined the effects of ivermectin (22,23-dihydroavermectin B.) and some closely related milbemycins. Both ivermectin and the milbemycins examined, with the exception of milbemycin a9, were... 

A continuous sucrose gradient of the total homogenate from young rat brain and electron microscopic examination of these fractions found most of the sialyltransferase activities to be localized in smooth microsomal membrane and Golgi complex derivatives and not associated with synaptosomes. 

The —50 kDa band (48-53 kDa) is identified as dysbindin-1 A in our WESTERNS, because it runs close to the molecular mass of our histidine-tagged recombinant mouse dysbindin-1 A. Its identity is confirmed by the fact that it is recognized by antibodies we have recently generated to amino acid sequences in the CTR of human dysbindin-lA, but not found in dysbindin-lB, -2, or -3. The —50 kDa band is the most consistently observed dysbindin-1 band across tissues. We find it in all tissues examined to date the adrenal gland, heart, kidney, liver, lung, spleen, skeletal muscle, testes, spinal cord, cerebellum, striatum, hippocampus, and cerebral cortex (e.g., Figure 2.2-12a and c). In mouse and human synaptosomes, the —50 kDa isoform is heavily concentrated in the PSD fraction with a much lesser amount in the presynaptic membrane and no detectable amount in the synaptic vesicle fraction (Talbot et al., in preparation). 

The phosphorescence of trivalent cations (as analogues of Ca ) is also widely used in binding studies. The photobinding of phenothiazine derivatives has been studied for different types of biological membranes. The specificity of binding is low, although general, and can be used to identify and localize membrane proteins. The influence of Ca " and phase behaviour in synaptosomal lipids have been examined by the steady-state fluorescence polarization of A fluorescent probe of the tumour promoter phorbol... 

Certain neurotoxicants act by directly influencing the electrical activity of the insect nerve membrane through a specific action at ion-selective channels. These phenomena can be studied using many of the neurobiochemical techniques that have successfully been applied to vertebrate nervous systems. In this study we use the technique of insect synaptosomes in superfusion to examine the interaction of a range of insecticidal agents with ion channels in the nerve terminal by monitoring effects on transmitter release. 

There were two clearly separated peaks, C and D, sedimenting at 1.2 M and 1.3 M-sucrose (Fig. 2). Examination by the electron microscope showed them both to have the morphological characteristics of synaptosomes. It is well established that a good enzyme marker for intact synaptosomes is occluded lactic dehydrogenase (L-lactate NAD oxidoreductase, EC 1.1.1.27) (Marchbanks, 1967), a component of the cell sap. As can be seen in Table I, 83 % of the occluded form of the enzyme of the original P2 fraction is shared between peaks C and D. Both also contained succinic dehydrogenase activity owing to the presence of intraterminal mitochondria. The membrane marker acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) was also present in these peaks and was notably absent from the mitochondrial and lysosomal fractions (Table I). 

In view of the recent results of Gullis Rowe (1975), who reported that the turnover of the hydrophobic chains of synaptosomal phospholipids was stimulated AJl )XJl/L0 by cyclic-AMP and putative neurotransmitters, the exchange of the hydrophylic heads (nitrogenous bases) of membrane phospholipids with externally added L-serine was examined in rat brain synaptosomes and synaptic membranes in the presence of cyclic-AMP or noradrenaline. This work was also prompted by some recent results of Lo Levey (1976), who showed that the rate of Ptd-Ser synthesis in heart slices, which certainly takes place by base-exchange (Kiss, 1976), is very efficiently stimulated by glucagon. 

Recently, a specific antibody against the purified cytosolic sialidase from rat skeletal muscle was prepared and its immunoreactivity with other sialidases examined (Miyagi et al., 1990b). The antibody completely immunoprecipitates the cytosolic enzyme in rat liver and skeletal muscle, but not the synaptosomal and lysosomal enzymes in rat brain and liver. These results suggest that a single cytosolic sialidase species may exist in rat tissues which is immunologically distinct from the lysosomal and plasma membrane enzymes. 

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