摘要:

Abstract:UDP‐galactose:ceramide galactosyltransferase (CGalT, EC 2.4.1.45) and UDP‐glucose:ceramide glucosyltransferase (CGlcT, EC 2.4.1.80) were determined in the glial cell lines G26‐20, G26‐24, C6, and C6TK−. The enzymatic assay for CGalT in cultured glial cells was complicated by a rapid conversion of UDP‐galactose to UDP‐glucose, due to the elevated UDP‐galactose‐4′‐epi‐merase activity in certain glial cell clones. It seems that mechanisms regulating UDP‐galactose‐4′‐epimerase activity and levels of UDP sugars in the glial cell lines differ from those in brain tissue. Compared with the maximum activity of CGalT in the myelinating rat brain, the enzyme activities in the oligodendroglioma clonal cell lines G26–20 and G26–24 were 16–30 times lower. On the other hand, CGalT levels in G26‐20 and G26‐24 cells were comparable to the values found in young rat brain before myelination starts. No CGalT activity could be detected in C6 or C6TK−cells by the method used in this study, whereas CGlcT activity was found in all glial cell lines tested and its levels were close to

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1981.tb06303.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract:The incorporation of [U‐14C] protein hydrolysate and [U‐14C]leucine into the trichloroacetic acid (TCA)‐insoluble membrane and the soluble synaptoplasm proteins of synaptosomes was studied. Following treatment with the depolarizing agents veratrine,Tityustoxin, or potassium, the specific radioactivity of both precursor pool and proteins was measured to examine the link between protein labeling and the fall in the free amino acid pool due to depolarization‐induced release of glutamate and aspartate. By reducing the size of the fall in precursor pool due to depolarization by using a nontransmitter amino acid such as leucine (as compared with the usual use of protein hydrolysate), it was shown that the amount by which the pool is reduced is proportional to the change in the protein labeling observed. These results confirm that membrane depolarization causes a large increase in the labeling of membrane‐bound proteins as compared with the soluble synaptosomal

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1981.tb06304.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract:The distribution of pyruvate kinase (ATP pyruvate phosphotransferase, EC 2.7.1.40) in the nervous system has been studied by both immunofluorescence and a histochemical procedure using nitro blue tetrazolium. The localization in various parts of rat central nervous systemin situ, cerebellar and cerebral cortex, was compared to that foundin vitroin cultures of cerebellum, spinal ganglia, cerebral astrocytes, and skin fibroblasts. (1) Pyruvate kinase was found predominantly in the cytoplasm of neuronal cell bodies. (2) Large neurons were better visualized than small ones. (3) No glial localization was clearly demonstratedin situ, although this does not rule out the presence of some M1pyruvate kinase. (4) Regions expected to be rich in nerve terminals, such as the cerebellar glomeruli or the cerebellar molecular layer, showed intense staining even when the cell bodies themselves were negative. This was expected, owing to the previous demonstration of the presence of M1pyruvate kinase in nerve ending by subcellular fractionation methods. (5) The localization was similarin situand in tissue culture, except that nerve processes were better seen in the latter and astrocytes were sometimes stainedin vitro.(6) Variation in intensity of staining was observed in similar cell types in the same section or in the same culture. This could represent different metabolic or functional or maturational states.

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1981.tb06305.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract:The relationship between plasma and brain tryptophan (TRP) concentrations and brain 5‐hydroxytryptamine (5‐HT) metabolism was studied in weanling rats fed diets containing either 0.4 g or 1.45 g TRP/ 100 g casein hydrolysate. Both groups gained weight comparably though food intakes were generally higher in the low‐TRP group. Severe depletion of plasma total and free TRP and of brain TRP, 5‐HT, and 5‐hydrox‐yindoleacetic acid (5‐HIAA) occurred within 1 day of feeding the 0.4% TRP diet. Levels became stable after 7 days. The decreased brain TRP concentration of the rats on the 0.4% TRP diet did not cause a compensatory rise of the tryptophan hydroxylase (TRP OHase) activityin vitro.In the low‐TRP group, neither plasma free TRP nor total TRP correlated significantly with brain TRP and although plasma TRP/large neutral amino acid (NAA) ratios (TRP/NAA) correlated significantly (P<0.05) with the time course of brain TRP, this statistical relationship depended almost completely on the variation of the TRP values alone. In the higher TRP group none of these correlations were significant. A plot of mean plasma free TRP versus brain TRP gave two distinct regression lines with similar slopes and corresponding to values before and after 7 days on the diet. The time course of brain 5‐hydroxyindole concentrations did not parallel those of brain TRP and suggested that changes of TRP OHase activity also had an influence

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1981.tb06306.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract:Mild detergent extraction of chick brain synaptic plasma membranes followed by gel electrophoresis suggests that synaptic plasma membrane tubulin is an integral component. Although some of the synaptic plasma membrane tubulin might be aggregates, that possibility is not supported by the observation that tubulin aggregates that are added to synaptosomes before synaptic subfractionation do not partition with synaptic plasma membranes during membrane isolation.

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1981.tb06307.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract:Aspartate uptake by membrane vesicles derived from rat brain was investigated. The uptake is dependent on a Na+gradient ([Na+] outside>[Na+] inside). Active transport of aspartate is strictly dependent upon the presence of sodium and maximal extent of transport is reached when both Na+and Cl−ions are present. The uptake is transport into an osmotically active space and not a binding artifact as indicated by the effect of increasing the medium osmolarity. The uptake of aspartate is stimulated by a membrane potential (negative inside), as demonstrated by the effect of the ionophore carbonyl cyanidem‐chlorophenylhydrazone and anions with different permeabilities. The presence of ouabain, an inhibitor of (Na++ K+)‐ATPase, does not affect aspartate transport. The kinetic analysis shows that aspartate is accumulated by two systems with different affinities, showingKmandVmaxvalues of similar order to those found in slightly “cruder“ preparations. Inhibition of thel‐aspartate uptake byd‐aspartate andd‐ andl‐glutamate indicates that a common carrier is involved in the process, this being stereospecific for thed‐ andl‐gl

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1981.tb06308.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract:We have investigated the properties of several ATPases present in synaptic membrane preparations from the cerebral cortex of rat. In addition to the intrinsic (Na++ K+)–ATPase and a low level of contaminating Mg2+–ATPase of mitochondrial origin, both of which could be controlled by the addition of ouabain and azide, respectively, four activities were studied: (1) a Mg2+–ATPase; (2) a Mg2+–independent activity requiring Ca2+ions at high concentrations; (3) a (Ca2++ Mg2+)–ATPase with a high affinity for Ca2+, which was enhanced further (4) by the inclusion of calmodulin (33 DM for half–maximal activity). In the presence of 0.5 mM–EGTA in the buffer used, half saturation for these respective metal ions was observed at 0.9 mM for (1), 1.0 DIM for (2), and –0.3 mM for (3) and (4); the latter values correspond to concentrations of free Ca2+of 0.38 and 0.18 /XM for (3) and (4), respectively. The level of activities observed, all in nmol × min−1× mg−′, under optimal conditions at 37°C, was in a number of preparations(nin parenthesis): for (1) 446 ± 19 (19); for (2) 362 ± 18 (3); for (3) 87 ± 13 (12); and for (4) 161 ± 29 (12). The (Ca2++ Mg2+)‐ATPase, both in the presence and absence of calmodulin, could be inhibited specifically by a number of agents (approximate I0.5in parentheses) which, at these concentrations, showed little or no potency against the other activities; among them were vanadate (≥10 μm), La3+(75 μm), trifluoperazine, and other phenothiazines (50μm). These properties suggest that the (Ca2++ Mg2+)‐ATPase described may be responsible for calcium transport across one (or more) of the several membranes present in nerve endings

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1981.tb06309.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract:Synaptosomes (vesicles of nerve endings) isolated from rabbit brain were studied as a model system for the uptake of inorganic phosphate. The phosphate uptake showed a sodium‐dependent, saturable component with aKtof 0.29 mm, The sodium‐dependent component was larger at pH 6 than at pH 7.4 or 8. Application of potassium salts, ouabain, monensin, nigericin or FCCP decreased the uptake. The results indicate that the sodium‐sensitive phosphate influx is dependent on the Na+gradient and on the membrane potential, which might act, preferentially, on the transport of the monovalent phosphat

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1981.tb06310.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract:The K+‐stimulated, Ca2+‐dependent release of glutamate, aspartate, ‐γ‐aminobutyric acid (GABA), alanine, taurine, and glycine was measured in slices of cerebella obtained from control, and granule cell‐, granule cell plus stellate cell‐, or climbing fiber‐deficient cerebella of the rat. The 55 mm‐K+‐stimulated release of glutamate and GABA was 10‐fold greater in the presence of Ca2+than in its absence. The stimulated release of aspartate was 4‐fold higher when Ca2+was present in the bathing media, while the value for alanine was twice as high as the amount obtained in the absence of Ca2+. There was no stimulated release of either taurine or glycine from the cerebellar slices. Increasing the Mg2+concentration to 16 HIM inhibited the K+‐stimulated, Ca2+‐dependent release of glutamate, GABA, aspartate, and alanine 85% or more. The K+‐stimulated, Ca2+dependent release of glutamate, aspartate, and alanine from x‐irradiated cerebella deficient in granule cells was reduced to 50–57% of control value. Additional x‐irradiation treatment, which further reduced the cerebellar granule cell population and also prevented the acquisition of stellate cells, decreased the release of glutamate by 77%, aspartate by 66%, alanine by 91%, and, in addition, decreased the release of GABA by 55%. The K+‐stimulated, Ca2+‐dependent release of glutamate, aspartate, GABA, and alanine was not changed in climbing fiber‐deficient cerebella obtained from 3‐acetylpyridine‐treated rats. The data support a transmitter role for GABA and glutamate in the cerebellum, but do not support a similar function for either taurine or glycine. The data also suggest that alanine and aspartate may be co‐re

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1981.tb06311.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract:PC12 cells, a nerve growth factor–responsive clone of rat pheochromocytoma, contain a membrane–bound adenylate cyclase, which can be activated by adenosine analogs. The characteristics of the cyclase response indicate the presence of stimulatory adenosine receptors. Adenosine analogs also produce a marked increase in the ornithine decarboxylase levels of the cells, and the characteristics of this response suggest that it is linked to the adenylate cyclase–stimulatory adenosine receptors. The ornithine decarboxylase response elicited by 5′‐N‐ethyIcarboxamideadenosine (NECA), a potent stimulatory adenosine analog, is synergistic with that produced by nerve growth factor. Differentiation of the cells with nerve growth factor, however, does not substantially alter either the response of cyclase to the adenosine analog or the magnitude of the adenosine–evoked ornithine decarboxylase response. Treatment of the cells with NECA produces an increase in the phosphorylation of a specific non–histone nuclear protein. While causing little or no morphological alteration by itself, NECA is synergistic with nerve growth factor in producing neurite outgrowth in PC12 cells. NECA does not cause an induction of acetylcholinesterase in the cells, nor does it appear to affect the induction of this enzyme by nerv

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1981.tb06312.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY