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1.
We have investigated the transport, biosynthesis and turnover of taurine in genetically seizure-susceptible (SS) and seizure-resistant (SR) rats. In SS rats, the rate of taurine uptake into the brain was half the rate in SR rats. As no difference was found in biosynthesis of taurine, these results imply a slower turnover of taurine in SS brain.The effect of taurine on the decarboxylation of glutamate in brain homogenates was determined. In homogenates of SR brains, taurine had no effect but in SS preparations taurine increased the rate of decarboxylation by 20%. Increased decarboxylation of glutamate may be one basis for the prolonged anticonvulsant action of taurine in the SS rat.  相似文献   

2.
Valinomycin is a potent inhibitor of taurine-stimulated ATP-dependent calcium ion uptake in rat retinal membrane preparations but had no effect on ATP-dependent calcium ion uptake in the absence of taurine and no effect on ATP-independent calcium ion uptake. The presence of potassium ions in the buffer systems were required for valinomycin to be inhibitory. On the contrary, monensin stimulated calcium ion uptake in the ATP-dependent system but had no effect on ATP-independent calcium ion uptake. The crude retinal homogenate was also fractionated into various subcellular components. The fraction which contained photoreceptor cell synaptosomes (P1) had a higher, specific activity for taurinestimulated ATP-dependent calcium ion uptake than the crude homogenate or either the fractions which contained synaptosomes derived from the plexiform layer (P2) or rod outer segments (ROS). No differences in calcium ion uptake were observed in the various subcellular fractions compared to the homogenate when assayed for ATP-dependent calcium ion uptake. Valinomucin inhibited both ATP-dependent and taurine-stimulated ATP-dependent calcium ion uptake in the P1, P2, and ROS fractions while monensin stimulated the ATP-dependent calcium ion uptake in the subcellular fractions.  相似文献   

3.
The concentration of taurine in the brain of the fetus in several species is higher than that found in the mature animal. In order to explore the functional significance of this, we have studied the subcellular distribution of taurine and [35S]taurine in the brain of the mother, the fetus and the neonate after [35S]taurine was administered to pregnant rats. In maternal brain, the distribution of taurine and of radioactivity (all of which was recovered from brain as taurine) in the subcellular fractions of maternal brain were essentially identical and were recovered primarily in two fractions (72% taurine, 71% [35S]taurine was soluble, S3; 16% and 17%, respectively, was in the crude mitochondrial and synaptosomal fraction, P2). After further fractionation of P2, most of the taurine and [35S]taurine were in the cytoplasmic, O, and the synaptosomal, B, fractions. In the neonatal brain, shortly after birth there was a decrease in taurine and [35S]taurine recovered in the supernatant fraction, S3, accompanied by an increase in the percentage of taurine and [35S]taurine recovered in the crude mitochondrial fraction. A small percentage of taurine and [35S]taurine was consistently recovered in the synaptic vesicle fraction. Fractionation of the synaptic vesicles on a gel column separated the vesicle bound taurine completely from the free taurine: approx 1% of the taurine in the synaptic vesicle fraction was eluted with vesicles and could not be released by hypo-osmotic shock. The pattern of development in subcellular fractions of neonatal rat brain labelled with [35S]taurine via intraperitoneal injections of the pregnant mother may be an indication of maturation or protection of putative taurinergic nerve endings.  相似文献   

4.
The ionophore X537A at concentrations of 5–20 M stimulated the release of [3H]GABA and [35S]taurine, from retinal subcellular crude nuclear (P1) and crude synaptosomal (P2) fractions. The release of [3H]GABA increased 114% and 136% over control values in P1 and P2 fractions, respectively. The efflux of [35S]taurine from P1 was increased by 45% and that from P2 by 21%. X537A increased45Ca2+ uptake in the P2 fraction but not in the P1 fraction. The effect of X537A on the amino acid release was not dependent on the presence of exogenous calcium. X537A did not affect [3H]GABA or [35S]taurine uptake by the retinal fractions. A23187 enhanced [3H]GABA release from P1 and P2 by 52% and 105%, respectively. The ionophore also increased [14C]glycine liberation in both P1 (35%) and P2 (50%) but failed to stimulate [35S]taurine release. A23187 produced a transient increase of45Ca2+ uptake of 38% in P1 and 30% in P2. The effects of A23187 on the release of amino acids were calcium dependent. The amino acid uptake was not affected by the ionophore. These results are consisent with the suggested neurotransmitter role for GABA at the outer synaptic layer and for GABA and glycine at the inner synaptic layer of the retina. A neurotransmitter role for taurine is not supported by the present results.  相似文献   

5.
P2-fractions were isolated from rat brain, and used to study net taurine transport. The fractions were incubated in increasing concentrations of [3H]taurine and the intraterminal concentration measured by liquid scintillation and amino acid analysis. The membrane potential of the isolated fractions was estimated using86Rb+ as a marker for intracellular K+. Taurine was synthesized in the P2-fraction when incubated in taurine free medium. At external taurine concentrations below 370 M a significant amount of the endogenous taurine was released to the incubation medium. Net taurine uptake into the P2-fraction was achieved at external taurine concentrations exceeding 370 M. The taurine antagonist 6-aminomethyl-3-methyl-4H, 1, 2, 4-benzothiadiazine-1, 1-dioxide (TAG) competitively inhibited taurine and [3H]taurine transport into the P2-fraction. As the external concentration of taurine was increased, the accumulation of86Rb+ into the P2-fraction was facilitated. This indicated an increasing hyperpolarization of the neuronal membrane as taurine transport shifted from release towards uptake. TAG reduced the hyperpolarization that paralleled taurine accumulation, in a dose dependent manner. Our results indicate that relatively low transmembranal gradients of taurine may be maintained by an electrogenic taurine transporter having a large transport capacity. Such a transporter may well serve the needs of osmotic regulation, i.e. to transport large amounts of taurine in any direction across the neuronal membrane.  相似文献   

6.
—The kinetics of the uptake of various compounds into the crude mitochondrial fraction (P2-fraction) of the pigeon optic tectum were studied. Aspartate, GABA, glutamate, glycine, proline and choline were taken up by high and low affinity systems. Only low affinity uptake was found for leucine and dopamine. The uptake for taurine was not saturable. The uptakes for all of the above compounds were temperature and sodium dependent. The high affinity system was more effected by sodium withdrawal than the low affinity system. Continuous sucrose gradients from 0.4 to 1.5 m were run with incubated P2 fractions. Particle-bound radioactivity sedimented in a density range of 1.0 to 1.2 m -sucrose. Additional experiments with glutamate showed that its uptake is competitively inhibited by aspartate. The addition of a 1000-fold excess of glutamate to a P2 fraction incubated at a concentration of 10–6m -glutamate led to a massive decrease of particle-bound radioactivity, suggesting a coupled action of uptake and efflux.  相似文献   

7.
We have investigated the catabolism of [3H] histamine (HA), after intraventricular (i.vt.) administration, in brains of the audiogenic seizure susceptible (SS) and resistant (SR) deermouse Peromyscus. Brains of SS mice had lower endogenous HA levels and contained less [3H]-HA 20, 60 and 300 sec after i.vt. [3H]-HA than did brains of SR deermice. Twenty sec after [3H]-HA, brain [3H] methylhistamine (MeHA) levels and the resulting MeHA conversion index were found to be increased in the SS animals while later, at 60 and 300 sec, these parameters were found to be decreased. There were no SS-SR differences in the levels of brain [3H] methylimidazoleacetic acid. The data indicate that SS deermice catabolize exogenous HA, at least initially, more rapidly than their SR counterparts, confirming a like result noted immediately prior to seizure activity elicited by the administration of L-methionine-dl-sulfoximine in Mus.  相似文献   

8.
Abstract— Ethanol administered in vivo or in vitro during incubation of brain slices was studied with respect to its effect on brain protein synthesis. In the in vivo series the rats were given a single intraperitoneal injection of ethanol 3 h before death. Slices of cerebral cortex and liver were incubated in isotonic saline media containing [3H]leucine. Amounts of free and protein-bound radioactivity were determined. Subcellular fractions and fractions enriched in neuronal perikarya and in glial cells were prepared from cortical slices subsequent to incubation, and the specific radioactivity determined for each cell type. The incorporation of [3H]leucine into brain proteins was inhibited while incorporation into liver proteins was stimulated in ethanol-treated rats. The levels of TCA-soluble radio-activity, however, did not differ between the ethanol group and the controls. In the fractionated material from cerebral cortex, the specific radioactivity in the neuronal fraction was unaffected by ethanol, while the radioactivity in the glial fraction was significantly depressed. In vitro administration of ethanol induced a non-linear response in both brain and liver, with depression of leucine incorporation into proteins of cerebral cortex at all concentrations used. When brain slices were exposed to ethanol in vitro, in concentrations corresponding to the in vivo experiments, a similar reduction of the leucine incorporation into the glial fraction was obtained. Incorporation of leucine into subcellular fractions from whole brain cortex was also investigated. The specific sensitivity of the glial fraction to ethanol is discussed in relation to the involvement of the different cell types with transport processes in the brain.  相似文献   

9.
Abstract— Crude synaptosomal (P2) preparations were obtained from the cerebella of rats in which the granule cell population had been selectively reduced by X-irradiation treatment and from the cerebella of control animals. In the P2 fraction from control cerebella, the level of glutamate was greater than any other of the 5 amino acids measured and was 2-fold higher than taurine, which was present at the next highest level. The content of taurine was slightly higher than that found for aspartate and was 3-fold greater than that observed for GABA. Alanine and glycine were present in the lowest amounts. The levels of glutamate and aspartate were significantly (P < 0.05) lower by 25 and 15%, respectively, in the P2 fraction isolated from the X-irradiated cerebella in comparison to control values. The content of taurine, GABA, glycine, and alanine were not changed by the X-irradiation treatment. The uptake of 1.0 μm -l -[3H]glutamate and l -[3H]aspartate was reduced approx 20% by X-irradiation treatment, whereas the uptake of 1.0 μm -[3H]GABA and [3H]taurine was unchanged. A more detailed kinetic analysis of l -[3H]glutamate uptake revealed there was a 20% decrease in the Vmax value with X-irradiation treatment and no change in the apparent Km value. In a second study, the uptake of l -[3H]glutamate, l -[3H]aspartate and [3H]GABA was measured using P2 fractions obtained from the cerebella of rats in which the population of granule, stellate and basket cells had been reduced by X-irradiation treatment. The uptake of 1.0μm -l -[3H]glutamate, l -[3H]aspartate and [3H]GABA was significantly (P < 0.05) reduced to 57, 68, and 59%, respectively, of control values. A more detailed kinetic analysis of [3H]GABA uptake revealed no significant change in the apparent Km and a 35% decrease in the Vmax value. The data are discussed in terms of glutamate being the excitatory neurotransmitter released from granule cells and GABA being the inhibitory neurotransmitter released from basket cells.  相似文献   

10.
Abstract– (1) The uptake and release of glutamic acid by guinea-pig cerebral cortex slices and rat synaptosomal fractions were studied, comparing the naturally occurring l - and non-natural d -isomers. Negligible metabolism of d -glutamic acid was observed in the slices. (2) Whereas in the cerebral slices the accumulation of glutamic acid was almost the same for the two isomers, d -glutamic acid was accumulated into the synaptosomal fraction at a markedly lower rate than was the L-isomer. (3) The uptake systems for d -isomer into the slices and synaptosomal fraction were found to be of single component, in contrast with the two component systems, high and low affinity components, for the uptake of l -glutamic acid. The apparent Km values for the uptake of d -glutamic acid into the slices and synaptosomal fraction were comparable with those reported for the low affinity components for l -isomer. The uptake systems for d -glutamic acid were dependent on the presence of Na+ ions in the medium, like those for l -glutamic acid and GABA. (4) The evoked release of radioactive preloaded d -glutamic acid was observed both from the slices and synaptosomal fraction following stimulation by high K+ ions in the medium. From these observations, it is evident that the evoked release of an amino acid by depolarization in vitro is not necessarily accompanied by a high affinity uptake process. (5) The uptake of l -glutamic acid, expecially into the synaptosomal fraction, was highly resistant to ouabain. On the other hand, the uptake rate of d -glutamic acid and GABA into the synaptosomal fraction was inhibited by varying concentrations of ouabain in accordance with the inhibition for brain Na-K ATPase. (6) The uptake of l -glutamic acid into subfractions of the P2 fraction was studied in relation to the distribution of the ‘synaptosomal marker enzymes’. An attempt to correlate the activities of enzymes of glutamic acid metabolism with the uptake of l -glutamic acid into the synaptosomal fraction from various parts of brain was unsuccessful. The high affinity uptake of l -glutamic acid was found to be very active in the synaptosomal fraction from any part of brain examined.  相似文献   

11.
In a study of the role of taurine in the genesis of epilepsy the effects of metrazol-induced convulsions on the uptake and distribution of taurine in the brain were measured.In vivo we found no significant uptake of taurine in the mouse brain; in rabbit brain in most areas significant taurine uptake was found. The physiological levels of taurine were much higher in mouse brain than in rabbit brain.In vivo the regional levels and the uptake of taurine were not significantly changed after generalized convulsions. Uptakein vivo was lowered in slices obtained from mice treated with metrazol. The lack of effect of metrazol convulsions on cerebral taurinein vivo indicates that further studies are needed to clarify the relationship between taurine, a putative inhibitory transmitter, and epilepsy.Supported in part by a grant from the C.N.R., Rome, Italy  相似文献   

12.
1. By digitonin lysis of penicillin spheroplasts of Escherichia coli a particulate fraction P1 was previously obtained that supported the sustained synthesis of alkaline phosphatase when supplied with amino acids, nucleotide triphosphates and other cofactors. This P1 fraction, when subjected to mild ultrasonic treatment in the presence of sucrose and Mg2+, yielded the P1(S) fraction, consisting of integrated particulate subcellular particles containing DNA and RNA. 2. The P1(S) fraction from E. coli K10 wild type (R+1R+2P+) grown under repressed conditions supported the immediate synthesis of alkaline phosphatase in vitro. The synthesis occurred in phases. The first was followed by a lag, and then there was a linear rapid phase that continued for at least 3hr. Actinomycin D inhibited the appearance of the second phase. It was concluded that the particles are programmed to synthesize enzyme even when prepared from repressed cells, and therefore that synthesis of the specific messenger RNA for alkaline phosphatase in vivo was not inhibited when the bacteria were grown in an excess of inorganic phosphate. 3. Phosphate inhibited synthesis of enzyme to the same extent with the P1(S) fractions of two constitutive strains as with the P1(S) fraction of the wild-type strain. 4. Inorganic phosphate inhibited amino acid incorporation with the P1(S) fraction and also inhibited enzyme synthesis in vitro. The effect on amino acid incorporation could be partially overcome by adding Mn2+ to the incubation mixtures. However, Mn2+ inhibited the synthesis of alkaline phosphatase. Also, inhibition of the incorporation of [32P]CTP into RNA was overcome by Mn2+. The effect of phosphate on amino acid uptake was most probably due to a phosphorolysis of RNA by polynucleotide phosphorylase, also present in the P1(S) fraction. This phosphorolysis may be responsible for the instability of messenger RNA in vitro and in vivo. 5. Phosphate also specifically inhibited the formation of alkaline phosphatase, since it did not affect markedly the induced formation of β-galactosidase by the same P1(S) fraction. The specific effect is attributed to the prevention of formation of the enzymically active dimer from precursors, a Zn2+-dependent reaction. It is suggested that the repression of the synthesis of alkaline phosphatase in vivo in the wild-type strain was the sum of these two effects.  相似文献   

13.
Cysteine sulfinic acid decarboxylase activity is not affected when measured in vitro in the presence of pyridoxal phosphate in the brains of vitamin B6-deficient rats. Activity of this enzyme was not detectable in the brains of vitamin B6-deficient animals when assayed in the absence of pyridoxal phosphate. The activity of cysteine sulfinic acid decarboxylase in crude particulate and soluble fractions of rat brain reflects the distribution of the enzyme in vivo and the distribution of endogenous B6 vitamers when assayed in the presence and absence of vitamin B6. This study indicates that virtually no taurine is synthesized by any component of brain when the animal is subjected to a deficiency of vitamin B6.  相似文献   

14.
Sites of synthesis of plasma proteins in the foetal rat   总被引:4,自引:4,他引:0       下载免费PDF全文
1. The foetal rat of 16 or more days incorporates 14C-labelled amino acids into all the demonstrable plasma protein fractions in vivo. 2. Slices of foetal rat liver incubated in vitro incorporate 14C-labelled amino acids into the main plasma protein fractions, including the foetal-specific `post-albumin'. 3. Slices of placenta are unable to incorporate 14C-labelled amino acids into plasma proteins in vitro. 4. Liver slices from maternal rats incubated in vitro incorporate 14C-labelled amino acids into plasma proteins. The presence of post-albumin cannot be demonstrated after incubation. 5. Liver slices from foetal rats, but not from adult rats, contain demonstrable amounts of haemoglobin into which 14C-labelled amino acids are incorporated.  相似文献   

15.
Liver microsomes, isolated from rats which had been treated with phenobarbital in vivo, were found to exhibit increased activities of oxidative demethylation and TPNH-cytochrome c reductase and an increased amount of CO-binding pigment. Simultaneous administration of actinomycin D or puromycin abolished the phenobarbital-induced enzyme synthesis. Increased rate of Pi32 incorporation into microsomal phospholipid was the first sign of phenobarbital stimulation and appeared 3 hours after a single injection of this drug. Microsomes were divided into smooth-surfaced and rough-surfaced vesicle fractions. The fraction consisting of smooth-surfaced vesicles exhibited the greatest increase in protein content and oxidative demethylation activity after phenobarbital administration in vivo. Ultrastructural studies revealed that drug treatment also gave rise to proliferation of the endoplasmic reticulum in the hepatic parenchymal cells, first noticed after two phenobarbital injections. The phenobarbital-induced synthesis of the metabolizing enzymes is discussed with special reference to the relationship to the stimulated synthesis of the endoplasmic membranes.  相似文献   

16.
l-Glutamate has an excitatory and cytotoxic effect on the central nervous system. It was shown previously that norepinephrine and dopamine uptake and release were affected by in vivo administration of glutamate to adult rats. The kinetic parameters, Km and Vmax of [14C]DA uptake and release were measured on synaptosomal and slices from caudate nucleus under in vitro conditions at different glutamate concentrations. Results showed an important increase in [14C]DA uptake on synaptosomal (> 100%) and slices by lower glutamate concentrations, the affinity for transport system was increased (100%) and its release of high potassium evoked was also increased at 0.5 μM of glutamate. The results suggest the possibility that glutamate may modify DA uptake and release interacting with the DA transporter complex at the synaptic level.  相似文献   

17.
—The distribution of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (EC 1.1.1.34) relative to that of several biochemical markers has been studied in subcellular fractions prepared from the brains of rats, aged 4 days to adult, by differential centrifugation. In the brains of 10-day-old animals fractions which sedimented at 800 g (P1 and 9000 g (P2) contained 28% and 65% respectively of the total reductase activity. A similar distribulion of the microsomal marker, NADPH-cytochrome c reductase, suggested that the HMG-CoA reductase activity in the low-speed pellets was due to substantial contamination of these fractions with endoplasmic reticulum. When P2 was fractionated on a discontinuous sucrose gradient, the distributions of protein, RNA and NADPH-cytochrome c reductase paralleled that of HMG-CoA reductase, indicaling a non-specific association of endoplasmic reliculum and HMG-CoA reductase with all of the structures sedimenting in P2. As brain maturation proceeded and a greater percentage of total brain protein (primarily associated with myelin) sedimenled in P1, the subcellular distributions of HMG-CoA reductase and the microsomal marker changed in a parallel way. By 21 days P1 contained nearly all of the reductase activity. Because the specific activity of HMG-CoA reductase in P1 decreased steadily between 4 and 21 days, while the specific activity of 2′:3′-cyclic nucleotide 3′-phosphohydrolase in this fraction increased in a coordinate fashion, we conclude that the reductase is not an integral component of myelin, and probably is associated exclusively with the endoplasmic reticulum included in P1. In view of the developmental changes in the distribution of HMG-CoA reductase among subcellular fraclions, we suggest that whole homogenates (or comparable tissue extracts) should be utilized to evaluate reductase activity in the developing brain.  相似文献   

18.
Water-soluble sulfated polysaccharides extracted from Enteromorpha prolifera and fractionated using ion-exchange chromatography (crude, F1, F2 and F3 fractions) were investigated to determine their in vitro and in vivo immunomodulatory activities. The sulfated polysaccharides, especially the F1 and F2 fractions, stimulated a macrophage cell line, Raw 264.7, inducing considerable nitric oxide (NO) and various cytokine production via up-regulated mRNA expression. The in vivo experiment results show that the sulfated polysaccharides (the crude and F2 fractions) significantly increased Con A-induced splenocyte proliferation, revealing their potential comitogenic activity. In addition, IFN-γ and IL-2 secretions were considerably increased by the F2 fraction without altering the release of IL-4 and IL-5. This implies that the F2 fraction can activate T cells by up-regulating Th-1 response and that Th-1 cells might be the main target cells of the F2 fraction. These in vitro and in vivo results suggest that the sulfated polysaccharides are strong immunostimulators.  相似文献   

19.
  • 1.1. The objective of the present study was to determine the effect of age and taurine on chick B cell calcium uptake and membrane (Ca2+ + Mg2+)-ATPase activity in 1–4-week-old chicks.
  • 2.2. The calcium uptake rate decreased with age (P < 0.05) and was further decreased by taurine (P < 0.05).
  • 3.3. (Ca2+ + Mg2+)-ATPase activity increased with age (P < 0.05) and was stimulated by taurine (P < 0.05).
  • 4.4. The data demonstrate that the flux of calcium across the B-cell membrane changes during early post-hatch development, and that taurine regulates both the influx and efflux of calcium in chick B-cells.
  相似文献   

20.
The glutamate metabolism in cerebral cortical slices from young (12 weeks) and aged (100 weeks) rats was studied. A highly significant reduction of low affinity glutamate uptake and its metabolism in the aged rats by 14.5% of the amount of the young rats was observed (Pº0.001). When the ratio of the radioactivity of respective metabolite divided by the sum total radioactivity of overall glutamate metabolites was compared, the incorporation to aspartate was significantly small (P<0.01), while that of the CO2 liberated and the GABA synthesized were increased (P<0.05). These results support the hypothesis that in cerebral cortical slices from aged rats the transamination of glutamate is suppressed and its decarboxylation is enhanced despite markedly reduced low affinity glutamate uptake into the cerebral cortex. The difference could be explained by the fact that cerebral cortical slices from aged rats are more vulnerable to anoxia than those from young rats when exposed during slice preparation.  相似文献   

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