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1.
IN VITRO EXPERIMENTS ON THE METABOLISM, ACCUMULATION AND RELEASE OF 5-HT IN THE NERVOUS SYSTEM OF THE SNAIL HELIX POMATIA 总被引:1,自引:0,他引:1
Abstract— The accumulation, metabolism and stimulated-induced release of 5-HT in the nervous system of the snail was studied. When nervous tissue was incubated at 24°C in a medium containing [14C]5-HT or [3H]tryptophan, tissue: medium ratios of about 25:1 and 4:1 respectively were obtained after 45 min incubation. The process responsible for [14C]5-HT accumulation showed properties of an active transport system: it was temperature sensitive and was greatly inhibited by dinitrophenol and ouabain. Furthermore, the accumulation process was inhibited by imipramine and desipramine. Of a number of analogues of indole, N-acetyl-5-HT and 5-hydroxytryptophan were the most potent in the inhibition of the accumulation of [14C]5-HT. The presence of a large molar excess of amino acids had little effect. A small amount (less than 14 per cent) of the accumulated [14C]5-HT was metabolized to form 5-hydroxyindole acetic acid, even after long periods (2 h) of incubation. The accumulated [3H]tryptophan was metabolized to form 5-hydroxytryptophan and 5-HT; the content of formed [3H]5-HT increased with incubation time whilst the [3H]5-hydroxytryptophan remained more or less constant. The presence of p-chlorophenylalanine in the incubation medium did not interfere with the accumulation of [3H]tryptophan, though it inhibited the formation of [3H]5-hydroxytryptophan and to a greater extent [3H]5-HT. A rapid efflux of the accumulated [14C]5-HT from snail nervous tissue was observed on electrical stimulation. Slower release resulted when the Ca2+ ion content of the incubation medium was replaced by Mg2+ ions. There is also a slight efflux of radioactive substances following electrical stimulation in tissues previously incubated in [3H]tryptophan. Most of this radioactivity was attributed to the formed [3H]5-HT. The data support the idea that 5-HT is a transmitter-substance in the snail Helix pomatia, and that re-uptake of the substance is a method of inactivating the released amine. 相似文献
2.
Maria Elena Sandoval 《Journal of neurochemistry》1980,35(4):915-921
It has been suggested that mitochondria might modify transmitter release through the control of intracellular Ca2+levels. Treatments known to inhibit Ca2+retention by mitochondria lead to an increased transmitter liberation in the absence of external Ca2+, both at the frog neuromuscular junction and from isolated nerve endings. Sodium ions stimulate Ca2+efflux from mitochondria isolated from excitable tissues. In the present study, the effect of increasing internal Na+ levels on [3H]γ-aminobutyric acid ([3H]GABa) release from isolated nerve endings is reported. Results show that the efflux of [3H]GABA from prelabeled synaptosomes is stimulated by ouabain, veratrine, gramicidin D, and K+-free medium, which increase the internal sodium concentration. This effect was not observed when Na+ was omitted from the incubation medium and it was independent of external Ca2+, the experiments having been performed in a Ca2+-free, EGTA-containing medium. Since preincubation of synaptosomes with 2,4-diaminobutyric acid did not prevent the stimulatory effect of increased internal Na+ levels on [3H]GABA efflux, it appears to be unrelated to an enhanced activity of the outward carrier-mediated GABA transport. These results suggest that the augmented release of [3H]GABA may be due to an increased Ca2+efflux from mitochondria eiicited by the accumulation of Na+ at the nerve endings. Sandoval M. E. Sodium-dependent efflux of [3H]GABA from synaptosomes probably related to mitochondrial calcium mobilization. J. Neurochem. 35 , 915–921 (1980). 相似文献
3.
《Insect Biochemistry》1987,17(6):911-918
High yields of relatively pure, morphologically well-preserved, functionally competent synaptosomes were prepared from brains of moths of Mamestra configurata using a modified microscale Ficoll flotation technique. Typical preparations yielded 10 mg of synaptosomal protein per gram of moth brains. The moth brain synaptosomes were virtually free of endoplasmic reticulum and mitochondrial contaminants as judged from marker enzyme studies and electron microscopy.Voltage-dependent Ca2+ ion transport was studied using the moth brain synaptosome preparations. Synaptosomes took up radioactive 45Ca2+ from the incubation medium. The rate of uptake was increased up to three-fold when the synaptosomes were incubated in a depolarizing, high [K+] medium. Time course studies indicated that voltage-dependent Ca2+ uptake was composed of an early (<2 sec) fast phase and a late (>10 sec) slow phase.ATP-dependent Ca2+ ion transport was studied in moth brain synaptosome membrane vesicles prepared from synaptosomes by osmotic shock and purified on a second Ficoll gradient. The inside-out synaptosome membrane vesicles contained an ATP-dependent calcium ion pump which transported 45Ca2+ from the incuation medium into the interior of the vesicle in the presence of ATP. The calcium ionophore A23187 rapidly released accumulated 45Ca2+ from the vesicles. The maximal rate of ATP-dependent Ca2+ transport occurred at a [Ca2+ free] of 0.1 to 0.2 nM, indicating that the transport process has a very high affinity for Ca2+ ions. 相似文献
4.
The effects of omission of Ca2+ and Mg2+ from the incubation medium on three aspects of insulin action in isolated fat cells have been investigated. In the (Ca2+ + Mg2+)-free incubation medium incorporation of L-[14C]leucine into fat cell protein was reduced in the absence of insulin. Insulin stimulated L-[14C]-leucine incorporation only in the presence of added CaCl2 or MgCl2. Incubation of the cells in the (Ca2+ + Mg2+)-free medium reduced but did not abolish the ability of adrenaline to stimulate lipolysis or the ability of insulin to inhibit the adrenaline-stimulated lipolysis. Specific binding of 125I-labelled insulin to the fat cells was reduced in the absence of Ca2+ and Mg2+ but was not abolished, even in the presence of EDTA. Ca2+ was routinely the most effective divalent cation in supporting these aspects of insulin action, but similar responses were obtained with Mg2+, Sr2+ and Ba2+.Since insulin still binds to the cells under conditions in which some of the cellular effects of the hormone are abolished, it is suggested that divalent cations may have a role, either direct or indirect, in the processes linking the insulin-insulin receptor complex to certain effector systems in the cells. It is tentatively suggested that this action occurs at the level of the fat cell plasma membrane. 相似文献
5.
6.
—The effects of Ca2+ ions on the metabolism of [3H]serotonin and [3H]-labelled catecholamines have been examined in hippocampal slices or synaptosomes. The formation of [3H]-5 hydroxyindoles ([3H]serotonin + [3H]-5 hydroxyindoleacetic acid) from [3H]tryptophan and that of [3H]-labelled catecholamines from [3H]tyrosine were increased when Ca2+ was omitted from the incubating medium. However, the total synthesis of 5-HT from tryptophan and that of catecholamines from tyrosine did not seem to be significantly changed. Altered formation of tritiated amines were due to changes in the specific activities of respective precursor amino acids. This reflected altered sizes of the free amino acid pools caused by Ca2+-dependent in vitro proteolysis. This must be taken into consideration when studying in vitro Ca2+ dependency of neutrotransmitter metabolism. 相似文献
7.
RAPID AXONAL TRANSPORT IN VITRO IN THE SCIATIC SYSTEM OF THE FROG OF FUCOSE-, GLUCOSAMINE- AND SULPHATE-CONTAINING MATERIAL 总被引:5,自引:3,他引:2
—An in vitro system from the frog has been used to study fast axonal transport of glycoproteins. The migration of [3H]fucose-, [3H]glucosamine- and [35S]sulphate-labelled material was followed from the dorsal ganglia, along the sciatic nerve towards the gastrocnemius muscle. The distribution in different subcellular fractions, effect of cycloheximide and transport kinetics did not differ very much between fucose- and glucosamine-incorporation into the nerve. Cycloheximide blocked the synthesis of TCA-insoluble radioactivity, which was transported at a rate of 60–90 mm per day at 18°C, more effectively than the synthesis of stationary proteins in the ganglia. About 10 per cent of the TCA-insoluble and transported radioactivity was extracted by chloroform-methanol (2:1, v/v) and might be glycolipids and the rest glycoproteins. Results suggest that TCA-soluble activity, which was recovered in the nerve, originated in part from labelled macromolecules consumed along the axons. The rapidly transported TCA-insoluble radioactivity was 85 per cent particulate and mainly associated with structures sedimenting in the microsomal fraction. [35S]Sulphate-labelled TCA-insoluble material was resistant towards chloroform-methanol (2:1, v/v) extraction and rapidly transported from the ganglia into the nerve. The synthesis was inhibited by cycloheximide. The material, probably proteoglycans, represented a quantitatively minor part of transported glycoproteins. 相似文献
8.
The axonal transport of labelled proteins was studied in the optic system of adult rabbits after an intraocular injection of [3H]Ieucine. It was demonstrated that the precursor was incorporated into protein, which was transported along the axons of the retinal ganglion cells. Intraocularly injected puromycin inhibited protein synthesis in the retina and markedly inhibited the appearance of labelled protein in the optic nerve and tract. It was further demonstrated by intracisternal injection of [3H]leucine that an intraocular injection of puromycin did not affect the local protein synthesis in the optic nerve and tract. Cell fractionation studies of the optic nerve and tract showed that the rapidly migrating component, previously described as moving at an average rate of 110-150 mm/day, was largely associated with the microsomal fraction. About 40 per cent of the total protein-bound radioactivity in this component was found in the microsomal fraction and about 15 per cent was recovered in the soluble protein fraction. Most of the labelled material moving at a rate of 1-5-2 mm/day was soluble protein. The specific radioactivity of this component was about ten times greater than that of the fast one. In the slow component about 50 per cent of the radioactivity was found in the soluble protein fraction and about 10 per cent of the radioactivity was recovered in the microsomal fraction. Radioautography demonstrated incorporated label in the neuropil structures in the lateral geniculate body as early as 4-8 hr after intraocular injection. The labelling of the neuropil increased markedly during the first week, and could be observed after 3 weeks. 相似文献
9.
The presence of a requirement for calcium during the fast transport of [3H]protein in axons was assessed in desheathed spinal nerves of bullfrog. The nerves were desheathed locally along 4 mm of their length, and desheathing was judged effective on the basis of an enhanced uptake of [3H]leucine into that region of nerve trunk. Desheathing per se had a slight inhibitory effect on transport. Incubation of desheathed nerve trunks in calcium-free medium reduced transport by 60-80% relative to that in desheathed nerves incubated in normal medium. Addition of Mg2+ or Sr2+ to the calcium-free medium allowed transport to proceed normally. Addition of Co2+ or Mn2+ to normal medium did not affect transport in desheathed isolated nerve trunks. When ganglia and nerve trunks were both incubated in medium containing 0.18 mM-CoCl2, transport was depressed to a similar extent proximal and distal to the desheathed region. This again indicates that Co2+ does not inhibit transport in desheathed nerves, whereas it does inhibit transport in the ganglia. Additive inhibitory effects were observed when ganglia were incubated in medium containing 0.018 mM-CoCl2, and desheathed nerves were incubated in calcium-free medium. Differences in the divalent cation specificities of the axonal and ganglionic calcium requirements suggest that calcium supports transport in nerves in a manner distinct from its role in maintaining transport in spinal ganglia. It is concluded that the ganglionic calcium requirement involves initiation of axonal transport in the soma rather than translocation in the intraganglionic region of axon. 相似文献
10.
Richard Hammerschlag Charles Bakhit Arlene Y. Chiu Anant R. Dravid 《Developmental neurobiology》1977,8(5):439-451
Fast axonal transport of [3H]protein has been examined in bullfrog primary afferent neurons incubated in media supplemented with divalent cations that can act as agonists or antagonists of calcium ions. Incubation in calcium-free medium (CFM) had no effect on the rate of transport, but reduced the amount of transported [3H]protein by 40–60% relative to transport in the contralateral preparation maintained in normal medium. Preparations incubated in CFM supplemented with 1.8 mM SrCl2 (equimolar to the CaCl2 concentration in normal medium) carried out transport at control levels. Incubation conditions in which primary afferent somata were exposed to the Sr2+-medium while nerve trunks were maintained in CFM also supported normal transport. By contrast, selective exposure of nerve trunks to Sr2+-medium, and somata to CFM resulted in a reduced level of transport similar to that observed when the whole preparation was incubated in CFM. The depression of transport resulting from incubation in CFM was shown to be reversible when preparations were transferred from CFM to either Sr2+-supplemented CFM or to normal medium. By contrast to the effects of Sr2+, Ba2+ (up to 18 mM) did not substitute for Ca2+ in the transport process. When normal medium was supplemented with calciumantagonist cations, the amount of transport was depressed (Co2+ > Mn2+ >> Mg2+), with no concomitant effect on the rate of transport. Results of studies with Co2+, as well as those with Sr2+, suggest that a major locus of action of these cations is within the neuronal soma at a step subsequent to protein synthesis, and prior to the onset of protein translocation via the transport system. Thus, it is inferred that these divalent cations affect a calcium-dependent step that occurs during the initiation phase of fast axonal transport. 相似文献
11.
Abstract: γ-Aminobutyric acid (GABA) is thought to be a neurotransmitter in the vetebrate retina. We studied the voltage and Ca2+ dependency of the process of release of [3H]GABA from the retina of the teleost Eugenes plumieri, using a microsuperfusion technique. Two depolarizing agents, veratridine and high potassium, produced a concentration-dependent release of [3H]GABA. The veratridine effect was inhibited in Na+-free solution, but was not affected by 1 μM tetrodotoxin. A substantial inhibition (about 75%) of the veratridine-and potassium-stimulated release of [3H] GABA occurred in Ca2+-free medium. Inhibitors of the Ca2+ channel, such as Mg2+(20 mM), La3+ (0.1 mM), and methoxy-verapamil (4 μM-0.4 mM), inhibited the veratridine-and K+-stimulated release. However, Co2+ and Cd2+ caused a potentiation and no change of the K+-and veratridine-stimulated release, respectively. This release process is apparently specific, since both depolarizing agents were unable to release [3H]methionine, a nontransmitter amino acid, under the same experimental conditions. Autoradio-graphic studies with [3H]GABA, using the same incubation conditions as for the release experiments, showed a high density of silver grains over the horizontal cells with almost no accumulation by amacrine cells and Muller cells. β-Alanine and nipecotic acid were used as two relative specific inhibitors of the glial and neuronal GABA uptake mechanisms, respectively. Only a small heteroexchange with [3H]GABA was found with β-alanine, and no inhibition of the subsequent veratridine-stimulated release. On the other hand, nipecotic acid produced a strong heteroexchange with [3H]GABA and lacked the capacity to induce the veratridine-stimulated release of [3H]GABA. These results suggest a voltage-and Ca2+-dependent neuronal release of [3H]GABA from retina. 相似文献
12.
Hajime Otani Hitomi Otan Masao Morita Dipak K. Das 《Molecular and cellular biochemistry》1989,90(2):111-120
We investigated the effect of Ca2+ overload on the phospholipase C-catalyzed hydrolysis of phosphoinositides in the rat left ventricular papillary muscle. Ca2+ overload on the papillary muscle was induced by treatment with 0.3 mM ouabain in Ca2+-containing medium following either Ca2+-containing or Ca2+-free superfusion. The phosphoinositide breakdown was evaluated by determining accumulations of [3H]inositol phosphates ([3H]IPs) in the tissues prelabeled with [3H]inositol. Ca2+ repletion following Ca2+-free superfusion resulted in a rapid but small increase in resting tension that was not followed by contracture, nor was it associated with a significant increase in [3H]IPs accumulations. Treatment with ouabain following Ca2+-containing superfusion increased resting tension after a lag period of several minutes and produced contracture associated with an increase in [3H]IPs accumulations. The ouabain induced increases in resting tension, and accumulations of [3H]IPs were significantly potentiated by prior Ca2+-free superfusion instead of Ca2+-containing superfusion. There was a significant positive correlation between increases in resting tension and the phosphoinositide breakdown. The increased resting tension and the accumulations of [3H]IPs were not antagonized by treatments with prazosin plus atropine or indomethacin, but were abolished by superfusion with Ca2+-free buffer solution. Although the enhanced phospholipase C-catalyzed hydrolysis of phosphoinositides appears to be a consequence rather than a cause of increased intracellular Ca2+, such a biochemical change may provoke a positive feedback mechanism to develop the muscle contracture through the putative intracellular messenger action of inositol triphosphate and diacylglycerol.Abbreviations [3H]IPs
[3H]Inositol Phosphates
- IP
Inositol Phosphate
- IP2
Inositol Bisphosphate
- IP3
Inositol Trisphosphate
- PI
Phosphatidylinositol
- PI-4-P
Phosphatidylinositol-4-phosphate
- PI-4,5-P2
Phosphatidylinositol 4,5-bisphosphate
- PRZ
Prazosin
- ATR
Atropine
- INDO
Indomethacin
- min
Minutes 相似文献
13.
Abstract— The uptake and release of [3H]dopamine was studied in the goldfish retina with the following results: (1) when goldfish retinas were incubated with 2 ± 10-7m -[3H]dopamine for less than 20min and processed for autoradiography. most of the label was associated with dopaminergic terminals that contact certain horizontal cells. Biochemical analysis showed that > 93% of this label was [3H]-dopamine. (2) [3H]dopamine uptake saturated with increasing dopamine concentration and followed Michaelis-Menten kinetics. This uptake could be explained by a single ‘high-affinity’ mechanism with a Km of 2.61 ± 0.41 ± 10-7m and a Vmax of 66 ± 12 ± 10-12 mol/min/mg protein. (3) [3H]dopamine uptake was temperature-dependent with a temperature coefficient of 1.7 and an energy of activation of 11.4 kcal/mol. (4) The initial rate of uptake was unaffected by the absence of Ca2+ or the presence of Co2+; however, more than 85, uptake was blocked in the absence of external Na+. (5) Neither 1 mm -cyanide nor 5 mm -iodoacetate blocked more than 30% of uptake individually; however, in combination > 70% of uptake was blocked. (6) Centrally acting drugs benztropine and diphenylpyraline inhibited at least 60–70% of [3H]dopamine uptake. (7) [3H]dopamine in the retina could be released by increasing the external K+ concentration. This release was Ca2+ -dependent and was blocked by 10mm -Co2+ or 2Omm -Mg2+. The amount of [3H]dopamine released was not affected by the presence of benztropine, diphenylpyraline or fluphenazine in the incubation medium. These studies add further support for dopamine as a neurotransmitter used by interplexiform cells of the goldfish retina. 相似文献
14.
Abstract— Ethyleneglycol-bis (β-aminoethyl ether)-N-N'-tetraacetic acid (EGTA) inhibited the incorporation of 32Pi into phosphatidylinositol (PI) in rat diaphragm incubated in Ca2+-free Krebs-Ringer medium. Only the labelling of the PI was altered, and no effects on the pool size of PI or on the incorporation of 32Pi into other phospholipids were observed. The effect of EGTA was concentration-dependent and appeared to be related to its Caa+-chelating properties; the inhibition of the incorporation of 32Pi could be completely reversed by the addition of excess Ca2+ but not Mg2+. The inhibitory effect of the EGTA was progressively enhanced by lengthening the preincubation of the tissue with EGTA, an observation suggesting that chelation of intracellular or membrane-bound Ca2+, rather than extracellular Ca2+, was involved in the effect. In contrast to its inhibition of the incorporation of 32Pi EGTA enhanced the incorporation of [3H]inositol into PI, but this effect was accompanied by an appreciable increase in total uptake of [3Hlinositol by the tissue. Our results suggest that the level of intracellular Ca2+ plays a role in the regulation of the incorporation of 32Pi into PI. Addition of unlabelled α-glycerophosphate to the incubation medium of tissues which had been preincubated with 2-deoxy-d -glucose failed to cause a significant diminution in the inhibition by EGTA of the incorporation of 32Pi into PI. This experiment suggests, but does not prove, that the effect of EGTA was not at the level of incorporation of 32Pi into α-glycerophosphate. 相似文献
15.
Yuzuru Ito Shigeru Nakashima Hiroyuki Kanoh Yoshinori Nozawa 《Journal of neurochemistry》1997,68(1):419-425
Abstract: The mechanism for carbachol (CCh)-induced phospholipase D (PLD) activation was investigated in [3H]palmitic acid-labeled pheochromocytoma PC12 cells with respect to the involvement of protein tyrosine phosphorylation and Ca2+. PLD activity was assessed by measuring the formation of [3H]phosphatidylbutanol in the presence of 0.3% butanol. Pretreatment of cells with the tyrosine kinase inhibitors herbimycin A, genistein, and tyrphostin inhibited PLD activation by CCh. Western blot analysis revealed several apparent tyrosine-phosphorylated protein bands (111, 91, 84, 74, 65–70, 44, and 42 kDa) in PC12 cells treated with CCh. Phosphorylation of the 111-, 91-, 84-, and 65–70-kDa proteins peaked within 1 min, and their time-dependent changes seemingly correlated with that of PLD activation. Others (74, 44MAPK, and 42MAPK kDa) were phosphorylated rather slowly, and maximal tyrosine phosphorylation was observed at 2 min. Herbimycin A inhibited PLD activity and tyrosine phosphorylation of four proteins (111, 91, 84, and 65–70 kDa) in a preincubation time- and concentration-dependent fashion. In Ca2+-free buffer, CCh-induced [3H]phosphatidylbutanol formation and protein tyrosine phosphorylation were abolished. A Ca2+ ionophore, A23187, caused PLD activation and tyrosine phosphorylation of four proteins of 111, 91, 84, and 65–70 kDa only in the presence of extracellular Ca2+. Extracellular Ca2+ dependency for CCh-induced PLD activation was well correlated with that for tyrosine phosphorylation of the four proteins listed above, especially the 111-kDa protein. These results suggest that Ca2+-dependent protein tyrosine phosphorylation is closely implicated in CCh-induced PLD activation in PC12 cells. 相似文献
16.
Protein synthesis in neuronal perikarya isolated from cerebral cortex of the immature rat 总被引:2,自引:1,他引:1
Abstract— Homogenates of neuronal perikarya isolated from the cerebral cortex of the 8-day-old rat were incubated with [3H]leucine, and the characteristics of the protein synthetic process were studied. Incorporation of leucine into protein was linear up to 90 min, proceeded optimally at pH 7.6 and was stimulated by K+ and NH4+, unaffected by Li+ and inhibited by Na+. Puromycin, cycloheximide, RNAse, sulphhydryl blocking agents and phospholipase A exerted a pronounced inhibition, whereas chloramphenicol and phospholipase C had no effect. About 42 per cent of the total radioactive protein formed in the optimally fortified in uitro system was recovered in non-sedimentable form. Incorporation into the subcellular fractions of the neuronal perikarya increased steadily with increasing time of incubation. The microsomal fraction acquired the highest specific radioactivity (d.p.m./mg of protein), followed by the mitochondrial and the nuclear + cell debris fractions. The high-speed soluble fraction exhibited the lowest specific radioactivity. Although the addition of L-methionine to a suitably fortified incubation medium inhibited neuronal protein synthesis by about 80 per cent, the addition of D-methionhe, α-methyl-DL-methionine or L-tryptophan was relatively ineffective by comparison. 相似文献
17.
The influence of tetanus toxin in vitro on the release of exogenous [3H]GABA was studied with rat cerebral cortex slices. The influx, long-term accumulation and spontaneous efflux of GABA were not modified by the toxin. The release induced by high K+ (50 mM) medium from the superfused slices pretreated with the toxin was significantly inhibited in a time- and dose-dependent fashion. This release was attenuated during superfusion with Ca2+-free medium and the toxin no longer affected the remaining Ca2+-independent release. The release induced by Na+-free media did not require extracellular Ca2+ ions, and the toxin inhibited the release both with and without Ca2+. The toxin treatment had no marked influence on the ouabain (20 μM) or veratrine (25–50 μM)-induced release of GABA. The toxin treatment in vitro appears to modify some step(s) in the stimulated release of GABA without affecting its unstimulated membrane transport. Tetanus toxin may thus prove a valuable tool in studying the mechanisms of the release of GABA and possibly other inhibitory transmitters in synapses of the central nervous system. 相似文献
18.
Muscle proteins were labeled by incubating isolated frog sartorius muscles with [3H]- or [14C]phenylalanine. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis of plasma membrane fractions revealed a major protein band with an apparent molecular weight of approx. 96 000. Radioactivity in this band showed a clearly delineated decrease, relative to other bands, when previously labeled muscles were induced to contract either by electrical stimulation or by increasing the influx of Ca2+ from the incubation medium. It is postulated that a Ca2+-activated neutral protease may account for this decrease in labeled membrane protein. 相似文献
19.
Abstract— The optic system of Scardinius erythrophthalmus has been used to study the axonal translocation of radioactivity from [3H]glucose. Intraocularly injected precursors were transported intra-axonally along the optic nerve towards the contralateral optic tectum. In comparison with the well known properties of axonal protein transport there were remarkable differences in the proximo-distal translocation of [3H]glucose. These were: (1) a delay in the labelling of the structures investigated, after tracer application; (2) only a rapid phase of transport; and (3) no accumulation of radioactivity in the region of nerve terminals in the optic tectum connected with the injected eye. The transported material was almost exclusively in the form of TCA-soluble compounds and was mainly glucose itself or its low molecular derivatives, but not glycogen. The rate of transport was decreased by lowered temperatures and was not immediately dependent on retinal protein synthesis. Colchicine blocked the axonal transport of glucose by up to 60–70 per cent. 相似文献
20.
P. D. Swanson 《Journal of neurochemistry》1968,15(2):57-67
—(1) Cerebral slices were incubated in Ca2+-free media or in media which contained 2.8 mm -Ca2+. Omission of Ca2+ brought about a drop in creatine phosphate content of 28 per cent, as well as a drop of 3–10 per cent in non-inulin K+ content. There was little change in content of 10-min phosphate or of non-inulin Na+. (2) Ouabain in concentrations of to M increased the loss of K+ from the slice and caused a rise in Na+ content. The changes were most marked in Ca2+-free media. Creatine phosphate levels were depressed by ouabain both in the presence or absence of Ca2+. In the absence of Ca2+, the lowering of phosphocreatine did not occur until significant shifts in K+ had taken place. In contrast, slices incubated in Ca2+-containing media lost creatine phosphate and K+ at about the same rate. (3) When ouabain and labelled phosphate were added simultaneously, there was little difference in the rate of incorporation of label into creatine phosphate in media which differed in Ca2+ concentration. However, incorporation of azP-labelled phosphate into creatine phosphate was decreased by 30–40 per cent in media which lacked Ca2+ when ouabain was added 15 min prior to the labelled phosphate. This change was not observed when the media contained Ca2+. (4) Ouabain did not affect oxidative phosphorylation or respiratory control when added directly to bovine brain mitochondrial preparations. (5) The results suggest that the previously observed depression of respiration brought about by ouabain in Ca2+-deficient media is not a good indicator of the proportion of the cell's metabolism used for active cation transport. Under these conditions, the inhibition of cation transport is accompanied by a drop in slice content of high-energy phosphate which may represent a secondary effect of ouabain, or of cytoplasmic alterations brought about by ouabain, on energy-producing processes. 相似文献