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101.
Basic and Regulatory Mechanisms of In Vitro Release of Met-Enkephalin from the Dorsal Zone of the Rat Spinal Cord 总被引:6,自引:3,他引:3
Abstract: Under control conditions, superfused slices of the dorsal half of the lumbar enlargement from adult rats released Met-enkephalin-like material (MELM) that behaved as authentic Met-enkephalin under two different chromatographic procedures (Bio-gel filtration, HPLC). MELM release increased markedly on exposure of slices to batrachotoxin (0.5 μ M ) or to an excess of K+ (28 and 56 m M instead of 5.6 m M ). The K + -evoked release was totally dependent on the presence of Ca2+ in the super-fusing fluid whereas the spontaneous efflux of MELM was only partially Ca2+ -dependent. Further experiments performed with tissues of polyarthritic rats indicated that the increase in their MELM levels was associated with a lower fractional rate constant of MELM release, therefore suggesting that spinal Met-enkephalin turnover might be reduced in chronically suffering animals. Examination of the possible modulation of MELM release by various neuroactive compounds present within the dorsal horn revealed that cholecystokinin (10 μ M ), but not its desulphated derivative, substance P-sulphoxide (10 μ M ), and to a lesser extent substance P, enhanced the K+ -evoked MELM release. In contrast, γ-aminobutyric acid (10 μ M ) and (–)-baclofen (1 μ M ) partially prevented the stimulatory effect of K+ on MELM release. Other compounds such as serotonin, somatostatin, and neurotensin altered neither the spontaneous nor the K+ -evoked release of MELM. 相似文献
102.
The temperature dependence of the electric field-induced chlorophyll luminescence in photosystem II was studied in Tris-washed, osmotically swollen spinach chloroplasts (blebs). The system II reaction centers were brought in the state Z+P+-QA
-QB
- by preillumination and the charge recombination to the state Z+PQAQB
- was measured at various temperatures and electrical field strengths. It was found that the activation enthalpy of this back reaction was 0.16 eV in the absence of an electrical field and diminished with increasing field strength. It is argued that this energy is the enthalpy difference between the states IQA
- and I-QA and accounts for about half of the free energy difference between these states. The redox state of QB does not influence this free energy difference within 150 s after the photoreduction of QA. The consequences for the interpretation of thermodynamic properties of QA are discussed.Abbreviations DCMU
3(3,4-dichlorophenyl)-1,1-dimethylurea
- I
intermediary electron acceptor
- Mops
3-(N-morpholino)propanesulphonic acid
- P
(P680) primary electron donor
- PS II
photosystem II
- QA and QB
first and second quinone electron acceptors
- Tricine
N-tris(hydroxymethyl)methylglycine
- Tris
tris-(hydroxymethyl)aminomethane
- Z
secondary electron donor
Dedicated to Professor L.N.M. Duysens on the occasion of his retirement 相似文献
103.
I. S. Chohan 《Journal of biosciences》1986,10(2):243-249
Piretanide, 4-phenoxy-3-(pyrrolidinyl)-5-sulphamoyl benzoic acid, apart from being an efficient diuretic, enhances endogenous
plasma fibrinolytic activity after a single dose of 6 mg administered by oral route. After ingestion of the drug, acceleration
of fibrinolytic acitivity became manifest within 1 h, reached its peak in 3 h and was associated with a fall in fibrinogen
and diminished urokinase excretion. Piretanide did not cause lysis of fibrinin vitro. Primary platelet aggregation, induced by adenosine-diphosphate, was inhibited by piretanide. Inin vitro experiments piretanide led to effective inhibition of adenosine-diphosphate-induced platelet aggregation with complete inhibition
at 5 mM concentration. Piretanide led to a highly significant decrease of platelet factor-4 release. 相似文献
104.
R. de Leeuw Y. A. Wurth M. A. Zandbergen J. Peute Dr. H. J. Th. Goos 《Cell and tissue research》1986,243(3):587-594
Summary To study the feedback mechanism of gonadal hormones on GTH secretion in male African catfish, the effects of castration and steroid replacement on GTH release, pituitary GTH content, and ultrastructural appearance of gonadotropes were investigated.Castration resulted in an increase in plasma GTH levels, a decrease in pituitary GTH content, and a degranulation of many gonadotropes. The aromatizable androgens testosterone and androstenedione were able to abolish the castration-induced increase in plasma GTH. This was accompanied with a restoration of pituitary GTH content and a regranulation of gonadotropes. The non-aromatizable androgens 5-dihydrotestosterone and 11-hydroxyandros tenedione did not have these effects. Replacement with estrone or estradiol resulted in an increase in pituitary GTH, however, without abolishing the elevated plasma GTH levels; ultrastructurally, many gonadotropes showed a welldeveloped granular endoplasmic reticulum together with a regranulation.The results of the present study indicate the significance of androgen aromatization in the feedback mechanism of gonadal steroids on the brain-pituitary axis. 相似文献
105.
Habitat choice of some field-inhabiting carabid beetles (Coleoptera: Carabidae) studied by recapture of marked individuals 总被引:2,自引:0,他引:2
HENRIK WALLIN 《Ecological Entomology》1986,11(4):457-466
ABSTRACT.
- 1 Habitat choice of some field-inhabiting carabid beetles was studied in the field, and included the adult-overwintering Bembidion lampros Herbst, Pterostichus cupreus L. and Agonum dorsale Pontoppidan, and the larval-overwintering Trechus secalis Paykull, Pterostichus melanarius Illiger, P.niger Schaller and Harpalus rufipes De Geer. These were compared to the forest-inhabiting and adult-overwintering species, Carabus nemoralis Müller.
- 2 Marked beetles were released in the centre of a circular enclosure which was placed on the edge between a cereal field and a wood. The direction of movement in this circle was compared with that in a control circle placed entirely in the cereal field.
- 3 In the field/wood circle, adult-overwinterers and the larval-overwin-terer H.rufipes choose to move into the cereal field. The majority of T.secalis. P.melanarius and C.nemoralis, however, moved into the wood, while P.niger exhibited no preference.
- 4 In the field circle, adult-overwinterers moved towards the more sun-exposed parts of the circle, whereas the movements of larval-overwin-terers were random.
- 5 Some species-specific characteristics considered important for habitat choice by these carabid beetles, and the relevance of these characteristics for their dispersal behaviour are discussed.
106.
麻黄碱抑制小鼠输精管电场刺激致收缩的机制 总被引:1,自引:0,他引:1
麻黄碱(10 nmol/L~(-0.1) mmol/L)对电场刺激所致输精管收缩的浓度依赖性抑制作用可被育亨宾(0.1 μmol/L)减弱。去甲肾上腺素(0.1 nmol/L~(-10)μmol/L )和酪胺(0.1 μmol/L~(-0.1) mmol/L)也有类似麻黄碱的作用,去氧肾上腺素则缺乏此种作用。利血平处理和可卡因(10 μmol/L)可减弱麻黄碱和酪胺的抑制效应,但能增敏去甲肾上腺素的作用。高 Ca~( )和4-氨基吡啶(50 μmol/L)明显减弱甚至取消麻黄碱对电场刺激的抑制效应。以上结果提示麻黄碱抑制电场刺激所引起的输精管收缩。至少部分通过促进神经末梢释放去甲肾上腺素间接作用,后者激动突触前α_2-肾上腺素受体,从而抑制去甲肾上腺素的进一步释放。麻黄碱和其释放的去甲肾上腺素的作用,又可能与阻遏 Ca~( )内流有关。 相似文献
107.
Applications of recombinant DNA technology are discussed as a backdrop for evaluation of the environmental impacts of this technology. Some of applications include using traditional biological techniques for specific purposes, including nitrogen fixation, microbial pesticides, and waste treatment. In these instances the final product lies along a continuum, beginning with an organism marginally performing its function, and ending with one that is highly specialised and very efficient in what it does. One may move along this continuum toward the ‘perfect’ microorganism by using traditional methodologies of mutagenesis and selection, recombinant DNA technology, or a combination of the two. 相似文献
108.
Evoked Release of Proteins from Central Neurons In Vivo 总被引:3,自引:1,他引:2
Push-pull cannulae were implanted in both substantiae nigrae and caudate nuclei of the halothane-anesthetized cat. The release of total protein, acetylcho-linesterase, and nonspecific cholinesterases was examined. Following direct application of potassium to one substantia nigra, changes occurred in the local release of total protein and acetylcholinesterase, but not nonspecific cholinesterases; changes also were observed in both caudate nuclei and the contralatera/ substantia nigra. The local evoked release of acetylcholinesterase and of total protein differed in the extent to which they were calcium-dependent. Control studies suggest that release of these compounds, both spontaneous and evoked, is related, at least in part, to neuronal activity. The significance of the neuronal release of proteins is discussed. 相似文献
109.
Modulatory Action of Taurine on the Release of GABA in Cerebellar Slices of the Guinea Pig 总被引:6,自引:4,他引:2
Abstract: For the purpose of demonstrating the action of taurine as a neuromodulator in addition to its suggested neurotransmitter function, the effects of taurine and muscimol on the depolarization-induced Ca-dependent release of [3 H]γ-aminobutyric acid (pH]GABA) and l -[3 H]glutamate in cerebellar slices from guinea pigs were investigated. The release of [3 H]GABA was found to be greatly decreased by a GABA agonist, muscimol, and by taurine, but not by glycine. The release of l -[3 H]glutamate was little affected by taurine. The release of [3 H]GABA was enhanced by bicuculline and strychnine, but not by picrotoxin, and the suppressive action of muscimol on the GABA release was antagonized by bicuculline, picrotoxin, and strychnine, suggesting the possible existence of presynaptic autoreceptors for GABA in the cerebellum. The suppressive action of taurine on the release of [3 H]GABA, on the other hand, was blocked only by bicuculline. These results suggest that taurine reduced the release of [3 H]GABA from cerebellar slices by acting on the GABA autoreceptors or, more likely, on other types of receptors that are sensitive to bicuculline. As a possible mechanism for this modulatory action of taurine, the blockade by this amino acid of the influx of Ca2+ into cerebellar tissues was tentatively suggested. 相似文献
110.
Acetylcholine Releases ATP from Varicosities Isolated from Guinea Pig Myenteric Plexus 总被引:2,自引:1,他引:1
The effects of cholinergic agonists and antagonists on the release of ATP from isolated myenteric varicosities were studied using a firefly luciferin-luciferase technique. In a previous study, acetylcholine and nicotine released ATP from isolated myenteric varicosities, whereas the muscarinic agonist bethanechol did not. In the present study, release of ATP by acetylcholine was shown to be Ca2+ dependent. d-Tubocurarine competitively antagonized the release of ATP by either acetylcholine or nicotine. Maximal release of ATP by acetylcholine (10(-3) M) was approximately 24% that observed with the depolarizing drug veratridine (5 X 10(-5) M), suggesting either that not all of the varicosities capable of releasing ATP possess nicotinic receptors or that acetylcholine does not depolarize the varicosities to the degree that veratridine does. Tetrodotoxin slightly but significantly reduced ATP release induced by acetylcholine or nicotine, indicating some involvement of Na+ channels in the release process. Finally, 6-hydroxydopamine pretreatment produced a 48% reduction in the acetylcholine-evoked release of ATP, suggesting that much, but possibly not all, of the ATP release occurs from noradrenergic varicosities present in the preparation. 相似文献