摘要:

Abstract:Some data on the concentration range of response and the concentration for half‐response (EC50) of γ‐aminobutyric acid (GABA) for the GABAAreceptor are reviewed and compared. An analysis of the36CI−flux assay demonstrates that both the EC50and the slope of a Hill plot depend on the ion influx or efflux assay time. The effects of depletion of the36CI−concentration gradient during the assay and of receptor desensitization on the result for a range of assay times are considered. The EC50can be decreased by orders of magnitude by increasing the assay time. The EC50measured in a finite time is less than the half‐response concentration for the response(s) of the receptor. The extent of this difference depends on the receptor concentration per internal volume. The maximal decrease of EC50depends on the rate of receptor desensitization. The computer simulations showed that a GABAAreceptor with a half‐response concentration of 100 μMGABA can give36CI−flux measurements with an EC50value

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb03110.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:Disulfide‐bridged S100b protein formation, air‐catalyzed and induced by thiol/disulfide exchange, was studied under various ionic conditions. As native, physiological disulfide‐bridged proteins are obtained easily from their reduced counterparts under appropriate redox conditions, this work was performed to determine whether this was the case for disulfide‐bridged S100b proteins, reported to have neurite extension activity. In nondenaturating native medium, no disulfide‐bridged species could be generated from reduced proteins in any of the ion‐induced conformations tested (no ions, Ca2+, Zn2+, or K+) under widely different redox conditions. Only mixed disulfides accumulated, in certain cases.In contrast, intrasubunit monomeric and intersubunit dimeric disulfide‐bridged species were readily and efficiently generated under denaturating conditions. A brief characterization of these oxidized species suggested that they differed widely in structure from their reduced counterparts and that they probably did not bind Ca2+. Taken together, these data question the physiological relevance of these disulfide‐bridged S100b

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb03111.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:The effect of inhibitors of protein synthesis (actinomycin D, cycloheximide), proteases (leupeptin), and intracellular transport (colchicine, monensin) on the γ‐aminobutyric acid (GABA) agonist [4,5,6,7‐tetrahydroisoxazolo[5,4‐c]pyridin‐3‐ol (THIP)]‐induced changes in morphological differentiation and GABA receptor expression was investigated in cultured cerebellar granule cells. After 4 days in culture the neurons were exposed to the inhibitors for 6 h in the simultaneous presence of THIP. Subsequently, cultures were either fixed for electron microscopic examination or used for preparation of membranes for [3H]GABA binding assays. In some experiments the functional activity of the newly induced low‐affinity GABA receptors was assessed by investigation of the ability of GABA to inhibit neurotransmitter release from the neurons. These experiments were performed to differentiate between an intracellular and a plasma membrane localization of the receptors. In all experiments cultures treated with THIP alone served as controls. The inhibitors of protein synthesis totally abolished the ability of THIP to induce low‐affinity GABA receptors. In contrast, the inhibitors of intracellular transport as well as the protease inhibitor did not affect this parameter. However, studies of effects of GABA on transmitter release from monensintreated cultures showed that transmitter release could not be inhibited by GABA in these cells in spite of the presence of low‐affinity GABA receptors in the membrane preparations. This indicates that the low‐affinity receptors were not located in the plasma membrane. This is in good agreement with the corresponding morphological findings, that monensin treatment led to an intense vacuolization of the Golgi apparatus, thereby preventing intracellular transport of the newly synthesized GABA receptors. No qualitative alteration of the general ultrastructure was observed in cells cultured in the simultaneous presence of THIP and actinomycin, cycloheximide. or colchicine. However, these inhibitors reduced the cytoplasmic density of the different organelles involved in the cellular machinery for synthesis and intracellular transport compared to cells grown in the presence of THIP alone. These results suggest that the THIP‐induced alterations in the GABA receptor expression in cerebellar granule cells requires de novo synthesis of low‐affinity GABA receptors, which in turn is dependent on proper function of the organelles involved in synthesis and intracellular transport of proteins destined for insertion

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb03112.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:The subcellular and regional distribution of endooligopeptidase (EC 3.4.22.19), an enzyme capable of generating enkephalin by single cleavage from enkephalin‐containing peptides, was determined by an enzymatic assay using metorphamide and by immunochemical techniques in the CNS of the rat. The rat CNS contains a membrane‐associated form of endo‐oligopeptidase, an enzyme predominantly associated with the soluble fraction of brain homogenates. Sub‐cellular fractionation showed that ∼17% of the total activity of the enzyme is associated with membrane fractions including synaptosomes. Synaptosomal membranes were prepared from neocortex, striatum, hypothalamus, medulla, spinal cord, and cerebellum. The amount of EC 3.4.22.19 activity solubilized by 3‐([3‐cholamidopropyl]dimethylammonio)‐1‐propanesulfonate from synaptosomal membranes was similar in neocortex, striatum, and hypothalamus, being three‐ to 10‐fold greater than in spinal cord, cerebellum, and medulla. A polyclonal antibody exhibiting high affinity for endo‐oligopeptidase was raised in rabbits against the purified rat brain enzyme and used to localize endo‐oligopeptidase by Western blotting and by immunoperoxidase techniques. A strong band corresponding to the Mrof EC 3.4.22.19 was found in solubilized proteins obtained from synaptosomal membranes prepared from hypothalamus, neocortex, and striatum when subjected to Western blotting. The immunohistochemical localization of endo‐oligopeptidase indicated that the immunoreactivity was confined to gray matter in regions known to be rich in peptide‐containing neurons such as the striatum. In the cerebellum, a region poor in peptides, no staining could be detected. The nonuniform distribution of endo‐oligopeptidase in rat brain suggests a role in neurotr

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb03113.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:Biochemical mapping of five different peptide‐like materials—calcitonin gene‐related peptide (CGRP), substance P (SP), Met5‐enkephalin (ME), cholecystokinin (CCK), and dynorphin A (1–8) (DYN)—was conducted in the dorsal and ventral zones of the spinal cord at the cervical, thoracic, and lumbar levels in 3‐month‐old rats 10 days after unilateral dorsal rhizotomy at the cervical level (C4‐T2) or after neonatal administration of capsaicin (50 mg/kg s.c). In control rats, all peptide‐like materials were more abundant in the dorsal than in the ventral zone all along the spinal cord. However, in both zones, absolute concentrations of CGRP, SP, ME, and CCK were significantly higher at the lumbar than at the cervical level. Rhizotomy‐induced CGRP depletion (‐85%) within the ipsilateral dorsal zone of the cervical cord was more pronounced than that due to neonatal capsaicin (‐60%), a finding suggesting that this peptide is contained in both capsaicin‐sensitive (mostly unmyelinated) and ‐insensitive (myelinated) primary afferent fibers. In contrast, similar depletions of SP (‐50%) were observed after dorsal rhizotomy and neonatal capsaicin treatment, as expected from the presence of SP only in the capsaicin‐sensitive small‐diameter primary afferent fibers. Although the other three peptides remained unaffected all along the cord by either intervention, evidence for the existence of capsaicin‐insensitive CCKergic primary afferent fibers could be inferred from the increased accumulation of CCK (together with SP and CGRP) in dorsal root gangli

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb03114.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:The purpose of the present study is to clarify the effects of hypoxia on catecholamine release and its mechanism of action. For this purpose, using cultured bovine adrenal chromaffin cells, we examined the effects of hypoxia on high (55 mM) K+‐induced increases in catecholamine release, in cytosolic free Ca2+concentration ([Ca2+]i), and in45Ca2+uptake. Experiments were carried out in media pre‐equilibrated with a gas mixture of either 21% O2/79% N2(control) or 100% N2(hypoxia). High K+‐induced catecholamine release was inhibited by hypoxia to ∼40% of the control value, but on reoxygenation the release returned to control levels. Hypoxia had little effect on ATP concentrations in the cells. In the hypoxic medium, [Ca2+]i(measured using fura‐2) gradually increased and reached a plateau of ∼1.0 μMat 30 min, whereas the level was constant in the control medium (∼200 nM). High K+‐induced increases in [Ca2+]Iwere inhibited by hypoxia to ∼30% of the control value. In the cells permeabilized by digitonin, catecholamine release induced by Ca2+was unaffected by hypoxia. Hypoxia had little effect on basal45Ca2+uptake into the cells, but high K+‐induced45Ca2+uptake was inhibited by hypoxia. These results suggest that hypoxia inhibits high K+‐induced catecholamine release and that this inhibition is mainly the result of the inhibition of high K+‐induced increases in [Ca2+]isubsequent to the inhibition of Ca2+influx through voltag

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb03115.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:In this report, we show that under conditions designed to provide an initially uniform incorporation of [3H]inositol into mouse and guinea pig cerebral cortical slices prior to agonist stimulation, the accumulation of3H‐inositol phosphates (3H‐InsPx, x = 1–4) induced by histamine in mouse and guinea pig cerebral cortical slices increased in a quasilinear manner with increasing added calcium. Raising the ambient calcium ion concentration failed to reduce the adenosine receptor‐mediated inhibition of the histamine‐induced3H‐InsPxresponse in mouse cerebral cortical slices. Similarly, the potentiation of the histamine response by adenosine receptor activation in guinea pig cerebral cortical slices was unaffected by lowering the added calcium ion concentration. The presence of the calcium ionophore A23187 (33 μM) produced3H‐InsPxresponses in both mouse and guinea pig cerebral cortical slices, which were not affected by the presence of the stable adenosine analogue 2‐chloroadenosine. A23187 also potentiated the accumulation of3H‐InsPxinduced by histamine in both species. Both the inhibitory and potentiatory modulations of the histamine response by 2‐chloroadenosine in mouse and guinea pig, respectively, were still apparent in the presence of A23187. These results indicate that the histamine‐induced3H‐InsPxaccumulations in both mouse and guinea pig cerebral cortical slices are sensitive to variations in calcium ion concentrations. However, the adenosine receptor modulations of the histamine responses are relatively insensitive to fluctuations in either extra‐or intracellular calcium ion concentrations, and thus cannot be mediated by effect

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb03116.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:After a relatively mild course of uncontrollable shocks, two distinct groups of rats can be defined in terms of their performance in learning to escape from a controllable stressor. Response‐deficient (RD) rats do not learn to terminate the controllable stressor, whereas nondeficient (ND) rats learn this response as readily as do untreated control rats. The current studies were designed to determine the neu‐rochemical correlates of the behavioral differences between these groups of rats. The major findings concerned postsyn‐aptic β‐adrenergic effects in the hippocampus of RD rats. These included an up‐regulation of β‐adrenergic receptors and, in parallel experiments, an increase in the sensitivity of adenylyl cyclase to stimulation by norepinephrine. There was no difference in brain levels of catecholamines between the three groups of rats. A statistically significant increase in levels of 5‐hydroxytryptamine was noted in the hippocampus and hypothalamus of RD rats as compared to levels in ND rats, but no significant differences were measured between groups of rats in terms of S1or S2serotonergic receptor binding. These results implicate both β‐adrenergic and serotonergic mechanisms in the behavioral deficit caused by un

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb03117.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:Vasoactive intestinal peptide (VIP) is known to mimic the effects of β‐adrenergic receptor stimulation in the rat pineal, including marked potentiation by α1‐adrenergic receptor stimulation, and to cause increased melatonin synthesis. In contrast, the chick pineal does not respond to β‐adrenergic stimulation, and melatonin synthesis is inhibited by norepinephrine via an α2‐adrenergic receptor. The present experiments show that chick pineal cells in primary culture do, however, respond to VIP with increased melatonin production. The effect of VIP was inhibited by addition of norepinephrine or of nitrendipine or by exposing the cells to “unexpected” white light. Stimulation by VIP was enhanced by addition of forskolin or Bay K 8644 but not by α1adrenergic receptor stimulation. Although stimulation by VIP appears similar in the chick pineal to that seen in the rat pineal and other systems, “dual‐receptor regulation,” at least with α1‐adrenergic recept

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb03118.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:Using antibodies raised against human platelet phenol sulfotransferase (PST), immunohistochemical studies were performed to determine the cellular localization of PST in several areas of human brain. In the hippocampus PST immunoreactivity was localized in both the pyramidal and nonpyramidal neurons and was in greatest abundance in the CA2 and CA3 areas. In the striatum the immunoreactivity was most predominant in the large neurons of the globus pallidus and in the medulla the staining was scattered throughout the neurons of the raphe nucleus and the reticular formation. The selective presence of PST in the neurons of the CNS raises the issue as to the role of this enzyme in sulfating neurotransmitters because PST has been shown to be capable of conjugating a variety of neurotransmitters including the catecholamines as well as the tyrosine moiety of a number of small peptides such as enkephalin and cholecystokinin.

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb03119.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY