共查询到20条相似文献,搜索用时 31 毫秒
1.
Fumi Katoh Kazuo Kitamura Hiromi Niina Ryuichi Yamamoto Hisanori Washimine †Kenji Kangawa Yoshitaka Yamamoto Hideyuki Kobayashi Tanenao Eto Akihiko Wada 《Journal of neurochemistry》1995,64(1):459-461
Abstract: In cultured bovine adrenal medullary cells, stimulation of nicotinic receptors by carbachol evoked the Ca2+ -dependent exocytotic cosecretion of proadrenomedullin N-terminal 20 peptide (PAMP) (EC50 = 50.1 µ M ) and catecholamines (EC50 = 63.0 µ M ), with the molar ratio of PAMP/catecholamines secreted being equal to the ratio in the cells. Addition of PAMP[1–20]NH2 inhibited carbachol-induced 22 Na+ influx via nicotinic receptors (IC50 = 2.5 µ M ) in a noncompetitive manner and thereby reduced carbachol-induced 45 Ca2+ influx via voltage-dependent Ca2+ channels (IC50 = 1.0 µ M ) and catecholamine secretion (IC50 = 1.6 µ M ). It did not alter high K+ -induced 45 Ca2+ influx via voltage-dependent Ca2+ channels or veratridine-induced 22 Na+ influx via voltage-dependent Na+ channels. PAMP seems to be a novel antinicotinic peptide cosecreted with catecholamines by a Ca2+ -dependent exocytosis in response to nicotinic receptor stimulation. 相似文献
2.
Abstract: The excitatory amino acid analogues l -glutamate ( l -Glu), l -aspartate ( l -Asp), d -Asp, and trans -(±)-1-amino-1,3-cyclopentanedicarboxylate ( trans -ACPD) stimulate the hydrolysis of phosphoinositides (PI). In the present studies, the effects of noncompetitive and competitive inhibitors on PI hydrolysis stimulated by excitatory amino acid analogues were examined. When agonist and inhibitor were added simultaneously to hippocampal tissue, the noncompetitive inhibitor l -2-amino-3-phosphonopropionate ( l -AP3) did not block the effects of l -Glu, l -Asp, or d -Asp at concentrations that block the effects of trans -ACPD by more than 80%. When tissue was pre-incubated with l -AP3, the effects of l -Glu, l -Asp, or d -Asp were blocked (IC50 values between 65 and 210 µ M ). Unlike l -AP3, l -aspartate-β-hydroxamate ( l -AβHA) inhibited PI hydrolysis stimulated by trans -ACPD, l -Glu, l -Asp, or d -Asp when agonist and inhibitor were added simultaneously in hippocampus; its effects were not time-dependent. In cerebellum, both l -AP3 and l -AβHA had agonist activity. Inhibition by the recently identified competitive inhibitor (+)-α-methyl-4-carboxyphenylglycine [(+)-MCPG] of PI hydrolysis was also examined. (+)-MCPG blocked PI hydrolysis stimulated by trans -ACPD, l -Asp, or d -Asp in both hippocampus and cerebellum (IC50 values between 220 and 1,700 µ M ). The effects of (+)-MCPG were consistent with a competitive mechanism of action. (+)-MCPG (up to 3 m M ) blocked PI hydrolysis stimulated by l -Glu by less than 25% in both hippocampus and cerebellum. 相似文献
3.
Dean C. Crick Julie Suders Catherine M. Kluthe Douglas A. Andres Charles J. Waechter 《Journal of neurochemistry》1995,65(3):1365-1373
Abstract: The effect of squalestatin 1 (SQ) on squalene synthase and other enzymes utilizing farnesyl pyrophosphate (F-P-P) as substrate was evaluated by in vitro enzymological and in vivo metabolic labeling experiments to determine if the drug selectively inhibited cholesterol biosynthesis in brain cells. Direct in vitro enzyme studies with membrane fractions from primary cultures of embryonic rat brain (IC50 = 37 n M ), pig brain (IC50 = 21 n M ), and C6 glioma cells (IC50 = 35 n M ) demonstrated that SQ potently inhibited squalene synthase activity but had no effect on the long-chain cis -isoprenyltransferase catalyzing the conversion of F-P-P to polyprenyl pyrophosphate (Poly-P-P), the precursor of dolichyl phosphate (Dol-P). SQ also had no effect on F-P-P synthase; the conversion of [3 H]F-P-P to geranylgeranyl pyrophosphate (GG-P-P) catalyzed by partially purified GG-P-P synthase from bovine brain; the enzymatic farnesylation of recombinant H-p21 ras by rat brain farnesyltransferase; or the enzymatic geranylgeranylation of recombinant Rab1A, catalyzed by rat brain geranylgeranyltransferase. Consistent with SQ selectively blocking the synthesis of squalene, when C6 glial cells were metabolically labeled with [3 H]mevalonolactone, the drug inhibited the incorporation of the labeled precursor into squalene and cholesterol (IC50 = 3–5 µ M ) but either had no effect or slightly stimulated the labeling of Dol-P, ubiquinone (CoQ), and isoprenylated proteins. These results indicate that SQ blocks cholesterol biosynthesis in brain cells by selectively inhibiting squalene synthase. Thus, SQ provides a useful tool for evaluating the obligatory requirement for de novo cholesterol biosynthesis in neurobiological processes without interfering with other critical reactions involving F-P-P. 相似文献
4.
Sarah Grimwood Elizabeth Gilbert C. Ian Ragan Peter H. Hutson 《Journal of neurochemistry》1996,66(6):2589-2595
Abstract: A 45 Ca2+ influx assay has been used to investigate the pharmacology of stably expressed recombinant human NR1a/NR2A and NR1a/NR2B N -methyl- d -aspartate (NMDA) receptors. Inhibition of glutamate-stimulated 45 Ca2+ influx by six glycine-site antagonists and inhibition of glycine-stimulated 45 Ca2+ influx by five glutamate-site antagonists revealed no significant differences between affinity values obtained for NR1a/NR2A and NR1a/NR2B receptors. The polyamine site agonist spermine showed differential modulation of glutamate- and glycine-stimulated 45 Ca2+ influx for recombinant NMDA receptors, inhibiting and stimulating 45 Ca2+ influx into cells expressing NR1a/NR2A receptors (IC50 = 408 µ M ) and NR1a/NR2B receptors (EC50 = 37.3 µ M ), respectively. The antagonist ifenprodil was selective for NR1a/NR2B receptors (IC50 = 0.099 µ M ) compared with NR1a/NR2A receptors (IC50 = 164 µ M ). The effects of putative polyamine site antagonists, redox agents, ethanol, and Mg2+ and Zn2+ ions were also compared between NR1a/NR2A and NR1a/NR2B receptors. This study demonstrates the use of 45 Ca2+ influx as a method for investigating the pharmacology of the numerous modulatory sites that regulate the function of recombinant human NMDA receptors stably expressed in L(tk-) cells. 相似文献
5.
Ryoichi Ishitani Mitsutoshi Kimura Masami Takeichi De-Maw Chuang 《Journal of neurochemistry》1994,63(6):2080-2085
Abstract: Tryptamine dose-dependently increased phosphoinositide (PI) hydrolysis by approximately fourfold in primary cultures of rat cerebellar granule cells (EC50 = 56 µ M ). The PI response stimulated by tryptamine was dependent on the presence of extracellular Ca2+ and Na+ . Tryptamine-induced PI breakdown could be partially inhibited by pretreatment with 4β-phorbol 12-myristate 13-acetate but not pertussis toxin. The presence of tryptamine markedly attenuated PI responses induced by norepinephrine (NE) and carbachol, with no apparent effect on the responses to 5-hydroxytryptamine and glutamate. The inhibition of NE- and carbachol-induced PI turnover by tryptamine was dose dependent with IC50 values of ∼0.4 and ∼2.5 m M , respectively. Pretreatment of cells with tryptamine (0.5 m M ) also attenuated NE- and carbachol-induced PI turnover, but failed to affect 5-hydroxytryptamine- and glutamate-induced responses. Furthermore, ketanserin, atropine, and prazosin did not have any effect on inositol phosphate formation induced by tryptamine. These observations indicate that tryptamine markedly increased Ca2+ - and Na+ -dependent PI turnover in cerebellar neurons and selectively inhibited NE- and carbachol-induced PI hydrolysis. 相似文献
6.
Abstract: Termination of synaptic glutamate transmission depends on rapid removal of glutamate by neuronal and glial high-affinity transporters. Molecular biological and pharmacological studies have demonstrated that at least five subtypes of Na+ -dependent mammalian glutamate transporters exist. Our study demonstrates that Y-79 human retinoblastoma cells express a single Na+ -dependent glutamate uptake system with a K m of 1.7 ± 0.42 µ M that is inhibited by dihydrokainate and dl - threo -β-hydroxyaspartate (IC50 = 0.29 ± 0.17 µ M and 2.0 ± 0.43 µ M , respectively). The protein kinase C activator phorbol 12-myristate 13-acetate caused a concentration-dependent inhibition of glutamate uptake (IC50 = 0.56 ± 0.05 n M ), but did not affect Na+ -dependent glycine uptake significantly. This inhibition of glutamate uptake resulted from a fivefold decrease in the transporter's affinity for glutamate, without significantly altering the V max . 4α-Phorbol 12,13-didecanoate, a phorbol ester that does not activate protein kinase C, did not alter glutamate uptake significantly. The phorbol 12-myristate 13-acetate-induced inhibition of glutamate uptake was reversed by preincubation with staurosporine. The biophysical and pharmacological profile of the human glutamate transporter expressed by the Y-79 cell line indicates that it belongs to the dihydrokainate-sensitive EAAT2/GLT-1 subtype. This conclusion was confirmed by western blot analysis. Protein kinase C modulation of glutamate transporter activity may represent a mechanism to modulate extracellular glutamate and shape postsynaptic responses. 相似文献
7.
D. R. Gehlert D. A. Schober P. A. Hipskind B. D. Gitter J. J. Howbert 《Journal of neurochemistry》1996,66(3):1095-1102
Abstract: We synthesized a potent and selective antagonist radioligand for the neurokinin (NK)-1 receptor and characterized its binding to guinea pig striatal membranes. ( R ) - N - [2 - [Acetyl[3 H3 ][(2 - methoxyphenyl) - methyl]amino] - 1 - (1 H - indol - 3 - ylmethyl)ethyl][1,4' - bipiperidine]-1'-acetamide ([3 H]LY303870) binds to a single class of sites with an equilibrium K D of 0.22 n M and a B max of 723 fmol/mg of protein. Unlabeled LY303870 potently inhibited the binding with an IC50 of 0.56 n M , whereas the less active ( S )-enantiomer (LY306155) was substantially less potent. The nonpeptide NK-1 antagonists (±)-CP96,345 and (±)-RP 67580 had IC50 values of 0.74 and 49 n M , respectively. Substance P (SP) was also a potent inhibitor with with an IC50 of 3.1 n M . The inhibition by SP could be separated into two components: a high-affinity component with a K i of 0.53 n M and a lower-affinity component with a K i of 155 n M . Addition of 100 µ M guanylyl 5'-imidodiphosphate [Gpp(NH)p] in the incubation increased the relative amount of the low-affinity agonist state of the receptor. Consistent with the antagonist properties of LY303870, the dissociation rate of [3 H]LY303870 was not changed by the presence of 100 µ M Gpp(NH)p. The distribution of [3 H]LY303870 binding sites in the guinea pig brain closely matched the distribution of NK-1 receptors labeled by [3 H]SP. Therefore, [3 H]LY303870 is a potent and selective antagonist radioligand for NK-1 receptors in guinea pig brain. In addition, regulation of NK-1 agonist affinity by guanine nucleotides is similar to that seen for monoaminergic receptors. 相似文献
8.
Dopamine Neurotoxicity: Inhibition of Mitochondrial Respiration 总被引:15,自引:6,他引:9
Abstract: Dopamine, due to metabolism by monoamine oxidase or autoxidation, can generate toxic products such as hydrogen peroxide, oxygen-derived radicals, semiquinones, and quinones and thus exert its neurotoxic effects. Intracerebroventricular injection of dopamine into rats pretreated with the monoamine oxidase nonselective inhibitor pargyline caused mortality in a dose-dependent manner with LD50 = 90 µg. Norepinephrine was less effective with LD50 = 141 µg. The iron chelator desferrioxamine completely protected against dopamine-induced mortality. In the absence of pargyline more rats survived, indicating that the products of dopamine enzymatic metabolism are not the main contributors to dopamine-induced toxicity. Biochemical analysis of frontal cortex and striatum from rats that received a lethal dose of dopamine did not show any difference from control rats in lipid and protein peroxidation and glutathione reductase and peroxidase activities. Moreover, dopamine significantly reduced the formation of iron-induced malondialdehyde in vitro, thus suggesting that earlier events in cell damage are involved in dopamine toxicity. Indeed, dopamine inhibited mitochondrial NADH dehydrogenase activity with IC50 = 8 µ M , and that of norepinephrine was twice as much (IC50 = 15 µ M ). Dopamine-induced inhibition of NADH dehydrogenase activity was only partially reversed by desferrioxamine, which had no effect on norepinephrine-induced inhibition. These results suggest that catecholamines can cause toxicity not only by inducing an oxidative stress state but also possibly through direct interaction with the mitochondrial electron transport system. The latter was further supported by the ability of ADP to reverse dopamine-induced inhibition of NADH dehydrogenase activity in a dose-dependent manner. 相似文献
9.
Di- n -butyl phthalate (DBF) is widely used as a plasticizer and has been found in all types of ecosystems. It inhibits growth and photosynthesis of green algae ( Chlorella emersonii CCAP strain 211/8 h and Selenastrum capricornutum CCAP strain 278/4) at concentrations higher than 10-5 M . The IC50 value for CO2 -dependent oxygen evolution in algae was 3 × 10-4 M. The CO2 -reduction in isolated protoplasts prepared from barley ( Hordeum vulgare L. cv. Simba) was also inhibited by phthalate. The IC50 value was 2 × 10-4 M . The electron transport in isolated thylakoids prepared from spinach was inhibited with an IC50 value of 3 × 10-4 M . The IC50 value for uncoupled electron transport extrapolated to zero chlorophyll concentration was 2.5 × 10-5 M . The effect of di-n-butyl phthalate was localized to reactions in photosystem II. Di-n-butyl phthalate could thus be a pollutant which affects growth and photosynthesis of plants. The reported IC50 values may be underestimated since di- n -butyl phthalate can attach to surfaces. The results are discussed in relation to observed effects of di- n -butyl phthalate on other organisms. 相似文献
10.
M. J. Oset-Gasque M. Parramón S. Hortelano L. Boscá M. P. González 《Journal of neurochemistry》1994,63(5):1693-1700
Abstract: In this work, we have studied the effects of pure nitric oxide (NO) on the regulation of catecholamine (CA) secretion by chromaffin cells, as well as the possible presence of its synthesizing enzyme l -arginine:NO synthase (NOS) in these cells. Our results show that NO produces a large stimulation of basal CA secretion. This effect was calcium- and concentration-dependent (EC50 = 64 ± 8 µ M ) and was not due to nonspecific damage of the tissue by NO. NO also modulates the CA secretion evoked by nicotine in a dose-dependent manner. Although it has a stimulatory effect on the CA secretion evoked by low doses of nicotine (<3 µ M ; EC50 = 16 ± 3 µ M ), it produces a dose-dependent inhibition of the CA secretion induced by high doses of nicotine (≥30 µ M ; IC50 = 52 ± 6 µ M ). The mechanism by which NO modulates CA secretion seems to be through the increase in the cyclic GMP levels, because there was a close correlation between the CA secretion and the cyclic GMP levels. The presence of a specific activity of NOS in chromaffin cells has been demonstrated by two independent methods: release of [14 C]citruiline from [14 C]arginine and formation of an NO-hemoglobin complex. NOS activity was about 0.5 pmol/min/mg of protein. It was calcium- and mainly calmodulin-dependent and could be specifically blocked by the NOS inhibitor N -methyl- l -arginine. These results suggest that NO could be an important intracellular messenger in the regulation of neurosecretion in chromaffin cells. 相似文献
11.
Anti-Candida activity of four antifungal benzothiazoles 总被引:1,自引:0,他引:1
Helena Bujdáková Tomá Kuchta Eva Sidóová Anna Gvozdjaková 《FEMS microbiology letters》1993,112(3):329-334
Abstract Anti- Candida activity of 6-amino-2- n -pentylthiobenzothiazole (I), benzylester of (6-amino-2-benzothiazolylthio)acetic acid (II) and of 3-butylthio-(1,2,4-triazolo)-2,3-benzothiazole (III) was followed and compared to that of 2-mercaptobenzothiazole (IV). I and II exhibited good activity against the C. albicans yeast form, similar to IV. They were inhibitorily active against other Candida strains, IC50 values being of the order of 10−5 M, which means better activity than IV. Compound I also exhibited inhibitory activity on germ-tube formation and mycelial growth in the C. albicans strains, while II, III and IV were not active in these tests. III was the least active form of the compounds tested, IC50 values being of the order of 10−4 M. All the compounds tested were highly active on a nystatin-resistant C. albicans mutant, with IC50 s of the order of 10−6 M−10−5 M. 相似文献
12.
Possible Mechanism of Dantrolene Stabilization of Cultured Neuroblastoma Cell Plasma Membranes 总被引:2,自引:0,他引:2
Teruo Hayashi Ariyuki Kagaya Nobutaka Motohashi Shigeto Yamawaki 《Journal of neurochemistry》1994,63(5):1849-1854
Abstract: Some reports have suggested that dantrolene interacts directly with the membrane bilayer. We investigated effects of dantrolene on changes in membrane properties induced by compound 48/80 (C48/80), a membrane stimulator. The addition of C48/80 for 1 min elicited a rapid, dose-dependent Ca2+ influx, which was reduced to 14% by the absence of external Ca2+ . Dantrolene inhibited the C48/80-induced increase in Ca2+ permeability of plasma membranes in a concentration-dependent manner (0.33–10 µ M , IC50 value was 5 µ M ). We next examined C48/80-induced changes in structural and dynamic membrane properties by electron spin resonance (ESR). The ratio h 0 / h −1 was determined to evaluate membrane fluidity. C48/80 increased the membrane fluidity in a concentration-dependent manner (0.1–0.56 mg/ml). Dantrolene (10 µ M ) itself did not change the membrane fluidity, but it significantly reduced the C48/80-induced increase in membrane fluidity (0.56 mg/ml). Moreover, the C48/80-induced increase in fluidity was dependent on extracellular Ca2+ . We conclude that dantrolene protects neuroblastoma cell plasma membrane from C48/80-induced membrane perturbation, which causes Ca2+ influx and an increase in membrane fluidity. These findings strongly suggest that dantrolene directly stabilizes the neuronal plasma membrane. 相似文献
13.
Abstract: The influence of putrescine, spermidine, spermine, and some aliphatic α,ω-diamines on the uptake of neurotransmitters by rat forebrain synaptosomes was investigated. Choline uptake was most effectively inhibited by spermine (IC50 = 0.22 m M ), less so by spermidine (IC50 = 4.0 m M ), but not by putrescine (IC50 > 100 m M ). At 10 m M, 1,3-diaminopropane, cadaverine, and 1,8-diaminooctane all inhibited choline uptake by 50% or more. Spermine and spermidine inhibited the uptake of dopamine with IC50 values of 2.7 and 2.2 m M , respectively. Putrescine was only slightly inhibitory (IC50 = 17.3 m M ) and the other diamines were inactive. The uptake of γ-aminobutyrate (GABA) was only slightly inhibited (15–40%) by the polyamines at 10 m M . With the exception of inhibition of glycine uptake by 1,8-diaminooctane (60%) and of glutamate uptake by cadaverine (35%) none of the polyamines, tested at 10 m M , affected the uptake of adenosine, glutamate, and glycine significantly. A possible modulatory role for polyamines in synaptic transmission through interaction by negatively charged groups of the synaptic membrane with the polycationic compounds is discussed. 相似文献
14.
Simon V. Avery Marvin E. Miller Geoffrey M. Gadd Geoffrey A. Codd Joseph J. Cooney 《FEMS microbiology letters》1991,84(2):205-210
Abstract Inhibition of photosynthesis by a range of organotin compounds in Plectonema boryanum was concentration-dependent and decreased in the order tributyltin (Bu3 SnCl) > tripropyltin (Pr3 SnCl) ≥ dibutyltin (Bu2 SnCl2 ) ≥ triphenyltin (Ph3 SnCl) > triethyltin (Et3 SnCl) > trimethyltin (Me3 SnCl) > monobutyltin (BuSnCl3 ). IC50 values were determined for the most toxic organotin species and varied from approximately 1.2 μM for Bu3 SnCl to approximately 13 μM for Ph3 SnCl. A similar order of inhibition of photosynthesis was observed in Anabaena cylindrica , although here IC50 values were slightly lower (e.g. approximately 1 μM for Bu3 SnCl and 5 μM for Ph3 SnCl).Nitrogenase activity was generally more sensitive to inhibition by organotin compounds than photosynthesis in A. cylindrica and this was particularlyy evident for Bu2 SnCl2 ; approximate IC50 values for Bu2 SnCl2 were 3 and 9 μM, as estimated by nitrogenase activity and photosynthesis, respectively. These results indicate that organotin compounds have the potential to inhibit cyanobacterial metabolism in aquatic systems. 相似文献
15.
Giudici AM Regente MC Villalaín J Pfüller K Pfüller U De La Canal L 《Physiologia plantarum》2004,121(1):2-7
Viscotoxins (Vts) are basic peptides expressed in mistletoe leaves, seeds and stems which have been shown to be cytotoxic to mammalian cells. The aim of this study was to analyse whether Vts were able to control and/or inhibit the growth of phytopathogenic fungi to obtain a clue to their biological function. Incubation of two Vt isoforms, VtA3 and VtB, at a final concentration of 10 µ M resulted in a complete blockage of the germination of spores from three different pathogenic fungi. It was also shown that lower concentrations than 10 µ M of VtA3 and VtB inhibit their mycelial growth in a dose-dependent manner. The protein dose required to inhibit the growth of Fusarium solani and Sclerotinia sclerotiorum to a 50% was between 1.5 and 3.75 µ M , which represents a potent activity. No significant differences in the antifungal potency for each Vt isoform, either VtA3 and VtB, were observed, although they have been shown to exert differential cytotoxicity on mammalian cells. It was also demonstrated that Vts act as fungicidal compounds. To explore the basis of the antifungal activity the ability of VtA3 to induce changes in membrane permeability and on the oxidative status of F. solani spores was analysed. By using a specific fluorescent probe on intact spores, it was demonstrated that VtA3 produces rapid changes in fungal membrane permeability. It also induces H2 O2 production verified by a histochemical staining. The data presented in this study support a direct role of Vts in the plant defence determined by their lethal effect on fungal pathogens. 相似文献
16.
Catherine Van Renterghem Paul Vigne Christian Frelin 《Journal of neurochemistry》1995,65(3):1274-1281
Abstract: A charybdotoxin-sensitive, Ca2+ -activated K+ channel was identified in cultured rat brain capillary endothelial cells by using conventional single-channel recording techniques and 86 Rb+ -influx and efflux experiments. Channel activity was dependent on the presence of Ca2+ on the cytosolic face of the membrane with a threshold concentration of 100 n M . It was inhibited by charybdotoxin (IC50 30 n M ) and quinine (IC50 0.1 m M ) but not by apamin. K(Ca) channels showed unusual inward rectifying properties under asymmetrical ionic conditions. They were activated by endothelin-1 (EC50 0.7 n M ) and endothelin-3 (EC50 7–10 n M ). The actions of endothelins were prevented by BQ-123 ( K i = 8 n M ) in a competitive fashion, hence suggesting the involvement of an ETA -receptor subtype. The channel activity was unaffected by cyclic AMP- or cyclic GMP-elevating agents. The possible role of the intermediate conductance, Ca2+ -activated K+ channels for mediating K+ movements across the blood-brain barrier is discussed. 相似文献
17.
Kari R. Hoyt Sunita Rajdev Cheryl L. Fattman Ian J. Reynolds 《Journal of neurochemistry》1995,64(5):2049-2056
Abstract: We investigated the modulation of (±)-α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-induced increases in intracellular free Ca2+ ([Ca2+ ]i ) and intracellular free Mg2+ ([Mg2+ ]i ) by cyclothiazide and GYKI 52466 using microspectrofluorimetry in single cultured rat brain neurons. AMPA-induced changes in [Ca2+ ]i were increased by 0.3–100 µ M cyclothiazide, with an EC50 value of 2.40 µ M and a maximum potentiation of 428% of control values. [Ca2+ ]i responses to glutamate in the presence of N -methyl- d -aspartate (NMDA) receptor antagonists were also potentiated by 10 µ M cyclothiazide. The response to NMDA was not affected, demonstrating specificity of cyclothiazide for non-NMDA receptors. Almost all neurons responded with an increase in [Ca2+ ]i to both kainate and AMPA in the absence of extracellular Na+ , and these Na+ -free responses were also potentiated by cyclothiazide. GYKI 52466 inhibited responses to AMPA with an IC50 value of 12.0 µ M . Ten micromolar cyclothiazide significantly decreased the potency of GYKI 52466. However, the magnitude of this decrease in potency was not consistent with a competitive interaction between the two ligands. Cyclothiazide also potentiated AMPA- and glutamate-induced increases in [Mg2+ ]i . These results are consistent with the ability of cyclothiazide to decrease desensitization of non-NMDA glutamate receptors and may provide the basis for the increase in non-NMDA receptor-mediated excitotoxicity produced by cyclothiazide. 相似文献
18.
Neil A. Turner John H. Walker Stephen G. Ball Peter F. T. Vaughan 《Journal of neurochemistry》1996,66(6):2381-2389
Abstract: The effect of inhibition and down-regulation of protein kinase C (PKC) subtypes α, ε, and ζ on noradrenaline (NA) secretion from human SH-SY5Y neuroblastoma cells was investigated. The PKC inhibitor Ro 31-7549 inhibited carbachol-evoked NA release (IC50 0.6 µ M ) but not 100 m M K+ -evoked release. In addition, Ro 31-7549 inhibited the enhancement of carbachol- and K+ -evoked release after pretreatment with 12- O -tetradecanoylphorbol 13-acetate (TPA; 100 n M ) for 8 min, with IC50 values of 0.7 and 2.4 µ M , respectively. Immunoblotting studies showed that prolonged exposure (48 h) of SH-SY5Y cells to phorbol 12,13-dibutyrate (PDBu) or bryostatin-1 caused down-regulation of PKC-α and PKC-ε but not PKC-ζ. Under these conditions, the acute TPA enhancement of NA release was inhibited. Moreover, the inhibition of TPA-enhanced secretion was also apparent after only 2-h exposure to either PDBu or bryostatin-1, conditions that caused down-regulation of PKC-α, but not PKC-ε or ζ. The PKC inhibitor Gö-6976 (2 µ M ), which has been shown to inhibit selectively PKC-α and β in vitro, also inhibited the TPA enhancement of carbachol- and K+ -evoked NA release by >50%. These data suggest that in SH-SY5Y cells, the ability of TPA to enhance carbachol- and K+ -evoked NA secretion is due to activation of PKC-\ga. 相似文献
19.
C. Mark Richardson Michael J. Dowdall A. Chris Green David Bowman 《Journal of neurochemistry》1995,64(2):944-947
Abstract: The presynaptic terminals of skate ( Raja montagui ) electric organ were tested for their sensitivity to calcium channel antagonists. Acetylcholine (ACh) release and the elevation of intraterminal Ca2+ concentrations triggered by K+ depolarisation were studied. ACh release was measured as 3 H efflux from slices of organ prelabelled with [3 H]choline. Depolarisation caused a marked, Ca2+ -dependent increase in 3 H efflux that was completely blocked by 100 µ M Cd2+ and by 300 n M ω-conotoxin-MVIIC (MVIIC). Inhibition by MVIIC was concentration dependent (IC50 of ∼20 n M ) and reversible. No inhibition was seen with nifedipine (5 µ M ) or the two other peptide antagonists studied: ω-conotoxin-GVIA (GVIA) at 5 µ M and ω-agatoxin-IVA (Aga-IVA) at 1 µ M . In a "nerve plate" preparation (a presynaptic plexus of nerve fibres, Schwann cells, and nerve terminals) changes in intraterminal Ca2+ concentrations were measured by microfluorimetry using fluo-3. An increase in fluorescence, indicating a rise in the free [Ca2+ ], rapidly followed K+ depolarisation, and this change was restricted to the nerve terminals. This response was insensitive to nifedipine (5 µ M ), GVIA (5 µ M ), and Aga-IVA (300 n M ) but almost completely abolished by MVIIC (1 µ M ). MVIIC inhibition was concentration dependent and partially reversible. These results show that the nerve terminals in skate electric organ have calcium channels with a pharmacological sensitivity that is markedly different from the established L, N, and P types in other systems but shares some, but not all, of the features of the recently described Q type. 相似文献
20.
Effect of Inhibitors of GABA Transaminase on the Synthesis, Binding, Uptake and Metabolism of GABA 总被引:15,自引:10,他引:5
W. Löscher 《Journal of neurochemistry》1980,34(6):1603-1608
Abstract: Four catalytic inhibitors of GABA aminotransferase (gabaculine, γ-acetylenic GABA, γ-vinyl GABA, ethanolamine O -sulphate) as well as aminooxyacetic acid and valproate were studied for effects on neurochemical assays for GABA synthesis, receptor binding, uptake and metabolism in mouse and rat brain preparations. Gabaculine did not interfere with GABA synthesis as reflected by the activity of glutamate decarboxylase (GAD), it was only a weak inhibitor (IC50 = 0.94 mM) of GABA receptor binding sites but was a moderately potent inhibitor of GABA uptake (IC50 = 81 μM) and very potent (IC50 = 1.8 μM) with respect to inhibition of the GABA-metabolizing enzyme GABA aminotransferase (GABA-T). γ-Acetylenic GABA was a weak inhibitor of GAD and GABA binding (IC50 > 1 mM), but virtually equipotent to inhibit uptake and metabolism of GABA (IC50 560 and 150 μM, respectively). This was very similar to γ-vinyl GABA, except that this drug did not decrease GAD activity. Ethanolamine O -sulphate was found to show virtually no inhibition of GAD and GABA uptake, but was a fairly potent inhibitor of GABA binding (IC50 = 67 μM) and in this respect, 500 times more potent than as an inhibitor of GABA-T. Aminooxyacetic acid was a powerful inhibitor of both GAD and GABA-T (IC50 14 and 2.7 μM, respectively), but had very little affinity to receptor and uptake sites for GABA. Valproate showed no effects on GABA neurochemical assays which could be related to anticonvulsant action. The present results suggest that the anticonvulsant properties of the four catalytic inhibitors of GABA-T tested are at least in part mediated through a direct influence on GABA receptors and uptake sites. 相似文献