胞内储备钙参与3,4—二氨基吡啶诱发去甲肾上腺素释放

目的：用大鼠海马脑片研究３，４－二氨基吡啶（ＤＡＰ）诱发去甲肾上腺素胞外钙－不依赖释放的机制，方法：大鼠海马脑片用（＾３Ｈ）ＮＥ孵育后，进行表面灌流，测（＾３Ｈ）ＮＥ释放。结果：在胞外无镍条件下，ＤＡＰ能显著加强（＾３Ｈ）ＮＥ释放，当用利血平使囊泡（＾３Ｈ）ＮＥ排空，则ＤＡＰ作用消失，用高浓度地昔帕明刺激ＩＰ３－敏感的胞内Ｃａ＾２＋储备库，能有力地增强（＾３Ｈ）ＮＥ释放，而高浓度咖啡因对（＾３Ｈ）     

胞内储备钙参与3,4-二氨基吡啶诱发去甲肾上腺素释放(英文)

目的:用大鼠海马脑片研究3,4-氨基吡啶(DAP)诱发去甲肾上腺素胞外钙-不依赖释放的机制。方法:大鼠海马脑片用[~3H]NE孵育后,进行表面灌流,测[~3H]NE释放。结果:在胞外无钙条件下,DAP能显著加强[~3H]NE释放,当用利血平使囊泡[~3H]NE排空,则DAP作用消失,用高浓度地昔帕明刺激IP_3-敏感的胞内Ca~(2 )储备库,能有力地增强[~3H]NE释放,而高浓度咖啡因对[~3H]NE释放只有很微弱的作用,丹曲林钠对DAP诱发[~3H]NE释放无任何抑制作用。结论:在胞外无钙条件下,DAP通过IP_3-敏感的Ca~(2 )储备库释放Ca~(2 ),从而诱发囊泡内的去甲肾上腺素释放。     

4—氨基吡啶和3,4—二氨基吡啶对兔实验自身免疫重症肌无力的治疗

以Ｎ－ＡＣｈＲ膜微囊免疫家兔，造成重症肌无力模型，ｉｖ４－ＡＰ０．８ｍｇ．ｋｇ＾－１后病兔的肌无力症状迅速缓解。以４ＨＺ电流刺激坐骨神经，腓肠肌复合肌电位和足趾收缩即由递减变为整齐；５０ＨＺ电流引起的强直收缩能保持。作用维持９．１±２．５ｈ。ｉｖ３，４－ＤＡＲ０．４ｍｇ．ｋｇ＾－１可获相似效果，持续９．３±３．１ｈ，两药有明显的对症治疗作用。     

3,4-二氨基吡啶易化鸡胚交感神经元去甲肾上腺素释放(英文)

目的:用鸡胚交感神经元研究3,4-二氨基吡啶(DAP)易化电刺激诱发[~3H]NE释放的机制. 方法:用[~H]NE或fura-2孵育神经元,测[~H]NE释放或[Ca~(2 )]_i. 结果:电刺激诱发[~3H]NE释放和[Ca~(2 )]_i升高被ω-conotoxine GVIA (CTX)抑制,被(—)isradipine(Isp)减弱,被Bay k 8644加强.当3,4-二氨基吡啶(DAP)存在时,电刺激诱发[~3H]NE释放被易化,这时CTX的作用减弱,Isp的作用增强,Bay k 8644不再显示作用. 结论:DAP对电刺激诱发[~3H]NE释放的易化作用,可能是通过L-型Ca~(2 )通道而实现的.     

3，4—二氨基吡啶诱发去甲肾上腺素释放及B—50（GAP—43）磷酸化

在胞外有Ca^2 或无Ca2 时，3，4－二氨基吡啶（3，4－DAP）都能诱发大鼠海马释放去甲肾上腺素，咐 拜醇基酯（phorbol ester) 或多粘菌素B对此诱发释放有加强或抑制作用，在胞外有Ca2 时，3，4－DAP显著地减弱B－50磷酸化，除去胞外Ca2 ,B-50磷酸化完全被抑制，结果表明，B－50磷酸化不参与3，4－DAP诱发海马去甲肾上腺素释放机制。     

海马胞外钙不依赖去甲肾上腺素释放及蛋白激酶C的调制作用(英文)

在细胞外无钙时,佛波醇基酯能加强3,4-二氨基吡啶、藜芦定或哇巴因所诱发的去甲上腺素(NE)释放,但对莫能星(Mon)诱发的NE释放无作用。河豚毒素能阻断前3种物质诱发的NE释放,但对Mon诱发的释放无作用。钙整合剂BAPTA-AM能抑制这4种物质诱发的NE释放。结果提示蛋白激酶c仅调制由膜去极化因素诱发的NE释放。     

Newly synthesized noradrenaline mediates the alpha 2-adrenoceptor inhibition of [3H]5-hydroxytryptamine release induced by beta-phenylethylamine in rat hippocampal slices

In slices of the rat hippocampus, alpha 2-adrenoceptors located presynaptically on serotonergic nerve terminals modulate the electrically evoked calcium-dependent release of [3H]serotonin [( 3H]5HT). We have investigated the effects of a naturally occurring trace amine, beta-phenylethylamine (beta-PEA), on noradrenergic transmission in the rat hippocampus. Under experimental conditions in which MAO of type B is inhibited by deprenyl-exposure to beta-PEA (0.1-10 microM) facilitates the spontaneous outflow of [3H]noradrenaline and inhibits the electrically evoked release of [3H]5HT. The inhibitory effect of beta-PEA (3 microM) on the evoked release of [3H]5HT was antagonized by the alpha 2-adrenoceptor antagonist idazoxan at 1 microM, and by pretreatment with alpha-methyl-p-tyrosine (alpha-MpT, 300 mg/kg i.p., 2 h). The inhibition of tyrosine hydroxylase activity by alpha-MpT does not modify the inhibition of the evoked release of [3H]5HT by the alpha 2-adrenoceptor agonist, 6-fluoronoradrenaline, or the serotonin receptor agonist, 5-methoxytryptamine. Pretreatment with the neurotoxin DSP4 (50 mg/kg i.p., 10 days) markedly antagonized the inhibitory action of beta-PEA on [3H]5HT release. These results indicate that the noradrenaline-releasing action of beta-PEA inhibits the electrically evoked release of [3H]5HT through the activation of alpha 2-adrenoceptors. This inhibitory effect appears to be mediated exclusively through the release of newly synthesized noradrenaline, and does not involve the direct activation by beta-PEA of the inhibitory 5HT autoreceptors which modulate [3H]5HT release in the rat hippocampus.     

Stimulation of [3H]norepinephrine release from hippocampal slices by excitatory amino acids

[3H]norepinephrine efflux from preloaded rat hippocampal slices was increased in a dose-dependent manner by excitatory amino acids (EAA) in the following potency order: N-methyl-D-aspartic acid (NMDA) greater than kainic acid greater than L-glutamic acid greater than or equal to D,L-homocysteic acid greater than L-aspartic acid greater than quinolinic acid greater than quisqualic acid. The effect of EAA was blocked by physiological concentration of Mg2+, with the exception of kainic acid. D,L-2-amino-7-phosphonoheptanoic acid (APH) dose-dependently inhibited NMDA effect (IC50 = 69 mumol/L), whereas at 1 mmol/L it was ineffective versus kainic acid. The release of [3H]norepinephrine induced by quinolinic acid was blocked by APH 0.1 mmol/L. gamma-D-glutamylglycine dose-dependently inhibited kainic acid effect with an IC50 = 1.15 mmol/L. Tetrodotoxin 2 mumol/L reduced NMDA and kainic acid effects by 40 and 20%, respectively. The data indicate a possible involvement of central noradrenergic system in the modulation of excitotoxic action of EAA and offer a reliable system for testing new compounds acting at EAA-receptors by measuring norepinephrine release in vitro.     

细胞外无钙条件下锂诱发海马去甲肾上腺素释放

在细胞外无钙条件下,Li~ 能诱发海马脑片释放去甲肾上腺素(NE)。佛波醇基酯(PDB)能加强这一诱发释放,而河豚毒素能抑制它,Ca~(2 )螯合剂BAPTA-AM对它无作用。如先用3,4-二氨基吡啶诱发NE释放,并用PDB加强这一释放,则Li~ 诱发NE释放的作用被抑制。结果提示:内源性Ca~ 释放并不参与Li~ 诱发NE释放的机制。     

Modulation of norepinephrine release through alpha 1- and alpha 2-adrenoceptors in rat isolated kidney

The aim of this study was to investigate alpha-adrenoceptor modulation of norepinephrine (NE) release from sympathetic nerves in rat isolated perfused kidney. After preincubation with [3H]NE, the renal nerves were stimulated. The stimulation-induced (S-I) outflow of radioactivity was used as an index of NE release. Clonidine (0.1 mumol/L) decreased the S-I outflow of radioactivity. This effect was abolished by the alpha 1-adrenoceptor antagonist idazoxan (0.1 mumol/L) but not by the alpha 2-adrenoceptor antagonist prazosin (0.1 mumol/L). Methoxamine (10 mumol/L) also had an inhibitory effect; this was abolished by prazosin (0.1 mumol/L), but not by idazoxan. Individually, these alpha-blocking drugs and the alpha 1-adrenoceptor antagonist corynanthine (0.3 mumol/L) enhanced S-I outflow of radioactivity. In the presence of indomethacin (10 mumol/L), the inhibitory effect of methoxamine was abolished but clonidine still inhibited S-I outflow of radioactivity. The facilitatory effect of prazosin was also unaltered by indomethacin. These results suggest the existence of inhibitory prejunctional alpha 1- and alpha 2-adrenoceptors in the kidney. The inhibitory effect of methoxamine seems to be mediated through prostaglandin inhibition of NE release. However, the evidence for inhibitory prejunctional alpha 1-adrenoceptors rests solely on the facilitatory effects of prazosin and corynanthine.     

Acetylcholine release from rat hippocampal slices is modulated by 5-hydroxytryptamine

Experiments were performed with slices of rat hippocampus in order to investigate whether the release of acetylcholine in this area is modulated through 5-hydroxytryptamine (5-HT) receptors. The slices were prelabeled with [3H]choline then stimulated electrically twice for 4 min each at a frequency of 3 Hz. The overflow of tritium evoked was inhibited by exogenous 5-HT in a concentration-dependent manner. The 5-HT2 receptor agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HC1 ((+/-)-DOI), did not mimic 5-HT. The effect of 5-HT was antagonized by methiothepin but not by the 5-HT2 antagonist, ketanserin. The 5-HT1 agonist, 5-methoxy-3-[1,2,3,6-tetrahydropyridin-4-yl]-1H-indole (RU 24969), inhibited the electrically evoked overflow of tritium, whereas the 5-HT1A-selective agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), was ineffective. Methiothepin itself, but not ketanserin, increased the evoked overflow of tritium. In contrast, the overflow was inhibited by the 5-HT uptake blocker, 6-nitroquipazine. The evoked overflow was also reduced by d-fenfluramine, a serotonin releaser. The concentration-inhibition curve for d-fenfluramine was shifted to the right by methiothepin. It is concluded that the release of ACh in rat hippocampus may be tonically inhibited by 5-HT through the activation of receptors, possibly belonging to the 5-HT1B subtype.     

Molecular mechanism for agonist-promoted alpha(2A)-adrenoceptor activation by norepinephrine and epinephrine

We present a mechanism for agonist-promoted alpha(2A)-adrenergic receptor (alpha(2A)-AR) activation based on structural, pharmacological, and theoretical evidence of the interactions between phenethylamine ligands and alpha(2A)-AR. In this study, we have: 1) isolated enantiomerically pure phenethylamines that differ both in their chirality about the beta-carbon, and in the presence/absence of one or more hydroxyl groups: the beta-OH and the catecholic meta- and para-OH groups; 2) used [(3)H]UK-14,304 [5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine; agonist] and [(3)H]RX821002 [2-(2-methoxy-1,4-benzodioxan-2-yl)-2-imidazoline; antagonist] competition binding assays to determine binding affinities of these ligands to the high- and low-affinity forms of alpha(2A)-AR; 3) tested the ability of the ligands to promote receptor activation by measuring agonist-induced stimulation of [(35)S]GTPgammaS binding in isolated cell membranes; and 4) used automated docking methods and our alpha(2A)-AR model to predict the binding modes of the ligands inside the alpha(2A)-AR binding site. The ligand molecules are sequentially missing different functional groups, and we have correlated the structural features of the ligands and ligand-receptor interactions with experimental ligand binding and receptor activation data. Based on the analysis, we show that structural rearrangements in transmembrane helix (TM) 5 could take place upon binding and subsequent activation of alpha(2A)-AR by phenethylamine agonists. We suggest that the following residues are important in phenethylamine interactions with alpha(2A)-AR: Asp113 (D(3.32)), Val114 (V(3.33)), and Thr118 (T(3.37)) in TM3; Ser200 (S(5.42)), Cys201 (C(5.43)), and Ser204 (S(5.46)) in TM5; Phe391 (F(6.52)) and Tyr394 (Y(6.55)) in TM6; and Phe411 (F(7.38)) and Phe412 (F(7.39)) in TM7.