新斯的明引起大鼠神经肌接头突触后膜持续性去极化特点

采用大鼠膈肌不均匀牵张肌肉标本,观察可逆性胆碱酯酶抑制剂新斯的明引起神经肌接头突触后膜持续性去极化特点. 结果发现,新斯的明（2.5-5 μmol·L^-1）浴槽内给药引起的持续性去极化（SD）时程比压力给药（1 mmol·L^-1,32 kPa, 2-5 s）时长,结果提示压力给药引起的SD时程仅相当于浴槽内低浓度药物所引起者. 在本实验条件的多数情况下,压力给药引起SD的平台期,复极期以及复极后的一段时间内出现频率显著增高的小终板电位（mEPP）,并且这种高频率的mEPP只伴随SD的产生而出现. 而在浴槽内给予高浓度新斯的明引起的SD过程中,mEPP显著减少. 结果提示,可逆性胆碱酯酶抑制剂新斯的明在低浓度时引起的SD过程中,不仅突触后膜的烟碱受体并没有完全失敏,而且突触前膜自发释放ACh显著增加.     

新斯的明引起大鼠神经肌接头突触后膜持续性去极化特点

采用大鼠膈肌不均匀牵张肌肉标本 ,观察可逆性胆碱酯酶抑制剂新斯的明引起神经肌接头突触后膜持续性去极化特点 .结果发现 ,新斯的明 ( 2 .5-5μmol· L-1)浴槽内给药引起的持续性去极化( SD)时程比压力给药 ( 1 mmol· L-1,32 k Pa,2 - 5s)时长 ,结果提示压力给药引起的 SD时程仅相当于浴槽内低浓度药物所引起者 .在本实验条件的多数情况下 ,压力给药引起 SD的平台期 ,复极期以及复极后的一段时间内出现频率显著增高的小终板电位 ( m EPP) ,并且这种高频率的 m EPP只伴随 SD的产生而出现 .而在浴槽内给予高浓度新斯的明引起的 SD过程中 ,m EPP显著减少 .结果提示 ,可逆性胆碱酯酶抑制剂新斯的明在低浓度时引起的 SD过程中 ,不仅突触后膜的烟碱受体并没有完全失敏 ,而且突触前膜自发释放 ACh显著增加 .     

梭曼引起大鼠膈肌终板区持续性去极化

在大鼠离休不均匀牵张膈肌标本（ＩＮＳＭＰ）上,选择接近正常电生理学状态的神经肌肉接头,研究了梭曼引起的串终板电位（ＴＥＰＰ）变化,观察到．梭曼浓度在５．５ｎｍｏｌ·Ｌ１到５５μｍｏｌ。Ｌ１范围内,间接串刺激时除在少数标本上出现ＴＥＰＰ幅度降低的第一种反应外,在大多数标本上出现持续性去极化（ＳＤ）．ＳＤ过程中,终板电位（ＥＰＰ）完全消失,ＳＤ－旦出现,持续时间相对稳定,具有“全或无”性质,梭曼浓度在５５ｎｍｏｌ·Ｌ到５５μｍｏｌ·Ｌ范围内,反应以ＳＤ为主（＞８０％）大鼠一个致死量梭曼中毒（０,１ｍｇ·ｋｇ１ｉｍ）后制备ＩＮＳＭＰ,间接串刺激时也产生这两种反应,仍以ＳＤ为主（９１％）冲洗掉残余梭曼,对ＳＤ各参数无影响,再加入高浓度梭曼（５５μｍｏｌ·Ｌ１）时,４５％标本上ＳＤ转化为第一种反应,另５５％标本上ＳＤ的７０％时程缩短至４２％,再冲洗梭曼后１００％标本上ＳＤ恢复。结果表明,ＳＤ与第一种反应有质的区别．ＳＤ是梭曼抑酶作用的结果,高浓度梭曼可能对神经肌肉接头有直接作用,但不是梭曼中毒的主要因素,ＳＤ是梭曼中毒后,间接串刺激时ＴＥＰＰ的主要变化,是在突触电位水平上梭曼等胆碱酯酶抑制剂中毒致神经肌肉传递阻断的?     

离体大鼠膈肌标本上梭曼引起终板区持续性去极化的机理分析

在离休大鼠膈肌标本上，细胞内记录终板区微电泳给乙酰胆碱（ＡＣｈ）的电位，以ＡＣｈ电位幅度为突触后反应性指标，观察了梭曼中毒后间接串刺激产生终板区持续性去极化反应的性质并分析了其产生的机理。持续性去极化过程中不仅串终板电位消失，ＡＣｈ电位也消失，持续性去极化之后ＡＣｈ逐渐恢复。在正常大鼠和肉毒毒素Ａ中毒大鼠膈肌标本上，梭曼中毒后，串ＡＣｈ电位（５－１０Ｈｚ）也可诱发与持续性去极化性质相同的去极化反应，结果表明，持续性去极化主要是突触后Ｎ型ＡＣｈ受体对高浓度ＡＣｈ的一种反应，不支持突触前ＡＣｈ“再生性”释放的假说。     

梭曼引起神经肌肉接头阻滞的机理研究

梭曼引起神经肌肉接头阻滞的机理研究刘传缋１纪占欣１邹飞２李军２１．军事医学科学院毒物药物研究所（北京１００８５０）２．第一军医大学神经性毒剂中毒引起肌无力和麻痹是严重的中毒症状，可导致呼吸肌无力和麻痹，使中毒者窒息死亡。神经毒中毒后，神经肌肉接头处Ａ...     

离体大鼠膈肌标本上梭曼引起终板区持续性去极化的机…

在离体大鼠膈肌标本上，细胞内记录终板区微电泳给乙酰胆碱的电位，以ＡＣＨ电位幅度为突触后反应性指标，观察了梭曼中毒后间接串刺激产生乡亲 反区持续性去极化反应的性质并分析了其产生的机理，持续性去极化反应的性质并分析了其产生的机理，持续性去极化过程中不仅串终板电位消失ＡＣＨ电位也消失，持续性去极化之后ＡＣＨ逐渐恢复，在正常大鼠和肉毒毒素Ａ中毒大鼠膈肌标本上，梭曼中毒后，串ＡＣＨ电位也可诱发与持续性去中毒     

维拉帕米对新斯的明或3,4-二氨基吡啶引起的大鼠膈肌持续性去极化的作用(英文)

目的　在经新斯的明或 3,4 二氨基吡啶孵浴的大鼠膈肌标本上研究维拉帕米对终板电位的影响。方法　采用传统的微电极细胞内记录技术。结果　 0 .2～ 5 .0 μmol·L- 1新斯的明或 1.0～ 4 .0 μmol·L- 13,4 二氨基吡啶 (3,4 DAP)均可以使膈肌终板电位产生持续性去极化。在正常台氏液中 ,维拉帕米 1、5、10、2 0 μmol·L- 1对单个和串终板电位以及小终板电位没有明显作用 ,但是 ,5～ 2 0 μmol·L- 1维拉帕米可以浓度依赖性方式抑制新斯的明或 3,4 DAP引起的持续性去极化。结论　成年大鼠膈神经末梢存在的L 型Ca2 +通道可以被新斯的明或 3,4 DAP所引起的突触间隙乙酰胆碱蓄积所激活 ,导致终板电位产生持续性去极化 ,而在正常生理状态下对突触传递不产生影响     

在不均匀牵拉的离体大鼠膈肌标本上梭曼的突触前和突触后作用

在离体大鼠膈肌上制备了一种不均匀牵拉肌肉以制动,便于用微电极记录终板电位(EPP)的标本(INSMP),避免了常规制动方法带来的制动药物、台氏液Ca~(2+),Mg~(2+)浓度改变或钳压肌肉导致膜电位(MP)下降的种种干扰。INSMP的MP和小终板电位(MEPP)正常,EPP幅度高达30mV以上,是研究药物对接头作用的较好标本。在INSMP上,梭曼(5.5μM)使MEPP频率加快,串刺激(50Hz)诱发的平均串EPPs幅度及其平均ACh 量子含量减少80％和77％。小剂量三碘季铵酚和六烃季铵可部分对抗梭曼的作用。梭曼引起强直收缩抑制主要原因为终板区蓄积的ACh作用于突触前N受体、负反馈地抑制ACh 量子释放;次要原因为作用突触后N受体、使其对ACh敏感性降低。     

HI-6对正常及梭曼抑制大鼠离体膈神经-膈肌标本收缩功能的影响

目的　探讨HI 6对抗梭曼中毒所致呼吸抑制重活化作用外的其他可能作用机制。方法　采用MS 30 2三道生理记录仪 ,建立大鼠离体膈神经 膈肌收缩标本 ,观察HI 6对梭曼中毒膈神经 膈肌标本收缩功能的影响。结果　①梭曼 (2mg·L- 1)中毒后 ,膈肌收缩功能明显下降 ,中毒 10min内强直收缩曲线下面积下降至最低点 ,且在 3h内无明显恢复。②梭曼中毒前给予不同浓度的HI 6 (0 .0 1,0 .1,1.0mmol·L- 1) ,发现HI 6 (0 .1,1.0mmol·L- 1)对梭曼中毒所致膈肌强直收缩具有明显保护作用 ,且保护作用随着浓度的增加逐渐增强。③梭曼中毒后再给予HI 6 (0 .0 1,0 .1,1.0mmol·L- 1) ,发现 0 .0 1mmol·L- 1HI 6对中毒大鼠离体膈肌收缩功能无任何拮抗作用 ;当浓度增至 0 .1mmol·L- 1时 ,对膈肌强直收缩有一定的拮抗作用 ,但无统计学意义 ;但 1.0mmol·L- 1HI 6可显著对抗梭曼中毒所致膈肌收缩功能下降。结论　HI 6对梭曼中毒所致大鼠离体膈神经 膈肌收缩功能抑制具有明显拮抗作用 ,提示HI 6对抗梭曼中毒所致呼吸抑制作用机制存在酶保护作用外的直接生理对抗作用     

The reversal by oximes and their de oximinomethyl analogues of neuromuscular block produced by soman

A series of oximes and related compounds were assessed for their ability to restore soman-induced neuromuscular block in the isolated diaphragm preparation of the rat, guinea-pig and marmoset. In the rat the bispyridinium oximes HS6, HI6 and HS14 were superior to P2S and all other compounds tested. Conversely, in the guinea-pig, most of the compounds tested produced a good reversal of neuromuscular block. In a limited number of experiments in the marmoset, only a partial reversal of neuromuscular block, was obtained with the oximes HI6 and HS6. The restoration of neuromuscular block was due to one or more of the following factors: (i) enzyme reactivation (ii) direct action (iii) adaptation. The results of this study suggest that both the acetylcholine receptor and the rate of 'ageing' of soman inhibited AChE are different in these three species.     

Effect of diazepam on the frog neuromuscular junction.

Diazepam (10(-5) M) had no effect on the compound action potential of frog sciatic nerve and its refractory period. At the neuromuscular junction, no changes were found in the amplitude and frequency of miniature endplate potentials in the presence of the drug. End-plate potential (e.p.p.) amplitude and early facilitation of the e.p.p. were unchanged. Diazepam had no effect on the amplitude of potentials evoked by ACh applied iontophoretically (0.1 Hz) at low frequencies in the chemosensitive region of the postjunctional membrane. Diazepam (10(-6) M) enhanced the progressive desensitization to ACh applied at a frequency of 1 Hz but did not affect recovery of sensitivity. A possible mechanism of action of diazepam at cholinergic synapses is discussed.     

Stimulation of the frequency of MEPPs at the frog neuromuscular junction by extracellular EGTA

Summary Exposure of the frog neuromuscular junction at 17° C or 23° C to salines with low [Ca²⁺], buffered with EGTA, causes mepp frequency to fall after 4–6 min to about 20% of the control rate. Results obtained in the presence of verapamil suggest that this fall is a consequence of a lower Ca²⁺-influx coupled with the action of the extracellular EGTA in promoting Ca²⁺-efflux from the terminals. These findings confirm the suggestion that [Ca²⁺]_i has a major role in determining mepp frequency.At 13° C, the fall in mepp frequency after addition of EGTA is preceded by a transient (1–2 min) rise in mepp rate which is not present at 17° C or in the presence of verapamil. This transient acceleration in spontaneous release is believed to be because EGTA promotes the emptying of a Ca²⁺-reservoir on or beneath the inner face of the membrane, thus causing a rapid Ca²⁺-efflux via the Ca²⁺-sensitive sites that trigger exocytosis of transmitter.The significance of the sensitivity of the response to temperature is discussed. The suppressive effect of higher temperatures can be reversed to some extent by hyperosmotic salines, an effect that may reflect the action of hypertonicity on the plasmalemma. It is concluded that the characteristics of the release system may change markedly at about 16° C.Ca²⁺-EGTA buffers are widely used; it is suggested that extracellular EGTA can also modify [Ca²⁺]_i in cellular systems.     

Presynaptic action of trifluoperazine at the frog neuromuscular junction

Summary Treatment of frog neuromuscular preparations bathed in basic frog saline (1.8 mM Ca²⁺) with trifluoperazine (25 M) caused an increase in MEPP frequency in 6 out of 10 preparations tested. The mean normalised MEPP frequency after 15 min of treatment was approximately 1.5. 10 M trifluoperazine had a similar effect. In salines containing low concentrations of Ca²⁺ (50 M Ca²⁺, 2 mM Mg²⁺ or 0 Ca²⁺, 1 mM EGTA) the stimulatory action of trifluoperazine was more marked and occurred in a higher proportion of the preparations tested (11 out of 14).When evoked release of transmitter was reduced to very low levels by Mg²⁺-containing salines treatment with trifluoperazine (2.5–25 M) caused an increase in quantal content of 20–60%.Depolarisation of preparations bathed in standard frog saline by increasing [K⁺]₀ to 10 mM resulted in a 10-fold increase in MEPP frequency. This response was inhibited by about 25% in 10 M trifluoperazine and by about 45% in 25 M trifluoperazine.Pre-treatment of preparations with trifluoperazine (25 M) caused a marked reduction in the response of MEPP frequency to tetanic stimulation (50 Hz) both in the presence of an inward electrochemical gradient for Ca²⁺ (50 M Ca²⁺, 2 mM Mg²⁺) and in a Ca²⁺-free saline (0 Ca²⁺, 1 mM EGTA). The effects of trifluoperazine on tetanic enhancement of MEPP frequency are compared to those of other agents and it is shown that the results are inconsistent with an effect of the drug on Ca²⁺-fluxes at the plasma membrane.It is concluded that trifluoperazine has both stimulatory and inhibitory effects on transmitter release at the frog neuromuscular junction and that the inhibitory effect is probably due to inhibition of excitation-secretion coupling at a point subsequent to Ca²⁺ mobilization.     

梭曼中毒大鼠脂质过氧化损伤及抗氧化剂的作用

目的 以大鼠血清乙酰胆碱酯酶(AChE)活力变化为梭曼(soman)中毒程度指标，研究维生素A和维生素E对急性中毒大鼠的血清、大脑和肝脏组织中超氧化物歧化酶(SOD)、一氧化氮合酶(NOS)和总抗氧化力(T—AoC)的影内，探讨抗氧化剂维生素A和维生素E对梭曼中毒大鼠AChE及脂质过氧化损伤的保护作用。方法 雄性大鼠40只，按体重随机分为阴性对照组、阳性对照组、维生素A组、维生素E组。阴性对照组和阳性对照组每日灌胃5ml/kg的菜籽油；维生素A组每日灌胃2ml/kg的维生素A；维生素E组每日灌胃2．5ml/kg的维生素E，共灌胃9d。第10日除阴性对照组外其余各组大鼠均皮下注射0．9LD50梭曼，2h后断头处死并取样。测定大鼠血清、大脑、肝脏的T—AOC、SOD和NOS及血清AChE活力。结果 梭曼中毒2h后，血清乙酰胆碱酷酶(AChE)及血清、大脑、肝脏组织中SOD活力和T—AoC水平下降，NOS活力提高；维生素A和维生素E均能提高SOD、T—AOC和AChE活力，而降低NOS活力。结论 经皮下注射0．9LD50梭曼可引起AChE活力显著下降，表明大鼠已严重中毒，中毒时伴有明显的脂质过氧化损伤。中毒前大鼠用维生素A和维生素E预处理，能够保护AChE活力，降低NOS活力，减少N0自由基的生成，同时，提高SOD、T—AoC水平。提示维生素A和维生素E对梭曼中毒有较好的预防作用。     

Presynaptic effects of 4-aminopyridine and streptomycin on the neuromuscular junction

Studies were done to assess the effects of 4-aminopyridine (4AP) and streptomycin (SM) on transmitter release parameters and extracellularly recorded presynaptic action potential. The application of 5 micrometer 4AP resulted in a marked increase in the mean quantal content (m1) associated with an increase in the total number of the store of available quanta (n) but had no effect on the probability of release (p) and the fractional release (P). Focal recording showed that 50 micrometer 4AP modified the shape of the presynaptic action potential from a triphasic configuration to a diphasic one. In contrast, prolongation of the muscle action potential was found only at higher concentrations (greater than 1 mM) of of 4AP. Thus, the increase in n with 4 AP was associated with prolongation of the presynaptic action potential evoked by blocking the K current. SM (172 micrometer mM) had no effect on p and P. Reduction of n by SM was completely reversed by 4AP. As the presynaptic action potential change induced by 4AP was not antagonised by SM, it may be that the decrease of n by SM followed a modification of the voltage-dependent Ca channel.     

Diamide,Temperature and spontaneous transmitter release at the neuromuscular junction: Stimulation of exocytosis by a direct effect on membrane fusion?

The thiol-oxidizing agent diamide markedly increases m.e.p.p. frequency at the frog neuromuscular junction, even at low [Ca2+]0 and also when the mitochondria are uncoupled with DNP. The effect is reversed by dithioerythritol and is very temperature-sensitive, with a marked transition at 16 degrees C; m.e.p.p. frequency is raised 2- to 5-fold at 13-15 degrees C and 55- to 60-fold at 17-20 degrees C. Diamide increases the frequency of large amplitude m.e.p.p.s, the effect being explicable as the fusion of two or more vesicles. It is concluded that (a) diamide does not act at the Ca2+ channels of the plasma membrane, nor at the mitochondria. It affects the release system directly via an alteration of membrane protein --SH groups; (b) the eventual decline in m.e.p.p. frequency after DNP treatment is because of the exhaustion of mitochondrial Ca2+ rather than a depletion of quanta; (c) the major effect of temperature is on the release mechanism, perhaps via a phase-change in the phospholipoproteins of the plasmalemma or vesicles, rather than an elevation of [Ca2+]i; (d) either diamide or temperatures above 16 degrees C make Ca2+ more effective in promoting vesicle-plasmalemma fusion.