眼睛蛇毒心脏毒素对大鼠心肌细胞收缩及细胞内钙离子的作用

目的研究眼睛蛇毒心脏毒素(Cardiotoxin,CTX)对心肌细胞的形态、收缩幅度和细胞内钙离子([Ca²⁺]_i)的作用。方法应用荧光计量法(以Fura-2/AM为荧光染料)及光学成像系统来测定单个心肌细胞[Ca²⁺]_i和收缩幅度。结果0.001～1μmol/L的CTX使心肌细胞由杆状变成圆形,药物的作用从第1分钟时开始,到第20分钟时趋于稳定。在电刺激存在的情况下,1μmol/L的CTX最初导致电诱导的[Ca²⁺]_i和收缩幅度瞬间增加,接下来[Ca²⁺]_i时程延长,最终细胞对电刺激不敏感、突然收缩、[Ca²⁺]_i持续增高。在缺乏电刺激的情况下,1μmol/L的CTX可诱导Ca²⁺震荡波、持续性[Ca²⁺]_i增高,这种作用与40mmol/L的KC l和10mmol/L咖啡因所引起的[Ca²⁺]_i瞬间增加不同。结论CTX作用初期使[Ca²⁺]_i增高,使细胞[Ca²⁺]_i超载,同时伴随细胞形状的改变。     

粉防己碱对培养乳牛基底动脉平滑肌细胞内游离钙浓度的影响

目的：研究粉防己碱对培养乳牛基底动脉平滑肌细胞游离钙浓度（[Ca^2 ]i)的影响。方法：利用AR－CM－MIC阳离子测定系统,采用Fura 2-AM为指示剂,测量单个细胞内[Ca^2 ]i。结果：粉防己碱10－100μmol/L对培养乳牛基底动脉平滑肌细胞静息[Ca^2 ]i无明显影响。在细胞外钙为1．3mmol/L,粉防己碱可浓度依赖性地抑制KC1引起[Ca^2 ]i的升高。咖啡因10mmol/L可诱导一次[Ca^2 ]i瞬间快速升高,随后自发回复到静息水平,粉防己碱10和30μmol/L对咖啡因诱导的[Ca^2 ]i瞬间升高没有作用,但高浓度（100μmol/L）粉防己碱抑制了[Ca^2 ]i瞬间升高。在细胞外钙为1.3mmol/L,苯肾上腺素10μmol/L可引起双相[Ca^2 ]i变化,包括快速升高相和持续升高相。在细胞外钙为零,苯肾上腺素仅引起[Ca^2 ]i的快速升高相。粉防己碱可浓度依赖性地抑制苯肾上腺素引起[Ca^2 ]i快速升高相。结论：在培养乳牛基底动脉平滑肌细胞,粉防己碱可能通过影响电压依赖性和苯肾上腺素受体介导的钙通道而抑制钙内流。高浓度粉防己碱也可能影响肌浆网钙释放或钙摄取。     

血管紧张素Ⅱ对大鼠肾入球小动脉细胞内钙离子浓度的影响及Losartan的拮抗作用

目的探讨血管紧张素Ⅱ（AngⅡ）对肾小球入球小动脉细胞内钙离子浓度（[Ca^2＋]i）的影响与高血压肾小动脉重建的关系及Losartan的治疗作用。方法细胞培养：大鼠肾小球入球小动脉细胞随机分为4组。对照组：不加AngⅡ处理;AngⅡ组：加入终浓度为0.1μmol.L^-1AngⅡ;Losartan组：加入终浓度为50μmol.L^-1Losartan;AngⅡ＋Losartan组：同时加入Losartan 50μmol.L^-1AngⅡ0.1μmol.L^-1负载后上机检测[Ca^2＋]i。结果细胞培养显示AngⅡ引起了细胞收缩变化,表现为胞突变细变短,胞突回缩,胞体变圆,细胞长度与直径均明显缩小。Losartan处理组较AngⅡ组细胞形态变化减轻且Losartan对AngⅡ增高RASMCs内[Ca^2＋]i有明显抑制作用。结论 AngⅡ可引起肾小球入球小动脉细胞内[Ca^2＋]i的上升,导致细胞收缩,因此Ca^2＋超载可能是肾素-血管紧张素系统起作用的重要环节。Losartan可抑制细胞内Ca^2＋超载。     

GDP对柴胡皂甙（I）促大鼠胰腺腺泡酶分泌和升高[Ca^2＋]i的影响

目的：研究鸟苷二磷酸（GDP）对柴胡皂甙（I）[SA(I)]刺激大鼠胰腺腺泡酶分泌和胞内钙离子升高的影响。方法：分离大鼠胰腺腺泡细胞,用链球菌溶血素－O（SLO）通透细胞膜,检测腺泡分泌蛋白量标志腺泡酶分泌功能。用钙离子荧光指示剂Fluo-3和荧光光谱测定胞内钙离子浓度。结果：GDP可凶制SA（I）促胰腺腺泡的酶分泌作用,抑制作用随剂量增加而加强;SA（I）10μmol/L以双峰值为特征使[Ca^2 ]i显著上升;GDP 5mmol/L,导致[Ca^2 ]i逐步升高且两个峰值消失。细胞通透以后,与正常细胞相比,SA（I）刺激的30min酶分泌的累积量下降了57％;GDP5mmol/L使SA（I）刺激的早期酶分泌速率进一步降低。结论：GDP通过抑制细胞[Ca^2 ]i的升高抑制了SA（I）刺激的胰腺腺泡酶分泌作用。     

在地昔帕明诱导胶质瘤C6细胞凋亡过程中caspase3基因表达和[Ca^2＋]i稳态^1

目的：研究抗抑郁药地昔帕明（Des)对胶质瘤C6细胞的凋亡诱导作用以及对凋亡关键效应分子caspase3和凋亡早期信号[Ca^2 ]i的调控作用。方法：采用流式细胞术（FCM）和凝胶电泳观察Des对C6细胞凋亡的DNA裂解作用,RT－PCR分析caspase3基因的表达以及激光扫描共聚焦显微镜测量单个活细胞[Ca^2 ]i浓度。结果：Des(10,20,40μmol/L)处理C6细胞24h后,FCM图的G1峰左侧出现凋亡特征性亚二倍体细胞峰,凋亡细胞百分率分别为5.2%,21.9%和41.9%。同时,凝胶电泳显示典型的DNA“梯带”.Des 20 μmol/L处理C6细胞24h可明显增强caspase 3基因的表达,而未经Des处理的C6细胞则检测不到caspase 3基因的表达。此外,Des 40μmol/L可使C6细胞[Ca^2 ]i迅速升高并维持超过28min,而钙螯合剂依他酸可显著降低C6细胞[Ca^2 ]i增高幅度,提示Des致C6细胞[Ca^2 ]i增高主要与细胞外钙内流有关。结论：Des诱导C6胶质瘤细胞凋亡可能与caspase 3基因表达的上调以及细胞内钙稳态的失衡有关。     

线粒体及内质网对铅引起的[Ca2+]i升高的作用

目的 研究线粒体、内质网Ca^2 -ATP酶以及Na^ 和K^ -ATP酶活力的改变对铅引起的[Ca^2 ]i升高的调节作用，探讨铅引起的[Ca^2 ]i增高对学习记忆功能的影响。方法 Wistar大鼠神经肉瘤C6细胞培养于含醋酸铅的培养液中，于不同时间终止染铅，检测[ca2’]；及线粒体、内质网Ca^2 -ATP酶、Na^ 和K^ -ATP酶活力。结果 (1)0．2μmol／L染铅组：[Ca^2 ]i轻度升高，线粒体Ca^2 -ATP酶、Na^ 和K^ -ATP酶活力升高，内质网酶活力略增高；(2)1．0μmol／L染铅组：[Ca^2 ]；于染铅后0．5h升至最高，以后逐渐降低，波动于iL60～190nmol／L之间；线粒体、内质网Ca^2 -ATP酶、Na^ 和K^ -ATP酶于染铅后0．5h升至最高(分别为未染铅前酶活力的29．1、39．2、10．8和19．8倍)，2d后降至接近正常水平。结论 (1)铅可使Wistar大鼠神经肉瘤C6细胞Ca^2 浓度及线粒体、内质网Ca^2 -ATP酶、Na^ 和K^ -ATP酶活力增高；(2)当[Ca^2 ]i增高不显著时以线粒体Ca^2 -ATP酶、Na^ 和K^ -ATP酶活力增高为主；当[Ca^2 ]i急剧升高时，线粒体、内质网Ca^2 -ATP酶、Na^ 和K^ -ATP酶活力均明显增高，尤其是线粒体Ca^2 -ATP酶、Na^ 和K^ -ATP酶活力增高更为显著。     

布比卡因对大鼠心室肌细胞内钙的影响

目的：运用激光扫描共聚焦显微镜观察不同浓度的布比卡因对KCI诱导的大鼠心室肌细胞内游离钙离子浓度（[Ca^2＋]。）的影响，进而探讨布比卡因心肌抑制作用的可能机制。方法：培养新生SD大鼠心室肌细胞，将培养的心室肌细胞随机分为4组．分别为对照组（C组）、10μmol／L布比卡因组（B2组）、50μmol／L布比卡因组（岛组）、100μmol／L布比卡因组（取组）。各组细胞均用钙荧光指示剂Fluo-3／AM染色，运用激光扫描共聚焦显微镜动态观察单个心室肌细胞内钙荧光强度（fluorescent intensity．FI）的变化。结果：与对照组比较10μmol／L的布比卡因对KCl诱导的大鼠心室肌细胞内钙FI变化无明显影响（P〉0.05），50μmol／L和100μmol／L的布比卡因则明显抑制KCl诱导的钙离子跨膜内流（P〈0．05）；抑制程度B2组〉B2组（P〈0．05）。结论：低浓度的布比卡因对KCl诱导的大鼠心室肌细胞内[Ca^2＋]i的变化无明显影响，高浓度则明显抑制钙离子跨膜内流。布比卡因呈浓度依赖性抑制兴奋收缩耦联时心室肌细胞内游离钙离子内流，可能是其心肌抑制作用的原因之一。     

龙葵碱对HepG2细胞线粒体膜电位及细胞内[Ca^2＋]i的影响

目的：观察龙葵碱对HepG2细胞线粒体膜电位及细胞内[Ca^2＋]i的影响，揭示龙葵碱诱导细胞凋亡的机制。方法：采用AO／EB双染HepG2细胞，激光共聚焦扫描显微镜观察细胞形态学改变；TMRE单染HepG2细胞，激光共聚焦扫描显微镜观察细胞线粒体膜电位的改变；Fluo-3／AM单染HepG2细胞，激光共聚焦扫描显微镜观察细胞内[Ca^2＋]i的改变；TMRE和Fluo-3／AM双染HepG2细胞，激光共聚焦扫描显微镜同时观察细胞线粒体膜电位和细胞内[Ca^2＋]i的改变。结果：形态学实验表明0．0032μg／mL、0．016μg／mL龙葵碱使细胞外周呈微弱皱缩状改变，0．08、0．4、2μg／mL龙葵碱使HepG2细胞出现大量碎片及凋亡小体等典型的细胞凋亡形态，即龙葵碱能够诱导HepG2细胞凋亡；TMRE单染激光共聚焦测定表明龙葵碱能够降低HepG2细胞膜电位；Fluo-3／AM单染激光共聚焦测定表明龙葵碱能够升高肿瘤细胞内[Ca^2＋]。浓度；TMRE和Fluo-3／AM双染激光共聚焦观察表明龙葵碱在降低线粒体膜电位的同时能够升高细胞内[Ca^2＋]i浓度。结论：龙葵碱能够诱导HepG2细胞凋亡，其机制为降低HepG2细胞膜电位，开放细胞膜PT通道，使细胞内Ca^2＋顺浓度梯度转运，从而升高细胞内Ca^2＋浓度启动细胞凋亡机制。     

J—894对人体血小板激活时胞浆内游离钙浓度的影响

细胞内游离钙浓度在细胞反应的调节中作为第二信使起很重要的作用。本文实验采用荧光钙指示剂quin-2测定血小板胞浆内游离钙浓度[Ca^2 ]i的变化。结果表明在1mmol/L外钙的存在下，凝血酶（0.3U/ml）使血小板[Ca^2 ]i增高4－5倍。但在外钙缺乏的情况下，凝血酶使血小板[Ca^2 ]i增加较少，似科凝血酶增加[Ca^2 ]i，部分是通过释放内钙，但主要是通过钙内.J-894通过减少钙内流和释放明显抑制凝血酶引起的血小板[Ca^2 ]i的升高，剂量与效应相关。提示J－894可能是一种钙通道阻滞剂。     

幼鼠肺炎合并心衰的分子机制研究

目的从细胞和分子水平揭示婴幼儿肺炎合并心衰的机制.方法健康清洁级50日龄Wistar大鼠,经气管注射金黄色葡萄球菌菌液,建立肺炎动物模型;开胸获取心脏,进行双心室灌流,测定心肌酶谱和心功能指标;酶解分离出单个右室心肌细胞后,以Fura-2/AM负载细胞并对静息和收缩状态时细胞内[Ca^2 ]i进行荧光测定;采用全细胞式膜片钳技术记录右室心肌细胞L型钙电流;采用高效液相色谱仪测定心肌组织腺苷酸含量.均采用气管内注射等量生理盐水的同龄Wistar大鼠作为对照.结果①肺炎组动物心肌酶谱显著增高.②肺炎组和对照组的左、右心室功能均随前负荷升高而增强;在同一负荷下,右心室功能均低于对照组.③静息状态下肺炎组右室心肌细胞内[Ca^2 ]i随病程显著增高;收缩时Ca^2 含量增加比率显著低于对照组.④接种后24小时的肺炎组L型钙通道电流峰值无显著变化;120小时显著高于对照组.⑤接种后120小时,心肌组织腺苷酸含量显著低于对照组.结论采用气管内接种的方法所建立肺炎动物模型是有效的;肺炎可以合并心衰,尤其是右心衰竭为主;重症肺炎时心肌细胞出现能量代谢障碍;静息期心肌细胞内[Ca^2 ]i增高,而收缩状态下Ca^2 含量增加比率下降,可能是心肌细胞舒张、收缩功能障碍的重要机制;心衰后期,心肌细胞跨膜钙内流增大,可能是病变发展的重要机制.     

Effects of sodium selenite on neuromuscular junction of the mouse phrenic nerve-diaphragm preparation

The effects of sodium selenite on the neuromuscular junction of the phrenic nerve-diaphragm of the mouse were studied. Nerve-evoked twitches of the diaphragm of the mouse, the frequency of miniature endplate potentials, the quantal content of endplate potentials and the compound action potentials of the axon were measured. Sodium selenite induced a slight increase of the amplitude of the twitch, followed by twitch depression. The amplitude of the twitch, increased by selenite, became more prominent after the suppression of the twitch induced by cadmium ions, d-tubocurarine or magnesium ions. It appeared that the increased amplitude of twitch was due to the facilitation of transmitter release, since selenite significantly increased the frequency of miniature endplate potentials, and the amplitude and quantal content of endplate potentials; the amplitude and half decay time of miniature endplate potentials were unaffected. Twitch depression induced by selenite was enhanced by ammonium ions, high potassium and low magnesium and attenuated by high calcium. During the period of gradual depression of the twitch, selenite decreased the amplitude of compound action potentials of the phrenic nerve axon and caused the disappearance of endplate potentials. Ammonium ions enhanced the blockade of axonal conduction induced by selenite. Moreover, the depolarizing agents, ammonium and high potassium also induced an initial increase of twitch amplitude followed by depression of the twitch. These findings indicate that selenite probably alters the release of the transmitter by depolarizing the nerve membrane. The effects of selenite were antagonized by glutathione and cyanide, suggesting that the binding of selenite to sulfhydryl groups of the membrane was essential for inducing its pharmacological actions.     

Effects of hypoxia, 2,4-dinitrophenol and ouabain on twitch potentiation elicited following conditioning pulses in the mouse phrenic nerve-diaphragm preparation

Hypoxia is suggested to increase intracellular Ca2+, thereby affecting cellular functions. If this is the case, the effect would be modified by other treatments which also elevate intracellular levels of Ca2+. To test this possibility, in mouse diaphragm preparations, the effects of hypoxia were examined on twitch potentiations after application of neural conditioning pulses which are considered to elevate intracellular Ca2+. The effects were compared with those of 2,4-dinitrophenol (DNP) and ouabain. Hypoxia increased the tension of twitches elicited directly or neurally with 0.1 or 0.5 Hz pulses at 36 degrees C but not at 24 degrees C. Paired pulses to the nerve induced a complex response profile in which the amplitude of the second twitch was enhanced (twitch facilitation). Tetanic pulses (50 Hz) to the nerve were followed by post-tetanic twitches of increased amplitude (post-tetanic twitch potentiation, PTP). Hypoxia little affected the twitch facilitation but abolished PTP at both temperatures. These effects differed from those of DNP and ouabain in some ways. Thus, present experiments indicate that hypoxia selectively influences the process which is responsible for the PTP phenomenon rather than for the twitch facilitation. It is possible that the mechanism by which hypoxia would accumulate intracellular Ca2+ may be included in the process through which PTP occurs.     

The effect of carbamazepine on the post-tetanic twitch tension in the diaphragm of the mouse

The effects of carbamazepine (0.084-0.25 mM) on the post-tetanic potentiation of the twitch tension, were studied on the isolated phrenic nerve diaphragm preparation of the mouse. Carbamazepine decreased the post-tetanic potentiation of the twitch tension. The maximal depressant effect was found after higher frequencies and longer durations of stimulation. After repetitive stimulation, the amplitude of the endplate potential and the frequency of miniature endplate potentials were potentiated. Carbamazepine decreased the post-tetanic potentiation of the amplitude of endplate potential and the frequency of miniature endplate potentials. The directly-elicited muscle action potential was not affected when post-tetanic potentiation of the twitch tension was decreased. It is concluded that carbamazepine suppressed the post-tetanic potentiation of the indirectly-elicited twitch tension, mainly due to its pre-synaptic inhibitory effect.     

Inhibition of neuromuscular transmission in isolated mouse phrenic nerve-diaphragm by the enterotoxin of Clostridium perfringens type A.

The enterotoxin of Clostridium perfringens type A, a channel forming protein toxin, inhibited neuromuscular transmission under conditions of low calcium. Twitch tension of isolated phrenic nerve-diaphragm preparations elicited by electrical stimulations to the phrenic nerve was recorded isometrically, and the preparations were exposed to the purified enterotoxin. In Krebs solution containing 0.5 mM calcium, the enterotoxin (20 micrograms/ml) reduced within 10 min the amplitude of the twitch tension to 34 +/- 7% (mean +/- S.D., n = 11) of that recorded before the treatment. The effects of the enterotoxin on the twitch tension were irreversible and proceeded independently of stimulation. The reduction of the twitch tension by the enterotoxin was apparent in Krebs solution containing less than 0.6 mM calcium and the degree of reduction was inversely related to the concentration of calcium. The reduction of the twitch tension by the enterotoxin was also dependent on temperature and concentration of the toxin. At temperatures below 20 degrees C, no obvious reduction of twitch tension was observed with 20 micrograms/ml of the enterotoxin. Enterotoxin at a concentration of 0.4 micrograms/ml caused 16 +/- 2% (mean +/- S.D., n = 4) reduction of twitch tension, and the degree of the reduction in twitch tension increased with toxin concentration, reaching a plateau of 65 +/- 4% (mean +/- S.D., n = 7) at 6.5 micrograms/ml of the enterotoxin. The effects of the enterotoxin were antagonized by 2 microM physostigmine. Unlike curare, pretreatment of the preparation with enterotoxin did not antagonize the neuromuscular block by decamethonium. Neither the tension of muscular twitch elicited by direct electrical stimulation to the muscle nor the resting membrane potentials of muscle fibers recorded intracellularly were affected by the enterotoxin. The enterotoxin (2.2 micrograms/ml) reduced the frequency, but not mean amplitude or amplitude distribution, of miniature end-plate potentials, from 0.91 +/- 0.07/sec to 0.72 +/- 0.07 (mean +/- S.E., n = 5). The results suggest that the enterotoxin will provide a novel tool for the studies on the mechanism of the neuromuscular transmission because of the unique characteristics of the inhibition and of the known mechanism of its action on the cell membrane.     

Effect of lignocaine on chick biventer cervicis skeletal muscle

The effect of lignocaine (0.01-100 micrograms.ml-1) on amplitude of indirectly and directly-elicited twitch contractions and on contractures produced by acetylcholine (ACh) (0.1-10 mM) and tetraethylammonium (TEA) (1.2-12 mM) was studied in isolated biventer cervicis skeletal muscle of the chick. Lignocaine (0.01-0.9 microgram.ml-1) increased the amplitude of the indirectly-elicited twitch contractions. At high concentrations (10-100 micrograms.ml-1), lignocaine decreased or blocked the twitch tension and produced a contracture in the chick skeletal muscle. Lignocaine also reduced or blocked the directly-elicited twitch contractions in a dose-dependent manner. Lignocaine (10 micrograms.ml-1) reduced the ACh-induced contracture whereas it increased that produced by TEA. Physostigmine (2 micrograms.ml-1) increased the stimulating effect of lignocaine, at low concentrations. However, repeated exposures to lignocaine followed by physostigmine resulted in both increase and decrease in the indirectly-elicited twitch contractions. It was concluded that lignocaine had a dual action at the neuromuscular junction. In low concentrations, lignocaine increases the twitch tension, possibly by an anticholinesterase action, and in high concentrations it reduces or blocks the twitch tension, produces a contracture in the muscle, and reduces the ACh-induced contractures, whereas it increases the TEA-induced responses. Some of these effects of lignocaine may be interpreted in terms of effects on excitation-contraction coupling in muscle.     

A comparison between the effects of a tetanus and the effects of sympathomimetic amines on fast- and slow-contracting mammalian muscles

The effects of adrenaline and isoprenaline on the tension and time-course of the contractions of the tibialis anterior and soleus muscles of cats and rabbits have been compared with the effects of previous high-frequency stimulation. Like a tetanus, adrenaline possessed a facilitating action on neuromuscular transmission and an action exerted directly on the muscle fibres. Isoprenaline possessed only the second of these two actions. The effect of adrenaline and isoprenaline on the muscle fibres was blocked by dichloroisoprenaline and by 1-(2 naphthyl)-2-isopropylaminoethanol, whereas the effect of adrenaline on neuromuscular transmission was blocked by phentolamine and by phenoxybenzamine. In the soleus muscle, both the catechol amines and a previous tetanus caused similar decreases in maximal twitch tension and in the times to peak tension and to half-relaxation. The muscle action potentials were unaltered or slightly increased in amplitude. In the tibialis anterior muscle, a previous tetanus and the catechol amines caused an increase in twitch tension and an increase in the overall duration of the twitch. The muscle action potentials were either unchanged or were slightly decreased in amplitude. In this muscle the effect of a tetanus differed from that of the catechol amines in that the large post-tetanic change was associated with a marked increase in the rate of rise of twitch tension.     

Effects of memantine on the twitch tension of mouse diaphragm

The effects of memantine (50-175 microM) on the post-tetanic potentiation of the twitch tension were studied on the isolated mouse nerve diaphragm preparation. Memantine completely abolished the twitch tension elicited indirectly while it had no effect on the directly elicited twitch tension. Memantine also decreased the post-tetanic potentiation of amplitude of endplate potential and twitch tension. The duration of tetanic stimulation that induced a maximal decrease of twitch tension was 10-20 s. It is suggested that the effect of memantine on post-tetanic potentiation may be due to its voltage- and time-dependent effect on the ion channel-acetylcholine receptor complex.     

Doxorubicin alters Ca(2+) transients but fails to change Ca(2+) sensitivity of contractile proteins

Doxorubicin produced a transient increase and a subsequent decrease in the amplitude of twitch contraction in myocytes isolated from guinea-pig heart and loaded with fura-2. These changes were associated with an increase and a subsequent decrease, respectively, in the amplitude of Ca(2+) transients (peak minus diastolic Ca(2+) concentrations). Doxorubicin increased the diastolic Ca(2+) concentration with a concomitant shortening of the diastolic myocyte length. The time to peak Ca(2+) transients and the time to peak twitch contraction increased in parallel. Doxorubicin failed to affect the Ca(2+) concentration-contraction curve in skinned fibers obtained from atrial muscle. We conclude that biphasic inotropic effects of doxorubicin result from biphasic changes in Ca(2+) transients, and that doxorubicin fails to alter Ca(2+) sensitivity of contractile proteins. These findings are consistent with the hypothesis that doxorubicin enhances Ca(2+) release and impairs Ca(2+) uptake by the sarcoplasmic reticulum.     

Effect of malathion on some kinesiological parameters of the gastrocnemius muscle of frog, Rana hexadactyla (Lesson) and the antagonistic action of atropine

Selected kinesiological parameters were studied in the gastrocnemius muscle of frog, R. hexadactyla Lesson, under different treatments with malathion and atropine. There is an apparent decrease of twitch amplitude, half contraction time, half relaxation time, twitch duration and fatigue time in control muscle during malathion treatment. In the denervated muscle, twitch amplitude, latency period, and fatigue time were lowered, with elevated phases of contraction and relaxation time. However, all these parameters except fatigue time showed an elevatory trend when atropine was given along with malathion revealing its antagonistic action against malathion toxicity. All these results indicate that the action of malathion is similar to that of a pharmacologically active myo- and neurotoxic agent.     

Neuromuscular actions of sodium selenite on chick biventer cervicis nerve-muscle preparation.

Sodium selenite was found to be toxic to chicks, with an LD50 of 8.5 micrograms/g, which was increased to 16.3 micrograms/g by NaCN. The major symptoms of chicks, treated with selenite, were sedation and then dyspnea and paralysis. The cause of death by selenite was apparently due to the respiratory failure. The possible mechanism of toxicity was explored in the isolated chick biventer cervicis nerve-muscle preparation. Selenite initially increased the amplitude of the twitch, reversed the suppression of the twitch caused by d-tubocurarine, Mg2+, Cd2+ or Mn2+ and significantly increased the quantal content and amplitude of endplate potentials. Subsequently, selenite depressed the amplitude of the twitch, blocked the axonal conduction and inhibited excitatory postsynaptic potentials. Both NH4+ and K+ enhanced the action of selenite in depressing the twitches. In addition, selenite induced a sustained contracture of the muscle, which was partially inhibited by removal of external Ca2+ and markedly blocked by EGTA. Entry of Ca2+ and release of the internal Ca2+ were considered to be responsible for inducing contracture by selenite. Pretreatment with trypsin, glutathione (GSH) and cyanide profoundly inhibited the effects of selenite, indicating that the site of action of selenite was on the outer membrane and the binding of selenite to the sulfhydryl groups of membrane proteins was proposed to be an essential step for selenite-induced contracture and neuromuscular action. These findings suggest that neuromuscular blockade and tetanic spasm, produced by selenite in chicks, may play a role in causing respiratory failure in vivo.