过氧化氢和11，12-环氧二十碳三烯酸对内皮依赖性超极化因子介导的脑基底动脉舒张作用的影响

目的：探讨过氧化氢（H2O2）和11,12-环氧二十碳三烯酸（11,12-EET）在内皮依赖性超极化因子（endothelium—dependent hyperpolarizing factor,EDHF）介导的基底动脉舒张中的作用。方法：采用离体血管舒缩功能测定实验,检测乙酰胆碱（ACh）、H2O2、11,12-EET及过氧化氢酶（CAT）等对大鼠离体脑基底动脉血管环的舒张作用。结果：在30mmol／L的KCl预收缩的大鼠脑基底动脉环上,ACh可产生浓度依赖性的舒张作用;血管用NO合酶抑制剂（L-NAME,3×10^5 mol／L）和前列环素（PGI2）合酶抑制剂（Indo,10^-5mol／L）预处理后,ACh对基底动脉仍存在部分舒张作用,即非NO和非PGI2介导的舒张。应用L-NAME和Indo后,11,12-EET对大鼠基底动脉无明显的舒张作用,H2O2仅有轻微舒张作用,CAT对ACh介导的非NO和非PGI2反应没有影响。结论：在大鼠基底动脉中ACh介导的EDHF反应即非NO和非PGI2介导的舒张中不涉及H2O2和11,12-EET。     

非NO、非PGI2介导大鼠大脑中动脉舒张反应与硫化氢的关系

目的 研究硫化氢(H2S)与非一氧化氮(NO)、非前列环素(PGI2)介导的大鼠大脑中动脉(MCA)舒张反应的关系.方法 采用离体微血管舒缩功能测定大鼠大脑中动脉舒张功能.结果 在U46619预收缩的大鼠大脑中动脉上,10-7~10-4.5mol·L-1的ACh可显著诱导大鼠大脑中动脉呈浓度依赖性舒张,但血管用NO合酶抑制剂L NAME(3×10- 5 mol·L-1)和PGI2合成抑制剂Indo (1×10- 5 mol·L-1)预处理后,ACh的舒张反应有明显的减弱,最大舒张率由78.2%±4.6%降至56.5%±4.0%,并且剩留舒张反应几乎可被内源性H2S合成酶抑制剂PPG(10-4mol·L-1)完全取消.H2S供体NaHS在10- 5~10-2.5mol·L-1范围内对U46619预收缩的大鼠大脑中动脉也呈一定的浓度依赖性舒张作用.结论 非NO、非PGI2介导的大鼠大脑中动脉舒张反应与H2S有关.     

乙酰胆碱介导的内皮超极化因子对海马神经元缺氧/再给氧损伤的保护作用

目的研究乙酰胆碱(acetylcholine,ACh)介导的大鼠大脑中动脉内皮释放的内皮超极化因子(endothelium-de-pendent hyperpolarizing factor,EDHF)对海马神经元缺氧/再给氧损伤的保护作用。方法用原代培养的大鼠海马神经元细胞建立缺氧/再给氧损伤模型,取大鼠大脑中动脉(mid-dle cerebral artery,MCA)血管段,PGI2和NO的阻断剂NG-ni-tro-L-argininemethyl ester(L-NAME)和indomethacin(Indo)预处理后,用ACh刺激血管内皮释放EDHF,用四甲基偶氮唑盐(MTT)染色吸光度和乳酸脱氢酶(LDH)活性作为细胞损伤指标,用激光共聚焦显微镜检测细胞内游离Ca2+浓度。结果与正常对照组相比,缺氧/再给氧损伤组细胞MTT染色吸光度明显降低,上清液中LDH活性和细胞内Ca2+浓度则明显升高。1μmol.L-1ACh合用含血管内皮的MCA血管段(MCA/Endo)或ACh+MCA/Endo+L-NAME+Indo均可抑制缺氧/再给氧致海马细胞MTT染色吸光度降低、培养上清液中LDH活性及细胞内Ca2+浓度的升高,但单用1μmol.L-1ACh或MCA/Endo却无上述抑制作用,合用1μmol.L-1ACh和去内皮MCA血管段(MCA/-Endo)也无明显抑制作用。K+在25~35μmol.L-1范围内,可明显减弱ACh+MCA/Endo+L-NAME+Indo对缺氧再给氧致海马神经细胞MTT染色吸光度降低、上清液LDH活性及细胞内Ca2+浓度升高的抑制作用,但Ba2+没有明显影响。结论假定的EDHF对原代培养的海马神经元缺氧/再给氧损伤具有保护作用,其机制可能与抑制缺氧/再给氧引起的钙超载有关。     

血管内皮细胞超极化因子

内皮细胞释放多种重要的生物活性物质 ,调节血管张力、血液纤溶与凝血机制、脂蛋白代谢、免疫反应等重要生命过程。内皮细胞释放的超极化因子 (EDHF)是一类既不同于一氧化氮 (NO) ,也不同于前列环素 (PGI2 )的活性成分 ,可能是花生四烯酸的非前列腺素类代谢物或细胞色素P45 0 ,也可能是K+ 或H2 O2 。EDHF可激活钙依赖性钾通道 ,诱导平滑肌膜电位超极化 ,诱发内皮依赖性舒血管反应。在病理状态下 ,尤其是NO通路障碍时 ,EDHF通路发挥重要作用。因此深入研究EDHF的药理学特征已形成心血管学科的又一热点     

外源性血管内皮衍生超极化因子对脑缺血再灌注损伤的影响

目的:硫化氢(hydrogen sulfide,H2S)为一种假定的血管内皮衍生超极化因子(endothelium-derived hyperpolarizing factor,EDHF),本研究探讨外源性H2S,即外源性假定的EDHF对脑缺血再灌注损伤的影响。方法:采用线栓法复制大鼠局灶性脑缺血(MCAO)再灌注损伤模型,测定动物行为功能、脑组织梗死体积、脑组织含水量、血清乳酸脱氢酶(LDH)活性及丙二醛(MDA)含量,用HE染色法观察脑组织学改变。结果:H2S供体硫氢化钠(NaHS,i.v.)0.195、0.390、0.780mg/kg能明显改善神经功能状态,降低缺血再灌注后脑梗死体积百分比,降低脑含水量,显著地抑制局灶性脑缺血再灌注损伤大鼠血清MDA含量和LDH活性,并不同程度地改善大鼠脑病理组织学的变化。结论:NaHS可明显改善大鼠脑缺血再灌注性损伤,提示外源性ED-HF(H2S)有抗脑缺血再灌损伤作用。     

硫化氢对自发性高血压大鼠主动脉平滑肌细胞增生的影响

目的探讨硫化氢(H2S)对自发性高血压大鼠(SHR)主动脉平滑肌细胞(ASMC)增生的影响。方法体外培养SHR ASMC,将其分成对照组、10-5、10-4和l0-3 mol/L NaHS组,检测经H2S处理后ASMC细胞的增生指数和丝裂原活化蛋白激酶(MAPK)活性。结果与对照组相比,10-5、10-4和10-3 mol/L NaHS组增生指数显著降低(P<0.01),MAPK活性明显下降(P<0.05或P<0.01)。结论 H2S可抑制SHR ASMC增生和MAPK活性,推测可能通过MAPK信号途径介导。     

硫化氢下调大鼠主动脉L-精氨酸/一氧化氮合酶/一氧化氮通路

目的观察H2S对血管L-精氨酸/一氧化氮(L-Arg/NO)通路的影响以探讨H2S和NO这两种气体信号分子间的相互作用。方法离体孵育大鼠主动脉薄片,加入H2S供体NaHS(10-7~10-4mol.L-1)孵育4 h,及50μmol.L-1NaHS分别孵育2、4和6 h。采用G re iss法测定血管亚硝酸盐含量;同位素示踪法检测血管组织一氧化氮合酶(NOS)活性及L-Arg转运,RT-PCR检测eNOS、CAT1基因表达。结果一次性给予50μmol.L-1NaHS,孵育2 h,孵育液中NO2-含量比对照组低62%,血管NOS活性下降48%,L-Arg转运减少50%(P<0.01);孵育6 h,NO2-含量比对照组低19%(P<0.05),而NOS活性和L-Arg转运已基本恢复(P>0.05)。NaHS(10-7~10-4mol.L-1),呈浓度依赖的抑制了L-Arg/NOS/NO通路,IC50分别为0.499、3.198及3.927μmol.L-1(P<0.01);而给予50μmol.L-1NaHS后,eNOS和CAT-1A的mRNA表达分别减少34.3%和55.1%(P<0.01)。结论H2S通过抑制血管组织L-Arg转运和NOS活性和基因表达,下调L-Arg/NOS/NO通路,从而减少血管NO生成。     

杜鹃花总黄酮对缺血/再灌注损伤模型大鼠脑基底动脉TRPV4的作用研究

目的探讨杜鹃花总黄酮(TFR)对缺血/再灌注损伤模型大鼠脑基底动脉(CBA)瞬时感受器电位通道香草酸受体亚型Ⅳ(TRPV4)的作用。方法以改良四血管阻断法(4-VO)建立大鼠缺血/再灌注模型(IR);运用加压灌注法和细胞膜电位记录法,离体观察TFR对KCl预收缩IR大鼠CBA的舒张作用和超极化反应及TRPV4阻断剂钌红(RR)对其的影响;采用实时荧光定量PCR法和蛋白质印迹法,在体观察TFR对IR大鼠脑血管内皮细胞TRPV4 mRNA和蛋白表达以及RR对其的影响。结果递增浓度的TFR可诱导IR大鼠离体CBA产生明显剂量依赖性的舒张效应和超极化反应。去除血管内皮细胞后,TFR仍能介导CBA产生较弱的舒张作用和超极化反应,与血管内皮完整组比较,差异有显著性(P<0.01);去除一氧化氮(NO)和前列环素(PGI2)舒张作用后,TFR仍能诱导IR大鼠CBA产生明显的舒张效应和超极化作用,此作用可被TRPV4通道阻断剂RR抑制;TFR可明显上调IR大鼠脑血管TRPV4 mRNA和蛋白表达,而阻断TRPV4可明显抑制TFR上调的TRPV4基因表达。结论 TFR能介导IR大鼠CBA产生较强的内皮依赖性和较弱的内皮非依赖性血管舒张反应和超极化作用,其内皮依赖性效应推测可能与TFR促使脑血管内皮激活,促进内皮细胞生成和释放内皮衍生性超极化因子(EDHF)增多,继而激活TRPV4,引发Ca~(2+)内流,导致血管平滑肌细胞膜超极化,产生血管舒张效应有关。     

内皮依赖性超极化因子在血管舒张中的作用

目的研究内皮依赖性超极化因子(EDHF)在血管舒张中的作用及机制。方法测定各种内皮依赖性舒张因子抑制剂、钾通道抑制因子、细胞色素P450单氧化酶抑制剂作用下的血管环张力。结果EDHF的血管舒张作用在大鼠肠系膜微动脉明显大于胸主动脉。一氧化氮(NO)合成受到慢性抑制时,胸主动脉的EDHF作用有增加趋势,在肠系膜微动脉投药后3 d和1周的EDHF作用明显增加。ChTx部分抑制、TBA明显抑制EDHF在肠系膜微动脉的舒张作用。结论EDHF在大鼠肠系膜微动脉的内皮依赖性舒张反应中起主要作用;在NO合成受抑制时其作用明显增加;其作用介导于K_Ca通道。     

硫化氢对正常及自发性高血压大鼠主动脉平滑肌细胞PCNA和p-ERK蛋白表达的影响

目的研究硫化氢(hydrogen sulfide,H2S)对正常大鼠及自发性高血压大鼠(spontaneous hypertensive rat,SHR)主动脉平滑肌细胞(aortic smooth muscle cell,ASMC)增殖的影响。方法分别将正常大鼠及SHR主动脉平滑肌细胞分为实验组和对照组,实验组中分别加入浓度为(10-5~10-3)mol.L-1H2S供体的硫氢化钠(sodium hydrosulfide,NaHS)或浓度为(2~10)mmol.L-1胱硫醚-γ-裂解酶抑制剂的炔丙基甘氨酸(DL-propargy lglycine,PPG),对照组加入等体积的生理盐水,分别以蛋白质印迹法观察6、12、18和24h时间点的平滑肌细胞中细胞增殖核抗原(PCNA)和磷酸化的细胞外信号调节激酶(p-ERK)蛋白表达情况。结果NaHS对正常大鼠ASMC增殖及p-ERK蛋白表达无影响。PPG显著促进正常大鼠ASMC增殖及p-ERK蛋白表达。NaHS显著抑制SHR的ASMC增殖及p-ERK蛋白表达。PPG显著促进SHR的ASMC增殖及p-ERK蛋白表达。结论内源性H2S下调可促进正常大鼠及SHR的ASMC增殖,而外源性补充H2S可抑制SHR的ASMC异常增殖,ERK信号途径可能介导H2S抑制ASMC增殖的分子机制。     

Spasmogen action in guinea-pig isolated trachealis: involvement of membrane K+-channels and the consequences of K+-channel blockade.

1. Acetylcholine (ACh), histamine, prostaglandin E2 and potassium chloride (KCl) each evoked concentration-dependent spasm of guinea-pig isolated trachealis treated with indomethacin (2.8 microM). 2. Neither tetraethylammonium (TEA; 0.1-10 mM) nor procaine (0.1-10 mM) potentiated these spasmogens. Indeed, procaine (10 mM) depressed the log concentration-effect curves of all the spasmogens while TEA (1-10 mM) caused some depression of the log concentration-effect curve of prostaglandin E2. 3. Intracellular electrophysiological recording was performed in trachealis bathed by normal Krebs solution or by Krebs solution containing 2.8 microM indomethacin. In either medium the majority of trachealis cells exhibited spontaneous electrical slow waves while some cells were electrically quiescent. In either medium the spasmogenic effects of ACh (1 mM) and histamine (0.2 mM) were accompanied by depolarization and abolition of slow wave discharge. In many cases the record of membrane potential subsequently exhibited noise which incorporated fast, hyperpolarizing transients. 4. In the absence and presence of indomethacin, TEA (10 mM) and procaine (5 mM) markedly reduced the membrane noise and hyperpolarizing transients evoked by ACh or histamine without augmenting the evoked tension. 5. It is concluded that slow wave discharge does not depend on prostaglandin synthesis. The membrane noise and hyperpolarizing transients evoked by ACh and histamine represent the opening of membrane K+-channels. While such K+-channel opening may offset spasmogen-induced depolarization it does not moderate the evoked tension.     

Possible mechanisms underlying the vasodilatation induced by olprinone, a phosphodiesterase III inhibitor, in rabbit coronary artery

The possible mechanisms underlying the vasodilatation induced by olprinone, a phosphodiesterase type III inhibitor, were investigated in smooth muscle of the rabbit coronary artery. Isometric force and membrane potential were measured simultaneously using endothelium-denuded smooth muscle strips. Acetylcholine (ACh, 3 microM) produced a contraction with a membrane depolarization (15. 2+/-1.1 mV). In a solution containing 5.9 mM K(+), olprinone (100 microM) hyperpolarized the resting membrane and (i) caused the absolute membrane potential level reached with ACh to be more negative (but did not reduce the delta membrane potential seen with ACh, 15.2+/-1.8 mV) and (ii) attenuated the ACh-induced contraction. In a solution containing 30 mM K(+), these effects were not seen with olprinone. Glibenclamide (10 microM) blocked the olprinone-induced membrane hyperpolarization. 4-AP (0.1 mM) significantly attenuated the olprinone-induced resting membrane hyperpolarization but TEA (1 mM) had no such effect. Glibenclamide (10 +microM), TEA (1 mM) and 4-AP (0.1 mM), given separately, all failed to modify the inhibitory actions of olprinone on (i) the absolute membrane potential level seen with ACh and (ii) the ACh-induced contraction. It is suggested that olprinone inhibits the ACh-induced contraction through an effect on the absolute level of membrane potential achieved with ACh in smooth muscle of the rabbit coronary artery. It is also suggested that glibenclamide-sensitive, ATP-sensitive K(+) channels do not play an important role in the olprinone-induced inhibition of the ACh-induced contraction.     

Na+-K+-ATPase is involved in the sustained ACh-induced hyperpolarization of endothelial cells from rat aorta

BACKGROUND AND PURPOSE: Inhibition of Na(+)-K(+)-ATPase is known to attenuate endothelium-dependent relaxation in many arteries. The purpose of this study was to evaluate the role of Na(+)-K(+)-ATPase in the regulation of endothelial membrane potential at rest and during stimulation by ACh. EXPERIMENTAL APPROACH: Membrane potential was recorded from the endothelium of rat aorta using the perforated patch-clamp technique. KEY RESULTS: Superfusion with K(+)-free solution produced a depolarization of about 11 mV from the resting value of -42.9+/-0.9 mV. Reintroduction of 4.7 mM K(+) transiently hyperpolarized endothelial cells to -52.4+/-1.8 mV and the membrane potential recovered within 10 min. Ouabain 500 microM depolarized endothelium by about 11 mV and inhibited the hyperpolarization induced by K(+) reintroduction into the K(+)-free solution. However, 500 nM ouabain did not affect the resting membrane potential or the hyperpolarization induced by K(+) reintroduction. Pre-exposure to ouabain 500 microM, but not 500 nM, attenuated the sustained component of hyperpolarization to ACh without affecting the amplitude of the transient peak hyperpolarization. In K(+)-free solution, the amplitude of peak hyperpolarization to ACh was increased, while the sustained component of hyperpolarization was attenuated. CONCLUSIONS AND IMPLICATIONS: These results indicate that electrogenic Na(+)-K(+)-ATPase partially contributes to the sustained hyperpolarization of endothelial cells from rat aorta in response to ACh. They also suggest that the alpha1, but not alpha2 or alpha3 isoforms, is involved in ACh-mediated hyperpolarization.     

Factors inducing endothelium-dependent relaxation in the guinea-pig basilar artery as estimated from the actions of haemoglobin

1. Factors inducing dilatation of guinea-pig basilar artery were investigated in intact and endothelium-denuded tissues by measurement of isometric tension and by electrophysiological methods. 2. The amplitudes of contractions induced by 9,11,epithio-11,12-methanothromboxane A2 (STA2) and by high K+ were enhanced by haemoglobin (oxyhaemoglobin, Hb) in a concentration-dependent fashion (above 1 microM). For the high K+-induced contraction, the initial tonic component was enhanced to a greater extent than the secondary phasic component. Mechanical responses evoked by STA2 and by high K+ were greater in endothelium-denuded tissues, but Hb (below 10 microM) had no effect on them. 3. Hb (10 microM) had no effect on the contractile proteins as estimated from the actions of Hb on Ca2+-induced contractions in skinned muscle tissues. Further, Hb had no effect on the release of Ca2+ from intracellular stores but it accelerated the Ca2+ accumulation into the sarcoplasmic reticulum as judged from the caffeine- or STA2-induced contraction generated in intact tissues. 4. Acetylcholine (ACh) relaxed tissues that were precontracted by STA2 but Hb prevented this relaxation, in a concentration-dependent fashion. The ACh-induced relaxation was sustained for over 10 min in the absence of Hb, but following application of Hb, ACh caused only a transient relaxation. 5. STA2 (up to 100 nM) did not modify the resting membrane potential of smooth muscle cells of the basilar artery. ACh (10 microM) caused transient hyperpolarization which was only slightly inhibited by Hb (10 microM) whether or not STA2 was present. The hyperpolarization induced by ACh required the presence of endothelial cells. 6. A23187 (0.01-1 microM) relaxed tissues which were precontracted by STA2, in a concentration-dependent fashion but had no effect on the membrane potential. 7. These results suggest that in guinea-pig basilar artery, ACh induces relaxation of tissues that were precontracted by STA2 by causing release of both endothelium-derived relaxing (EDRF) and endothelial dependent hyperpolarizing factor (EDHF) (sustained and initial transient relaxation, respectively), but via different mechanisms. Hb inhibits the former and to a lesser extent, the latter. Since A23187 produced relaxation of pre-contracted tissue but caused no detectable change in the membrane potential, this agent may release EDRF but not EDHF.     

Possible mechanisms of action of Gymnodinium breve toxin at the mammalian neuromuscular junction.

1 The mechanism of action of a crude fraction of Gymnodinium breve toxin (GBTX) was investigated by intracellular recording techniques in the rat phrenic nerve diaphragm preparation. 2 GBTX (2 micrograms/ml) decreased the input resistance of the muscle membrane concomitantly with a depolarization of the resting membrane potential. 3 A low sodium solution reversed or prevented a GBTX-induced membrane depolarization. 4 Tetrodotoxin (TTX) antagonized a GBTX-induced increase in miniature endplate potential (m.e.p.p.) frequency and repolarized a GBTX-depolarized membrane. Pretreatment with TTX prevented GBTX effects. 5 GBTX reversibly reduced depolarizations produced by bath applied acetylcholine (ACh). The membrane depolarization was not responsible for the depression of ACh responses. 6 These findings suggest that GBTX increases m.e.p.p. frequency and depolarizes the resting membrane potential by increasing sodium permeability. The reduction of ACh-induced depolarizations suggests that GBTX may be acting at some site on the ACh receptor.     

Inhibition of calcium spikes and transmitter release by gamma-aminobutyric acid in the guinea-pig myenteric plexus

The effect of gamma-aminobutyric acid (GABA) (1 microM-1 mM) on synaptic transmission in isolated myenteric ganglia of guinea-pig ileum was investigated with intracellular recording techniques. GABA (up to 1 mM) had no effect on the resting membrane potential and membrane conductance of S neurones. GABA reduced the amplitude of the fast excitatory postsynaptic potential e.p.s.p.) without changing the amplitude of the nicotinic response to ionophoretic application of acetylcholine (ACh). This effect was mimicked by baclofen (10-100 microM) and was not blocked by bicuculline (10 microM). The preparation did not become desensitized during prolonged GABA applications. Cholinergic and non-cholinergic slow e.p.s.ps evoked by single or repetitive presynaptic nerve stimulation were reduced in amplitude by GABA. GABA did not depress muscarinic responses to ionophoretic application of ACh. GABA reduced the duration of the action potential in AH neurones in concentrations that did not affect the membrane potential or conductance. The effect was very marked when electrodes were filled with CsCl, and tetrodotoxin was in the superfusing solution. This effect was also mimicked by baclofen, was insensitive to bicuculline and was not reduced with repeated application or GABA. It is concluded that GABA inhibits release of ACh and the transmitter mediating the slow e.p.s.p. This effect may result from inhibition of an inward calcium current.     

坎地沙坦,PD123319及金雀异黄素对大鼠血管平滑肌细胞迁移影响

目的:探讨血管紧张肽Ⅱ(AngⅡ)不同受体亚型(AT1,AT2)在血管平滑肌细胞(VSMC)迁移中的作用。方法:以体外培养VSMC为基础,采用改良Boyden小室,对不同浓度AT1拮抗剂坎地沙坦(CV)、AT2拮抗剂PD123319(PD)和酪氨酸激酶(PTKs)抑制剂金雀异黄素作用下AngII诱导产生的VSMC跨膜迁移细胞数进行评价。分对照组、AngII组、AngII+10-10～10-5mol·L-1CV组、AngⅡ+10-9～10-6mol·L-1PD组、AngⅡ+CV+PD组、AngⅡ+金雀异黄素组。结果:与对照组相比,AngⅡ组跨膜迁移细胞数明显增加,P<0.01。坎地沙坦在10-10～10-5mol·L-1的浓度范围内,呈剂量依赖性抑制由AngⅡ介导的VSMC迁移(r=0.95,P<0.05)。PD123319对此无明显的增强或抑制作用。金雀异黄素组VSMC跨膜迁移细胞数低于AngⅡ组,高于对照组。结论:AngⅡ影响VSMC迁移能力的生物学效应由AT1介导;AT2在VSMC迁移过程中不起作用或者不起主要作用。酪氨酸激酶的激活也参与了AngⅡ诱导的VSMC迁移的信号转导过程。     

Beta 2-adrenoceptors mediate the stimulating effect of adrenaline on active electrogenic Na-K-transport in rat soleus muscle

The relative role of beta 1- and beta 2-adrenoceptors in mediating the stimulating effect of adrenaline on active electrogenic Na-K-transport has been assessed in experiments on rat soleus muscles in vitro and in vivo. 2 In the rat isolated soleus muscle, adrenaline (10(-6) M) increases the resting membrane potential (EM) by 5.8 mV and stimulates 22Na-efflux and ouabain-suppressible 42K-uptake by 91 and 94%, respectively. 3 All of these effects are completely blocked by propranolol (10(-5) M), whereas the beta 1-selective adrenoceptor antagonist, metoprolol, was found to be at least 50 times less potent. 4 The beta 2-adrenoceptor agonist, salbutamol, was at least 100 times as potent as H133/22 (a beta 1-selective agonist) in stimulating 22Na-efflux and 42K-influx. 5 In experiments performed under pentobarbitone anaesthesia, the intravenous injection of adrenaline (5 microgram) or salbutamol (0.5 to 50 microgram) led to a rapid and marked increase in the EM of the exposed soleus muscle. This hyperpolarizing effect could not be accounted for by the concomitant, relatively modest change in extracellular K.     

Autoregulation of acetylcholine release from vagus nerve terminals through activation of muscarinic receptors in the dog trachea.

1. The effects of pirenzepine and gallamine on the membrane and contractile properties of smooth muscle cells and on excitatory neuro-effector transmission in the dog trachea were investigated by means of microelectrode, double sucrose gap and tension recording methods. 2. Pirenzepine (10(-7) M) and gallamine (10(-5) M) had no effect on the resting membrane potential or the input resistance of the smooth muscle cells. 3. Pirenzepine (10(-10)-10(-9) M) and gallamine (10(-7) M) enhanced the amplitude of twitch contractions evoked by field stimulation in the combined presence of indomethacin (10(-5) M) and propranolol (10(-6) M). At higher concentrations pirenzepine (10(-8) M) inhibited the twitch contractions in a dose-dependent manner. Both pirenzepine and gallamine in doses over 10(-7) and 10(-5) M, respectively, reduced muscle tone. 4. Pirenzepine (10(-10)-10(-9) M) and gallamine (10(-7) M) enhanced the amplitude of excitatory junction potentials (e.j.ps) evoked by field stimulation (single or repetitive stimulation). However, a high concentration of pirenzepine (10(-8) M) reduced the amplitude of e.j.ps. In parallel with its action on e.j.ps, pirenzepine (over 10(-9) M) reduced the response of smooth muscle cells to acetylcholine (ACh), in a dose-dependent manner. Gallamine (5 X 10(-5) M) markedly enhanced the amplitude of e.j.ps but also reduced the response of muscle cells to ACh. 5. ACh (10(-10)-10(-9) M) inhibited twitch contractions evoked by field stimulation, with a slight increase of resting tension. 6. Gallamine enhanced the summation of e.j.ps during repetitive field stimulation at a high frequency (20 Hz), but was without effect on the depression phenomena of e.j.ps observed during double stimulus experiments at different time intervals (5-60 s). 7. These results indicate that both pirenzepine and gallamine have dual actions on pre- and post-junctional muscarinic receptors in dog tracheal tissue. At low concentrations both agents potentiate excitatory neuro-effector transmission, presumably due to enhancement of release of ACh from vagal nerve terminals through blockade of a negative auto-regulatory process activated by endogenous ACh. At higher concentrations, these agents inhibit the response of smooth muscle cells to ACh through post-junctional muscarinic receptors and relaxation of the muscle tissue occurs.     

Effect of KC399, a newly synthesized K+ channel opener, on acetylcholine-induced electrical and mechanical activities in rabbit tracheal smooth muscle.

1. Effects of KC399, an opener of ATP-sensitive K+ channels were investigated on membrane potential, isometric force and intracellular Ca2+ ([Ca2+]i) mobilization induced by acetylcholine (ACh) in smooth muscle from the rabbit trachea. 2. In these smooth muscle cells, ACh (0.1 and 1 microM) depolarized the membrane in a concentration-dependent manner, KC399 (1-100 nM) hyperpolarized the membrane whether in the presence or absence of ACh. When the concentration of ACh was increased, the absolute values of the membrane potential induced by the maximum concentration of KC399 were less negative. 3. ACh (0.1 to 10 microM) concentration-dependently produced a phasic, followed by a tonic increase in both [Ca2+]i and force. KC399 (above 3 nM) lowered the resting [Ca2+]i and attenuated the ACh-induced phasic and tonic increases in [Ca2+]i and force, in a concentration-dependent manner. The magnitude of the inhibition was greater for the ACh-induced tonic responses than for the phasic ones. Nicardipine (0.3 microM), a blocker of the L-type Ca2+ channel, attenuated the ACh-induced tonic, but not phasic, increases in [Ca2+]i and force. KC399 further attenuated the ACh-induced tonic responses in the presence of nicardipine. 4. In beta-escin-skinned strips, Ca2+ (0.3-10 microM) produced a contraction in a concentration-dependent manner. KC399 (0.1 microM) had no effect on the Ca(2+)-force relationship in the presence or absence of ATP with GTP. However, at a very high concentration (1 microM), this agent slightly shifted the relationship to the right and attenuated the maximum Ca(2+)-induced contraction.(ABSTRACT TRUNCATED AT 250 WORDS)