硝苯吡啶对腹腔神经节突触传递的阻断作用

本文应用细胞内记录技术,观察了钙通道阻滞剂硝苯吡啶（nifedipine)对离体豚鼠腹腔神经节突触传递的影响,硝苯吡啶（0.1-10umol/L)不影响所检细胞的静息膜电位,膜电阻及细胞内刺激引起的动作电位,但能显著阻断N-型胆碱能的突触传递,并且这种作用可被低钙模拟、高钙拮抗,硝苯吡啶（10umol/L)也不影响突触后膜对乙酰胆碱（ACh)的敏感性;但在高钾克氏液中,能减少微小兴奋性突触后电位（mEPSPs)的频率;在低钙和高镁克氏液中,能减少量子含量,而对量子大小无影响。结果表明,治疗量的硝苯吡啶(0.1umol/L)通过阻滞突触前膜钙内流及ACh的量子性释放,产生突触阻断作用。这可能是硝苯吡啶降压机理的一个组成部分。     

硝苯吡啶降压作用与血浆中加压激素和降压激素的关系

硝苯吡啶是一种钙通道阻断剂,具有降血压作用。一般认为,硝苯吡啶的降压作用,是由于阻滞血管平滑肌的Ca~(2 )跨膜内流而使血管扩张以及促进肾脏排钠利尿所致。但是硝苯吡啶也能影响包括激素分泌在内的多种钙依赖性生理过程。因此,探讨硝苯吡啶的降压作用与血浆中加压激素和降压激素含量变     

辣椒素对离体大鼠胃平滑肌收缩性的影响

目的:考察辣椒素对离体大鼠胃平滑肌收缩性的影响。方法:本研究以大鼠的离体胃平滑肌条为模型,首先考察在正常钙克氏液、高钙克氏液和低钙克氏液中辣椒素对胃平滑肌收缩作用的影响。然后正常克氏液中,分别观察辣椒素对乙酰胆碱、新斯的明、阿托品分别存在下的胃平滑肌收缩性的影响。结果:辣椒素在2.5μmol/L-40μmol/L浓度范围内可剂量依赖性显著抑制高钙溶液(Ca2 终浓度5μmol/L)引起的大鼠胃平滑肌强烈收缩,在5μmol/L-40μmol/L浓度范围内可显著抑制正常克氏液中大鼠胃平滑肌条的运动,且具有明显剂量依赖性,在10μmol/L-40μmol/L浓度范围内可显著抑制低钙克氏液中大鼠胃平滑肌条的运动,且具有剂量依赖性。辣椒素(10μmol/L)可拮抗乙酰胆碱和新斯的明引起的收缩作用(P<0.01)。辣椒素(10μmol/L)的作用与阿托品具有相加作用(P<0.01)。结论:辣椒素对胃平滑肌的收缩具有明显的抑制作用。     

麻黄碱抑制小鼠输精管电场刺激致收缩的机制

麻黄碱(10 nmol/L~(-0.1) mmol/L)对电场刺激所致输精管收缩的浓度依赖性抑制作用可被育亨宾(0.1 μmol/L)减弱。去甲肾上腺素(0.1 nmol/L~(-10)μmol/L )和酪胺(0.1 μmol/L~(-0.1) mmol/L)也有类似麻黄碱的作用,去氧肾上腺素则缺乏此种作用。利血平处理和可卡因(10 μmol/L)可减弱麻黄碱和酪胺的抑制效应,但能增敏去甲肾上腺素的作用。高 Ca~( )和4-氨基吡啶(50 μmol/L)明显减弱甚至取消麻黄碱对电场刺激的抑制效应。以上结果提示麻黄碱抑制电场刺激所引起的输精管收缩。至少部分通过促进神经末梢释放去甲肾上腺素间接作用,后者激动突触前α_2-肾上腺素受体,从而抑制去甲肾上腺素的进一步释放。麻黄碱和其释放的去甲肾上腺素的作用,又可能与阻遏 Ca~( )内流有关。     

一氧化氮在血管紧张素Ⅱ激活蛋白激酶C中的作用

实验在培养新生大鼠心肌细胞中检测NO前体L－精氨酸（L－Arg）和NO供体硝普钠（SNP）对血管紧张素Ⅱ（AngⅡ）激活蛋白激酶C（PKC）的作用,以探讨心肌细胞PKC水平的信号转导途径,实验结果如下：（1）无血清DMEM培养心肌细胞24h后加入AngⅡ,PKC活性呈剂量依赖性增高;（2）培养基中加入L－Arg,PKC活性呈剂量依赖性降低;（3）用L－Arg100μmol/L进行预处理,30min后分别加入AngⅡ0.1μmol/L或PMA10μmol/L,PKC活性均明显降低,与单纯AngⅡ组和单纯PMA组相比均有显著性差异;用NOS抑制剂L－NAME预处理后,再加入L－Arg,可明显阻断L－Arg对上述两个效应的影响;（4）培养液中加入NO供体SNP,PKC活性呈剂量依赖性地降低;（5）用SNP10μmol／L预处理心肌细胞,5min后分别加入AngⅡ或PMA,PKC活性分别与单纯AngⅡ和单纯PMA组相比均明显降低。以上结果表明,AngⅡ能剂量依赖性激活PKC,而NO可剂量依赖性抑制PKC活性;NOS参与L－Arg抑制AngⅡ或PMA激活PKC的作用。这些观察提示,NO抑制AngⅡ对心肌细胞的作用可能是通过抑制PKC活性实现的,PKC可能是NO和AngⅡ在心肌细胞内信号转导的交汇点（cross talk）。     

内皮素刺激垂体前叶细胞胞浆钙和促性腺激素的分泌

在培养的大鼠垂体前叶细胞悬液内加入内皮素100 nmol/L,可诱发胞浆钙浓度升高,即刻出现一高峰波,随后为低平台波,此双相波约维持1.5 min。高峰波在10 s内出现,若消除细胞外Ca~(2+),不影响高峰波的产生,说明峰波与细胞内储存的Ca~(2+)有关。若加双氢吡啶钙通道拮抗剂硝苯啶(nifedipine)1 μmol/L,     

一种新型的α-纤维蛋白原酶对血小板聚集的影响

SDS-聚丙烯酰胺凝胶电泳(SDS-PAGE)检测中国眼镜蛇毒蛋白酶水解纤维蛋白原的作用方式,发现该蛋白酶可迅速水解纤维蛋白原Aα链,对γ链作用较弱,对Bβ链无作用,是一种新型的α-纤维蛋白原酶.用比浊法测定血小板聚集率,证实中国眼镜蛇毒蛋白酶低剂量(0.025 mg/kg)、中剂量(0.05 mg/kg)以及高剂量(0.1 mg/kg)体内给药浓度依赖性地抑制ADP(10 .Μmol/L)和胶原(100 mg/L)诱导的兔血小板聚集.     

血管钠肽抑制异丙肾上腺素增强的大鼠心肌细胞钙瞬变

采用光谱荧光法研究血管钠肽(vasonatrin peptide,VNP)对心肌细胞内钙瞬变的作用及其机制,观察钠尿肽鸟苷酸环化酶(guanylate cyclase,GC)受体的特异性阻断剂(HS-142-1)、8-溴-环磷酸鸟苷(8-Br-cGMP)和镁蓝(methylene blue,MB)对心肌细胞内钙瞬变的影响。结果显示,异丙肾上腺素(isoproterenol,Iso)(10~(-10)～10~(-6)mol/L)可剂量依赖性地引起心肌细胞内钙瞬变增强,相对于对照组分别增强(13±8)%(P>0.05)、(26±13)%(P<0.05)、(66±10)%(P<0.01)、(150±10)%(P<0.01)和(300±25)%(P<0.01)。此效应可被β肾上腺素受体阻断剂普萘洛尔(10~(-6)mol/L)所阻断。VNP(10~(-10)～10~(-6)mol/L)可剂量依赖性地抑制Iso(10~(-8)mol/L)引起的心肌细胞内钙瞬变幅值的升高,相对于Iso(10~(-8)mol/L)分别减弱(99±3)%(P>0.05)、(96±2)%(P<0.05)、(84±6)%(P<0.01)、(66±3)%(P<0.01)和(62±3)%(P<0.01)。8-Br-cGMP(10~(-7)～10~(-3)mol/L)也可剂量依赖性地抑制Iso(10~(-8)mol/L)引起心肌细胞内钙瞬变的增强。HS-142-1(2×10~(-5)mol/L)使VNP的作用几乎完全消失。MB是GC的抑制剂,10~(-5)mol/L MB不但使VNP的作用完全消失,而且增强Iso对心肌细胞内钙瞬变的效应。VNP和HS-142-1本身对心肌细胞内钙瞬变无显著影响。而MB使心     

冬虫夏草提取物的美白作用

以冬虫夏草提取物(Chinese cordyceps extract)为研究对象,通过蘑菇酪氨酸酶活性抑制试验和小鼠皮肤黑色素瘤细胞(B16-F10)黑素合成抑制试验考察冬虫夏草提取物的美白活性。结果显示冬虫夏草提取物(质量浓度40～200 mg/m L)呈剂量依赖性抑制蘑菇酪氨酸酶的活性,且在安全剂量(质量浓度0.1～0.5 mg/m L)下显著抑制小鼠皮肤黑色素瘤细胞(B16-F10)内的黑色素合成(P0.05)。说明冬虫夏草提取物能通过抑制酪氨酸酶活性有效阻滞黑色素的合成,从而实现美白作用。     

垂体腺苷酸环化酶激活多肽对鲤鱼脑垂体细胞内cAMP和Ca^2＋的影响

采用环腺苷酸 (cAMP)放射免疫测定法和活细胞内Ca2 荧光探针Indo 1,研究绵羊垂体腺苷酸环化酶激活多肽 (oPACAP)对原代培养的鲤鱼脑垂体细胞内cAMP和游离Ca2 ([Ca2 ]i)的影响 ,以期探讨PACAP调节脑垂体生长激素 (GH)分泌的机制受体后。oPACAP 38和oPACAP 2 7以剂量依存方式促进脑垂体细胞内cAMP释放和合成。oPACAP 38和oPACAP 2 7也能升高脑垂体细胞内 [Ca2 ]i 水平 ,该作用会因用EGTA消竭细胞外Ca2 ([Ca2 ]e)而迅速消失 ;L型电位敏感性Ca2 通道 (VSCC)阻断剂硝苯吡啶可抑制oPACAP 38诱导的 [Ca2 ]i 水平的升高 ,而当用硝苯吡啶预处理脑垂体细胞 ,oPACAP 38诱导 [Ca2 ]i 水平升高作用完全被抑制。可见 ,PACAP刺激鲤鱼脑垂体GH分泌机制包括依赖于cAMP和依赖于通过L型VSCC内流的 [Ca2 ]e 的机制。     

Involvement of K(+)-channel opening in endothelin-1 induced suppression of spontaneous contractions in the guinea pig taenia coli.

Effects of porcine-human endothelin-1 on mechanical as well as electrical activities and on intracellular free Ca2+ levels in the guinea pig taenia coli were compared with those of nifedipine, a voltage-dependent Ca2+ channel blocker. Endothelin-1 (0.1-100 nM) caused a concentration-dependent suppression of spontaneous contractions but did not significantly affect the sustained contraction evoked by 40 mM KCl. However, nifedipine (0.1-100 nM) inhibited both types of contractions in a concentration-dependent manner. In electrophysiological studies, endothelin-1 (30 nM) or nifedipine (30 nM) eliminated spontaneous spike discharges. Endothelin-1 produced hyperpolarization, while nifedipine did not change the resting membrane potential. The endothelin-1 induced suppression of spontaneous contractions was dose-dependently antagonized by apamin (0.01-10 nM), an inhibitor of a small conductance Ca(2+)-dependent K+ channel, and D-tubocurarine (10-100 microM), an inhibitor of Ca(2+)-dependent K+ channel, but was unaffected by 4-aminopyridine (0.01-1 mM), an inhibitor of a voltage-dependent K+ channel. In the study with fura 2 excited at 340 nm, endothelin-1 abolished, from the tissue, the fluorescence signals that were coupled with spontaneous contraction. It is suggested that the inhibitory action of endothelin-1 on spontaneous contraction may be caused by hyperpolarization of the membrane that reduces the spontaneous generation of spike discharge coupled normally to an increase in the intracellular free Ca2+ levels in the guinea pig taenia coli. The hyperpolarization may be caused by activating apamin-sensitive Ca(2+)-dependent K+ channels.     

Mechanisms underlying the nitric oxide inhibitory effects in mouse ileal longitudinal muscle

We investigated the mechanisms involved in the nitric oxide (NO)-induced inhibitory effects on longitudinal smooth muscle of mouse ileum, using organ bath technique. Exogenously applied NO, delivered as sodium nitroprusside (SNP; 0.1-100 micromol/L) induced a concentration-dependent reduction of the ileal spontaneous contractions. 1H-[1,2,4]oxadiazolol[4,3,a]quinoxalin-1-one (ODQ; 1 micromol/L), a guanilyl cyclase inhibitor, reduced the SNP-induced effects. Tetraethylammonium chloride (20 mmol/L), a non-selective K+ channel blocker, and charybdotoxin (0.1 micromol/L), blocker of large conductance Ca2+-dependent K+ channels, significantly reduced SNP-induced inhibitory effects. In contrast, apamin (0.1 micromol/L), blocker of small conductance Ca2+-dependent K+ channels, was not able to affect the response to SNP. Ciclopiazonic acid (10 micromol/L) or thapsigargin (0.1 micromol/L), sarcoplasmatic reticulum Ca2+-ATPase inhibitors, decreased the SNP-inhibitory effects. Ryanodine (10 micromol/L), inhibitor of Ca2+ release from ryanodine-sensitive intracellular stores, significantly reduced the SNP inhibitory effects. The membrane permeable analogue of cGMP, 8-bromoguanosine 3',5'-cyclic monophosphate (100 micromol/L), also reduced spontaneous mechanical activity, and its effect was antagonized by ryanodine. The present study suggests that NO causes inhibitory effects on longitudinal smooth muscle of mouse ileum through cGMP which in turn would activate the large conductance Ca2+-dependent K+ channels, via localized ryanodine-sensitive Ca2+ release.     

Photoinduced removal of nifedipine reveals mechanisms of calcium antagonist action on single heart cells

The currents through voltage-activated calcium channels in heart cell membranes are suppressed by dihydropyridine calcium antagonists such as nifedipine. Nifedipine is photolabile, and the reduction of current amplitude by this drug can be reversed within a few milliseconds after a 1-ms light flash. The blockade by nifedipine and its removal by flashes were studied in isolated myocytes from neonatal rat heart using the whole-cell clamp method. The results suggest that nifedipine interacts with closed, open, and inactivated calcium channels. It is likely that at the normal resting potential of cardiac cells, the suppression of current amplitude arises because nifedipine binds to and stabilizes channels in the resting, closed state. Inhibition is enhanced at depolarized membrane potentials, where interaction with inactivated channels may also become important. Additional block of open channels is suggested when currents are carried by Ba2+ but is not indicated with Ca2+ currents. Numerical simulations reproduce the experimental observations with molecular dissociation constants on the order of 10(-7) M for closed and open channels and 10(-8) M for inactivated channels.     

Calcium channel blockers nifedipine and diltiazem inhibit Ca2+ release from intracellular stores in neutrophils.

We have undertaken a detailed study of the mechanisms of maintenance of intracellular Ca2+ homeostasis in human polymorphonuclear neutrophils (PMN) and its implications for phagocytosis and IgG Fc receptor (FcR) signaling. When PMN were incubated in Ca(2+)-free medium, cytoplasmic calcium concentration ([Ca2+]i) was markedly depressed and intracellular stores were depleted of calcium. [Ca2+]i in these depleted cells increased within 1 min when PMN were placed in medium containing Ca2+ and then decreased to a level close to the normal basal [Ca2+]i, replenishing the intracellular Ca2+ pools. LaCl3 prevented entry of Ca2+ into Ca(2+)-depleted PMN, but the calcium channel blockers nifedipine, diltiazem, and verapamil did not. Nifedipine and diltiazem but not verapamil inhibited the movement of Ca2+ from cytosol to intracellular stores. Nifedipine and diltiazem inhibited the normal increase in [Ca2+]i from aggregated IgG binding to FcR and also prevented formyl-methionyl-leucyl-phenyl-alanine (fMLP)-induced [Ca2+]i rise. Verapamil had no effect on either an fMLP- or IgG-mediated increase in [Ca2+]i. Consistent with this, nifedipine and diltiazem inhibited fMLP-stimulated phagocytosis (which is dependent on an increase in [Ca2+]i) when PMN had repleted intracellular stores. In contrast, LaCl3 inhibited fMLP-stimulated ingestion only in PMN which had intracellular store depleted. None of these compounds had any effect on phorbol dibutyrate-stimulated ingestion (which is independent of a [Ca2+]i rise). In summary, these data show that Ca2+ is in rapid equilibrium between intracellular and extracellular compartments in PMN. Exchange of cytoplasmic Ca2+ with the extracellular space is inhibited by LaCl3, while exchange of Ca2+ between the cytosol and intracellular stores is inhibited by the dihydropyridine nifedipine and the benzothiazepine diltiazem. These data suggest that these drugs, which are known to regulate some plasma membrane Ca2+ channels in excitable cells, can also regulate Ca2+ release from intracellular stores in PMN and that this regulation may have significant effects on PMN function.     

Bay K8644及nifedipine对大鼠下丘脑神经元L—型Ca^2＋通道特性的影响

采用神经元急性分离和膜片箍技术以及细胞贴附式方式记录通道活动,探讨DHP类Ca^2 通道激动剂Bay K8644及拮抗剂nifedipine对下丘脑神经元L－型Ca^2 通道的影响,结果显示,在Bay K8644作用下,通道开放形式发生变化,明显可见多级开放;通道平均开放时间,平均开放概况显著增加,但单通道电导无明显变化。nifedipine的作用与Bay K8644相反。结果提示,Bay K8644对下丘脑神经元L－型Ca^2 通道有明显激动作用 nifedipine有显著抑制作用。     

Cyclopiazonic acid activates a Ca2+-permeable, nonselective cation conductance in porcine and bovine tracheal smooth muscle.

Capacitative Ca2+ entry has been examined in several tissues and, in some, appears to be mediated by nonselective cation channels collectively referred to as "store-operated" cation channels; however, relatively little is known about the electrophysiological properties of these channels in airway smooth muscle. Consequently we examined the electrophysiological characteristics and changes in intracellular Ca2+ concentration associated with a cyclopiazonic acid (CPA)-evoked current in porcine and bovine airway smooth muscle using patch-clamp and Ca2+-fluorescence techniques. In bovine tracheal myocytes, CPA induced an elevation of intracellular Ca2+ that was dependent on extracellular Ca2+ and was insensitive to nifedipine (an L-type voltage-gated Ca2+ channel inhibitor). Using patch-clamp techniques and conditions that block both K+ and Cl- currents, we found that CPA rapidly activated a membrane conductance (I(CPA)) in porcine and bovine tracheal myocytes that exhibits a linear current-voltage relationship with a reversal potential around 0 mV. Replacement of extracellular Na+ resulted in a marked reduction of I(CPA) at physiological membrane potentials (i.e., -60 mV) that was accompanied by a shift in the reversal potential for I(CPA) toward more negative membrane potentials. In addition, I(CPA) was markedly inhibited by 10 microM Gd3+ and La3+ but was largely insensitive to 1 microM nifedipine. We conclude that CPA induces capacitative Ca2+ entry in porcine and bovine tracheal smooth muscle via a Gd3+- and La3+-sensitive, nonselective cation conductance.     

Sites and ionic mechanisms of hypoxic vasoconstriction in frog skin

We tested the hypothesis that the cellular mechanisms mediating hypoxic vasoconstriction (HVC) in frog skin, an important vertebrate respiratory organ, are similar to those mediating HVC in the pulmonary vasculature of mammals. An accepted hypothesis in the lung is that alveolar hypoxia alters the redox potential in vascular smooth muscle cells of arterial vessels. This decreases membrane K+ conductance, causing depolarization. Depolarization increases the open probability of L-type Ca2+ channels, facilitating Ca2+ entry into the cell, which leads to vascular smooth muscle contraction and vasoconstriction. We studied the cutaneous microcirculation of the frog (Xenopus laevis) web by enclosing the web in a transparent chamber that was ventilated with different gas mixtures. Arteriolar and venular diameters were measured by video microscopy. Drugs were applied topically or intravascularly. A dose-dependent constriction to hypoxia occurred in arterioles but not venules, although both vessel types constricted to similar degrees to the thromboxane mimetic U-46619. The magnitude of HVC was not associated with arteriolar size. Constriction of arterioles with 4-amino pyridine, a K+-channel antagonist, was blocked by the L-type Ca2+-channel blocker nifedipine. Nifedipine also antagonized HVC and hypercapnic vasoconstriction. Bay K 8664, a drug that increases the open probability of L-type Ca2+ channels, augmented HVC. These data support our hypothesis that the cellular mechanisms mediating HVC are similar in frog skin and mammalian lungs. This similarity between amphibian and mammalian tissues suggests that the mechanisms of HVC may have arisen relatively early in vertebrate evolution. In addition, because of its structural simplicity and easy accessibility, frog skin may be a useful tissue for studying this general phenomenon in vivo.     

Bay K8644及nifedipine对大鼠下丘脑神经元L-型Ca~(2 )通道特性的影响

采用神经元急性分离和膜片箝技术以及细胞贴附式方式记录通道活动 ,探讨DHP类Ca2 通道激动剂BayK8644及拮抗剂nifedipine对下丘脑神经元L 型Ca2 通道的影响。结果显示 ,在BayK8644作用下 ,通道开放形式发生变化 ,明显可见多级开放 ;通道平均开放时间、平均开放概率显著增加 ,但单通道电导无明显变化。nifedipine的作用与BayK8644相反。结果提示 ,BayK8644对下丘脑神经元L 型Ca2 通道有明显激动作用 ,nifedip ine有显著抑制作用     

Effects of the calcium channel agonist, BAY K 8644, on electrical activity in mouse pancreatic B-cells.

We studied the effects of the dihydropyridine derivative BAY K 8644 on the membrane potential of B-cells in mouse pancreatic islets. BAY K 8644, in a dose-dependent manner, decreased the spike frequency but increased the duration of the spikes elicited by glucose with or without quinine or tetraethylammonium (TEA). These effects were antagonized by cobalt and nifedipine but not by tetrodotoxin. The interval between spikes was proportionate to the duration of the spikes and the ratio of the interval to the spike duration was constant at all concentrations of BAY K 8644 tested. Peak inward current, estimated from the derivative of the action potential recorded in the presence of TEA, was increased by BAY K 8644 and decreased by nifedipine. BAY K 8644 elicited spike activity when the membrane was moderately depolarized by either 5.6 mM glucose or 15 mM K+, but did not change the membrane potential of the resting hyperpolarized B-cell. These results suggest that BAY K 8644 acts on the open Ca2+-channels. The threshold occurs at a membrane potential of -50 mV. Also, the modifications of the shape of the spikes appear to reflect specific changes in Ca2+ entry. We propose the existence of a Ca2+-induced Ca2+-channel inactivation process in the pancreatic B-cell.