亮氨酸对蟾蜍卵母细胞膜电位的影响与孕酮的关系

我们以前实验发现,亮氨酸可诱导蟾蜍卵母细胞膜电位去极化。本实验进而探讨亮氨酸的作用与孕酮的关系。实验用1mM浓度亮氨酸培养卵母细胞16～24h,然后测定膜电位。结果发现:亮氨酸不能使裸化的卵母细胞膜电位去极化;也不能增强孕酮所致卵母细胞膜电位去极化。但亮氨酸对卵母细胞的去极化作用可以被雌二醇完全阻断。而且用放射免疫法测定卵母细胞孕酮含量发现,亮氯酸在引起卵母细胞膜电位明显去极化之前,能使卵母细胞孕酮含量增高一倍以上。这些结果提示,亮氨酸可能通过增高卵母细胞孕酮含量来使其膜电位去极化。     

蟾蜍卵母细胞发育过程中膜电位变化

作者对发育程度不同的蟾蜍卵母细胞膜电位测定观察到直径为0.2,1.0和1.6mm的卵母细胞膜电位分别为-6.0±2.0mv(n=13),-22±3.2my(n=13),-50±4.7my(n=10);有随着胞体增大膜电位逐渐超极化的趋势;然而卵母细胞成熟后,膜电位明显去极化。诱发成熟的和自发成熟的卵母细胞膜电位分别为-30.3±3.9mv(n=8),-37±8.4my(n=9)。这些变化的确切机制仍有待于进一步探讨。     

赖氨酸对蟾蜍卵母细胞膜电位的影响及其作用机理

用1mM浓度赖氨酸孵育16～24h后,蟾蜍卵母细胞膜电位显著去极化。同一条件下赖氨酸也能使膜对K~+、Na~+和Cl~-的通透性降低,卵母细胞孕酮含量明显增高与印母细胞成熟。赖氨酸这种去极化作用可因去除胞外游离Ca~(++)或应用1mM浓度的二丁酰cAMP而消失。而F~-的超极化作用并不受赖氨酸影响。这些实验结果提示,赖氨酸可能通过诱导卵母细胞成熟来使膜电位去极化;其作用机理与孕酮相似,但似乎不完全通过孕酮发挥作用。     

尼可地尔对豚鼠心肌细胞膜及线粒体膜电位的影响

研究KATP通道开放剂尼可地尔 (Nic)对豚鼠心肌细胞膜和线粒体膜电位的影响 .用激光共聚焦显微镜和特异性荧光探针 ,观察不同剂量的Nic及KATP通道阻滞剂格列本脲 (Gli)引起急性分离的豚鼠心肌细胞膜电位 ,线粒体膜电位荧光值的变化 .Nic1mmol·L- 1引起细胞膜电位在 1min内迅速超极化〔膜电位荧光值减少 ( 75± 12 ) %〕 ,Gli 3μmol·L- 1可阻断其变化 ;0 .1和 1mmol·L- 1Nic可使线粒体膜电位去极化和膜电位荧光值在 1,2 ,5min分别增加( 12± 3) %和 ( 32± 8) % ,( 2 5± 6) %和 ( 39± 9) % ,( 34± 6) %和 ( 4 5± 12 ) % ;3μmol·L- 1Gli可抑制其变化 .结果说明低浓度Nic只引起线粒体膜电位去极化 ,高浓度Nic还可使细胞膜电位发生超极化 ,引起KATP通道开放     

孕酮对卵母细胞膜电位影响的分析

本实验采用微电极细胞内记录方法,观察了不同浓度孕酮及不同作用时间对卵母细胞膜电位影响。发现孕酮具有致充分生长的蟾蜍卵细胞膜电位去极化的作用,其去极化效应有时间与剂量依赖性关系。     

亮氨酸对蟾蜍卵母细胞膜电位的影响及其作用机理

用1mM亮氨酸处理蟾蜍长足卵母细胞16～24h,然后用微电极技术测定其膜电化学特性。结果表明,亮氦酸可以使卵母细胞膜电位显著去极化;去极化伴随膜对K~+通透性降低与胞内Na~+活度增高。去极化可以被1mM二丁酰cAMP或茶碱完全阻断,但不受4mMF~-的影响。結果提示,亮氨酸可能通过使卵母细胞膜对K~+通透性降低和钠泵活动减弱导致膜电位去极化;亮氨酸的这些作用可能是通过抑制腺苷酸环化酶活性实现的。     

pH恒定条件下兔甲状腺腺泡电位的测定

本文报告了在采用“PH自动控制系统”控制培养液pH值的条件下,用微电极测定兔甲状腺切片腺泡细胞膜电位与泡腔电位的氏液p0.02,氧饱和)表面灌流下,0～3h内细胞膜电位相对稳定,平均为—33.31.6mv(n=19);～4h膜电位趋于去极化,～5h膜电位较～1h明显去极化、p<0.05),但至25～27h膜电位仍可维特在—22.7±2.0mv(n=7),腺泡腔电位始终没有明显变化,0～27h内平均为—12.4±0.4mv,(n=38)。与其他作者结果比较,我们认为在平衡盐溶液中甲状腺细胞膜电位可能为—42mv左右,腺泡腔电位为—12mv左右;本实验条件优于国外采用5％CO_2混合气控制pH的条件。     

白细胞介素-1对骨髓基质细胞膜电位的影响及其与Cl~-通道的关系

目的　研究重组人白细胞介素 1β(IL 1β)对骨髓基质细胞 (BMSC)膜电位的影响及其与Cl-通道的关系 ,探讨离子通道是否参与细胞因子IL 1的生物信号转导。方法　用荧光染料DiBAC4 (3)标记原代培养的BMSC ,在激光扫描共聚焦显微镜下直接监测IL 1β刺激下细胞膜电位的实时动态变化以及Cl-通道阻断剂呋喃苯胺酸 (furosemide)对IL 1β膜电位效应的影响。结果　IL 1β加入测定体系后浓度依赖性地引起BMSC膜电位的迅速改变。低浓度时 (8～ 10 0kU·L-1)发生去极化反应 ,高浓度时 (2 0 0～ 5 0 0kU·L-1)发生超极化反应。非受体方式作用的IL 1β肽段 16 3～ 171对膜电位无影响。Furosemide(2 0～ 5 0 0 μmol·L-1)浓度依赖性地抑制IL 1β的膜电位效应。结论　膜电位的变化为IL 1受体后早期信号事件 ,Cl-通道的活化参与了IL 1的生物信号转导。     

雌二醇对孕酮作用的影响

孕酮对充分生长的蟾蜍卵母细胞膜电位有去极化的作用.这种膜电位去极化作用可被同时应用的雌二醇所完全阻断。目前发现:孕酮作用于离体培养的卵母细胞有胚泡降解发生;给予孕烯醇酮同样可促进卵母细胞成熟;但孕酮促成熟作用却可被二丁酰CAMP(ab-CAMP)或雌二醇等所阻断。我们实验中发现,用10倍于孕酮剂量的雌二醇确实显著性减弱孕酮的去极化效应;进一步证明膜电位去极化与孕酮促成熟作用是有内在联系的。     

哇巴因和高钾对乙酰胆碱致家兔肺动脉内皮依赖性超极化的作用

采用标准微电极技术观察了哇巴因和高钾对乙酰胆碱（ａｃｅｔｙｌｃｈｏｌｉｎｅ，Ａｃｈ）致家兔肺动脉内皮依赖性超极化的作用。结果；Ａｃｈ１０μｍｏｌ·Ｌ－１可使内皮完整的肺动脉膜电位产生明显的超极化。该作用在去除内皮或预先用阿托品阻断Ａｃｈ受体的条件下消失。哇巴因可抑制无钾／复钾所致的膜电位超极化，但不影响Ａｃｈ所致的内皮依赖性超极化。高钾则可取消Ａｃｈ的内皮依赖性超极化。提示：Ａｃｈ引起的家兔肺动脉内皮依赖性超极化可能由细胞膜上钾通道开放所致，而和Ｎａ／Ｋ泵无关。     

Regulation of vascular tone by endothelium-derived hyperpolarizing factor

1. Endothelium-derived hyperpolarizing factor (EDHF) mediates the nitric oxide (NO)-independent component of the relaxation in rat mesenteric arteries. The relationship between hyperpolarization and vascular tone was studied by simultaneous recording of membrane potential with intracellular microelectrodes and tension in ring segments of rat mesenteric arteries. 2. By depolarizing arteries with high potassium solutions, it was determined that the threshold for contraction is approximately -46 mV. Maximum contraction was attained when the arteries were depolarized to -20 mV. Thus, 1 mV depolarization resulted in an approximate 4% increase in tone. This relationship was not altered in spontaneously hypertensive rats. 3. Noradrenaline (0.3 mumol/L) caused contraction and depolarized arteries by 13 mV. Acetylcholine caused endothelium-dependent relaxation and hyperpolarization up to 14 mV. In the presence of N omega-nitro-L-arginine, the EDHF-mediated relaxation was correlated to hyperpolarization. A hyperpolarization of 1 mV corresponded to a 4.3% decrease of the induced tone. 4. At concentrations (10 mumol/L) causing total relaxation, the maximum hyperpolarization induced by NO was only 7.6 mV. 5. A maximum relaxation of 88% was observed with pinacidil (3 mumol/L), despite a 25 mV hyperpolarization. Relaxations to NO and pinacidil were not correlated with hyperpolarization. At similar levels of hyperpolarization, NO and pinacidil elicited more relaxation than EDHF. 6. These studies show that vascular tone is very sensitive to membrane potential change in the range between -46 and -20 mV in the rat mesenteric artery. The relaxation response to EDHF, unlike that to NO and pinacidil, can be accounted for solely by its effect on the membrane potential.     

BK channel activation by NS-1619 is partially mediated by intracellular Ca2+ release in smooth muscle cells of porcine coronary artery

1. Effects of NS-1619, an opener of large conductance Ca2+-activated K+ (BK) channel, on intracellular Ca2+ concentration ([Ca2+]i) and membrane potential were examined in single myocytes freshly isolated from porcine coronary artery. 2. Under current clamp mode, the application of 1-30 microM NS-1619 hyperpolarized the membrane in concentration-dependent manner. The NS-1619-induced hyperpolarization was abolished by the presence of 100 nM iberiotoxin. 3. Application of 1-10 microM NS-1619 hyperpolarized the membrane by approximately 6 mV or less but did not change significantly the [Ca2+]i. When membrane hyperpolarization of 12 mV or so was caused by 30 microM NS-1619, [Ca2+]i was unexpectedly increased by approximately 200 nM. This increase in [Ca2+]i and the concomitant outward current activation were also observed under voltage-clamp at holding potential of -40 mV. 4. The increase in [Ca2+]i by 30 microM NS-1619 occurred mainly in peripheral regions than in the centre of the myocytes. The removal of extracellular Ca2+ affected neither the membrane hyperpolarization nor the increase in [Ca2+]i. 5. In the presence of 10 mM caffeine and 10 microM ryanodine, the increase in [Ca2+]i by 30 microM NS-1619 was not observed and the membrane hyperpolarization was reduced to approximately 67% of the control. 6. These results indicate that the opening of BK channels by NS-1619 at 30 microM, which is the most frequently used concentration of this agent, is partly due to Ca2+ release from caffeine/ryanodine-sensitive intracellular storage sites but is mainly due to the direct activation of the channels.     

The nucleotide receptors on mouse C2C12 myotubes.

1. The response of C2C12 mouse myotubes to stimulation with adenosine triphosphate (ATP) and other nucleotides was studied by measuring changes in membrane potential. 2. A transient hyperpolarization followed by a slowly declining depolarization of the cells was observed in the presence of ATP (10 microM-1 mM). 3. The hyperpolarization was not observed in the absence of external calcium, and was abolished in the presence of tetraethylammonium (20 mM) or the bee toxin, apamin (0.1 microM). The depolarization was reduced under low sodium conditions. 4. A biphasic change in membrane potential was also recorded in the presence of adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S) and the pyrimidine uridine triphosphate (UTP), while the ATP derivatives and analogues, adenosine diphosphate, adenosine, alpha,beta-methylene ATP and 2-methylthio ATP and the nucleotides, guanosine triphosphate and cytidine triphosphate, did not affect the membrane potential of the myotubes. 5. The hyperpolarization elicited by ATP gamma S or UTP was also blocked by apamin and abolished under Ca(2+)-free conditions. 6. In contrast to ATP and ATP gamma S, the depolarization evoked by UTP was unaffected under low Na+ and less sensitive to the antagonistic action of suramin. 7. The ATP and UTP responses at maximal concentration were not additive after simultaneous application. ATP elicited a depolarization if applied after UTP, while UTP did not change membrane potential following the application of ATP. 8. The concentration-response curves of the effective nucleotides were shifted to the right in the presence of suramin, suggesting competitive antagonism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clonidine activates membrane potassium conductance in myenteric neurones

1 Intracellular recordings were made from neurones in the myenteric plexus of the ileum removed from guinea-pigs. The effects of clonidine and adrenaline on membrane potential and resistance were observed.

2 Clonidine (100 pM—30 nM) caused a concentration-dependent membrane hyperpolarization associated with a fall in neurone input resistance.

3 The amplitude of the clonidine hyperpolarization, but not the conductance increase, was greater in cells with lower resting potentials and smaller in more polarized neurones. In a given cell, membrane hyperpolarization decreased and membrane depolarization increased the clonidine effect.

4 Low potassium solutions enhanced and high potassium solutions reduced the hyperpolarizing action of clonidine but did not significantly change the conductance increase caused by clonidine.

5 The concentration-effect curve for clonidine was displaced to the left when the extracellular calcium concentration was reduced. Conversely, clonidine was almost ineffective in elevated calcium concentrations. This was true for both the hyperpolarization and the conductance increase.

6 It is suggested that clonidine activates a potassium conductance by causing an elevation in the free intracellular calcium concentration.

7 Clonidine reversibly depressed the amplitude of the nicotinic fast excitatory postsynaptic potential and the noncholinergic slow excitatory postsynaptic potential.

8 All the effects of clonidine were shared by adrenaline and the actions of both were reversed or prevented by phentolamine (100 nM—1 μM).

     

Modulation of KCNQ2/3 potassium channels by the novel anticonvulsant retigabine

Retigabine is a novel anticonvulsant with an unknown mechanism of action. It has recently been reported that retigabine modulates a potassium channel current in nerve growth factor-differentiated PC12 cells (), however, to date the molecular correlate of this current has not been identified. In the present study we have examined the effects of retigabine on recombinant human KCNQ2 and KCNQ3 potassium channels, expressed either alone or in combination in Xenopus oocytes. Application of 10 microM retigabine to oocytes expressing the KCNQ2/3 heteromeric channel shifted both the activation threshold and voltage for half-activation by approximately 20 mV in the hyperpolarizing direction, leading to an increase in current amplitude at test potentials between -80 mV and +20 mV. Retigabine also had a marked effect on KCNQ current kinetics, increasing the rate of channel activation but slowing deactivation at a given test potential. Similar effects of retigabine were observed in oocytes expressing KCNQ2 alone, suggesting that KCNQ2 may be the molecular target of retigabine. Membrane potential recordings in oocytes expressing the KCNQ2/3 heteromeric channel showed that application of retigabine leads to a concentration-dependent hyperpolarization of the oocyte, from a resting potential of -63 mV under control conditions to -85 mV in the presence of 100 microM retigabine (IC(50) = 5.2 microM). In control experiments retigabine had no effect on either resting membrane potential or endogenous oocyte membrane currents. In conclusion, we have shown that retigabine acts as a KCNQ potassium channel opener. Because the heteromeric KCNQ2/3 channel has recently been reported to underlie the M-current, it is likely that M-current modulation can explain the anticonvulsant actions of retigabine in animal models of epilepsy.     

重组人白介素1α引起小鼠骨髓基质细胞膜超极化

重组人白介素１α引起小鼠骨髓基质细胞膜超极化１吴曙光肖学军徐伟鲍永耀（第一军医大学药物研究所，广州５１０５１５）白介素１（ｉｎｔｅｒｌｅｕｋｉｎ－１，ＩＬ－１）是具有广泛生物学活性的多肽，其生物活性通过受体介导［１］，但至今有关ＩＬ－１与受体结合后的...     

Characteristics of cromakalim-induced relaxations in the smooth muscle cells of guinea-pig mesenteric artery and vein.

1. The effects of cromakalim (BRL 34915) on the smooth muscle cells of guinea-pig mesenteric artery and vein were investigated with microelectrode and tension recording methods. 2. Cromakalim (greater than 10 microM) produced membrane hyperpolarization with an increase in ionic conductance. The hyperpolarization occurred to a greater extent and lasted longer in the vein than in the artery. 3. The hyperpolarization induced by cromakalim in mesenteric vein comprised two components, one of which was Mn sensitive. In mesenteric artery, the hyperpolarization was relatively insensitive to Mn. 4. From the current-voltage relationship measured from arterial smooth muscle membranes, the reversal potential of cromakalim was estimated to be -80 mV. The cromakalim-induced hyperpolarization was not modified in Na- or Cl-deficient solution. 5. In both mesenteric artery and vein, cromakalim relaxed tissues precontracted with high K with (below 40 mM) or without (above 40 mM) hyperpolarization of the membrane. 6. In the mesenteric artery, action potentials evoked by electrical stimulation ceased before the generation of hyperpolarization. 7. Cromakalim produced a cross-desensitization with nicorandil on the evoked membrane hyperpolarization in mesenteric artery. 8. It is concluded that the relaxing actions of cromakalim result from the hyperpolarization which follows the opening of Ca-dependent K channels. The inhibition of a voltage-dependent Ca current may also be involved in this inhibitory effect.