Effect of the organotin compound triethyltin on Ca2+ handling in human prostate cancer cells

The effects of triethyltin on Ca2+ mobilization in human PC3 prostate cancer cells have been explored. Triethyltin increased [Ca2+]i at concentrations larger than 3 microM with an EC50 of 30 microM. Within 5 min, the [Ca2+]i signal was composed of a gradual rise and a sustained phase. The [Ca2+]i signal was reduced by half by removing extracellular Ca2+. The triethyltin-induced [Ca2+]i increases were inhibited by 40% by 10 microM nifedipine, nimodipine and nicardipine, but were not affected by 10 microM of verapamil or diltiazem. In Ca2+-free medium, pretreatment with thapsigargin (1 microM), an endoplasmic reticulum Ca+ pump inhibitor, reduced 200 microM triethyltin-induced Ca+ increases by 50%. Pretreatment with U73122 (2 microM) to inhibit phospholipase C did not alter 200 microM triethyltin-induced [Ca2+]i increases. Incubation with triethyltin at a concentration that did not increase [Ca2+]i (1 microM) in Ca2+-containing medium for 3 min potentiated ATP (10 microM)- or bradykinin (1 microLM)-induced [Ca2+]i increases by 41 +/- 3% and 51 +/- 2%, respectively. Collectively, this study shows that the environmental toxicant triethyltin altered Ca2+ handling in PC3 prostate cancer cells in a concentration-dependent manner: at higher concentrations it increased basal [Ca2+]i; and at lower concentrations it potentiated agonists-induced [Ca2+]i increases.     

Separate analysis of nuclear and cytosolic Ca2+ concentrations in human umbilical vein endothelial cells

Ca²⁺ concentration inside human umbilical vein endothelial cells was studied separately in cytosol and nucleus by a confocal laser scanning microscopy using fluo-3. The in vivo calibration curve for cytosol and nucleus showed good linearity between fluorescence intensity and Ca²⁺ concentration in cytosol ([Ca²⁺]_i) and nuclei ([Ca²⁺]_n). After calibration, [Ca²⁺]_n was constantly higher than [Ca²⁺]_i before and after the chelation of extracellular Ca²⁺ suggesting an active Ca²⁺ accumulation system on nuclear membrane. [Ca²⁺]_n was also constantly higher than [Ca²⁺]_i after the stimulation of thrombin (0.05 U/ml), FCS (10%), and thapsigargin (Tsg, 1μM). The temporal change of [Ca²⁺]_n and [Ca²⁺]_i was identical, and [Ca²⁺]_i gradient towards the nucleus and peripheral or central [Ca²⁺]_n rise was observed after these stimulations. From these results, [Ca²⁺]_n is not only regulated by the active Ca²⁺ accumulation system on nuclear membrane at rest but also the generation of Inositol-triphosphate. FCS caused heterogeneous [Ca²⁺]_n or [Ca²⁺]_i rise from cell to cell; single spike or oscillatory change of [Ca²⁺]_n and [Ca²⁺]_i was observed in about 56% of cells, which were completely abolished by the chelation of extracellular Ca²⁺, suggesting that FCS stimulated [Ca²⁺]_n and [Ca²⁺]_i rise solely depending on Ca²⁺ influx from extracellular medium. The higher concentration of [Ca²⁺]_n and heterogeneous [Ca²⁺]_n rise may have important roles in nuclear-specific cellular responses. © 1996 Wiley-Liss, Inc.     

Effect of lignans isolated from Hernandia nymphaeifolia on estrogenic compounds-induced calcium mobilization in human neutrophils

The effect of five lignans isolated from Hernandia nymphaeifolia on estrogenic compounds (17β-estradiol, tamoxifen and clomiphene)-induced Ca²⁺ mobilization in human neutrophils was investigated. The five lignans were epi-yangambin, epi-magnolin, epi-aschantin, deoxypodophyllotoxin and yatein. In Ca²⁺–containing medium, the lignans (50–100 μM) inhibited 10 μM 17β-estradiol- and 5 μM tamoxifen-induced increases in intracellular free Ca²⁺ levels ([Ca²⁺]_i) without changing 25 μM clomiphene-induced [Ca²⁺]_i increase. 17β-estradiol and tamoxifen increased [Ca²⁺]_i by causing Ca²⁺ influx and Ca²⁺ release because their responses were partly reduced by removing extracellular Ca²⁺. In contrast, clomiphene solely induced Ca²⁺ release. The effect of the lignans on these two Ca²⁺ movement pathways underlying 17β-estradiol- and tamoxifen-induced [Ca²⁺]_i increases was explored. All the lignans (50–100 μM) inhibited 10 μM 17β-estradiol-and 5 μM tamoxifen-induced Ca²⁺ release, and 17β-estradiol-induced Ca²⁺ influx. However, only 100 μM epi-aschantin was able to reduce tamoxifen-induced Ca²⁺ influx while the other lignans had no effect. Collectively, this study shows that the lignans altered estrogenic compounds-induced Ca²⁺ signaling in human neutrophils in a multiple manner.     

Nordihydroguaiaretic acid-induced Ca2+ handling and cytotoxicity in human prostate cancer cells

The effect of nordihydroguaiaretic acid (NDGA), a compound commonly used as a lipoxygenases inhibitor, on intracellular free Ca2+ levels ([Ca2+]i) in PC3 human prostate cancer cells was investigated. [Ca2+]i was measured by using the Ca2+ -sensitive dye fura-2. NDGA increased [Ca2+]i in a concentration-dependent manner with an EC50 of 30 microM. The Ca2+ signal comprised a gradual and sustained increase. Removal of extracellular Ca2+ partly decreased the NDGA-induced [Ca2+]i increase, suggesting that the Ca2+ signal was due to both extracellular Ca2+ influx and intracellular Ca2+ release. NDGA-induced Ca2+ influx was independently confirmed by measuring NDGA-induced Mn2+ -coupled quench of fura-2 fluorescence. The NDGA-induced Ca2+ influx was not affected by L-type Ca2+ channel blockers. In Ca2+ -free medium, the NDGA-induced [Ca2+]i increase was abolished by pretreatment with 1 microM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor), and conversely, pretreatment with NDGA abolished thapsigargin-induced [Ca2+]i increase. NDGA-induced intracellular Ca2+ release was not altered by inhibition of phospholipase C. Overnight treatment with 20-50 microM NDGA inhibited cell proliferation rate in a concentration-dependent manner. Several other lipoxygenases inhibitors did not alter [Ca2+]i. Collectively, this study shows that in prostate cells, NDGA induced a [Ca2+]i increase via releasing stored Ca2+ from the endoplasmic reticulum in a manner independent of phospholipase C activity, and by causing Ca2+ influx. NDGA also caused cytotoxicity at higher concentrations.     

Ca2+ triggers a novel clathrin-independent but actin-dependent fast endocytosis in pancreatic beta cells

The existence of clathrin-independent recycling of secretory vesicles has been controversial. By combining patch-clamp capacitance recording, optical methods and specific molecular interventions, we dissect two types of mechanistically different endocytosis in pancreatic β cells, both of which require GTP and dynamin. The fast one is a novel clathrin-independent but actin-dependent endocytosis that is triggered by high cytoplasmic Ca²⁺ concentration ([Ca²⁺]_i). Large fluorescent dextran (10 nm in diameter) was able to be internalized by this pathway, indicating that it was not likely to be 'kiss and run'. The slow endocytosis is a clathrin-dependent process in which actin plays a complementary role. For the first time, we show that the rate constants for both types of endocytosis exhibit supralinear dependence on increase in [Ca²⁺]_i. Compared with the slow endocytosis, higher [Ca²⁺]_i level was required to fully accelerate the fast one, indicative of distinct Ca²⁺ sensors for different endocytosis. In the end, we show that physiologically relevant stimulation induces clathrin-independent endocytosis in intact β cells, implying that it may contribute to the normal recycling of secretory vesicles in vivo .     

Effect of clomiphene on Ca(2+) movement in human prostate cancer cells

The effect of clomiphene, an ovulation-inducing agent, on cytosolic free Ca(2+) levels ([Ca(2+)](i)) in populations of PC3 human prostate cancer cells was explored by using fura-2 as a Ca(2+) indicator. Clomiphene at concentrations between 10-50 microM increased [Ca(2+)](i) in a concentration-dependent manner. The [Ca(2+)](i) signal was biphasic with an initial rise and a slow decay. Ca(2+) removal inhibited the Ca(2+) signal by 41%. Adding 3 mM Ca(2+) increased [Ca(2+)](i) in cells pretreated with clomiphene in Ca(2+)-free medium, confirming that clomiphene induced Ca(2+) entry. In Ca(2+)-free medium, pretreatment with 50 microM brefeldin A (to permeabilize the Golgi complex), 1 microM thapsigargin (to inhibit the endoplasmic reticulum Ca(2+) pump), and 2 microM carbonylcyanide m-chlorophenylhydrazone (to uncouple mitochondria) inhibited 25% of 50 microM clomiphene-induced store Ca(2+) release. Conversely, pretreatment with 50 microM clomiphene in Ca(2+)-free medium abolished the [Ca(2+)](i) increase induced by brefeldin A, thapsigargin or carbonylcyanide m-chlorophenylhydrazone. The 50 microM clomiphene-induced Ca(2+)release was unaltered by inhibiting phospholipase C with 2 microM 1-(6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione (U73122). Trypan blue exclusion assay suggested that incubation with clomiphene (50 microM) for 2-15 min induced time-dependent decrease in cell viability by 10-50%. Collectively, the results suggest that clomiphene induced [Ca(2+)](i) increases in PC3 cells by releasing store Ca(2+) from multiple stores in an phospholipase C-independent manner, and by activating Ca(2+) influx; and clomiphene was of mild cytotoxicity.     

糖皮质激素快速抑制高钾离子诱导嗜铬细胞瘤细胞内游离钙浓度升高 …

本研究应用钙离子特异光指示剂Ｆｕｒａ－２／ＡＭ,使用Ｍｉｒａｃａｌ影像系统检测了糖皮质激素对高钾离子升高嗜铬细胞瘤细胞（ＰＣ１２细胞）内游离钙浓度（［Ｃａ＾＋］ｉ）作用的影响。结果表明：（１）皮质酮抑制高钾离子诱导ＰＣ１２细胞［Ｃａ＾２＋］ｉ升高与其预处理细胞时间的长短有关,预处理３ｍｉｎ时,皮质酮开始产生抑制作用;预处理５ｍｉｎ时,其呈现的抑制作用最;预处理２５ｍｉｎ时,抑制作用基本消失。（２）     

NPC-14686 (Fmoc-l-homophenylalanine)-induced CaCa2+ increases and death in human prostate cancer cells

The effect of NPC-14686, a potential anti-inflammatory drug, on cytosolic free Ca2+ levels ([Ca2+]i) and growth in PC3 human prostate cancer cells was examined by using fura-2 as a fluorescent Ca2+ indicator and WST-1 as a fluorescent growth dye. NPC-14686 at concentrations above 10 microM increased [Ca2+]i in a concentration-dependent manner with an EC50 value of 100 microM. NPC-14686-induced Ca2+ influx was confirmed by Mn2+ quench of fura-2 fluorescence. The Ca2+ signal was also reduced by removing extracellular Ca2+. Pretreatment with 1 microM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor) to deplete the endoplasmic reticulum Ca2+ nearly abolished 200 microM NPC-14686-induced Ca2+ release; and conversely pretreatment with NPC-14686 completely inhibited thapsigargin-induced Ca2+ release. The Ca2+ release induced by 200 microM NPC-14686 was not affected by inhibiting phospholipase C with 2 microM U73122. Overnight treatment with 1-500 microM NPC-14686 decreased cell viability in a concentration-dependent manner. These findings suggest that in human PC3 prostate cancer cells, NPC-14686 increases [Ca2+]i by evoking extracellular Ca2+ influx and releasing intracellular Ca2+ from the endoplasmic reticulum via a phospholiase C-independent manner. NPC-14686 may be cytotoxic to prostate cancer cells.     

Effect of thapsigargin on Ca2+ fluxes and viability in human prostate cancer cells

Effect of the carcinogen thapsigargin on human prostate cancer cells is unclear. This study examined if thapsigargin altered basal [Ca²⁺]_i levels in suspended PC3 human prostate cancer cells by using fura-2 as a Ca²⁺-sensitive fluorescent probe. Thapsigargin at concentrations between 10?nM and 10 µM increased [Ca²⁺]_i in a concentration-dependent fashion. The Ca²⁺ signal was reduced partly by removing extracellular Ca²⁺ indicating that Ca²⁺ entry and release both contributed to the [Ca²⁺]_i rise. This Ca²⁺ influx was inhibited by suppression of phospholipase A2, but not by inhibition of store-operated Ca²⁺ channels or by modulation of protein kinase C activity. In Ca²⁺-free medium, pretreatment with the endoplasmic reticulum Ca²⁺ pump inhibitor 2,5-di-(t-butyl)-1,4-hydroquinone (BHQ) nearly abolished thapsigargin-induced Ca²⁺ release. Conversely, pretreatment with thapsigargin greatly reduced BHQ-induced [Ca²⁺]_i rise, suggesting that thapsigargin released Ca²⁺ from the endoplasmic reticulum. Inhibition of phospholipase C did not change thapsigargin-induced [Ca²⁺]_i rise. At concentrations of 1-10 µM, thapsigargin induced cell death that was partly reversed by chelation of Ca²⁺ with BAPTA/AM. Annexin V/propidium iodide staining data suggest that apoptosis was partly responsible for thapsigargin-induced cell death. Together, in PC3 human prostate cancer cells, thapsigargin induced [Ca²⁺]_i rises by causing phospholipase C-independent Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ influx via phospholipase A2-sensitive Ca²⁺ channels. Thapsigargin also induced cell death via Ca²⁺-dependent pathways and Ca²⁺-independent apoptotic pathways.     

Mechanism of the persistent sodium current activator veratridine-evoked Ca2+ elevation: implication for epilepsy

Although the role of Na⁺ in several aspects of Ca²⁺ regulation has already been shown, the exact mechanism of intracellular Ca²⁺ concentration ([Ca²⁺]_i) increase resulting from an enhancement in the persistent, non‐inactivating Na⁺ current (I_Na,P), a decisive factor in certain forms of epilepsy, has yet to be resolved. Persistent Na⁺ current, evoked by veratridine, induced bursts of action potentials and sustained membrane depolarization with monophasic intracellular Na⁺ concentration ([Na⁺]_i) and biphasic [Ca²⁺]_i increase in CA1 pyramidal cells in acute hippocampal slices. The Ca²⁺ response was tetrodotoxin‐ and extracellular Ca²⁺‐dependent and ionotropic glutamate receptor‐independent. The first phase of [Ca²⁺]_i rise was the net result of Ca²⁺ influx through voltage‐gated Ca²⁺ channels and mitochondrial Ca²⁺ sequestration. The robust second phase in addition involved reverse operation of the Na⁺–Ca²⁺ exchanger and mitochondrial Ca²⁺ release. We excluded contribution of the endoplasmic reticulum. These results demonstrate a complex interaction between persistent, non‐inactivating Na⁺ current and [Ca²⁺]_i regulation in CA1 pyramidal cells. The described cellular mechanisms are most likely part of the pathomechanism of certain forms of epilepsy that are associated with I_Na,P. Describing the magnitude, temporal pattern and sources of Ca²⁺ increase induced by I_Na,P may provide novel targets for antiepileptic drug therapy.     

Effect of maprotiline on Ca(2+) movement in human neuroblastoma cells

In human neuroblastoma IMR32 cells, the effect of the anti-depressant maprotiline on baseline intracellular Ca2+ concentrations ([Ca2+]i) was explored by using the Ca2+-sensitive probe fura-2. Maprotiline at concentrations greater than 100 microM caused a rapid rise in [Ca2+]i in a concentration-dependent manner (EC50 = 200 microM). Maprotiline-induced [Ca2+]i rise was reduced by 50% by removal of extracellular Ca2+. Maprotiline-induced [Ca2+]i rises were inhibited by half by nifedipine, but was unaffected by verapamil or diiltiazem. In Ca2+-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca2+-ATPase, caused a monophasic [Ca2+]i rise, after which the increasing effect of maprotiline on [Ca2+]i was abolished. U73122, an inhibitor of phospholipase C, did not affect maprotiline-induced [Ca2+]i rises. These findings suggest that in human neuroblastoma cells, maprotiline increases [Ca2+]i by stimulating extracellular Ca2+ influx and also by causing intracellular Ca2+ release from the endoplasmic reticulum via a phospholiase C-independent manner.     

Effect of diindolylmethane on Ca2+ homeostasis and viability in PC3 human prostate cancer cells

The effect of the natural product diindolylmethane on cytosolic Ca²⁺ concentrations ([Ca²⁺]_i) and viability in PC3 human prostate cancer cells was explored. The Ca²⁺-sensitive fluorescent dye fura-2 was applied to measure [Ca²⁺]_i. Diindolylmethane at concentrations of 20–50 µM induced [Ca²⁺]_i rise in a concentration-dependent manner. The response was reduced partly by removing Ca²⁺. Diindolylmethane-evoked Ca²⁺ entry was suppressed by nifedipine, econazole, SK&F96365, protein kinase C modulators and aristolochic acid. In the absence of extracellular Ca²⁺, incubation with the endoplasmic reticulum Ca²⁺ pump inhibitor thapsigargin or 2,5-di-tert-butylhydroquinone (BHQ) inhibited or abolished diindolylmethane-induced [Ca²⁺]_i rise. Incubation with diindolylmethane also inhibited thapsigargin or BHQ-induced [Ca²⁺]_i rise. Inhibition of phospholipase C with U73122 reduced diindolylmethane-induced [Ca²⁺]_i rise. At concentrations of 50–100 µM, diindolylmethane killed cells in a concentration-dependent manner. This cytotoxic effect was not altered by chelating cytosolic Ca²⁺ with 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA). Annexin V/PI staining data implicate that diindolylmethane (50 and 100 µM) induced apoptosis in a concentration-dependent manner. In conclusion, diindolylmethane induced a [Ca²⁺]_i rise in PC3 cells by evoking phospholipase C-dependent Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ entry via phospholipase A₂-sensitive store-operated Ca²⁺ channels. Diindolylmethane caused cell death in which apoptosis may participate.     

Albumin-bound lipids induce free cytoplasmic calcium oscillations in human osteoblast-like cells

[Ca(2+)](i) oscillations were found in human osteoblast-like cells (hOB cells) exposed to high-lipid bovine serum albumin (BSA), but not when exposed to low-lipid BSA. These [Ca(2+)](i) oscillations were inhibited by heptanol and suramin, which implies that gap junctions and purinergic signalling may be important for these [Ca(2+)](i) oscillations. The high-lipid BSA preparation that was used contains arachidonic acid. [Ca(2+)](i) oscillations could be induced by low lipid albumin with arachidonic acid added. The albumin-bound lipids were also important for osteoblast growth since DNA synthesis and the total cell protein content was higher in hOB cells exposed to high-lipid BSA. The effect of arachidonic acid on hOB cell proliferation was bone-donor dependent; both stimulatory and inhibitory effects were observed. The physiological importance of albumin-bound lipids is unclear; given that albumin has only minimal contact with osteoblasts under normal conditions. Only when bone capillaries are disrupted, e.g. during a fracture, would significant amounts of albumin reach osteoblasts. Albumin-bound lipids could therefore contribute to stimulation of osteoblast proliferation during fracture healing.     

银杏苦内酯B对豚鼠模拟缺血心室肌细胞L-型钙电流及胞内游离钙的影响

应用全细胞膜片钳及激光共聚焦技术 ,研究银杏苦内酯B(ginkgolideB ,GB)对豚鼠心室肌细胞L 型钙电流及胞内游离钙的作用 ,并探讨GB心肌保护作用的机制。实验结果显示 ,在指令电压为 0mV时 ,GB对生理状态下豚鼠心室肌细胞L 型钙电流无明显作用。在模拟缺血状态下 ,L 型钙峰值电流减小 3 7 71% ,但加入 1μmol/LGB后 ,可逆转缺血引起的L 型钙电流的降低 ,与缺血对照组比较 ,有显著性差异 (P <0 0 5 )。 1μmol/LGB能使由于模拟缺血而上移的L 型钙电流 电压曲线回复正常。在生理状态下 ,0 1、1、10mol/LGB分别使心肌细胞内游离钙降低 10 5 8%(n =12 )、17 2 7% (n =12 )、16 3 5 % (n =10 ) ,与对照组相比有非常显著性差异。模拟缺血液灌流 12min时 ,细胞内游离钙浓度增加 2 0 15 % ,在模拟缺血液中分别加入 1μmol/Lnifedipine或 5mmol/LNiCl2 ,结果显示 :模拟缺血液灌流 12min ,与正常对照组相比细胞内钙分别增加 18 18% (P >0 0 5 )与 11% (P <0 0 5 )。在模拟缺血液中加入1mol/LGB灌流 12min时细胞内钙仅增加 9 60 % (n =12 ,P <0 0 0 1) ,与缺血对照组相比有显著性差异 (P <0 0 5 )。结果表明 ,GB可逆转模拟缺血造成L 型钙电流的降低 ,同时可部分减轻由于缺血所造成的细胞内钙的超载     

大豆黄酮对衰老小鼠不同脑区突触内[Ca2+]i的影响

目的: 检测大豆黄酮对衰老小鼠不同脑区突触内[Ca2 ]i影响.方法: 灌喂衰老模型小鼠大豆黄酮,利用荧光指示剂Fura-2/AM测定[Ca2 ]i.结果: 大豆黄酮使衰老小鼠大脑皮质、海马、间脑突触内游离[Ca2 ]i分别下降0.18倍(P<0.05)、0.34倍(P<0.01)、0.21倍(P<0.05).结论: 大豆黄酮可部分抑制由于突触[Ca2 ]i代谢失调引发的脑老化.     

Endothelins regulate arachidonic acid release and mitogen-activated protein kinase activity in Schwann cells

Immortalized rat Schwann cells (iSC) express endothelin (ET) receptors coupled to inhibition of adenylyl cyclase and stimulation of phospholipase C (PLC). These effects precede phenotypic changes and increased DNA synthesis. We have investigated the role of ETs in the regulation of arachidonic acid (AA) release and mitogen-activated protein kinases (MAPKs). Both ET-1 and ET-3 increased AA release in iSC. This effect was sensitive to the phospholipase A(2) (PLA(2)) inhibitors E:-6-(bromomethylene)tetrahydro-3-(1-naphthalenyl)-2H:-pyran-2-one and arachidonyl-trifluoromethyl ketone but was insensitive to inhibitors of PLC or phospholipase D-dependent diacylglycerol generation. ET-1-dependent AA release was also unaffected by removal of extracellular Ca(2+) and blocking the concomitant elevation in [Ca(2+)](i), consistent with participation of a Ca(2+)-independent PLA(2). Treatment of iSC with ETs also resulted in activation of extracellular signal-regulated kinase, c-Jun-NH(2)-terminal kinase (JNK), and p38 MAPK. A cause-effect relationship between agonist-dependent AA release and stimulation of MAPKs, but not the opposite, was suggested by activation of JNK by exogenous AA and by the observation that inhibition of MAPK kinase or p38 MAPK was inconsequential to ET-1-induced AA release. Similar effects of ETs on AA release and MAPK activity were observed in cultures expanded from primary SC and in iSC. Regulation of these effectors may mediate the control of proliferation and differentiation of SC by ETs during peripheral nerve development and regeneration.     

重组水母发光蛋白及其在植物钙离子信号检测中的应用

重组水母发光蛋白作为检测植物细胞钙信号的手段是近十几年发展起来的新方法,该文介绍了重组水母发光蛋白作为Ca2+检测探针的发展过程、测钙原理、Ca2+浓度检测方法、Ca2+浓度换算方法、优点与不足、及在植物细胞钙离子信号检测中的研究进展。并利用国外实验室提供的方法在国内首次得出冷激条件下植物细胞内细胞质中([Ca2+]cyt)和液泡膜附近([Ca2+]md)钙离子浓度动力学变化曲线。     

G蛋白调节剂对梨花粉萌发及花粉胞内Ca2+浓度变化的影响

用激光共聚焦技术研究了异三聚体G蛋白活性调节剂对梨花粉萌发、花粉管生长及花粉细胞内游离钙离子浓度动态的影响。结果表明：异三聚体G蛋白激活剂霍乱毒素(CTX)可促进梨花粉萌发与花粉管生长,而其抑制剂百日咳毒素(PTX)则抑制花粉萌发与花粉管生长;霍乱毒素处理后,花粉细胞内产生特异性的“钙瞬变”信号,而百日咳毒素处理后则引起花粉细胞内游离钙离子浓度的持续下降。这表明：异三聚体G蛋白可能参与了梨花粉萌发与花粉管生长的调控过程,G蛋白的活性变化对花粉萌发的效应可能是通过调控花粉细胞内游离Ca^2 浓度的动态变化产生特异性的钙信号来实现的。     

ATP 调控大鼠胰腺β细胞胰岛素分泌的双重作用

实验以大鼠胰腺β细胞为研究对象,采用荧光测钙和全细胞膜片钳膜电容测量技术,研究 ATP 对胞内钙离子信号和细胞分泌的影响,并初步探讨了其作用机制 . 实验表明：胞外 ATP 刺激通过动员细胞内 thapsigargin 敏感的钙库 Ca2+ 释放,使大鼠胰腺β细胞内的游离钙离子浓度显著升高,细胞外的 ATP 信号对β细胞胰岛素分泌有双向调节作用,其一,主要通过降低去极化引起的钙电流而对β细胞胰岛素分泌产生较弱的抑制作用,其二,细胞在静息状态下, ATP 通过动员胞内钙库的 Ca2+ 释放使胞浆中的钙离子浓度显著增加,触发β细胞强烈分泌胰岛素 . ATP 的这种双向调节可能对胰岛素分泌的精确调控具有重要的生理意义 .