肿瘤细胞内pH值改变与肿瘤多药耐药的关系

细胞内pH值(pHi)增高是许多耐药肿瘤的共同特点,其结果引起肿瘤细胞对化疗药物的敏感性下降,降低药物疗效。通过对pHi的调节,可纠正细胞内碱化,逆转肿瘤耐药。Na+-H+交换蛋白(Na+/H+exchanger,NHE)抑制剂可通过抑制NHE的活性调节pHi,为肿瘤的治疗提供了新的思路和手段。     

穿心草口山酮对激活细胞膜Na~+/H~+交换加重心脏缺血再灌注损伤的保护作用

目的　研究 3种穿心草口山酮 (xanthone ,Xan) :1,8 dihydroxy ,3 ,5 dimethoxyxanthone(Xan Ⅰ ) ;1 hydroxy ,3 ,5 dimethoxyxanthone(Xan Ⅱ ) ;1 hydroxy ,3 ,7,8 trithoxyxan thone(Xan Ⅲ )对激活细胞膜Na+/H+交换加重心脏缺血再灌注损伤的保护作用。方法　在离体大鼠等容收缩模型上 ,采用NH4 Cl负荷方法以激活细胞膜Na+/H+交换 ,观察在缺血前给予Xan对缺血再灌注损伤的影响。结果　Na+/H+交换组增加冠脉流出液中乳酸脱氢酶 (LDH)的含量 ,促进心肌组织脂质过氧化产物丙二醛 (MDA)的生成 ,加重心肌组织中Na+、Ca2 +超负荷和K+的丢失。浓度为 0 2 μmol·L-1的Xan可明显减轻上述作用 ,作用强度依次为Xan Ⅰ>Xan Ⅲ >Xan Ⅱ。结论　穿心草 3种Xan对激活细胞膜Na+/H+交换加重心脏缺血再灌注损伤有一定的保护作用。     

阿米洛利对大鼠压力超负荷性心肌肥厚的抑制作用

目的　观察钠氢交换体 (NHE)抑制剂阿米洛利 (Ami)对压力超负荷左室肥厚 (LVH)大鼠心功能、心肌细胞内游离钙浓度 ([Ca2 + ]i)及心肌细胞膜Na+ 、K+ ATP酶活性的影响。方法　①同步记录离体工作心脏LVSP、LVEDP、±dp/dtmax及T值 ;②测定Fura 2 /A负载后的单个心室肌细胞的 [Ca2 + ]i;③光电比色法测定Na+ 、K+ ATP酶的活性。结果　①与对照组相比 ,LVH组LVEDP和T值明显增加 ,-dp/dtmax明显降低 (均P <0 0 1) ;与LVH组相比 ,Ami组和Ena组的LVEDP及T值明显下降 (均P <0 0 1)。②与对照组相比 ,LVH组的心肌细胞 [Ca2 + ]i明显增高 ,细胞膜Na+ 、K+ ATP酶活性明显降低 (均P <0 0 1) ;Ami及Ena可降低LVH大鼠的 [Ca2 + ]i,升高其Na+ 、K+ ATP酶活性 (均P <0 0 1)。结论　压力超负荷大鼠心脏舒张功能明显下降 ,心室肌细胞 [Ca2 + ]i增高 ,心肌细胞膜Na+ 、K+ ATP酶活性受损 ,Ami及Ena均可抑制此类异常     

抗肝纤维化的新靶点:Na~+/H~+交换泵

Na+ /H+ 交换泵 (NHE)是调节细胞内pH和容积的重要膜蛋白。对启动细胞增殖、分化和凋亡起重要作用。NHE参与介导细胞因子和氧应激激活肝贮脂细胞和胶原的合成 ,因而与肝纤维化的形成密切相关。NHE有望成为重要的抗肝纤维化药物的靶点。     

细胞内镁离子平衡调节机制研究进展

Mg2+是细胞内第二位含量丰富的二价阳离子,与生物体的生理病理变化密切相关,但对其平衡调节的机制还不十分清楚。该文就细胞膜通道TRPM6、TRPM7,转运体Na+/Mg2+交换、Ca2+/Mg2+交换及细胞内ATP、蛋白、线粒体、内质网、细胞核与胞内游离镁离子稳态调节研究进展进行综述以为读者提供一个了解镁离子调节的机会。     

潜在治疗靶点:心肌Na+/H+交换器

细胞内pH（pH_i）的变化（如心肌缺血后细胞内酸中毒）对心脏收缩力影响很大,而其作用机制复杂。pH_i反映了碱化与酸化过程的净平衡。控制细胞内酸中毒主要有两种碱化交换器,即Na～+/H～+交换器（NHE）和Na～+-HCO_3～-同向转运（sympOrt）。NHE使质子外流,同时使Na～+内流,这对于缺血所     

AMP579与腺苷对大鼠心室肌细胞Na~+/Ca~(2+)交换电流作用的比较(英文)

目的阐明AMP579与腺苷不同药理作用与临床效果的机制。方法采用全细胞膜片钳记录Na+/Ca2 +交换电流。结果AMP579对Na+/Ca2 +交换的外向和内向电流均呈浓度依赖性增强。灌流腺苷A1受体阻断剂PD116948 30μmol·L-1,A2受体阻断剂DMPX10μmol·L-1,蛋白激酶A特异阻断剂KT5720 0 .2μmol·L-1或蛋白激酶C特异阻断剂GF109203X0 .4μmol·L-1对AMP579 Na+/Ca2 +交换电流的激动作用均无影响,提示AMP579对Na+/Ca2 +交换电流具有直接的激动作用。结论AMP579对Na+/Ca2 +交换电流可能具有直接的激动作用。     

pH对大鼠离体胸主动脉环静息张力的影响及机制

目的观察pH改变对大鼠离体胸主动脉环静息张力的影响,探讨其可能的作用机制。方法采用离体血管张力实验方法,观察pH改变对大鼠离体胸主动脉环静息张力的的影响。观察静息状态下外钙内流和内钙释放在pH=9.5收缩大鼠离体胸主动脉环中的作用,以及孵育钙通道阻断剂维拉帕米(VEP,10-5 mol.L-1)、Na+/Ca2+交换阻断剂KB-R7943(10-6 mol.L-1)、Na+/H+交换抑制剂氨氯吡咪(AM,10-4 mol.L-1)对pH=9.5时大鼠离体胸主动脉环收缩的影响。结果胞外酸性环境下随pH值逐渐降低,大鼠离体胸主动脉环静息张力无明显改变;碱性环境下随pH值逐渐增加,其静息张力明显升高,其中pH=8.5、pH=9.0、pH=9.5、pH=10.0时的Emax分别为(11.79±6.83)%、(30.25±3.57)%、(92.24±5.73)%、(110.85±7.78)%。外钙内流和内钙释放均参与pH=9.5时的胸主动脉环收缩,VEP可部分阻断其收缩。KB-R7943和AM对pH=9.5时大鼠离体胸主动脉环收缩有减弱作用(P<0.01),其Emax分别为(48.33±5.75)%、(32.12±4.45)%。结论胞外碱性环境下,大鼠离体胸主动脉环静息张力随pH值增大而明显升高,此作用依赖外钙内流和内钙释放,与Na+/Ca2+交换和Na+/H+交换均有关。     

再灌注早期给予5-N,N二甲基氨氯吡咪对心肌缺血再灌注损伤的保护作用机制研究

目的探讨再灌注早期给予20μmol/L5-N,N二甲基氨氯吡咪(DMA)减轻心肌缺血再灌注损伤的作用机制。方法采用Langendorff法建立离体大鼠心肌缺血再灌注模型,全心缺血45min后,再灌注30min,在再灌注初始5min期间给予药物干预[空白对照;20μmol/LDMA组;低浓度(0.5mmol/L)氨氯吡咪组;高浓度(2.0mmol/L)氨氯吡咪组],其中20μmol/LDMA可以抑制Na+/H+交换,激动Na+/Ca2+交换;低浓度氨氯吡咪主要抑制Na+/H+交换;高浓度氨氯吡咪同时抑制Na+/H+交换和Na+/Ca2+交换。观察不同的药物对离体灌流心脏再灌注期间血流动力学指标(LVSP-LVDP,+dp/dtmax,-dp/dtmax)的影响,同时观察再灌注期间冠状动脉流出液中肌酸激酶(CK)的活性变化。结果与对照组相比,3个药物干预组对再灌后各项血流动力学指标的恢复均有明显的促进作用;流出液中CK的活性较对照组也明显下降。但是再灌注30min后3个给药组血流动力学指标以及流出液中CK的活性差异无统计学意义。结论20μmol/LDMA可明显减轻心肌缺血再灌注损伤,其机制主要是通过抑制Na+/H+交换来发挥其作用,与它对Na+/Ca2+交换的激动作用关系不大。     

细胞保护新靶点——Na~+-Ca~(2+)交换体

Na+ Ca2 +交换体 (Sodium calciumexchanger,NCX)是一种双向转运蛋白 ,具生电特性 ,其产生的电流称为Na+ Ca2 +交换电流 (INa Ca)。Na+ Ca2 +交换是调节细胞内Ca2 +平衡的主要途径之一 ,更是将过多的Ca2 +排出细胞的主要方式。NCX活性受多种因素调节 ,且在心 (脑 )缺血 /再灌 ,心衰 ,早老性痴呆等病理状态下有不同程度的改变。NCX是一潜在的、重要的药物作用靶点 ,目前尚无特异性作用于NCX本身的药物     

心肌钠氢交换抑制药在心血管疾病治疗中的应用

心肌钠氢交换抑制药通过抑制心肌细胞内外钠氢交换,从而防止或减少心肌细胞内钙超负荷。研究表明心肌钠氢交换抑制药对心肌缺血、再灌注损伤、心肌肥厚和心力衰竭有明确的治疗作用。     

Role of the cardiac Na(+)/H(+)exchanger in [Ca(2+)](i)and [Na(+)](i)handling during intracellular acidosis. Effect of cariporide (Hoe 642).

Intracellular acidosis is one of the alterations occurring in cardiac ischemia and has been discussed to be important in altering excitation--contraction coupling. The aim of this study was to determine how intracellular acidosis may affect intracellular sodium and calcium handling. Cardiomyocytes were isolated from the hearts of adult male guinea-pigs by standard techniques and superfused with modified Tyrode's solution at room temperature, either HEPES buffered containing 10 mM NaHCO(3)or HEPES buffered without NaHCO(3), in order to examine a possible interaction with the sodium bicarbonate symport. The whole cell voltage clamp technique was used utilizing 3 M Omega pipettes filled with (mM): Cs aspartate 120, CsCl 20, MgCl(2)1, NaCl 5, Mg-ATP 2, HEPES 10 and either 100 microM Fura-2 or 100 microM SBFI. The pH of the pipette solution was either 7.2 or 6.5. Cells were kept at a holding potential of -80 mV and after a pre-pulse to -40 mV the membrane was continuously clamped to potentials from -30 to +80 mV in 10 mV steps. Intracellular Ca(2+)or Na(+)were estimated using the Fura-2 or SBFI technique (impermeable salt), respectively. The cardiac Na(+)/H(+)exchanger was inhibited using the Na(+)/H(+)- exchange inhibitor cariporide (Hoe 642) (1 microM), when indicated. In NaHCO(3)-free experiments we found an increase in intracellular sodium reflected by a rise in the SBFI ratio of 0.326 +/- 0.01 upon intracellular acidification, in contrast to cells perfused at pH = 7.2 (no significant increase in intracellular Na(+)) (P< 0.05). There was no difference in intracellular calcium handling between cells perfused with solutions of pH = 7.2 or 6.5 (Fura-2 Delta ratio: 0.79 +/- 0.10 vs 0.82 +/- 0.07, n.s.). The l -type calcium current also remained unchanged. Blockade of the Na(+)/H(+)exchanger by Hoe 642 had no influence on cells perfused at pH = 7.2 but inhibited the increase in intracellular Na(+)at pH = 6.5 (0.023 +/- 0.026 in the presence of Hoe 642 vs 0.326 +/- 0.01 without Hoe 642, P< 0.05) without affecting [Ca(2+)](i)or the L-type calcium current. In cells superfused with a Tyrode solution containing NaHCO(3), the increase in intracellular sodium concentration was even more pronounced. Under these conditions Hoe 642 also antagonized this increase in intracellular sodium but without reaching the control level. We conclude that under these experimental conditions intracellular acidification causes an increase in [Na(+)](i)without changing intracellular Ca(2+)or the L-type calcium current. In addition in bicarbonate-buffered systems the acidosis-induced increase in sodium is enhanced which may involve the Na(+)/HCO(3)(minus sign)symport. The effect of cariporide (Hoe 642) in intracellular acidosis seems to be based on antagonization of the rise in intracellular sodium rather than calcium in this model.     

Protective effect of SM-20550, a selective Na+ - H+ exchange inhibitor, on ischemia-reperfusion-injured hearts

The protective effects of Na+ - H+ exchange inhibitors SM-20550 (SM) and 5-(N-ethyl-N-isopropyl)-amiloride (EIPA) against ischemia-reperfusion injury were investigated in guinea pig Langendorff hearts. The changes in intracellular pH (pHi), high-energy phosphates, and biologic intracellular active ions ([Na+]i and [Ca2+]i) were regarded using the 31P-NMR and specific fluorescent signals from the heart tissues together with simultaneous recordings of the left ventricular developed pressure (LVDP). The recovery rate of LVDP from ischemia (40 min) by reperfusion was 36.8% in the control experiments, whereas in the presence of SM 10(-7) M, a gradual increase to 75.9% (55.5% with 10(-8) M), in contrast to EIPA (10(-7) M), 47.5% was observed. SM 10(-7) M restored the ATP level by 70% in 40-min reperfusion, which was already higher than the control in the latter half (20-40 min) of the ischemic period. The recovery rate of phosphocreatine by pretreatment of the heart with SM 10(-7) M was 75% in 40 min reperfusion. The pHi estimated from Pi/phosphocreatine chemical shift became highly acidic in ischemic heart so that SM 10(-7) M caused slight but significant pHi reduction from control pHi of 5.89 to 5.75. The level returned to pHi at around 7.38 during 30-40 min reperfusion, and the recovery was significantly greater than the control pHi of 7.24. The fura-2 Ca2+ or SBFI-Na+ signals during Langendorff ischemia heart increased, and rapidly returned to the control level after the reperfusion. SM suppressed the [Na+]i or [Ca2+]i elevation induced in the late stage during ischemia, resulting in LVDP restoration after reperfusion; Diastolic Ca2+ in the end period of ischemia, SM 10(-7) M 194% versus drug-free 220.7%. Na+: SM 10(-7) M 121.6% versus drug-free 128.0%. The present results suggest that the selective Na+ - H+ exchange inhibitor SM is promising as a potent and specific protective agent against ischemia-reperfusion injuries with Ca2+ overload induced via Na+ - H+, Na+ - Ca2+ exchange.     

内钙动员调控凝血酶诱导的血小板Na^＋／H^＋交换

目的：研究凝血酶诱导的血小板活化中细胞内钙动员和Ｎａ＾＋／Ｈ＾＋交换的关系。方法Ｆｕｒａ－２负载测［Ｃａ＾２］ｉ和ＢＣＥＣＦ负载测ｐＨｉ。结果：凝血酶０．１ＩＵ·Ｌ＾－１引起［Ｃａ＾２＋］ｉ和ｐＨｉ，［Ｃａ＾２］ｉ增加先于ｐＨｉ增加。在无钠溶液中，Ｎａ＾＋／Ｈ＾＋交换被抑制而［Ｃａ＾２］ｉ增加不受影响；用尼日利亚菌素（１ｍｇ·Ｌ＾－１）使胞内酸化可抑制［Ｃａ＾２＋］ｉ增加，用依他酸（ＢＧＴＡ）阻断     

The Na(+)/H(+) exchanger: a target for cardiac therapeutic intervention

The Na(+)/H(+) exchanger (NHE) is a ubiquitous protein present in mammalian cells. In higher eukaryotes this integral membrane protein removes one intracellular H(+) for one extracellular Na(+) protecting cells from intracellular acidification. NHE is of essential importance in the myocardium. It prevents intracellular acidosis that inhibits contractility. NHE also plays a key role in damage to the mammalian myocardium that occurs during ischemia and reperfusion and is involved in hypertrophy of the myocardium. NHE is composed of a membrane bound domain of approximately 500 amino acids plus a hydrophilic regulatory cytoplasmic domain of approximately 315 amino acids. The NHE1 isoform is the only significant plasma membrane isoform present in the myocardium. The activity of NHE1 is elevated in animal models of myocardial infarcts and in left ventricular hypertrophy. During ischemia and reperfusion of the myocardium, NHE activity catalyzes increased uptake of intracellular sodium. This in turn is exchanged for extracellular calcium by the Na(+)/Ca(2+) exchanger resulting in calcium overload and damage to the myocardium. Numerous inhibitors of NHE have been developed to attempt to break this cycle of calcium overload. In animal models excellent success has been obtained in this regard. However in humans, clinical trials have resulted in only modest success and recently, significant detrimental side effects were note of one NHE inhibitor. The mechanisms by which these inhibitors affect NHE activity are presently being investigated and regions of the protein important in NHE activity and inhibitor efficacy are related but not identical. Future studies may develop superior inhibitors that may circumvent recently reported side effects. Recently, NHE inhibition has been shown to be remarkably effective in preventing hypertrophy in some animal models. Whether this proves to be a practical treatment for hypertrophy in humans has yet to be determined.     

Preischemic and postischemic treatment with a new Na+/H+-exchange inhibitor, FR183998, shows cardioprotective effects in rats with cardiac ischemia and reperfusion

This study describes the pharmacologic profile of a new Na+/H(+)-exchange inhibitor, FR183998, in anesthetized rats. FR183998 had a potent inhibitory effect on Na+/H+ exchange of rat lymphocytes with median inhibitory (IC50) value of 0.3 nM. Treatment with FR183998 (0.01-0.32 mg/kg, i.v.) reduced or completely abolished ventricular fibrillation and mortality induced by 5-min ischemia followed by reperfusion, when it was administered not only 5 min before ischemia but also 1 min before reperfusion. Myocardial infarct size induced by 30-min ischemia and 60-min reperfusion was reduced significantly in a dose-dependent manner by FR183998 (0.1-1.0 mg/kg, i.v.) when the drug was administered preischemically or at an early phase of ischemia. The ventricular tachycardia and the ventricular fibrillation observed during the ischemic period also were suppressed significantly. These results indicate that FR183998 has a strong inhibitory effect on Na+/H+ exchange and suggest that treatment with FR183998 either before or immediately after the onset of ischemia can prevent the occurrence of arrhythmias and myocardial cell necrosis in situations of ischemia and reperfusion.     

ACTIVATION OF Na+/H+ EXCHANGE IS UNNECESSARY IN THE INDUCTION OF c-fos mRNA IN SERUM-STIMULATED VASCULAR SMOOTH MUSCLE CELLS

1. The effects of extracellular Na+ concentration ([Na+]o) on serum-stimulated c-fos mRNA induction in vascular smooth muscle cells (VSMC) were studied to examine whether the activation of Na+/H+ exchange and the following intracellular alkalinization are necessary in the induction of c-fos in VSMC. 2. When monitored with 2', 7'-bis (carboxylethyl)-5(6)-carboxyfluorescein, the reduction in [Na+]o in HCO(3-)-free buffer caused a dose-dependent inhibition of Na(+)-dependent intracellular pH recovery in acid-loaded VSMC. In addition, serum-stimulated intracellular alkalinization in VSMC was completely blocked by the removal of extracellular Na+. 3. By contrast, c-fos induction, quantified by slit blot hybridization of c-fos mRNA, was not fully inhibited by the reduction of [Na+]o. Furthermore, amiloride and ethylisopropyl-amiloride, inhibitors of Na+/H+ exchange, only partially blocked c-fos induction by serum. 4. We concluded from the observation above, that the intracellular alkalinization caused by the activation of Na+/H+ exchange was unnecessary in serum-stimulated induction of c-fos mRNA in VSMC.