Verapamil和Mn~（2＋）对缺氧及缺氧复氧心肌细胞内pH的影响

采用荧光探针ＢＣＥＣＦ／ＡＭ结合计算机图像处理技术测定不同时间的缺氧和缺氧复氧单心肌细胞内ｐＨ的变化以及Ｃａ２＋通道阻滞剂Ｖｅｒａｐａｍｉｌ和Ｎａ＋－Ｃａ２＋交换抑制剂Ｍｎ２＋对其的影响。结果显示随着缺氧时间的延长，细胞内ｐＨ也逐渐降低。复氧开始４０ｍｉｎ内，细胞内ｐＨ并未恢复正常。Ｖｅｒａｐａｍｉｌ能减轻缺氧细胞内酸化程度并使其接近正常水平（Ｐ＞０．０５），却未能减轻缺氧复氧细胞内的酸化。无论是缺氧或缺氧复氧心肌细胞，Ｍｎ２＋均未能减轻细胞内的酸化程度。本实验结果提示缺氧和缺氧复氧时细胞内酸化途径并非完全一致。ＶｅｒａＰａｍｉｌ抑制缺氧细胞内ｐＨ下降是其保护缺氧心肌作用的机制之一。     

Effects of captopril and enalaprilat on intracellular Ca~(2 ),Na~ contents and pH in hypoxic and reoxygenated cardiomyocytes

探讨卡托普利（Ｃａｐ）和依那普利拉（Ｅｎａ）保护缺氧和复氧心肌细胞作用机制．方法：采用荧光探针结合图象处理技术测定细胞内离子浓度．结果：缺氧和复氧心肌细胞内Ｃａ２＋（分别为１６５±８和１９６±１４ｎｍｏｌ·Ｌ－１）和Ｎａ＋（分别为９２±０８和９３±１３ｍｍｏｌ·Ｌ－１）高于正常而ｐＨ低于正常（分别为６７±０３和６６１±０１９）．Ｃａｐ和Ｅｎａ减少缺氧细胞内Ｃａ２＋浓度并减轻细胞内酸化．Ｃａｐ也减少缺氧细胞内Ｎａ＋浓度（８１±０９ｍｍｏｌ·Ｌ－１）．Ｃａｐ减少复氧细胞内Ｃａ２＋和Ｎａ＋浓度，但Ｅｎａ无此作用．Ｃａｐ或Ｅｎａ与Ｖｅｒ合用无协同作用．结论：Ｃａｐ和Ｅｎａ对缺氧和复氧心肌细胞有保护作用，但机制并不完全一致．     

Mobilization of intracellular Ca~(2 ) modulates activation of Na~ /H~ exchange in thrombin-stimulated platelets

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［Ｃａ２＋］ｉ和ＢＣＥＣＦ负载测ｐＨｉ．结果：凝血酶０１ＩＵ·Ｌ－１引起［Ｃａ２＋］ｉ和ｐＨｉ增加，［Ｃａ２＋］ｉ增加先于ｐＨｉ增加．在无钠溶液中，Ｎａ＋／Ｈ＋交换被抑制而［Ｃａ２＋］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［Ｃａ２＋］ｉ增加．用依他酸（ＥＧＴＡ）阻断外钙内流，胞浆碱化不受影响．伊屋诺霉素加ＥＧＴＡ耗竭胞内钙池时，胞浆硷化效应被取消，且静息ｐＨｉ更低，加入１ｍｍｏｌ·Ｌ－１外钙重新充填钙池，胞浆碱化效应又被恢复．结论：细胞内钙动员调控Ｎａ＋／Ｈ＋交换，后者需［Ｃａ２＋］ｉ增加达一定有效浓度．     

氯丙烯对神经细胞内Ca~(2 ),游离钙调蛋白,环腺苷酸含量和钙/钙调蛋白依赖性蛋白激酶Ⅱ活性的影响

用培养的鸡胚脑神经细胞研究了１．０２和２．０４ｍｍｏｌ·Ｌ－１氯丙烯作用２４ｈ后细胞内Ｃａ２＋，游离钙调蛋白（ＣａＭ）和环腺苷酸（ｃＡＭＰ）含量及钙／钙调蛋白依赖性蛋白激酶Ⅱ（Ｃａ２＋／ＣａＭ－ＰＫⅡ）活性的改变．结果显示，随着氯丙烯浓度的增加，细胞内Ｃａ２＋分别增加了４．２和６．２倍，ｃＡＭＰ含量增加了２２％和３９％，Ｃａ２＋／ＣａＭ－ＰＫⅡ活性增加了２．８和５．０倍（Ｐ＜０．０１）；而游离ＣａＭ含量则分别减少了５５％和６９％（Ｐ＜０．０１）．结果提示氯丙烯引起病理性神经轴浆内微管和神经微丝堆积与细胞内Ｃａ２＋增加有关．这可能由于细胞内Ｃａ２＋增加，激活ＣａＭ，继而激活Ｃａ２＋／ＣａＭ－ＰＫⅡ，催化微管相关蛋白２和ｔａｕ－蛋白磷酸化，抑制微管组装，使解聚的微管堆积在轴浆内．     

间硝苯地平对老龄肾性高血压大鼠心肌和脑微粒体Na~＋，K~＋－ATP酶，Ca~

间硝苯地平（ｍ－Ｎｉｆ，ｉｇ２０ｍｇ·ｋｇ－１·ｄ１持续给药９周）可显著降低老龄肾性高血压大鼠（ＲＶＨＲ）血压和左室重量（Ｐ＜０．０１），增高心、脑微粒体Ｎａ＋，Ｋ＋－ＡＴＰ酶和Ｃａ２＋－ＡＴＰ酶活性（Ｐ＜０．０１），降低Ｍｇ２＋－ＡＴＰ酶活性，体外量效关系研究发现，ｍ－Ｎｉｆ在较高剂量（１０～１０００μｍｏｌ·Ｌ－１）时可增高ＲＶＨＲ心脑微粒体Ｎａ＋，Ｋ＋－ＡＴＰ酶和Ｃａ２＋－ＡＴＰ酶活性，且随剂量增加而增高。上述结果表明，ｍ－Ｎｉｆ可改善老龄ＲＶＨＲ心脑微粒体Ｎａ＋，Ｋ＋泵和Ｃａ２＋泵功能。     

卡托普利和依那普利拉对分离的大鼠心肌细胞内游离Ca~（2＋）浓度的影响

目的：研究转换酶抑制剂卡托普利（Ｃａｐ）和依那普利拉（Ｅｎａ）对ＳＨＲ和ＷＫＹ大鼠心肌细胞内游离Ｃａ２＋浓度的影响．方法：用荧光探针Ｆｕｒａ２ＡＭ结合计算机图象处理技术测定分离心肌细胞内游离Ｃａ２＋浓度．结果：ＳＨＲ心肌细胞内游离Ｃａ２＋浓度（１７４±５ｎｍｏｌ·Ｌ－１）较ＷＫＹ大鼠（１４８±１５ｎｍｏｌ·Ｌ－１）高（Ｐ＜００１）．Ｃａｐ和Ｅｎａ能明显降低ＳＨＲ心肌细胞内游离Ｃａ２＋浓度（分别为１６１±１１和１６６±７ｎｍｏｌ·Ｌ－１，Ｐ分别＜００５），但对ＷＫＹ的无影响（Ｐ＞００５）．两药均能明显降低ＮＥ和ＡｎｇＩ引起的ＳＨＲ和ＷＫＹ大鼠心肌细胞内Ｃａ２＋升高，同时也能明显降低ＫＣｌ引起的ＳＨＲ细胞内Ｃａ２＋升高（Ｐ＜００５），但对ＷＫＹ大鼠的无明显影响（Ｐ＞００５）．结论：Ｃａｐ和Ｅｎａ对病理性电压依赖性Ｃａ２＋通道有直接抑制作用．     

卡托普利和依那普利拉对分离的大鼠心肌细胞内游离Ca^2＋浓度的影响

目的：研究转换酶抑制剂卡托普利（Ｃａｐ）和依那普利拉（Ｅｎａ）对ＳＨＲ和ＷＫＹ大鼠心肌细胞内游离Ｃａ＾２＋浓度的影响，方法：用荧光探针Ｆｕｒａ２－ＡＭ结合计算机图象处理技术测定分离心肌细胞内游离Ｃａ＾２＋浓度，结果：ＳＨＲ心理细胞内游离Ｃａ＾２＋浓度（１７４±５ｎｍｏｌ．Ｌ＾－１）较ＷＫＹ大鼠（１４８±１５ｎｍｏｌ．Ｌ＾－１）高（Ｐ〈０．０１），Ｃａｐ和Ｅｎａ能明显降低ＳＨＲ心肌细胞内游离Ｃａ＾２     

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     

牛磺酸抗脂质过氧化作用与调节Ca~（2＋）作用

在培养心肌细胞缺氧－再给氧模型上，发现牛磺酸（２０ｍｍｏｌ·Ｌ－１，终浓度）能显著降低细胞内脂质过氧化物（ＬＰＯ）荧光强度；剂量依赖性地提高心肌细胞超氧化物歧化酶（ＳＯＤ）活性；以荧光比率法（荧光探针为Ｉｎｄｏ－１－ＡＭ）在粘附式细胞仪（ＡＣＡＳ５７０）上测定细胞内游离Ｃａ２＋荧光比率，结果显示缺氧及再给氧后细胞内Ｃａ２＋荧光比率明显升高，２０ｍｍｏｌ·Ｌ－１牛磺酸能显著减少Ｃａ２＋荧光比率；分别以２０ｍｍｏｌ·Ｌ－１、０．４ｍｍｏｌ·Ｌ－１Ｃａ２＋及０．１ｍｍｏｌ·Ｌ－１维拉帕米处理细胞，牛磺酸能降低高Ｃａ２＋引起的细胞搏动加快；而提高低Ｃａ２＋及维拉帕米处理后的细胞搏动。提示牛磺酸对培养心肌细胞再给氧损伤有保护作用，其机理与其提高心肌细胞ＳＯＤ活性、降低细胞内游离Ｃａ２＋浓度及对细胞Ｃａ２＋双向调节作用有关。     

牛磺酸对缺血大鼠心肌腺苷三磷酸酶的影响

目的观测牛磺酸（ｔａｕｒｉｎｅ，Ｔａｕ）对心肌缺血损伤时心肌肌膜和线粒体ＡＴＰ酶活性的影响。方法以异丙肾上腺素（Ｉｓｏ，５ｍｇ·ｋｇ－１）诱导心肌缺血损伤模型，用定磷法分别测定Ｃａ２＋－ＡＴＰ酶、Ｍｇ２＋－ＡＴＰ酶及Ｎａ＋，Ｋ＋－ＡＴＰ酶活性。结果与对照组比较，缺血组心肌肌膜和线粒体Ｃａ２＋－ＡＴＰ酶、Ｍｇ２＋－ＡＴＰ酶及Ｎａ＋，Ｋ＋－ＡＴＰ酶活性均降低，在注射ＩＳＰ前３０ｍｉｎ腹腔注射Ｔａｕ（２００ｍｇ·ｋｇ－１），则上述酶活性未见显著性变化。结论Ｔａｕ具有拮抗缺血大鼠心肌肌膜及线粒体Ｃａ２＋－ＡＴＰ酶、Ｍｇ２＋－ＡＴＰ酶及Ｎａ＋，Ｋ＋－ＡＴＰ酶活性降低的细胞保护作用     

Comparison of the effect of amiloride and its analogue dichlorobenzamil on cardiac chronotropic responses to ouabain in myocardial cell aggregates in culture

The purpose of this study was to compare the effects of amiloride, an inhibitor of Na(+)-H+ exchange, and its analog 3',4'-dichlorobenzamil, a more specific inhibitor of Na(+)-Ca2+ exchange on the response of cardiac myocytes to ouabain. Cardiac myocyte aggregates were prepared from myocytes obtained from 7-day-old chick embryo hearts. Ouabain at 10(-6) M produced a marked and significant (p less than 0.05) reduction in contractile frequency. Amiloride, at 10(-7) to 10(-5) M produced a definite, significant (p less than 0.05) and dose-dependent reduction in this effect of ouabain. In contrast, dichlorobenzamil, 10(-7) to 10(-6) M, significantly (p less than 0.05) accentuated this effect of ouabain. Thus, amiloride and its analog dichlorobenzamil have different effects on the cardiac responses to ouabain presumably because of the differences in the specificity of their inhibition of Na+/H+ and Na+/Ca2+ exchange. Thus to the extent that the effects of amiloride and dichlorobenzamil are mediated through, respectively Na(+)-H+ and Na(+)-Ca2+ exchange, these data suggest that ouabain-induced reduction in contractile frequency is mediated through Na(+)-H+ exchange while Na(+)-Ca2+ exchange acts to minimize this action of ouabain. Amiloride may be useful to oppose the negative chronotropic effect of ouabain while dichlorobenzamil accentuates this effect of ouabain.     

Na(+)-Ca2+ exchange activity in central nerve endings. II. Relationship between pharmacological blockade by amiloride analogues and dopamine release from tuberoinfundibular hypothalamic neurons

The aim of the present study was to investigate the possible role played by the Na(+)-Ca2+ exchange system in the modulation of [3H]dopamine ([3H]DA) release from tuberoinfundibular hypothalamic (TIDA) neurons. 2',4'-Dimethylbenzamil (DMB) dose-dependently (10-100 microM) inhibited Na(+)-dependent 45Ca2+ efflux from brain synaptosomes. This compound (30-300 microM), as well as alpha-phenylbenzamil amiloride (30-100 microM), another inhibitor of the Na(+)-Ca2+ antiporter, was also able to stimulate basal release of [3H]DA from superfused TIDA neurons. This stimulation was completely prevented by the removal of extracellular Ca2+ ions, in the presence of 1 mM ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. In addition, DMB-induced [3H]DA release was unaffected by the dopamine transport inhibitor nomifensine (10 microM). On the other hand, 5-[N-methyl-N-guanidinocarbonylmethyl]amiloride (MGCMA) (100-300 microM), which lacks inhibitory properties on the Na(+)-Ca2+ exchanger but behaves as an inhibitor of the Na(+)-H+ antiporter, failed to modify basal [3H]DA release from TIDA neurons. When the Na(+)-Ca2+ antiporter operates as a Ca2+ influx pathway, as occurs upon the removal of extracellular Na+ ions, Na(+)-dependent 45Ca2+ uptake in brain synaptosomes was dose-dependently (10-300 microM) inhibited by DMB, whereas DMB itself was unable to prevent 55 mM K(+)-induced 45Ca2+ uptake, which mainly reflects the activation of voltage-operated Ca2+ channels. In keeping with these results, ouabain (500 microM)-induced [3H]DA release, which depends on the activation of the Na(+)-Ca2+ exchanger due to inhibition of the Na(+)-K(+)-ATPase pump, was prevented by superfusion of TIDA neurons with DMB (50 microM). By contrast, MGCMA (100 microM) failed to modify either Na(+)-dependent 45Ca2+ influx or ouabain-induced [3H]DA release. In conclusion, the results of the present study appear to suggest that the pharmacological inhibition of the Na(+)-Ca2+ antiporter by amiloride analogues may affect DA release from central neurons. Opposite effects are observed, depending on the direction of operation of the exchanger. In fact, when the Na(+)-Ca2+ exchanger operates as a Ca2+ efflux pathway, its pharmacological blockade can produce a stimulation of DA release. In contrast, when this antiporter operates as a Ca2+ influx pathway, as occurs as a consequence of the inhibition of the Na(+)-K(+)-ATPase pump by ouabain, its pharmacological blockade can prevent ouabain-induced DA release from TIDA neurons.     

Protection of cardiomyocytes by pinacidil during metabolic inhibition and hyperkalemia.

The objective of this study is to understand the mechanism underlying the cardioprotective effects of pinacidil, an ATP-sensitive K+ channel (K(ATP)) opener. We examined the effects of 10 microM pinacidil in cultured chicken cardiomyocytes. Pinacidil caused a concentration-dependent delay in metabolic inhibition-induced increase in intracellular calcium concentration ([Ca2+]i) and creatine phosphokinase release, and this action was antagonized by glyburide, a K(ATP) blocker. Neither verapamil, an L-type Ca2+ channel blocker, nor bepridil, a Na+-Ca2+ exchange inhibitor, affected the time course of increase in [Ca2+]i induced by metabolic inhibition. Pinacidil did not have an effect on the amplitude of K+-induced increase in [Ca2+]i, but accelerated the rate of decline following peak stimulation. In contrast, glyburide reduced the amplitude of K+-induced increase in [Ca2+]i and prolonged the rate of decline. These results provide direct evidence that pinacidil protects cardiomyocytes from metabolic inhibition-induced injury by cyanide (CN) through a delay in the onset of increase in [Ca2+]i, rather than by inhibition of the L-type Ca2+-channels or by alteration of Na+-Ca2+ exchange.     

Involvement of anion exchange in the hypoxia/reoxygenation-induced changes in pH(i) and

The involvement of Cl(-)/HCO(3)(-) exchange in hypoxia/reoxygenation-induced changes in pH(i) and Ca(2+) concentration ([Ca(2+)](i)) was examined in rat ventricular myocytes. During 10-min hypoxia, the initial pH(i) (7.21+/-0.04) fell to below 6.8. Subsequent reperfusion with reoxygenated buffer returned this acidic pH(i) to the neutral range with increases in [Ca(2+)](i). These responses were reduced by the removal of Cl(-) or HCO(3)(-) and by the addition of anion exchange inhibitors, SITS (4-acetamido-4'isothiocyanato-stilbene-2,2'disulfonic acid) and DIDS (4,4'-diisothiocyano-stilbene-2,2'-disulfonic acid), while inhibitors for the Cl(-) channel and Na(+)/K(+)/2Cl(-) cotransport were without effects. The hypoxia-induced acidification was attenuated by protein kinase C inhibitors, calphostin C and chelerythrine, but not by a protein kinase A inhibitor, KT5720. Under normoxic condition, protein kinase C activation induced a SITS-sensitive acidification. Furthermore, in electrically driven rat papillary muscle, SITS and DIDS improved the recovery of developed tension during the reoxygenation. These results suggest that the hypoxia-induced decrease in pH(i) is mediated at least in part by anion exchange stimulation through protein kinase C activation, and this exchange takes part in the reoxygenation-induced Ca(2+) overload as well as contractile dysfunction.     

Ranolazine inhibits an oxidative stress-induced increase in myocyte sodium and calcium loading during simulated-demand ischemia

Ranolazine inhibits the late Na current and is proposed to reduce angina by decreasing [Na]i during ischemia, thereby reducing Ca influx via Na/Ca exchange (NCX). We sought to test this hypothesis and to determine whether oxidative stress during simulated-demand ischemia activates the late Na current. We measured [Ca]i and [Na]i in rabbit ventricular myocytes by flow cytometry during metabolic inhibition (MI) with 2 mM cyanide and 0 mM glucose at 37 degrees C plus pacing (P) at 0.5 Hz (P-MI), and in P-MI + 1, 10, or 50 microM ranolazine. In the clinically relevant concentration range (1-10 microM), ranolazine decreased Na and Ca loading and the development of myocyte contracture. P-MI caused an increase in fluorescence of the oxidative radical probe CM-H2DCFDA, which was inhibited by the radical scavenger Tiron 20 mM. The NCX inhibitor KB-R7943 (10 microM) and Tiron 20 mM reduced the rise in [Ca]i during P-MI and eliminated the effect of 10 microM ranolazine on [Ca]i. These results indicate that oxidative stress increases the late Na current during MI. Inhibition of the resulting increase in Na and Ca loading and contracture seems to account for the observed antiischemia effects of ranolazine.     

Restoration of osmotically inhibited twitch force in rat cardiac trabeculae: role of Na+-H+ exchange

1. When rat cardiac muscle is subjected to an increase of osmolality, its peak twitch force is immediately inhibited. Subsequently, over a period of several minutes, twitch force undergoes restoration, the extent of which is determined by the osmolality. The aim of the present study was to determine the factors that contribute to this restorative phenomenon. 2. Trabeculae were isolated from the right ventricles of rat hearts and mounted in an organ bath at 37 degrees C. The osmolality of the bathing solution was increased by 100 mOsmol (to 400 mOsmol) by the addition of various proportions of NaCl and sucrose while recording twitch force production. The role of Na+-H+ exchange in restoring twitch force was examined by use of the specific inhibitor cariporide (HOE 642). The role of Na+-Ca2+ exchange was examined by reducing [Ca2+]o (from 2 mmol/L to 0.5 mmol/L) or by substituting LiCl for NaCl. 3. Cariporide (25 micro mol/L) completely abolished twitch force restoration, thereby implicating a central role for the Na+-H+ exchanger. At constant [Na+]o, the extent of restoration was [Ca2+]o dependent, suggesting an independent contribution by the Na+-Ca2+ exchanger. This suggestion was supported by the finding that Li+, which substitutes for Na+ on the Na+-H+ exchanger, but not on the Na+-Ca2+ exchanger, also reduced the extent of restoration of hyperosmotically inhibited twitch force. 4. We conclude that the immediate inhibition of peak twitch force of rat cardiac muscle by hyperosmotic solutions reflects, in part, elevation of [H+]i, subsequent to reduction of cell volume. Hyperosmotic activation of Na+-H+ exchange then progressively relieves the inhibitory effect of protons on force development. The accompanying increase in [Na+]i in turn enhances Ca2+ influx on the Na+-Ca2+ exchanger, with the result that twitch force undergoes further restoration.     

Influence of a Na+-H+ exchange inhibitor ethylisopropylamiloride, a Na+-Ca2+ exchange inhibitor KB-R7943 and their combination on the increases in contractility and Ca2+ transient induced by angiotensin II in isolated adult rabbit ventricular myocytes

In rabbit, ventricular myocytes loaded with indo-1/AM, angiotensin II (0.1 nM-0.1 microM) exerted a positive inotropic effect with a significant increase in the amplitude of Ca2+ transients. For a given increase in cell shortening, the increase in Ca2+ transients induced by angiotensin II was less than that induced by elevation of extracellular Ca2+ concentration ([Ca2+]0) or isoprenaline, an indication that both the increase in mobilization of intracellular Ca2+ ions and myofibrillar sensitivity to Ca2+ ions contribute to the positive inotropic effect of angiotensin II. The effects of angiotensin II on Ca2+ transients and cell shortening were inhibited by the AT1 receptor antagonist losartan. A Na+ -H+ exchange inhibitor EIPA [5-(N-ethyl-N-isopropyl)amiloride] at 1 and 3 microM did not affect the Ca2+ transients and cell shortening, but it inhibited the angiotensin-II-induced responses in a concentration-dependent manner more effectively than the responses to elevation of [Ca2+]0, indicating that EIPA elicited a selective inhibitory action on the effects of angiotensin II. The observation that EIPA at 10 microM abolished the positive inotropic effect of angiotensin II without a significant depression of the inotropic response to elevation of [Ca2+]0 supports the selective action of EIPA at the high concentration on the response to angiotensin II. A novel selective Na+ -Ca2+ exchange (reverse mode) inhibitor KB-R7943, 2-[2-[4-(-nitrobenzyloxy)phenyl]ethyl] isothiourea methanesulphonate, at 0.3 and 1 microM inhibited also the responses to angiotensin II more effectively than the response to elevation of [Ca2+]0; however, over the same concentration range it suppressed significantly the amplitude of Ca2+ transients and cell shortening. Combination of EIPA (3 microM) and KB-R7943 (0.3 microM), each of which attenuated partially the angiotensin-II-induced responses, abolished the positive inotropic effect and the increase in Ca2+ transients induced by angiotensin II with much less depressant effect on the responses to elevation of [Ca2+]0. Thus, these ion exchange inhibitors exerted selective actions on the respective targets. The results with these selective inhibitors indicate that the activation of Na+ -H+ exchanger and subsequent modulation of the activity of Na+ -Ca2+ exchanger may be responsible for the increase in [Ca2+]i and the myofilament Ca2+ sensitization induced by stimulation of AT1 receptors by angiotensin II in rabbit ventricular myocytes.     

Inhibition of sodium-calcium and sodium-proton exchangers by amiloride congeners in arterial muscle cells.

The inhibitory potencies of several amiloride congeners towards Na(+)-Ca2+ and Na(+)-H+ exchange were compared in rat aortic myocytes. N-(2,4-Dimethylbenzyl)amiloride (DMB) was 10 times more potent towards Na(+)-Ca2+ than Na(+)-H+ exchange. Amiloride and ethylisopropylamiloride were about 5,000 and 10,000 times more potent toward Na(+)-H+ than Na(+)-Ca2+ exchange respectively. N-(3,4-Dichlorobenzyl)amiloride was almost equipotent towards both exchangers. About 40 nM ethylisopropylamiloride inhibited Na(+)-H+ exchange by 50%. Ethylisopropylamiloride (10 microM) had no effect on basal or angiotensin-evoked 45Ca2+ efflux or net Ca2+ efflux. In contrast to ethylisopropylamiloride, 25-50 microM DMB, which strongly inhibits Na(+)-Ca2+ exchange, markedly decreased both 45Ca2+ efflux and net Ca2+ efflux produced by angiotensin. Replacing extracellular Na+ with N-methyl-D-glucamine inhibited angiotensin-evoked 45Ca2+ efflux similarly to DMB. Neither DMB nor Na+ placement had any effect on basal or angiotensin-evoked production of [3H]inositol phosphates. These findings suggest that Na(+)-H+ exchange has no major influence on short-term Ca2+ regulation and provide evidence that Na(+)-Ca2+ exchange is a major pathway of rapid Ca2+ efflux in stimulated arterial muscle cells.