Simchowitz L, Foy M A, Cragoe E J
Department of Medicine, Veterans Administration Medical Center, St. Louis, Missouri.
J Biol Chem. 1990 Aug 15;265(23):13449-56.
A Na+/Ca2+ exchange mechanism has been recently described in human neutrophils that constitutes the principal pathway for Ca2+ influx into resting cells. The potential role of this system in regulating the respiratory burst in response to activation by the chemotactic tripeptide N-formyl-methionyl-leucyl-phenylalanine was explored. In the presence of 1 mM Ca2+, a variety of di- and trivalent cations suppressed the generation of O(-2) radicals in a series of decreasing efficacy: La3+ approximately Zn2+ much greater than Sr2+ approximately Cd2+ greater than Ba2+ greater than Co2+ greater than Ni2+ approximately Mg2+. This sequence is similar to their rank order of activity in inhibiting 45Ca2+ influx via Na+/Ca2+ counter-transport. Benzamil, phenamil, and 2',4'-dichlorobenzamil, analogues of amiloride which selectively block Na+/Ca2+ exchange in neutrophils, likewise suppressed the release of O(-2) with apparent Ki values of approximately 30 microM. The effect of the cations was competitive with Ca2+, while the interaction between the benzamil derivatives and Ca2+ appeared to be noncompetitive in nature. Both the divalent cations and benzamil also inhibited the rise in cytoplasmic Ca2+ as monitored by fura-2 fluorescence: these agents reduced peak cytosolic Ca2+ levels after N-formyl-methionyl-leucyl-phenylalanine stimulation to values seen in the absence of extracellular Ca2+. These results are compatible with the hypothesis that the influx of Ca2+ via Na+/Ca2+ exchange contributes to the transient elevation in intracellular free Ca2+. The polyvalent cations block the entry of critical Ca2+ ions by competing with Ca2+ for binding to the translocation site on the exchange carrier, while benzamil acts by lowering the maximal transport rate. These studies emphasize that Na+/Ca2+ exchange through its effects on cytoplasmic Ca2+ plays a major regulatory role in activation of the respiratory burst in chemotactic factor-stimulated neutrophils.
最近在人类中性粒细胞中描述了一种Na⁺/Ca²⁺交换机制，它是Ca²⁺流入静息细胞的主要途径。探讨了该系统在调节趋化三肽N-甲酰甲硫氨酰-亮氨酰-苯丙氨酸激活后的呼吸爆发中的潜在作用。在1 mM Ca²⁺存在下，多种二价和三价阳离子以一系列递减的效力抑制O⁻₂自由基的产生：La³⁺≈Zn²⁺远大于Sr²⁺≈Cd²⁺大于Ba²⁺大于Co²⁺大于Ni²⁺≈Mg²⁺。该序列与其通过Na⁺/Ca²⁺逆向转运抑制⁴⁵Ca²⁺流入的活性顺序相似。苯甲米、非那米和2',4'-二氯苯甲米是氨氯地平的类似物，它们选择性地阻断中性粒细胞中的Na⁺/Ca²⁺交换，同样抑制O⁻₂的释放，表观Ki值约为30 μM。阳离子的作用与Ca²⁺具有竞争性，而苯甲米衍生物与Ca²⁺之间的相互作用在本质上似乎是非竞争性的。二价阳离子和苯甲米也抑制了用fura-2荧光监测的细胞质Ca²⁺的升高：这些试剂将N-甲酰甲硫氨酰-亮氨酰-苯丙氨酸刺激后的胞质Ca²⁺峰值水平降低到无细胞外Ca²⁺时所见的值。这些结果与以下假设一致，即通过Na⁺/Ca²⁺交换的Ca²⁺流入有助于细胞内游离Ca²⁺的短暂升高。多价阳离子通过与Ca²⁺竞争结合交换载体上的转运位点来阻止关键Ca²⁺离子的进入，而苯甲米则通过降低最大转运速率起作用。这些研究强调，Na⁺/Ca²⁺交换通过其对细胞质Ca²⁺的影响，在趋化因子刺激的中性粒细胞呼吸爆发激活中起主要调节作用。
