Laneuville O, Reynaud D, Grinstein S, Nigam S, Pace-Asciak C R
Research Institute, Hospital for Sick Children, Toronto, Canada.
Biochem J. 1993 Oct 15;295 ( Pt 2)(Pt 2):393-7. doi: 10.1042/bj2950393.
We have previously shown that the hepoxilins are capable of increasing the intracellular free concentration of calcium ([Ca2+]i) in human neutrophils through a pertussis toxin-sensitive, extracellular calcium-independent pathway involving the mobilization of calcium from internal stores. A subsequent hepoxilin-induced and extracellular calcium-dependent influx of calcium is observed. In an effort to investigate further the role of these compounds in the human neutrophil, we investigated their potential effects on the action of known agonists such as formyl-methionine-leucine-phenylalanine (fMLP), platelet-activating factor (PAF) and leukotriene B4 (LTB4) on the mobilization of calcium. Hepoxilis dose-dependently inhibited the increases in [Ca2+]i induced by fMLP, PAF and LTB4. The hepoxilin concentration required for inhibition was around 100 ng/ml (3 x 10(-7) M). This concentration of hepoxilin did not cause any measurable change in [Ca2+]i. The extent of inhibition of the agonist-evoked rise in [Ca2+]i by hepoxilins was proportional to the increase in the calcium response evoked by hepoxilin beyond its threshold concentration. Additional experiments were carried out to investigate the mechanism for the hepoxilin effect. Using calcium-free medium and in the presence of sufficient amounts of thapsigargin (200 ng/ml) to maximally block the calcium pump (thereby achieving a constant rate of calcium leakage from stores), hepoxilin A3 increased further this rate of calcium leakage, indicating that hepoxilin acts by rapidly draining calcium from stores. Its potential (additional) thapsigargin-like action in blocking the pump, however, cannot be ruled out by these experiments. These observations suggest that the hepoxilins may serve an important negative regulatory function in the agonist-induced mobilization of calcium in these cells by depleting calcium stores.
我们之前已经表明，hepoxilins能够通过一种对百日咳毒素敏感、不依赖细胞外钙的途径，增加人中性粒细胞内的游离钙浓度（[Ca2+]i），该途径涉及从内部储存库中动员钙。随后观察到hepoxilin诱导的、依赖细胞外钙的钙内流。为了进一步研究这些化合物在人中性粒细胞中的作用，我们研究了它们对已知激动剂（如甲酰甲硫氨酸亮氨酸苯丙氨酸（fMLP）、血小板活化因子（PAF）和白三烯B4（LTB4））钙动员作用的潜在影响。Hepoxilins剂量依赖性地抑制fMLP、PAF和LTB4诱导的[Ca2+]i升高。抑制所需的hepoxilin浓度约为100 ng/ml（3×10(-7)M）。该浓度的hepoxilin不会引起[Ca2+]i的任何可测量变化。Hepoxilins对激动剂诱发的[Ca2+]i升高的抑制程度与hepoxilin超过其阈值浓度后诱发的钙反应增加成正比。进行了额外的实验来研究hepoxilin作用的机制。使用无钙培养基，并在存在足够量的毒胡萝卜素（200 ng/ml）以最大程度阻断钙泵（从而实现从储存库中恒定的钙泄漏速率）的情况下，hepoxilin A3进一步增加了这种钙泄漏速率，表明hepoxilin通过快速从储存库中排出钙起作用。然而，这些实验不能排除其在阻断泵方面潜在的（额外的）毒胡萝卜素样作用。这些观察结果表明，hepoxilins可能通过耗尽钙储存库，在这些细胞中激动剂诱导的钙动员中发挥重要的负调节功能。
