Berger M, Birx D L
Department of Pediatrics, Case Western Reserve University School of Medicine, Cleveland, OH 44106.
J Lab Clin Med. 1988 Apr;111(4):384-92.
To better define the relationship between membrane depolarization and extracellular Ca2+ influx during neutrophil activation, we compared stimulation by elevating the extracellular K+ concentration, [K+]o, with stimulation by the chemoattractant N-formyl-methionyl-leucyl-phenylalanine (fMLP). Elevation of [K+]o resulted in uniform depolarization of the entire population of cells. This was associated with an influx of Ca2+ that was temporally delayed and quantitatively less than that induced by fMLP. K+ depolarization also caused increased expression of type 1 (C3b/C4b) complement receptor (CR1) and type 3 (C3bi) complement receptor (CR3), but the increments were less than with fMLP. We then used pertussis toxin to determine if guanosine triphosphate (GTP)-binding proteins were involved in these responses. Toxin inhibited the fMLP-induced membrane depolarization as well as the uptake of extracellular Ca2+ and the expression of both CR1 and CR3 induced by the chemoattractant. This indicates that the fMLP receptor is not directly coupled to an ion channel. The membrane depolarization induced by elevating [K+]o was not inhibited by toxin, but the uptake of Ca2+ and the increased expression of CR1 and CR3 were all significantly inhibited. The toxin failed to block increased CR1 and CR3 expression induced by ionomycin, demonstrating that its effects were not attributable to general toxicity. The results suggest that voltage gating is not the major mechanism by which polymorphonuclear leukocytes (PMNs) increase their permeability to extracellular Ca2+. Initial signals, whether generated by chemoattractants binding to their receptors or by small initial influxes of extracellular Ca2+, must be amplified by pertussis toxin-sensitive steps to fully increase the Ca2+ permeability and optimally activate the cell.
为了更好地确定中性粒细胞激活过程中膜去极化与细胞外Ca2+内流之间的关系，我们比较了通过提高细胞外K+浓度（[K+]o）进行的刺激与趋化因子N-甲酰甲硫氨酰-亮氨酰-苯丙氨酸（fMLP）进行的刺激。[K+]o的升高导致整个细胞群体均匀去极化。这与Ca2+内流有关，Ca2+内流在时间上延迟且在数量上少于fMLP诱导的内流。K+去极化还导致1型（C3b/C4b）补体受体（CR1）和3型（C3bi）补体受体（CR3）的表达增加，但增加幅度小于fMLP诱导的增加幅度。然后我们使用百日咳毒素来确定鸟苷三磷酸（GTP）结合蛋白是否参与这些反应。毒素抑制了fMLP诱导的膜去极化以及细胞外Ca2+的摄取和趋化因子诱导的CR1和CR3的表达。这表明fMLP受体不直接与离子通道偶联。通过提高[K+]o诱导的膜去极化不受毒素抑制，但Ca2+的摄取以及CR1和CR3表达的增加均受到显著抑制。毒素未能阻断离子霉素诱导的CR1和CR3表达增加，表明其作用并非归因于一般毒性。结果表明，电压门控不是多形核白细胞（PMN）增加其对细胞外Ca2+通透性的主要机制。初始信号，无论是由趋化因子与其受体结合产生的，还是由细胞外Ca2+的少量初始内流产生的，都必须通过百日咳毒素敏感步骤进行放大，以充分增加Ca2+通透性并最佳地激活细胞。
