Song L Y, Ahkong Q F, Baldwin J M, O'Reilly R, Lucy J A
Department of Biochemistry and Chemistry, Royal Free Hospital, School of Medicine, University of London, UK.
Biochim Biophys Acta. 1993 May 14;1148(1):30-8. doi: 10.1016/0005-2736(93)90157-u.
We have previously reported that acidic phospholipids are exposed at the surface of human erythrocytes when the cells are subjected to electrical breakdown. It has now been shown that the prothrombinase assay, which was used previously for the determination of acidic phospholipids, is specific for phosphatidylserine under the conditions of our experiments. In the light of this finding, we have investigated and characterised factors that govern cell lysis, cell fusion, and the formation of giant cells induced by electrical breakdown with human erythrocytes in media of low ionic strength. Divalent cations (1.1 mM) protected the cells against haemolysis, in the order Mn2+ > Ca2+ > Ba2+ > Mg2+ >> Zn2+, whereas about 99% of the cells lysed immediately on breakdown in the presence of Na+ or K+ (2.1 mM), or Al3+ (0.95 mM). The lengths of pearl chains of fused erythrocytes formed was similarly greatest with Mn2+ and decreased progressively with Ba2+, Zn2+, Ca2+ and Mg2+. No cell fusion occurred with Na+, K+, or Al3+. It is suggested that interactions with phosphatidylserine, which is exposed at the cell surface by electrical breakdown, may enable Mn2+, Ba2+ and Ca2+ ions to inhibit cell lysis (via membrane resealing) and facilitate cell fusion. Following electrically-induced cell fusion, erythrocytes round-up into giant cells. It has previously been proposed that Ca2+ ions accelerate the rounding-up process. However, data are presented which show that, as with erythrocytes treated with Sendai virus, the formation of rounded, giant cells following cell fusion depends on the osmotic swelling properties of permeabilised erythrocytes. Osmotic swelling may also have induced any hemi-fused cells present to fuse completely. Zn2+ ions anomalously enabled erythrocytes to round-up very rapidly into giant cells following electrical breakdown. This phenomenon may result from an interaction of Zn2+ ions with cysteine groups in membrane proteins, which decreases the immediate loss of ions that occurs when erythrocytes are subjected to electrical breakdown in low-ionic-strength media.
我们之前曾报道，当人体红细胞受到电击穿时，酸性磷脂会暴露于细胞表面。现已表明，先前用于测定酸性磷脂的凝血酶原酶测定法，在我们的实验条件下对磷脂酰丝氨酸具有特异性。鉴于这一发现，我们研究并表征了在低离子强度介质中，控制人体红细胞电击穿诱导的细胞裂解、细胞融合和巨细胞形成的因素。二价阳离子（1.1 mM）可保护细胞免于溶血，其保护顺序为Mn2+ > Ca2+ > Ba2+ > Mg2+ >> Zn2+，而在存在Na+（2.1 mM）、K+（2.1 mM）或Al3+（0.95 mM）的情况下，约99%的细胞在电击穿后立即裂解。融合红细胞形成的珍珠链长度同样以Mn2+时最长，并随着Ba2+、Zn2+、Ca2+和Mg2+逐渐减小。Na+、K+或Al3+存在时未发生细胞融合。这表明，与因电击穿而暴露于细胞表面的磷脂酰丝氨酸相互作用，可能使Mn2+、Ba2+和Ca2+离子抑制细胞裂解（通过膜重封）并促进细胞融合。电诱导细胞融合后，红细胞会聚集形成巨细胞。此前有人提出Ca2+离子会加速聚集过程。然而，所提供的数据表明，与经仙台病毒处理的红细胞一样，细胞融合后圆形巨细胞的形成取决于通透红细胞的渗透肿胀特性。渗透肿胀也可能促使任何存在的半融合细胞完全融合。Zn2+离子异常地使红细胞在电击穿后能非常迅速地聚集形成巨细胞。这种现象可能是由于Zn2+离子与膜蛋白中的半胱氨酸基团相互作用，减少了红细胞在低离子强度介质中受到电击穿时立即发生的离子损失。
