Lew Virgilio L, Etzion Zipora, Bookchin Robert M
Physiological Laboratory, University of Cambridge, United Kingdom.
Blood. 2002 Apr 1;99(7):2578-85. doi: 10.1182/blood.v99.7.2578.
Interaction of hemoglobin S polymers with the red blood cell (RBC) membrane induces a reversible increase in permeability ("P(sickle)") to (at least) Na(+), K(+), Ca(2+), and Mg(2+). Resulting changes in [Ca(2+)] and [H(+)] in susceptible cells activate 2 transporters involved in sickle cell dehydration, the Ca(2+)-sensitive K(+) ("Gardos") channel (K(Ca)) and the acid- and volume-sensitive K:Cl cotransport. We investigated the distribution of P(sickle) expression among deoxygenated sickle cell anemia (SS) RBCs using new experimental designs in which the RBC Ca(2+) pumps were partially inhibited by vanadate, and the cells' dehydration rates were detected as progressive changes in the profiles of osmotic fragility curves and correlated with flow cytometric measurements. The results exposed marked variations in (sickling plus Ca(2+))-induced dehydration rates within populations of deoxygenated SS cells, with complex distributions, reflecting a broad heterogeneity of their P(sickle) values. P(sickle)-mediated dehydration was inhibited by clotrimazole, verifying the role of K(Ca), and also by elevated Ca(2+), above 2 mM. Very high P(sickle) values occurred with some SS discocytes, which had a wide initial density (osmotic resistance) distribution. Together with its previously shown stochastic nature, the irregular distribution of P(sickle) documented here in discocytes is consistent with a mechanism involving low-probability, reversible interactions between sickle polymers and membrane or cytoskeletal components, affecting only a fraction of the RBCs during each deoxygenation event and a small number of activated pathways per RBC. A higher participation of SS reticulocytes in P(sickle)-triggered dehydration suggests that they form these pathways more efficiently than discocytes despite their lower cell hemoglobin concentrations.
血红蛋白S聚合物与红细胞（RBC）膜的相互作用会导致（至少）对Na⁺、K⁺、Ca²⁺和Mg²⁺的通透性（“P（镰状）”）出现可逆性增加。易感细胞中[Ca²⁺]和[H⁺]的变化会激活参与镰状细胞脱水的2种转运蛋白，即Ca²⁺敏感的K⁺（“加尔多斯”）通道（KCa）和酸及容量敏感的K⁺:Cl共转运。我们使用新的实验设计研究了脱氧镰状细胞贫血（SS）红细胞中P（镰状）表达的分布情况，在该实验设计中，钒酸盐可部分抑制RBC的Ca²⁺泵，并将细胞的脱水速率检测为渗透脆性曲线轮廓的渐进变化，并与流式细胞术测量结果相关联。结果显示，在脱氧SS细胞群体中，（镰状化加Ca²⁺）诱导的脱水速率存在显著差异，分布复杂，反映出其P（镰状）值具有广泛的异质性。克霉唑可抑制P（镰状）介导的脱水，证实了KCa的作用，2 mM以上的[Ca²⁺]o升高也可抑制。一些SS双凹圆盘状红细胞出现了非常高的P（镰状）值，其初始密度（渗透抗性）分布较宽。连同之前显示的随机性，此处记录的双凹圆盘状红细胞中P（镰状）的不规则分布与一种机制一致，该机制涉及镰状聚合物与膜或细胞骨架成分之间低概率、可逆的相互作用，在每次脱氧事件中仅影响一小部分RBC，且每个RBC激活的途径数量较少。SS网织红细胞在P（镰状）引发的脱水中参与度更高，这表明尽管其细胞血红蛋白浓度较低，但它们比双凹圆盘状红细胞更有效地形成这些途径。
