Vest Rebekah S, Gonzales Laurie J, Permann Seth A, Spencer Emily, Hansen Lee D, Judd Allan M, Bell John D
Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84620, USA.
Biophys J. 2004 Apr;86(4):2251-60. doi: 10.1016/S0006-3495(04)74283-6.
Elevated concentrations of intracellular calcium in erythrocytes increase membrane order and susceptibility to secretory phospholipase A2. We hypothesize that calcium aids the formation of domains of ordered lipids within erythrocyte membranes by interacting directly with the inner leaflet of the cell membrane. The interface of these domains with regions of more fluid lipids may create an environment with weakened neighbor-neighbor interactions that would facilitate phospholipid migration into the active site of bound secretory phospholipase A2. This hypothesis was investigated by determining the effects of seven other divalent ions on erythrocyte membrane properties. Changes in membrane order were assessed with steady-state fluorescence spectroscopy and two-photon microscopy with an environment-sensitive probe, laurdan. Each ion increased apparent membrane order in model membranes and in erythrocytes when introduced with an ionophore, suggesting that direct binding to the inner face of the membrane accounts for the effects of calcium on membrane fluidity. Furthermore, the degree to which ions affected membrane properties correlated with the ionic radius and electronegativity of the ions. Lastly, erythrocytes became more susceptible to enzyme hydrolysis in the presence of elevated intracellular levels of nickel and manganese, but not magnesium. These differences appeared related to the ability of the ions to induce a transition in erythrocyte shape.
红细胞内钙离子浓度升高会增加膜的有序性以及对分泌型磷脂酶A2的敏感性。我们推测，钙通过与细胞膜内小叶直接相互作用，有助于红细胞膜内有序脂质结构域的形成。这些结构域与流动性更强的脂质区域的界面可能会创造一个相邻分子间相互作用减弱的环境，这将有利于磷脂迁移到结合的分泌型磷脂酶A2的活性位点。通过测定其他七种二价离子对红细胞膜特性的影响来研究这一假设。使用稳态荧光光谱法和双光子显微镜，结合环境敏感探针劳丹，评估膜有序性的变化。当与离子载体一起引入时，每种离子都会增加模型膜和红细胞中的表观膜有序性，这表明与膜内表面的直接结合是钙对膜流动性产生影响的原因。此外，离子影响膜特性的程度与离子的离子半径和电负性相关。最后，在细胞内镍和锰水平升高但镁水平不升高的情况下，红细胞对酶水解变得更敏感。这些差异似乎与离子诱导红细胞形状转变的能力有关。
