Mishima K, Nakamae S, Ohshima H, Kondo T
Department of Physics, College of Art and Sciences, Showa University, Yamanashi, Japan.
Biochim Biophys Acta. 1994 Apr 20;1191(1):157-63. doi: 10.1016/0005-2736(94)90244-5.
Orientation induced by an alternating electric field was studied for myelin tubes of egg phosphatidylcholine (egg-PC) in water and in KCl electrolyte solution. The orientation was also studied for myelin tubes of egg-PC/cholesterol mixtures in water. The orientation effect was measured by the bending curvature of myelin tubes with hairpin-like deformation at frequencies between 10 kHz and 20 MHz. The bending deformation of egg-PC myelin tubes in water decreased abruptly with a decreasing frequency within the low-frequency range below 100 kHz, and shrinkage of myelin tubes was often observed. The bending deformation decreased as the frequency was increased in a higher frequency range. The profile of the frequency dependence for egg-PC in KCl solution was similar to that in water but shifted towards a higher frequency. At low KCl concentrations below 3 mM, the relaxation frequency increased proportionally with increasing an KCl concentration, which was due to a proportional increase in the conductivity of the surrounding medium. Similar profiles of the frequency dependence were observed for egg-PC/cholesterol mixtures but with no shift in the relaxation frequency. These data in the high-frequency range fitted well with calculations based on theoretical equations for the electric-field-induced orientation of nonspherical particles. The conductivity of myelin tubes was estimated to be in the order of 10(-4) S/m in water and of 10(-3) S/m at the low KCl concentrations. The bending modulus of a bilayer membrane was estimated to be (1.0 +/- 0.5) x 10(-19) J for egg-PC in water. No change in the bending modulus was observed for egg-PC in KCl solution. However, for egg-PC/cholesterol mixtures in water, the bending modulus abruptly increased to (1.8 +/- 0.5) x 10(-19) J at a cholesterol concentration of 40 mol%.
研究了交变电场对水中和KCl电解质溶液中卵磷脂（egg-PC）髓鞘管的取向作用。还研究了水中egg-PC/胆固醇混合物髓鞘管的取向。通过在10 kHz至20 MHz频率范围内具有发夹状变形的髓鞘管的弯曲曲率来测量取向效应。在低于100 kHz的低频范围内，水中egg-PC髓鞘管的弯曲变形随频率降低而急剧下降，并且经常观察到髓鞘管的收缩。在较高频率范围内，弯曲变形随频率增加而减小。KCl溶液中egg-PC的频率依赖性曲线与水中相似，但向更高频率偏移。在低于3 mM的低KCl浓度下，弛豫频率随KCl浓度增加而成比例增加，这是由于周围介质电导率成比例增加所致。对于egg-PC/胆固醇混合物也观察到类似的频率依赖性曲线，但弛豫频率没有偏移。高频范围内的这些数据与基于非球形颗粒电场诱导取向的理论方程的计算结果拟合良好。估计髓鞘管在水中的电导率约为10^(-4) S/m，在低KCl浓度下为10^(-3) S/m。估计双层膜的弯曲模量对于水中的egg-PC为(1.0±0.5)×10^(-19) J。在KCl溶液中未观察到egg-PC的弯曲模量变化。然而，对于水中的egg-PC/胆固醇混合物，在胆固醇浓度为40 mol%时，弯曲模量突然增加到(1.8±0.5)×10^(-19) J。
