Villegas R, Barnola F V
J Gen Physiol. 1972 Jan;59(1):33-46. doi: 10.1085/jgp.59.1.33.
Saxitoxin (STX) and tetrodotoxin (TTX) have the same striking property of blocking the Na(+) channels in the axolemma. Experiments with nerve plasma membrane components of the squid Dosidicus gigas have shown that TTX interacts with cholesterol monolayers. Similar experiments were carried out with STX. The effect of STX on the surface pressure-area diagrams of lipid monolayers and on the fluorescence emission spectra of sonicated nerve membranes was studied. The results indicate a TTX-like interaction of STX with cholesterol monolayers. The expansion of the monolayers caused by 10(-6)M STX was 2.2 A(2)/cholesterol molecule at 25 degrees C. From surface pressure measurements at constant cholesterol area (39 A(2)/molecule) in media with various STX concentrations, it was calculated that the STX/cholesterol surface concentration ratio is 0.54. The apparent dissociation constant of the STX-cholesterol monolayer complex is 4.0 x 10(-7)M. The STX/cholesterol ratio and the apparent dissociation constant are similar to those determined for TTX. The presence of other lipids in the monolayers affects the STX-cholesterol association. The interactions of STX and TTX with cholesterol monolayers suggest (a) that cholesterol molecules may be part of the nerve membrane Na(+) channels, or (b) that the toxin receptor at the nerve membrane shares similar chemical features with the cholesterol monolayers.
石房蛤毒素（STX）和河豚毒素（TTX）具有相同的显著特性，即阻断轴膜中的钠通道。对太平洋褶柔鱼神经质膜成分进行的实验表明，TTX与胆固醇单分子层相互作用。对STX也进行了类似的实验。研究了STX对脂质单分子层表面压力-面积图以及超声处理的神经膜荧光发射光谱的影响。结果表明STX与胆固醇单分子层存在类似TTX的相互作用。在25℃时，10^(-6)M STX引起的单分子层膨胀为2.2 Å^2/胆固醇分子。通过在不同STX浓度的介质中，在恒定胆固醇面积（39 Å^2/分子）下进行表面压力测量，计算出STX/胆固醇表面浓度比为0.54。STX-胆固醇单分子层复合物的表观解离常数为4.0×10^(-7)M。STX/胆固醇比值和表观解离常数与TTX的测定值相似。单分子层中其他脂质的存在会影响STX与胆固醇的结合。STX和TTX与胆固醇单分子层的相互作用表明：（a）胆固醇分子可能是神经膜钠通道的一部分；或者（b）神经膜上的毒素受体与胆固醇单分子层具有相似的化学特征。
