Grover A K, Kwan C Y, Crankshaw J, Daniel E E
Can J Physiol Pharmacol. 1981 Nov;59(11):1128-33. doi: 10.1139/y81-174.
Isopycnic centrifugation experiments using sucrose density gradients showed that in digitonin-treated microsomes the distribution of the plasma membrane (PM) marker 5'-nucleotidase was shifted to higher densities. The treatment also caused similar but less pronounced changes in the distribution of protein, the putative endoplasmic reticulum (ER) marker NADPH-dependent cytochrome c reductase, and the inner mitochondrial marker cytochrome c oxidase. Similar experiments using more purified membrane fractions showed that the digitonin treatment led to a comparable increase in the densities of the fractions N1 and N2 previously described as subfractions of plasma membrane and to considerably less increase in the density of the fraction N3B which is enriched in the endoplasmic reticulum and the inner mitochondrial markers. Digitonin inhibited the ATP-dependent Ca uptake by the N1 fraction in a concentration-dependent manner (I50 = 0.3 mg/mL). Digitonin (0.5 mg/mL) inhibited the ATP-dependent azide-insensitive Ca uptake by all the fractions. The results support the hypothesis that (a) N1 and N2 are subfractions of plasma membrane, and (b) ATP-dependent azide-insensitive Ca uptake in rat myometrium is a property of plasma membranes.
使用蔗糖密度梯度的等密度离心实验表明，在用洋地黄皂苷处理的微粒体中，质膜（PM）标志物5'-核苷酸酶的分布向更高密度转移。该处理还导致蛋白质、假定的内质网（ER）标志物NADPH依赖性细胞色素c还原酶以及线粒体内膜标志物细胞色素c氧化酶的分布发生类似但不太明显的变化。使用更纯化的膜组分进行的类似实验表明，洋地黄皂苷处理导致先前描述为质膜亚组分的N1和N2组分的密度有相当程度的增加，而富含内质网和线粒体内膜标志物的N3B组分的密度增加则要少得多。洋地黄皂苷以浓度依赖性方式抑制N1组分对ATP依赖的钙摄取（I50 = 0.3 mg/mL）。洋地黄皂苷（0.5 mg/mL）抑制所有组分对ATP依赖的叠氮化物不敏感的钙摄取。这些结果支持以下假设：（a）N1和N2是质膜的亚组分，（b）大鼠子宫肌层中ATP依赖的叠氮化物不敏感的钙摄取是质膜的一种特性。
