Dean W L, Delamere N A, Borchman D, Moseley A E, Ahuja R P
Department of Biochemistry, University of Louisville, KY 40292, USA.
Biochem J. 1996 Mar 15;314 ( Pt 3)(Pt 3):961-7. doi: 10.1042/bj3140961.
Na,K-ATPase was studied in the two cell types that make up the lens of the eye. Membrane material was isolated from lens fibre cells, which make up the bulk of the lens cell mass, and also from lens epithelial cells, which are present only as a monolayer on the anterior lens surface. Judged by immunoblotting, greater amounts of Na,K-ATPase alpha1 and beta1 polypeptides were found in fibre cell membrane material than in epithelial cell membrane material. However, the NA,K-ATPase activity in epithelial cell membrane material was 20 times that measured in fibre cell membrane material. In 86Rb uptake experiments with intact lenses, ouabain-inhibitable 86Rb uptake was observed for lens epithelium but not for lens fibres. These findings are consistent with a low Na,K-ATPase activity in lens fibre cells even though these cells express a considerable amount of Na,K-ATPase alpha1 and beta1 polypeptides. The lipid composition of lens fibre cell membranes causes them to be more ordered than epithelial cell membranes; this was confirmed by measurements of the infrared CH2 symmetric stretching band frequency. Because lipid composition can influence Na,K-ATPase activity, experiments were conducted to determine whether the activity of Na,K-ATPase alpha1 beta1 is inhibited by lens fibre lipid. However, no significant difference in Na,K-ATPase activity was detected when Na,K-ATPase alpha1 beta1 was purified from rabbit kidney and then reconstituted with lipid that had been isolated from either lens epithelium or lens fibre cells. These studies indicate that lens fibre cells contain both Na,K-ATPase alpha1 and beta1 polypeptides but have low Na,K-ATPase activity. However, the results do not support the notion that this is due to the lipid composition of lens fibre cell membranes.
在构成眼球晶状体的两种细胞类型中对钠钾ATP酶进行了研究。从构成晶状体细胞主体的晶状体纤维细胞中分离出膜材料，也从仅以前单层形式存在于晶状体前表面的晶状体上皮细胞中分离出膜材料。通过免疫印迹判断，在纤维细胞膜材料中发现的钠钾ATP酶α1和β1多肽的量比上皮细胞膜材料中的多。然而，上皮细胞膜材料中的钠钾ATP酶活性是纤维细胞膜材料中测得活性的20倍。在对完整晶状体进行的⁸⁶Rb摄取实验中，观察到晶状体上皮细胞有哇巴因抑制的⁸⁶Rb摄取，而晶状体纤维细胞则没有。这些发现与晶状体纤维细胞中钠钾ATP酶活性较低一致，尽管这些细胞表达了相当数量的钠钾ATP酶α1和β1多肽。晶状体纤维细胞膜的脂质组成使其比上皮细胞膜更有序；这通过对红外CH₂对称伸缩带频率的测量得到了证实。由于脂质组成会影响钠钾ATP酶活性，因此进行了实验以确定钠钾ATP酶α1β1的活性是否受到晶状体纤维脂质的抑制。然而，当从兔肾中纯化钠钾ATP酶α1β1，然后用从晶状体上皮细胞或晶状体纤维细胞中分离出的脂质进行重构时，未检测到钠钾ATP酶活性有显著差异。这些研究表明，晶状体纤维细胞同时含有钠钾ATP酶α1和β1多肽，但钠钾ATP酶活性较低。然而，结果并不支持这是由于晶状体纤维细胞膜的脂质组成所致的观点。
