Dordas C, Brown P H
Department of Pomology, University of California, Davis 95616, USA.
Biol Trace Elem Res. 2001 Aug;81(2):127-39. doi: 10.1385/BTER:81:2:127.
Boron is an essential element for vascular plants and for diatoms, cyanobacteria, and a number of species of marine algal flagellates. Boron was recently established as an essential micronutrient for frogs (Xenopus laevis) and preliminary evidence suggests that it may be essential for all animals. The main form of B, which is available in the natural environment, is in the form of undissociated boric acid. The permeability coefficient and the mechanism of transport of boric acid, however, have not been experimentally determined across any animal membrane or cell. In the experiments described here, the permeability coefficient of boric acid in Xenopus oocytes was 1.5 x 10(-6) cm/s, which is very close with the permeability across liposomes made with phosphatidylcholine and cholesterol (the major lipids in the oocyte membrane). Moreover, we investigated the mechanism of boric acid movement across the membrane of Xenopus oocytes and we compared it with the transport across artificial liposomes. The transport of boric acid across Xenopus oocytes was not affected by inhibitors such as HgCl2, phloretin, or 4,4-diisothiocyanatostilbene-2,2'-D-sulfonic acid (DIDS). The kinetics of B uptake was linear with concentration changes, and the permeability remained the same at different external boric acid concentrations. These results suggest that B transport occurs via simple passive diffusion through the lipid bilayer in Xenopus oocytes.
硼是维管植物、硅藻、蓝细菌以及一些海洋藻类鞭毛虫的必需元素。最近，硼被确定为青蛙（非洲爪蟾）的必需微量营养素，初步证据表明它可能对所有动物都至关重要。在自然环境中，硼的主要存在形式是未离解的硼酸。然而，硼酸在任何动物膜或细胞上的渗透系数和转运机制尚未通过实验确定。在本文所述的实验中，硼酸在非洲爪蟾卵母细胞中的渗透系数为1.5×10⁻⁶厘米/秒，这与用磷脂酰胆碱和胆固醇（卵母细胞膜中的主要脂质）制成的脂质体的渗透率非常接近。此外，我们研究了硼酸跨非洲爪蟾卵母细胞膜的转运机制，并将其与跨人工脂质体的转运进行了比较。硼酸跨非洲爪蟾卵母细胞的转运不受HgCl₂、根皮素或4,4 - 二异硫氰酸根合芪 - 2,2'-二磺酸（DIDS）等抑制剂的影响。硼摄取的动力学与浓度变化呈线性关系，并且在不同的外部硼酸浓度下渗透率保持不变。这些结果表明，硼的转运是通过简单的被动扩散穿过非洲爪蟾卵母细胞的脂质双层进行的。
