Baltz J M
Ottawa Health Research Institute, Department of Obstetrics and Gynecology, University of Ottawa, Ontario, Canada.
Curr Top Dev Biol. 2001;52:55-106. doi: 10.1016/s0070-2153(01)52009-8.
The early preimplantation mammalian embryo possesses mechanisms that regulate intracellular osmolarity and cell volume. While transport of osmotically active inorganic ions might play a role in this process in embryos, the major mechanisms that have been identified and studied are those that employ organic osmolytes. Organic osmolytes provide a substantial portion of intracellular osmotic support in embryos and are required for their development under in vivo conditions. The main osmolytes that have been identified in cleavage stage embryos are accumulated via two transport systems of the neurotransmitter transporter family active in early preimplantation embryos--the glycine transport system (GLY) and the beta-amino acid transport system (system beta). While system beta has been established to have a similar role in many other cells, this is a novel function for the GLY transport system. The intracellular concentration of organic osmolytes such as glycine in early preimplantation embryos is regulated by tonicity, allowing the embryo to regulate its volume against shrinkage and to control its internal osmolarity. In addition, the cells of the embryo can regulate against an increase in volume via controlled release of osmolytes from the cytoplasm. This is mediated by a swelling-activated anion channel that is also highly permeable to a range of organic osmolytes, and which closely resembles similar channels found in many other cell types (VSOAC channels). Together, these mechanisms appear to regulate cell volume in the egg through the early cleavage stages of embryogenesis, after which there are indications that the mechanisms of osmoregulation change.
早期植入前的哺乳动物胚胎具有调节细胞内渗透压和细胞体积的机制。虽然具有渗透活性的无机离子的转运可能在胚胎的这一过程中发挥作用，但已被识别和研究的主要机制是那些利用有机渗透物的机制。有机渗透物在胚胎中提供了细胞内渗透压支持的很大一部分，并且是胚胎在体内条件下发育所必需的。在卵裂期胚胎中已识别出的主要渗透物是通过在早期植入前胚胎中活跃的神经递质转运体家族的两个转运系统积累的——甘氨酸转运系统（GLY）和β-氨基酸转运系统（β系统）。虽然β系统在许多其他细胞中已被确定具有类似作用，但这是GLY转运系统的一个新功能。早期植入前胚胎中诸如甘氨酸等有机渗透物的细胞内浓度受张力调节，使胚胎能够调节其体积以防收缩，并控制其内部渗透压。此外，胚胎细胞可以通过控制细胞质中渗透物的释放来调节体积增加。这是由一种肿胀激活的阴离子通道介导的，该通道对一系列有机渗透物也具有高度通透性，并且与许多其他细胞类型中发现的类似通道非常相似（容积敏感性外向阴离子通道）。总之，这些机制似乎在胚胎发生的早期卵裂阶段调节卵子中的细胞体积，此后有迹象表明渗透调节机制发生了变化。
