School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington, UK.
Cell Biochem Biophys. 2010 Apr;56(2-3):73-90. doi: 10.1007/s12013-009-9072-5.
The theoretical and experimental description of fluid phase endocytosis (FPE) requires an asymmetry in phospholipid number between the two leaflets of the cell membrane, which provides the biomechanical torque needed to generate membrane budding. Although the motor force behind FPE is defined, its kinetic has yet to be determined. Based on a body of evidences suggesting that the mean surface tension is unlikely to be involved in endocytosis we decided to determine whether the cytosolic hydrostatic pressure could be involved, by considering a constant energy exchanged between the cytosol and the cell membrane. The theory is compared to existing experimental data obtained from FPE kinetic studies in living cells where altered phospholipid asymmetry or changes in the extracellular osmotic pressure have been investigated. The model demonstrates that FPE is dependent on the influx and efflux of vesicular volumes (i.e. vesicular volumes recycling) rather than the membrane tension of cells. We conclude that: (i) a relationship exists between membrane lipid number asymmetry and resting cytosolic pressure and (ii) the validity of Laplace's law is limited to cells incubated in a definite hypotonic regime. Finally, we discuss how the model could help clarifying elusive observations obtained from different fields and including: (a) the non-canonical shuttling of aquaporin in cells, (b) the relationship between high blood pressure and inflammation and (c) the mechanosensitivity of the sodium/proton exchanger.
流体相内吞作用（FPE）的理论和实验描述需要细胞膜的两个叶层之间的磷脂数量不对称，这为产生膜出芽提供了所需的生物力学扭矩。尽管 FPE 的动力已被定义，但它的动力学尚未确定。基于大量证据表明平均表面张力不太可能参与内吞作用，我们决定通过考虑细胞质和细胞膜之间的恒定能量交换来确定细胞质静水压力是否可能参与其中。该理论与从活细胞中进行的 FPE 动力学研究中获得的现有实验数据进行了比较，其中研究了磷脂不对称性的改变或细胞外渗透压的变化。该模型表明，FPE 取决于囊泡体积的流入和流出（即囊泡体积的再循环），而不是细胞的膜张力。我们得出的结论是：（i）膜脂质数量不对称性与静止细胞质压力之间存在关系；（ii）拉普拉斯定律的有效性仅限于在特定的低渗条件下孵育的细胞。最后，我们讨论了该模型如何帮助澄清从不同领域获得的难以捉摸的观察结果，包括：（a）水通道蛋白在细胞中的非典型穿梭；（b）高血压和炎症之间的关系；（c）钠/质子交换器的机械敏感性。
