Pohl P, Saparov S M, Antonenko Y N
Martin-Luther-Universităt, Medizinische Fakultät, Institut für Medizinische Physik und Biophysik, Halle, Germany.
Biophys J. 1997 Apr;72(4):1711-8. doi: 10.1016/S0006-3495(97)78817-9.
The osmotically induced transmembrane water flow is accompanied by solute concentration changes within the unstirred layer adjacent to membranes. Experimental concentration profiles, measured by means of microelectrodes in the immediate vicinity of a planar lipid bilayer, are compared with theoretical ones predicted from the standard physiological model in which the osmotic advection is countered by back-diffusion of the solute only. An increase of the apparent osmotic flow rate is induced by an increase of the osmotic gradient and by rigorous stirring. The polarization effect decreases in the latter case due to an increase of the transfer rate of solutes between the bulk solutions and the membrane surfaces, whereas it increases in the former case. The observations show that the concentration profile is not well described by the standard approximation. The discrepancy becomes increasingly large with increased volume flow. Based on a modified theoretical description of the interaction between water flux and diffusion, the hydraulic conductivity of the bilayer is calculated from the measured uniexponential concentration profiles. The common approximation that there is a discrete boundary between the stirred and unstirred regions adjacent to the membrane is substituted by the model of a stagnant point flow that takes into account a gradual change of the stirring velocity in the immediate membrane vicinity. Supported by experimental observations, this approach predicts a shortening of the unstirred layer if the transmembrane osmotic gradient is increased under gentle stirring conditions.
渗透诱导的跨膜水流伴随着与膜相邻的未搅拌层内溶质浓度的变化。通过平面脂质双分子层紧邻区域的微电极测量得到的实验浓度分布，与仅通过溶质反向扩散抵消渗透平流的标准生理模型预测的理论浓度分布进行了比较。渗透梯度的增加和剧烈搅拌会导致表观渗透流速增加。在后一种情况下，由于溶质在本体溶液和膜表面之间的转移速率增加，极化效应降低，而在前一种情况下则增加。观察结果表明，标准近似法不能很好地描述浓度分布。随着体积流量的增加，差异变得越来越大。基于对水通量与扩散相互作用的改进理论描述，根据测量的单指数浓度分布计算双层膜的水力传导率。膜相邻的搅拌区和未搅拌区之间存在离散边界这一常见近似，被考虑了膜紧邻区域搅拌速度逐渐变化的驻点流模型所取代。在实验观察的支持下，该方法预测在温和搅拌条件下增加跨膜渗透梯度时未搅拌层会缩短。
