Lucas M L, Sood L, McGregor M, Sattar N, Watt A, Taylor J C
Institute of Physiology, The University, Glasgow, Scotland, U.K.
J Theor Biol. 1992 Dec 7;159(3):271-86. doi: 10.1016/s0022-5193(05)80724-6.
Estimation of intestinal unstirred layer thickness usually involves inducing transmural potential difference changes by altering the content of the solution used to perfuse the small intestine. Osmotically active solutes, such as mannitol, when added to the luminal solution diffuse across the unstirred water layer (UWL) and induce osmotically dependent changes in potential difference. As an alternative procedure, the sodium ion in the luminal fluid can be replaced by another ion. As the sodium ion diffuses out of the UWL, the change in concentration next to the intestinal membrane alters the transmural potential difference. In both cases, UWL thickness is calculated from the time course of the potential difference changes, using a solution to the diffusion equation. The diffusion equation solution which allows the calculation of intestinal unstirred layer thickness was examined by simulation, using the method of numerical solutions. This process readily allows examination of the time course of diffusion under various imposed circumstances. The existing model for diffusion across the unstirred layer is based on auxiliary conditions which are unlikely to be fulfilled in the same intestine. The present simulation additionally incorporated the effects of membrane permeability, fluid absorption and less than instantaneous bulk phase concentration change. Simulation indicated that changes within the physiologically relevant range in the chosen auxiliary conditions (with the real unstirred layer length kept constant) can alter estimates of the apparent half-time. Consequently, changes in parameters unassociated with the unstirred layer would be misconstrued as alterations in unstirred layer thickness.
肠道未搅动层厚度的估算通常涉及通过改变用于灌注小肠的溶液成分来诱导跨膜电位差变化。渗透活性溶质，如甘露醇，添加到肠腔溶液中时会扩散穿过未搅动水层（UWL），并诱导电位差的渗透压依赖性变化。作为一种替代方法，肠腔液中的钠离子可以被另一种离子取代。当钠离子从UWL扩散出来时，靠近肠膜处浓度的变化会改变跨膜电位差。在这两种情况下，UWL厚度都是根据电位差变化的时间进程，使用扩散方程的解来计算的。通过数值解方法进行模拟，研究了用于计算肠道未搅动层厚度的扩散方程解。这个过程很容易对各种给定条件下的扩散时间进程进行研究。现有的跨未搅动层扩散模型基于一些辅助条件，而这些条件在同一肠道中不太可能得到满足。目前的模拟还纳入了膜通透性、液体吸收以及非瞬时的整体相浓度变化的影响。模拟表明，在所选辅助条件下生理相关范围内的变化（保持实际未搅动层长度不变）会改变表观半衰期的估计值。因此，与未搅动层无关的参数变化会被误解为未搅动层厚度的改变。
