Weinstein A M
Am J Physiol. 1986 May;250(5 Pt 2):F860-73. doi: 10.1152/ajprenal.1986.250.5.F860.
The equations of mass conservation and electroneutrality are used to extend a nonequilibrium thermodynamic model of the rat proximal tubule epithelium to a representation of a 0.5-cm segment of tubule. The output of the tubule model includes the luminal profiles and absolute proximal reabsorption of Na, K, Cl, HCO3, HPO4, H2PO4, glucose, and urea, generated by the epithelial model. Transport rates and permeabilities, chosen in agreement with those of the rat, result in luminal glucose and bicarbonate depletion and a transition from an electronegative to positive lumen. Despite the development of significant transepithelial osmotic driving forces (a transepithelial glucose gradient and Cl-HCO3 asymmetry), intraepithelial solute-solvent coupling remains an important force for water reabsorption along the proximal tubule length. In particular, this means that when osmotic gradients that appear under free-flow conditions are used in the calculation of the epithelial water permeability, a substantial overestimate of this permeability will be obtained. A single first-order differential equation has been derived in conjunction with an approximate nonelectrolyte model of the proximal tubule that represents both coupled and gradient-driven water reabsorption. In the present work, this equation is shown to yield an accurate description of water transport by the comprehensive tubule model.
质量守恒方程和电中性方程被用于将大鼠近端肾小管上皮的非平衡热力学模型扩展为对0.5厘米长肾小管段的描述。肾小管模型的输出包括由上皮模型生成的管腔中钠、钾、氯、碳酸氢根、磷酸氢根、磷酸二氢根、葡萄糖和尿素的浓度分布以及近端的绝对重吸收量。与大鼠的转运速率和通透性一致的选择，导致管腔中葡萄糖和碳酸氢根减少，以及管腔从带负电转变为带正电。尽管产生了显著的跨上皮渗透驱动力（跨上皮葡萄糖梯度和氯-碳酸氢根不对称），上皮内溶质-溶剂耦合仍然是沿近端肾小管长度进行水重吸收的重要力量。特别是，这意味着当在计算上皮水通透性时使用自由流动条件下出现的渗透梯度时，将得到对该通透性的大幅高估。结合近端肾小管的近似非电解质模型推导了一个一阶微分方程，该模型同时表示耦合和梯度驱动的水重吸收。在本研究中，该方程被证明能准确描述综合肾小管模型的水转运。
