Nonequilibrium thermodynamic model of the rat proximal tubule epithelium.
Nonequilibrium thermodynamic model of the rat proximal tubule epithelium.
复制标题
大鼠近曲小管上皮的非平衡热力学模型。
DOI：
10.1016/s0006-3495(83)84287-8
复制
发表时间：
1983
影响因子：
3.4
通讯作者：
Weinstein,AM
中科院分区：
文献类型：
--
作者：
Weinstein,AM
大鼠近端小管上皮表现为搅拌均匀、柔顺的细胞和细胞旁隔室，由粘膜和浆膜洗液包围。在pCO2均匀分布于上皮的情况下，模型变量包括Na、K、Cl、HCO3、H2PO4、HPO4和H的浓度，以及静水压力和电势。除了基底外侧细胞膜上代谢驱动的Na-K交换器外，上皮内的所有膜运输都是被动的，并由非平衡热力学的线性方程表示。特别是，这包括Na-Cl和Na-H2PO4在顶端细胞膜的共同运输和Na-H的反运输。通过允许K-Cl在基底侧膜上的共输运，满足了离子电导率选择的实验约束。模型方程包括非反应物质的质量平衡方程和酸化反应的化学平衡方程。保留了与时间有关的术语，以便对瞬态现象进行研究。在稳定状态下，计算并验证了能量耗散等于Na-K交换器输入的能量加上加入系统的质量的吉布斯自由能。研究了耦合水输运的参数依赖性，结果与以往胞间空间分析模型的预测一致。研究了在近端（hco3耗尽）腔内溶液存在下的水输送。在这里，低渗透率和高反射系数的HCO3增强了净钠和水的输送。由于通过紧密连接处的通量增强，这一过程可能允许近端小管Na运输以减少能量耗散进行。
The rat proximal tubule epithelium is represented as well-stirred, compliant cellular and paracellular compartments bounded by mucosal and serosal bathing solutions. With a uniform pCO2 throughout the epithelium, the model variables include the concentrations of Na, K, Cl, HCO3, H2PO4, HPO4, and H, as well as hydrostatic pressure and electrical potential. Except for a metabolically driven Na-K exchanger at the basolateral cell membrane, all membrane transport within the epithelium is passive and is represented by the linear equations of nonequilibrium thermodynamics. In particular, this includes the cotransport of Na-Cl and Na-H2PO4 and countertransport of Na-H at the apical cell membrane. Experimental constraints on the choice of ionic conductivities are satisfied by allowing K-Cl cotransport at the basolateral membrane. The model equations include those for mass balance of the nonreacting species, as well as chemical equilibrium for the acidification reactions. Time-dependent terms are retained to permit the study of transient phenomena. In the steady state the energy dissipation is computed and verified equal to the sum of input from the Na-K exchanger plus the Gibbs free energy of mass addition to the system. The parameter dependence of coupled water transport is studied and shown to be consistent with the predictions of previous analytical models of the lateral intercellular space. Water transport in the presence of an end-proximal (HCO3-depleted) luminal solution is investigated. Here the lower permeability and higher reflection coefficient of HCO3 enhance net sodium and water transport. Due to enhanced flux across the tight junction, this process may permit proximal tubule Na transport to proceed with diminished energy dissipation.