Baerentsen H, Giraldez F, Zeuthen T
J Membr Biol. 1983;75(3):205-18. doi: 10.1007/BF01871951.
This paper presents a numerical model for the movement of Na+, K+, Cl-, H+ and HCO3- in a leaky epithelium. The model describes the active transport of Na+ and K+ at the serosal membrane and electrodiffusive permeation across the mucosal, serosal and junctional pathways. The model accounts for H+ and HCO3- production in the cell. The influx of Na+ and Cl- is assumed to occur mainly via Na/H and Cl/HCO3 exchange. The behavior of the cell, with this influx mechanism, is compared to a cell with an obligatory neutral coupled influx of Na+ and Cl-. All parameters are obtained from the literature, primarily from studies utilizing the Necturus gallbladder. The analysis shows (i) that it is virtually impossible in steady-state experiments to distinguish between cells with Na/H - HCO3/Cl transport and cells with Na/Cl transport mechanisms. (ii) That nonsteady-state experiments can decide whether Na/H - HCO3/Cl or Na/Cl transport mechanisms mediate the influx of salt. A comparison between studies with ion-selective microelectrodes and the model predictions indicates that the influx of Na+ and Cl- is mediated by Na/H - HCO3/Cl transport when the external solutions contain CO2 and HCO3. (iii) The model also explains the diuretic effects of furosemide and carbonic anhydrase inhibitor, as well as the stimulatory effects on salt transport of elevated levels of HCO3- at a constant pH. (iv) The model fails to explain some experiments performed in HCO3/Co2-free media and some experiments using inhibitors.
本文提出了一种用于描述漏性上皮中Na⁺、K⁺、Cl⁻、H⁺和HCO₃⁻运动的数值模型。该模型描述了浆膜处Na⁺和K⁺的主动转运以及跨黏膜、浆膜和连接途径的电扩散渗透。该模型考虑了细胞内H⁺和HCO₃⁻的产生。假定Na⁺和Cl⁻的内流主要通过Na⁺/H⁺和Cl⁻/HCO₃⁻交换发生。将具有这种内流机制的细胞行为与具有Na⁺和Cl⁻强制中性偶联内流的细胞进行了比较。所有参数均取自文献，主要来自利用美西螈胆囊进行的研究。分析表明：（i）在稳态实验中，几乎不可能区分具有Na⁺/H⁺ - HCO₃⁻/Cl⁻转运的细胞和具有Na⁺/Cl⁻转运机制的细胞。（ii）非稳态实验可以确定是Na⁺/H⁺ - HCO₃⁻/Cl⁻还是Na⁺/Cl⁻转运机制介导盐的内流。离子选择性微电极研究与模型预测之间的比较表明，当外部溶液含有CO₂和HCO₃⁻时，Na⁺和Cl⁻的内流由Na⁺/H⁺ - HCO₃⁻/Cl⁻转运介导。（iii）该模型还解释了呋塞米和碳酸酐酶抑制剂的利尿作用，以及在恒定pH值下HCO₃⁻水平升高对盐转运的刺激作用。（iv）该模型无法解释在不含HCO₃⁻/CO₂的培养基中进行的一些实验以及使用抑制剂的一些实验。
