Lucas M L, Whitehead R R
Institute of Physiology, Glasgow University, Scotland, U.K.
J Theor Biol. 1994 Mar 21;167(2):147-59. doi: 10.1006/jtbi.1994.1059.
The three-compartment model for intestinal weak-electrolyte transport provides an equation which predicts the flux ratio (the ratio of the forward and reverse fluxes of weak electrolyte across the intestine) from the dissociation constant, given that coefficients in the equation are specified. Using the equation to evaluate the coefficients from flux ratio and dissociation constant data fails to provide a unique set of values for the coefficients, although it does provide four dissimilar but related sets of values. Differentiation to determine the position and size of the maximum flux ratio provides a relationship between the model coefficients which shows why it is that four sets of coefficients can be used in the equation when it is applied to experimental data. Coefficient sets are derived for all available flux ratio data in the literature. These always contain a variant which requires the intermediate compartment to be more acid than the end compartment. Further specification of the flux ratio equation either by combining data from different physiological circumstances or by adding voltage terms, reduces the four possible coefficient sets to a single set, again requiring the intermediate compartment to be more acid than the end compartment. Estimates of the intermediate-compartment pH agree well with electrode estimates of mucosal surface pH. The present re-evaluation of the three-compartment model resolves an apparent contradiction between experimental and previous theoretical results which indicated a more alkaline intermediate compartment. Instead of contradicting experimental findings, results from the modelling process confirm that the "acid microclimate" version of the model is the better representation of the system that causes asymmetry in weak electrolyte flows across the small intestine.
肠道弱电解质转运的三室模型提供了一个方程，该方程在给定方程系数的情况下，可根据解离常数预测通量比（弱电解质在肠道中正向和反向通量的比值）。利用该方程从通量比和解离常数数据评估系数时，虽然能得到四组不同但相关的系数值，但无法提供唯一的一组系数值。通过求导来确定最大通量比的位置和大小，可得出模型系数之间的一种关系，这解释了为何在将该方程应用于实验数据时可以使用四组系数。文中推导了文献中所有可用通量比数据的系数集。这些系数集总是包含一个变体，该变体要求中间隔室比末端隔室的酸性更强。通过结合不同生理情况的数据或添加电压项对方程进行进一步的细化，可将四组可能的系数集减少为一组，同样要求中间隔室比末端隔室的酸性更强。中间隔室pH的估计值与黏膜表面pH的电极估计值吻合良好。目前对三室模型的重新评估解决了实验结果与先前理论结果之间的明显矛盾，先前的理论结果表明中间隔室的碱性更强。建模过程的结果并未与实验结果相矛盾，而是证实了该模型的“酸性微环境”版本能更好地描述导致弱电解质在小肠中流动不对称的系统。
