Andreoli T E, Schafer J A
Am J Physiol. 1978 Apr;234(4):F349-55. doi: 10.1152/ajprenal.1978.234.4.F349.
This paper examines the possibility that osmotic disequilibrium between luminal and bathing solutions may account for isotonic fluid absorption coupled to active Na+ absorption observed when superficial proximal straight tubules isolated from rabbit kidney are perfused and bathed with NaCl solutions in the absence of CO2, HCO3-, and luminal organic solutes. If luminal hypotonicity provides a driving force for isotonic fluid absorption under these conditions, the luminal fluid must be nearly isotonic; and steady-state luminal hypotonicity should develop sufficiently rapidly that the absolute rate of volume absorption ('JV, nl min-1) coupled to active Na+ transport is relatively independent of perfusion rate, so that the normalized rate of fluid absorption (JV, nl min-1 mm-1) is approximately constant. Our theoretical calculations indicate that these expectations are fulfilled. A 0.42-0.56 mM reduction in luminal NaCl concentration adequately accounts for the JV observed under such conditions, because of the high hydraulic conductivity of these tubules; and within the range of tubule lengths normally employed with isolated proximal straight tubules, JV is relatively indepedent of perfusion rate within the generally observed range of experimental error.
本文探讨了在从兔肾分离的浅表近端直管在无二氧化碳、碳酸氢根和管腔有机溶质的情况下用氯化钠溶液灌注和浸泡时，管腔溶液与浸泡溶液之间的渗透不平衡可能解释与主动钠吸收相关的等渗液体吸收的可能性。如果在这些条件下管腔低渗为等渗液体吸收提供驱动力，管腔液必须接近等渗；并且稳态管腔低渗应足够迅速地发展，使得与主动钠转运相关的体积吸收绝对速率（‘JV，nl min-1）相对独立于灌注速率，从而液体吸收归一化速率（JV，nl min-1 mm-1）大致恒定。我们的理论计算表明这些预期是可以实现的。由于这些小管的高水力传导率，管腔氯化钠浓度降低0.42 - 0.56 mM足以解释在这种条件下观察到的JV；并且在通常用于分离近端直管的小管长度范围内，在通常观察到的实验误差范围内，JV相对独立于灌注速率。
