Green R, Giebisch G
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
Am J Physiol. 1989 Oct;257(4 Pt 2):F669-75. doi: 10.1152/ajprenal.1989.257.4.F669.
Simultaneous microperfusion of proximal tubules and peritubular capillaries in kidneys of rats anesthetized with Inactin was used to measure reabsorption of fluid in response to an imposed osmotic gradient. The tubular fluid was isotonic and the peritubular capillaries were made hypertonic with NaCl or NaHCO3. Mean gradients and ionic fluxes were measured. When no gradient was imposed tubular fluid became hypotonic and rate of fluid reabsorption was 0.700 nl.mm-1.min-1. Imposition of a 25 mM NaCl gradient increased fluid flux to 3.887 nl.mm-1.min-1, whereas 25 mM NaHCO3 stimulated 5.226 ml/mm fluid reabsorption. This gave a relative reflection coefficient of NaCl:NaHCO3 of 0.73. Apparent water permeability varied with highest values for the smallest gradients. This suggests the possibility of a compartment in the epithelium that is hypertonic to the peritubular capillaries. The hypertonicity required to account for fluid movement was 6-16 mosmol/kg.
利用对用安泰酮麻醉的大鼠肾脏近端小管和肾小管周围毛细血管进行同步微量灌注，来测量在施加渗透梯度时液体的重吸收情况。管内液是等渗的，而用氯化钠或碳酸氢钠使肾小管周围毛细血管变为高渗。测量了平均梯度和离子通量。当不施加梯度时，管内液变为低渗，液体重吸收率为0.700纳升·毫米⁻¹·分钟⁻¹。施加25毫摩尔/升的氯化钠梯度使液体通量增加到3.887纳升·毫米⁻¹·分钟⁻¹，而25毫摩尔/升的碳酸氢钠刺激液体重吸收达5.226毫升/毫米。这得出氯化钠与碳酸氢钠的相对反射系数为0.73。表观水渗透率随最小梯度时的最高值而变化。这表明上皮细胞中可能存在一个相对于肾小管周围毛细血管为高渗的区室。解释液体移动所需的高渗性为6 - 16毫摩尔渗透压/千克。
