Concentration dependence of urea and thiourea transport in rat inner medullary collecting duct.
Concentration dependence of urea and thiourea transport in rat inner medullary collecting duct.
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大鼠内髓集合管中尿素和硫脲转运的浓度依赖性。
DOI：
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发表时间：
1990
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通讯作者：
M. Knepper
中科院分区：
文献类型：
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作者：
C. Chou;J. Sands;H. Nonoguchi;M. Knepper
大鼠延髓终末集合管(IMCD)对加压素依赖的尿素通透性远高于脂相渗透或细胞旁扩散，提示存在加压素刺激的易化转运途径。我们使用离体灌流管技术来测试尿素转运途径是否表现出与易化途径一致的饱和特征。当管腔尿素浓度在0~800 mm(管周无尿素)范围内变化时，尿素通量与管腔浓度呈线性关系，y轴截距与0无显著差异，表明在此浓度范围内尿素通量与管腔浓度无显著差异。由于技术限制，无法测试更高浓度的尿素。然而，在类似的实验中，当硫脲(一种与尿素具有相同转运途径的尿素类似物)取代尿素时，在10-200 mm范围内，随着硫脲浓度的增加，表观硫脲渗透率下降，表明尿素-硫脲转运体饱和。当槽和腔内尿素浓度变化时，腔间尿素通量在400-500 mm尿素处接近一个极限值，与转运体的饱和度一致。然而，在这些实验中不能排除浴尿素对尿素转运的非特异性抑制。我们认为，在IMCD末端，尿素和硫脲的传输路径呈现饱和特征。然而，饱和途径所需的尿素浓度显然很高，在一组实验中至少为400-500 mM，在另一组实验中可能超过800 mM。
The vasopressin-dependent urea permeability of the rat terminal inner medullary collecting duct (IMCD) is much greater than can be explained by lipid-phase permeation or paracellular diffusion, suggesting the presence of vasopressin-stimulated facilitated transport pathway. We used the isolated perfused tubule technique to test whether the urea transport pathway exhibits saturation characteristics consistent with a facilitated pathway. When the luminal urea concentration was varied between 0 and 800 mM (no urea in peritubular bath), the relationship between the urea flux and the luminal concentration was linear with a y-axis intercept that was not significantly different from zero, indicating an absence of saturation in this concentration range. Higher concentrations of urea could not be tested due to technical limitations. However, when thiourea (a urea analogue that shares the urea transport pathway with urea) was substituted for urea in similar experiments, the apparent thiourea permeability fell with increasing thiourea concentration in the range 10-200 mM, indicative of saturation of the urea-thiourea transporter. When the urea concentration was varied in both bath and lumen, the lumen-to-bath urea flux approached a limiting value at 400-500 mM urea, consistent with saturation of the transporter. However, nonspecific inhibition of urea transport by bath urea could not be ruled out in those experiments. We conclude that the urea and thiourea transport pathway in the terminal IMCD exhibits saturation characteristics. However, the urea concentration required to saturate the pathway is apparently high, at least 400-500 mM in one set of experiments and probably greater than 800 mM in another.