Renal Inner Medulla: Integrated Structure and Function

描述(申请人提供)：主要目标是通过确定哺乳动物肾脏内髓Henle‘S环、集合管和直血管的下降和上升细肢的三维结构组织，以及该结构与综合功能的关系，包括尿素、无机离子和水的通量，从而促进对哺乳动物肾脏内髓的功能和结构关系的了解。观察到：1)许多内髓细肢含有纯升肢细胞形态和功能的细胞片段与纯降肢细胞形态和功能的细胞片段混杂在一起，2)内髓1 mm以下弯曲的纯降支细肢中有60%的下位出现缺水和氯离子通道，3)内髓长降细肢在集合管周围呈环状排列；4)预弯节段的长度相似，并以氯离子通道的出现而突然开始，提示这些节段及其转运体和通道的结构安排可能对延髓内离子和渗透梯度的发展至关重要。一个初始的数学模型支持后一种概念。计划中的研究将主要涉及慕尼黑-Wistar大鼠，并利用内髓管状结构的三维功能重建技术和通过体外灌流研究细长肢体节段功能的技术的重大进展。它们将涉及1)完整的三维定量重建来自连续切片的Henle‘s环、集合管和直肠血管的所有内髓细肢，使用生理功能的免疫细胞化学标记物来识别运输功能的小管段和小管部位；2)通过体外微灌流直接测量重建中确定的特定细肢段的尿素、NaCl2和水的通透性；3)基于从功能重建和体外微融合获得的信息，通过数学建模整合内髓细肢、直血管和集合管的功能。

DESCRIPTION (provided by applicant): The primary goal is to advance understanding of the functional and structural relationships in the mammalian renal inner medulla by determining the three-dimensional structural organization of the descending and ascending thin limbs of Henle' s loops, collecting ducts, and vasa recta in the inner medulla and the relationship of this structure to integrated function, including the fluxes of urea, inorganic ions, and water, and, thus, development of the inner medullary osmotic gradient. Observations that: 1) many inner medullary thin limbs contain segments of cells with the appearance and function of cells in pure ascending limbs intermixed with segments of cells with the appearance and function of cells in pure descending limbs; 2) the lower 60% of all pure descending thin limbs with bends below the first millimeter of the inner medulla appear to lack water and chloride channels; 3) the inner medullary long descending thin limbs tend to be arranged in a ring-like arrangement around collecting ducts; and 4) the prebend segments are all of similar length and begin abruptly with the appearance of chloride channels suggest that the architectural arrangement of these segments and their transporters and channels may be critical to the development of inner medullary ionic and osmotic gradients. An initial mathematical model supports the latter concept. The planned studies will involve primarily Munich-Wistar rats and take advantage of major developments in techniques for three-dimensional functional reconstruction of tubular structures in the inner medulla and of techniques for studying functions of segments of thin limbs by perfusion in vitro. They will involve 1) complete three-dimensional, quantitative reconstruction of all inner medullary thin limbs of Henle's loops, collecting ducts, and vasa recta from serial sections, using immunocytochemical markers of physiological function to identify tubule segments and tubular sites of transport functions; 2) direct measurements, by in vitro microperfusions, of the urea, NaC1, and water permeabilities of specific thin limb segments defined in the reconstructions; and 3) integration of the function of the inner medullary thin limbs, vasa recta, and collecting ducts in the process of producing a concentrated urine via mathematical modeling based on information obtained from the functional reconstructions and the in vitro microperfusions.