Relationship Of Three-Dimensional Architecture Of Thin Limbs Of Henle'S Loops To The Renal Inner Medullary Concentrating Mechanism

Clusters of collecting ducts (CDs) form the lateral organizing structural motif for the arrangement of thin limbs of Henle's loops and of vasa recta in the renal inner medulla (IM). Within CD clusters (intracluster region), CDs, ascending vasa recta (AVR), and ascending thin limbs (ATLs), form transverse arrays of compartments called interstitial nodal spaces (INSs). The purpose of this study was to investigate quantitatively the relationship of inner medullary thin limbs of Henle's loops to the intracluster region and INSs. With serial section of the IM, Amira imaging software was used to determine the points AQP1‐null descending thin limbs (DTLs) and ATLs enter and exit INSs by tracking DTLs and ATLs as they descended/ascended through the IM. Their distance to the nearest CD was measured on each section. DTLs and ATLs contacting CDs were assumed to lie within the intracluster region, where they may contribute to the generation of an IM osmotic gradient by fluid and solute mixing within an INS. 40 AQP1‐null DTLs were on average 8.6 μm away from their nearest CDs at the base of the IM, and were on average 1.3 μm from CDs at the terminal portion of their length. 21 ATLs were on average 1.79 μm away from CDs as they began to ascend and were 8.02 μm on average from CDs at the IM base. The points at which DTLs and ATLs enter and exit CD clusters is likely related to NaCl reabsorption that occurs at the prebend and ATL. NIH DK 083338; NSF IOS‐0952885.