Products of Arachidonic Acid Metabolism

Segmentation of the nephron relative to transport mechanisms and secretory activity has been recognized for decades, beginning with the pioneering studies of Alfred Newton Richards (1 ). Nephron segmentation regarding transcellular sodium and water movement has been subjected to a “comprehensive analysis of sodium transporter and water-channel protein abundance along the renal tubule” by Knepper and Masilamani (2 ). This experimental approach, based on targeted proteomics, uses an “ensemble of rabbit polyclonal antibodies directed to the major sodium transporters and water channels expressed in each renal tubule segment.” It allows and facilitates characterization and analysis of tubular functional differences that define individual nephron segments. However, individual tubular segments can be further subdivided according to secretory activity and transport mechanisms as, for example, the proximal tubules which have three portions (S₁ , S₂ , S₃ ) distinguished by morphological differences and exhibiting multiple segregated functions such as the organic and anion secretory system (3 ) housed primarily in the straight segment (S₂ ), and angiotensin II (ANGII) regulated reabsorptive function, localized primarily in the first few mm of the proximal tubules S₁ segment (4 ).