Localization of canine, feline, and mouse renal membrane proteins

Immunohistochemistry allows the localization of proteins to specific regions of the nephron. This article reports the identification and localization of proteins in situ within normal canine, feline, and mouse kidney by immunohistochemistry; maps their distribution; and compares results to previously reported findings in other species. The proteins investigated are aquaporin 1, aquaporin 2, calbindin D-28k, glutathione S-transferase-α, and Tamm-Horsfall protein. Aquaporins are integral membrane proteins involved in water transport across cell membranes. Calbindin D-28k is involved in renal calcium metabolism. Glutathione S-transferase-α is a protein that aids in detoxification and drug metabolism. The role of Tamm-Horsfall protein is not fully understood. Proposed functions include inhibition of calcium crystallization and reduction of bacterial urinary tract infection. The authors' findings in the dog are similar to those in other species: Specifically, the authors localize aquaporin 1 to the proximal convoluted tubule epithelium, vasa recta endothelium, and descending thin limbs; aquaporin 2 to collecting duct epithelium; and calbindin D-28k within distal convoluted tubule epithelium. Glutathione S-transferase-α has variable expression and is found in only the renal transitional epithelium in some individuals, in only the proximal straight tubules in others, or in both locations in others. Tamm-Horsfall protein localizes to thick ascending limb epithelium. These findings are similar in the cat, with the exception that aquaporin 1 is located in glomerular podocytes, in addition to proximal convoluted tubule epithelium, and glutathione S-transferase-α is found solely within the proximal convoluted tubule within all kidney samples examined. The mouse kidney is almost identical to the dog but expresses glutathione S-transferase-α in the glomeruli only.