Differential Regulation of B/K Protein Expression in Proximal and Distal Tubules of Rat Kidneys With Ischemia-Reperfusion Injury

Am J Physiol Renal Physiol. 2007 Jan;292(1):F100-6. doi: 10.1152/ajprenal.00009.2006. Epub 2006 Aug 8.


Brain/kidney (B/K) protein is a novel double C2-like-domain protein that is highly expressed in rat brain and kidney, but its cellular localization and functional role in the kidney are still undetermined. We examined the cellular localization of B/K protein in the rat kidney under normal and ischemic conditions. Ischemia-reperfusion (I/R) injury was induced by clamping both renal arteries for 45 min, and animals were killed at 1 and 6 h and 1, 2, 3, 5, 7, 14, and 28 days after the reperfusion. Kidney tissues were processed for immunohistochemistry and immunoblot analyses using rabbit anti-B/K polyclonal antibodies. In control kidneys, B/K protein was expressed primarily in distal tubules including the thick ascending limb, distal convoluted and connecting tubules, and collecting duct. Notably, B/K protein was also expressed in the straight portion (S3 segment), but not in the S1 or S2, of proximal tubules, and podocytes of the glomerulus. In rat kidneys with I/R injury, expression of B/K protein was differentially regulated according to the anatomic location. In distal tubules, overall expression of B/K protein was markedly decreased. On the other hand, I/R injury significantly increased B/K protein expression in the S3 segment of the outer medulla as well as in the rat proximal tubular epithelial cell line NRK-52E in vitro. Furthermore, B/K protein was strongly expressed in many exfoliated cells in the lumen and urine. These findings suggest that B/K protein is closely associated with cell death in proximal tubules, which are vulnerable to I/R injury in the kidney.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blotting, Western
  • Cell Death / physiology
  • Gene Expression Regulation / physiology
  • Immunoenzyme Techniques
  • Immunohistochemistry
  • In Vitro Techniques
  • Kidney Cortex / metabolism
  • Kidney Medulla / metabolism
  • Kidney Tubules, Distal / metabolism*
  • Kidney Tubules, Proximal / metabolism*
  • Male
  • Nerve Tissue Proteins / biosynthesis*
  • Nerve Tissue Proteins / genetics
  • Rats
  • Rats, Sprague-Dawley
  • Reperfusion Injury / metabolism*
  • Synaptotagmins
  • Urine / cytology


  • Nerve Tissue Proteins
  • Syt17 protein, rat
  • Synaptotagmins