title: Histochemical distribution and expression of aquaporin 1 in the peritoneum of patients undergoing peritoneal dialysis: relation to peritoneal transport.
abstract: BACKGROUND
  Aquaporin 1 (AQP-1) channels have been claimed to be responsible for osmotically driven free-water movement across the peritoneal membrane. Data about AQP-1 expression and its location in the human peritoneum related to clinical findings concerning ultrafiltration (UF) and free-water transport are still lacking.
  
  
  METHODS
  Fifty-seven peritoneal biopsy specimens obtained from peritoneal dialysis (PD) patients were investigated. AQP-1 expression was detected by means of immunohistochemistry and a semiquantitative scoring system. Histological findings were related to peritoneal transport properties measured by means of an extended peritoneal equilibration test (PET) using dextran 70 as a volume marker.
  
  
  RESULTS
  AQP-1 expression in the peritoneum was detected in both vascular endothelial cells (capillaries and small venules; score, 2.96 +/- 0.92) and the mesothelial cell layer (score, 2.31 +/- 1.54). There was significantly greater AQP-1 expression in vascular endothelial cells of patients showing increased thickness of the submesothelial fibrous layer of the peritoneum greater than 400 microm compared with less than 400 microm. Free-water transport through AQP-1 was 42% +/- 12% from total UF after 1 hour. There was a significant correlation between AQP-1 expression and free-water transport after 1 hour of equilibration with 3.86% glucose in the PET (r = 0.753; P < 0.001).
  
  
  CONCLUSIONS
  Our data indicate that AQP-1 is located not only in the endothelial cell layer of capillaries and small vessels in the peritoneum of PD patients, but also in the mesothelial cell layer. AQP-1 expression correlated with free-water transport after 1 hour of equilibration, reaching a significant part from total UF at this time.
authors.affiliation: Department of Nephrology and Rheumatology, University of Duesseldorf, Duesseldorf, Germany. schoenic@uni-duesseldorf.de
authors.forename: Gerrit
authors.initials: G
authors.lastname: Schoenicke
authors.forename: Roman
authors.initials: R
authors.lastname: Diamant
authors.forename: Andreas
authors.initials: A
authors.lastname: Donner
authors.forename: Ansgar
authors.initials: A
authors.lastname: Roehrborn
authors.forename: Bernd
authors.initials: B
authors.lastname: Grabensee
authors.forename: Joerg
authors.initials: J
authors.lastname: Plum
mesh_terms: D000328:Adult; D051398:Aquaporin 1; D020346:Aquaporins / Q000378:metabolism*; D001706:Biopsy; D001789:Blood Group Antigens; D002408:Catheters, Indwelling; D003911:Dextrans / Q000493:pharmacokinetics; D004730:Endothelium, Vascular / Q000378:metabolism / Q000473:pathology; D004848:Epithelium / Q000378:metabolism / Q000473:pathology; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007668:Kidney / Q000378:metabolism / Q000473:pathology; D007674:Kidney Diseases / Q000378:metabolism / Q000473:pathology / Q000628:therapy; D008297:Male; D008875:Middle Aged; D010530:Peritoneal Dialysis; D010537:Peritoneum / Q000378:metabolism* / Q000473:pathology; D014018:Tissue Distribution; D014462:Ultrafiltration
chemical_list: C496020:AQP1 protein, human; D020346:Aquaporins; D001789:Blood Group Antigens; D003911:Dextrans; D051398:Aquaporin 1