Aquaporin-1 and endothelial nitric oxide synthase expression in capillary endothelia of human peritoneum.
Water transport during peritoneal dialysis (PD) requires ultrasmall pores in the capillary endothelium of the peritoneum and is impaired in the case of peritoneal inflammation. The water channel aquaporin (AQP)-1 has been proposed to be the ultrasmall pore in animal models. To substantiate the role of AQP-1 in the human peritoneum, we investigated the expression of AQP-1, AQP-2, and endothelial nitric oxide synthase (eNOS) in 19 peritoneal samples from normal subjects (n = 5), uremic patients treated by hemodialysis (n = 7) or PD (n = 4), and nonuremic patients (n = 3), using Western blotting and immunostaining. AQP-1 is very specifically located in capillary and venule endothelium but not in small-size arteries. In contrast, eNOS is located in all types of endothelia. Immunoblot for AQP-1 in human peritoneum reveals a 28-kDa band (unglycosylated AQP-1) and diffuse bands of 35-50 kDa (glycosylated AQP-1). Although AQP-1 expression is remarkably stable in all samples whatever their origin, eNOS (135 kDa) is upregulated in the three patients with ascites and/or peritonitis (1 PD and 2 nonuremic patients). AQP-2, regulated by vasopressin, is not expressed at the protein level in human peritoneum. This study 1) supports AQP-1 as the molecular counterpart of the ultrasmall pore in the human peritoneum and 2) demonstrates that AQP-1 and eNOS are regulated independently of each other in clinical conditions characterized by peritoneal inflammation.
Devuyst
O
O
Department of Nephrology, University of Louvain Medical School, B-1200 Brussels, Belgium.
Nielsen
S
S
Cosyns
J P
JP
Smith
B L
BL
Agre
P
P
Squifflet
J P
JP
Pouthier
D
D
Goffin
E
E
D000293:Adolescent; D000328:Adult; D051398:Aquaporin 1; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D001706:Biopsy; D001789:Blood Group Antigens; D002196:Capillaries; D002648:Child; D002675:Child, Preschool; D004730:Endothelium, Vascular / Q000378:metabolism*; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007473:Ion Channels / Q000032:analysis / Q000096:biosynthesis*; D007676:Kidney Failure, Chronic / Q000378:metabolism / Q000473:pathology / Q000628:therapy; D008297:Male; D008875:Middle Aged; D019001:Nitric Oxide Synthase / Q000032:analysis / Q000096:biosynthesis*; D052250:Nitric Oxide Synthase Type III; D010537:Peritoneum / Q000098:blood supply / Q000166:cytology / Q000473:pathology; D012016:Reference Values; D006435:Renal Dialysis; D014511:Uremia / Q000378:metabolism / Q000473:pathology / Q000628:therapy; D014699:Venules
C496020:AQP1 protein, human; C496023:AQP2 protein, human; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D001789:Blood Group Antigens; D007473:Ion Channels; D051398:Aquaporin 1; C496314:NOS3 protein, human; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III