Expression of aquaporin-1 in the peritoneal tissues: localization and regulation by hyperosmolality.
OBJECTIVE
The purpose of this study was to determine the localization of the aquaporin-1 (AQP1) water channel in peritoneal tissues and the effect of hyperosmolality on the peritoneal expression and function of AQP1.


METHODS
Immunohistochemical localization of AQP1 was identified in rat peritoneal tissues. Cultured rat peritoneal mesothelial cells (RPMCs) were exposed to hyperosmolality by adding 4% glucose to the culture medium. After 1 hour, 4 hours, 24 hours, and 48 hours, AQP1 was identified by semiquantitative immunoblot and immunocytochemistry. Osmotic water permeability was measured using a light-scattering method.


RESULTS
Immunohistochemistry of rat peritoneal tissues showed the presence of AQP1 in mesothelial cells, venular endothelial cells, and capillary endothelial cells, but not in arteriole and interstitial cells. Semiquantitative immunoblot revealed that exposure to hyperosmolality significantly increased AQP1 expression after 24 hours in whole RPMC lysates (3.3-fold at 24 hours and 3.9-fold at 48 hours). Consistent with the immunoblot, osmotic water permeability of RPMC was augmented 1.7-fold and 2.7-fold after 1 hour and 24 hours, respectively, in a hyperosmotic environment. In RPMC membrane fractions, AQP1 expression was significantly increased after 1 hour of exposure to hyperosmolality (3.9-fold at 1 hour, 7.1-fold at 4 hours, and 8.7-fold at 24 hours). Immunocytochemistry of RPMCs showed that AQP1 was gradually redistributed from the perinuclear area to the peripheral cytoplasm, and then to the plasma membrane after a 1-hour hyperosmotic challenge, suggesting hyperosmolality-induced translocation of AQP1. Upregulation of AQP1 was also observed in the omentum of rats loaded intraperitoneally with hyperosmotic dialysate every day for 10 weeks.


CONCLUSIONS
AQP1 is widely distributed in the peritoneal cavity and may provide the major aqueous pathway across the peritoneal barrier. In addition, our findings suggested that hyperosmolality increases AQP1-dependent water permeability in peritoneal tissues by regulatIng the translocation and synthesis of AQP1 protein.
Ota
Tomoko
T
Department of Blood Purification Tokyo Medical and Dental University, Japan.
Kuwahara
Michio
M
Fan
Shuling
S
Terada
Yoshio
Y
Akiba
Takashi
T
Sasaki
Sei
S
Marumo
Fumiaki
F
D000818:Animals; D051398:Aquaporin 1; D020346:Aquaporins / Q000032:analysis* / Q000502:physiology*; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004847:Epithelial Cells / Q000473:pathology / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D009994:Osmolar Concentration; D010532:Peritoneal Diseases / Q000473:pathology* / Q000503:physiopathology*; D010537:Peritoneum / Q000473:pathology* / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
C496022:Aqp1 protein, rat; D020346:Aquaporins; D051398:Aquaporin 1