Aquaporin-2 in the immature rat: expression, regulation, and trafficking.
The immature kidney is resistant to arginine vasopressin. To define the role of aquaporin-2 (AQP-2), the developmental expression of this water channel was studied in rats. AQP-2 levels were lower during early postnatal life, reaching maximal expression at 10 wk of age. Concurrently, urine osmolality increased from 242 +/- 60 to 1267 +/- 311 mosmol/kg. To study the regulation of AQP-2, immature and adult rats were kept on ad libitum intake or were water-deprived. Under normal conditions, AQP-2 levels in the immature rat were significantly lower (52.3 +/- 5.8%, P < 0.001) than in the adult. However, after dehydration the expression increased to adult levels. Interestingly, the increase in AQP-2 observed in the immature kidney was not accompanied by a proportional increase in urine osmolality. To rule out a potential alteration in AQP-2 trafficking, the transport of this water channel was investigated in a group of rats subjected to dehydration, treated with desmopressin acetate (dDAVP), or water loaded. Dehydration and dDAVP stimulated translocation of AQP-2 from intracellular vesicles to the plasma membrane, whereas water loading caused a shift of AQP-2 channels back to intracellular vesicles in both adult and immature animals. In summary, AQP-2 expression and trafficking in the immature kidney is appropriately stimulated by water deprivation and dDAVP. However, urine osmolality remained significantly decreased. From this study, it is concluded that although AQP-2 expression may play a role in the development of urine concentrating abilities, there still is a significant defect, yet to be defined, distal to AQP-2.
Bonilla-Felix
M
M
Department of Pediatrics, University of Texas-Houston Health Science Center 77030, USA.
Jiang
W
W
D000818:Animals; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D001127:Arginine Vasopressin / Q000494:pharmacology; D001483:Base Sequence; D001693:Biological Transport, Active; D002462:Cell Membrane / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D007473:Ion Channels / Q000235:genetics* / Q000378:metabolism*; D007668:Kidney / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D007671:Kidney Concentrating Ability; D007700:Kinetics; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley
C496025:Aqp2 protein, rat; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D017931:DNA Primers; D007473:Ion Channels; D012333:RNA, Messenger; D001127:Arginine Vasopressin