Regulation of aquaporin mRNA expression in rat kidney by water intake

Three aquaporins (AQP) are present in the membrane of the principal collect ing duct cells. On the apical side, the levels of AQP2 protein are increase d in response to both arginine vasopressin and water deprivation. However, whether this change parallels changes in the abundance of AQP3 and AQP4 in the basolateral membrane is less well known. This study evaluates the effec t of either dehydration or water loading on the rat kidney mRNA expression of AQP2, AQP3, and AQP4. Poly(A(+))RNA was prepared from renal cortex and m edulla of control, water-deprived, well hydrated, and water-deprived rats t reated with OPC31260, a V2 receptor antagonist. Northern blots were done an d mRNA levels were quantified using a PhosphorImager system. Relative to co ntrol, water deprivation increased the expression of cortical AQP2, -3, and -4, whereas water loading decreased the cortical and medullar expression o f AQP2, -3, and -4. Therefore, in addition to AQP2 and -3, AQP4 expression is also regulated by water intake. Treatment with OPC31260 (40 mg/kg of wei ght per d) inhibited up to 20 to 30% the upregulation of AQP-mRNA induced b y water deprivation. Blood values of arginine vasopressin and aldosterone w ere significantly increased by water deprivation, whereas they were unchang ed by water overloading. Taken together, these results indicate that renal AQP2, -3, and -4 expression is regulated in a coordinated manner. Simultane ous up- or downregulation of the three transcripts occurred upon either wat er deprivation or water loading of animals, respectively. However, the sign aling mechanism for the two longterm adaptive processes may be different, a nd, in addition to arginine vasopressin, other factors may be involved in t he transcriptional regulatory processes.