Regulation of AQP2 in Collecting Duct : An emphasis on the Effects of Angiotensin II or Aldosterone

Abstract

Vasopressin, angiotensin II (AngII), and aldosterone are essential hormones in the regulation of body fluid homeostatsis. We examined the effects of AngII or aldosterone on the regulation of body water balance. We demonstrated that 1) short-term treatment with AngII in the primary cultured inner medullary collecting duct cells played a role in the regulation of AQP2 targeting to the plasma membrane through AT1 receptor activation. This potentiated the effects of dDAVP on cAMP accumulation, AQP2 phosphorylation, and AQP2 plasma membrane targeting; 2) pharmacological blockade of the AngII AT1 receptor in rats co-treated with dDAVP and dietary NaCl-restriction (to induce high plasma endogenous AngII) resulted in an increase in urine production, a decrease in urine osmolality, and blunted the dDAVP-induced upregulation of AQP2; 3) long-term aldosterone infusion in normal rats or in rats with diabetes insipidus was associated with polyuria and decreased urine concentration, accompanied by decreased apical but increased basolateral AQP2 labeling intensity in the connecting tubule and cortical collecting duct; and 4) in contrast to the effects of dDAVP and AngII, short-term aldosterone treatment does not alter the intracellular distribution of AQP2. In conclusion, angiotensin II, and aldosterone could play a role in the regulation of renal water reabsorption by changing intracellular AQP2 targeting and/or AQP2 abundance, in addition to the vasopressin.

Keywords: Aldosterone; Angiotensin II; Aquaporin 2; Collecting kidney tubules; Urine concentration.

Fig. 1

Increased AQP2 targeting in response to short-term treatment of dDAVP in Brattleboro rats. A) AQP2 immunolabeling in the outer medullary collecting duct in kidneys of Brattleboro rats 2 hours after vehicle. B) AQP2 immunolabeling in the outer medullary collecting duct in kidneys of Brattleboro rats 2 hours after dDAVP treatment. OMCD, outer medullary collecting duct.

Fig. 2

Overview of vasopressin controlled AQP2 membrane targeting in AQP2-expressed collecting duct principal cells. Vasopressin binding to the G-protein linked V2-receptor stimulates adenylyl cyclase leading to elevated cAMP levels and activation of protein kinase A. AQP2 is subsequently translocated to the apical plasma membrane.

Fig. 3

Cyclic-AMP measurement in primary cultured IMCD cells. A) cAMP levels were unchanged in response to the treatment of dDAVP, whereas the levels increased in response to AngII. The increase of cAMP levels was potentiated by co-treatment with dDAVP+AngII. Cyclic-AMP level was expressed in picomoles/mL of cell lysate (number of cell seeding per chamber : 2×10⁵ cells). ^*P<0.05 when compared with vehicle-treated control, ^*P<0.05 when compared with AngII-treated group. ^#P<0.05 when compared with dDAVP-treated group.

Fig. 4

Immunofluorescent labellingof AQP2 in primary cultured IMCD cells. A) AQP2 labelling was exclusively localized at the cytoplasm in response to vehicle treatment (Con). B) In contrast, increased AQP2 targeting to the plasma membrane was seen in response to the single treatment of AngII (AngII 10^-8M, 15 min).