Aim: 

Aquaporin-1 mRNA is expressed in juxtaglomerular granular (JG) cells that synthesize and release renin. It was hypothesized that AQP-1 is necessary for recruitment of JG cells and contributes in the pathway for renin release.

Methods: 

AQP1-/- and +/+ mice were given a diet with 0.004% NaCl (LS) for 7 days and enalapril (ACEI, 0.1 mg/ml) in the drinking water for 3 days. Plasma renin concentration and renal renin mRNA level was determined. Renal vasculature was dissected from acid-macerated kidneys and afferent arterioles were counted in a blinded fashion as either 1) JG-cell negative; 2) with JG cells in a juxtaglomerular position or 3) with upstream JG-cell recruitment. Isolated perfused kidneys from AQP1+/+ and AQP1-/- were used to determine renin release in response to standard stimuli. Perfusion-fixed kidneys from ACEI-treated mice were immunostained for renin and alpha-actin and serial sections were used to 3D- reconstruct the renal vasculature.

Results: 

At baseline, there were no differences in plasma renin concentration, renal renin mRNA, renin release from isolated perfused kidneys or tail-cuff blood pressure in AQP1-/- compared to AQP1+/+. Plasma renin concentration was stimulated significantly in response to LS-ACEI in both genotypes, but reached a significantly higher level in AQP1+/+. Renin mRNA level was elevated significanlty and to a similar extent in both genotypes by LS-ACEI. In AQP1-/-, the number of afferent arterioles with recruitment was significantly lower after LS-ACEI compared to +/+, while the number of arterioles with juxtaglomerular JG-cells was increased in AQP1-/-. 3-D reconstruction confirmed a predominantly juxtaglomerular position of renin-positive cells after ACEI in AQP1-/-.

Conclusion: 

Aquaporin-1 is not necessary for baseline regulation of renin secretion or expression but contributes to the recruitment of JG-cells and plasma renin concentration during chronic stimulation of the renin-angiotensin system.