Dysregulation of renal aquaporins and Na-Cl cotransporter in CCl4-induced cirrhosis.

BACKGROUND: Severe hepatic cirrhosis is associated with abnormal renal water retention.
METHODS: Semiquantitative immunoblotting was employed to investigate the abundance of the major renal aquaporins (water channels) and sodium-dependent cotransporters in kidneys from control rats and rats with cirrhosis secondary to chronic CCl4 inhalation.
RESULTS: The cirrhotic rats had ascites and manifested a water excretion defect detected by a standard water-loading test. The abundance of aquaporin-1 (the major aquaporin in the proximal tubule) was increased, an effect markedly accentuated in high-density membrane fractions prepared by differential centrifugation. Differential centrifugation studies demonstrated a redistribution of aquaporin-2 from high-density to low-density membranes, compatible with increased trafficking of aquaporin-2 to the plasma membrane. The abundance of aquaporin-3, but not aquaporin-2, was increased in collecting ducts of rats with CCl4-induced cirrhosis. The Na-K-2Cl cotransporter of the thick ascending limb showed no change in abundance. However, the abundance of the thiazide-sensitive Na-Cl cotransporter of the distal convoluted tubule was markedly suppressed in cirrhotic rats, possibly contributing to a defect in urinary dilution.
CONCLUSIONS: In this model of cirrhosis, the development of a defect in urinary dilution may be multifactorial, with contributions from at least four abnormalities in transporter regulation: (1) an increase in the renal abundance of aquaporin-1, (2) a cellular redistribution of aquaporin-2 in the collecting duct compatible with trafficking to the plasma membrane without an increase in total cellular aquaporin-2, (3) an increase in the renal abundance of aquaporin-3, and (4) a decrease in the abundance of the thiazide-sensitive cotransporter of the distal convoluted tubule.