Alteration in water channel AQP-2 by removal of AVP stimulation in collecting duct cells of dehydrated rats

Dehydration increased the expression of aquaporin of collecting duct (AQP-2) and translocated AQP-2 to the apical plasma membranes from cytoplasmic vesicles of collecting duct cells. We determined whether the abrupt decrease in circulating arginine vasopressin (AVP) by giving excess water affects the expression of AQP-2 mRNA and subcellular localization of AQP-2 in collecting duct cells of the dehydrated rats. The 72-h water deprivation increased plasma AVP levels to 3.1 pg/ml and the expression of AQP-2 mRNA by 336% in rats, which were concomitantly abolished by the 40 ml/kg oral water load. A 50% inhibition of AQP-2 mRNA expression was obtained with 20 min after the forced water load. In immunohistochemistry and electron microscopy, the AQP-2 was manifestly present around the apical edge of collecting duct cells in the 72-h dehydrated rats. The AQP-8 was diffusely translocated into the cytoplasm 1 h after the forced water administration. These results indicate that AVP plays the on-off regulation of AQP-8 mRNA expression and that a majority of AQP-8 is regulated by the shuttle recycling in the collecting duct cells.