REGULATION OF COLLECTING DUCT WATER CHANNEL EXPRESSION BY VASOPRESSININ BRATTLEBORO RAT

AQP-CD is a vasopressin regulated water channel expressed exclusively in the renal collecting duct. We have previously shown that AQP-CD is present in the apical plasma membrane and subapical vesicles of collec ting duct cells, consistent with membrane-shuttling mechanisms that ha ve been proposed to explain the short-term action of [Arg(8)]vasopress in (AVP) to regulate apical water permeability. We propose here that A VP may also have long-term actions on the collecting duct to regulate the expression of the AQP-CD water channel. We used immunoblotting, im munohistochemistry, and in vitro perfusion of renal tubules to investi gate water channel regulation in collecting ducts of diabetes insipidu s (Brattleboro) rats treated with a 5-day infusion of AVP or vehicle. Immunoblotting and immunohistochemistry demonstrated that collecting d ucts of vehicle-infused Brattleboro rats had markedly reduced expressi on of AQP-CD relative to normal rats. In response to AVP infusion ther e was a nearly 3-fold increase in AQP-CD expression as detected by imm unoblotting. Immunocytochemistry demonstrated that the increased expre ssion was predominantly in the apical plasma membrane and subapical ve sicles of collecting duct cells. Inner medullary collecting ducts of A VP-infused Brattleboro rats displayed a 3-fold increase in osmotic wat er permeability relative to vehicle-infused controls, in parallel with the change in AQP-CD expression. Based on these findings, we conclude that (i) long-term infusion of AVP, acting either directly or indirec tly, regulates expression of the AQP-CD water channel and (ii) AQP-CD is the predominant AVP-regulated water channel.