IMMUNOHISTOCHEMICAL LOCALIZATION OF V2 VASOPRESSIN RECEPTOR ALONG THENEPHRON AND FUNCTIONAL-ROLE OF LUMINAL V2 RECEPTOR IN TERMINAL INNER MEDULLARY COLLECTING DUCTS

We investigated immunohistochemical localization of V2 vasopressin rec eptor along the nephron using a specific polyclonal antibody. Staining was observed in some of thick ascending limbs and all of principal an d inner medullary collecting duct (IMCD) cells. Not only basolateral b ut also luminal membrane was stained in collecting ducts, especially i n terminal IMCD (tIMCD). To learn the functional role of luminal V2 re ceptor in tIMCD, we studied the luminal effects of arginine vasopressi n (AVP) on osmotic water permeability (Pf), urea permeability (Pu), an d cAMP accumulation using isolated perfused rat tIMCD. In the absence of bath AVP, luminal AVP caused a small increase in cAMP accumulation, Pf and Pu, confirming the presence of V2 receptor in the lumen of tIM CD. In contrast, luminal AVP inhibited Pf and Pu by 30-65% in the pres ence of bath AVP by decreasing cAMP accumulation via V1a or oxytocin r eceptors and by an unknown mechanism via V2 receptors in the luminal m embrane of tIMCD. These data show that V2 receptors are localized not only in the basolateral membrane but also in the luminal membrane of t he distal nephron, Luminal AVP acts as a negative feedback system upon the basolateral action of AVP in tIMCD.