The mutation of the type-2 vasopressin receptor (V2R) apparently responsible for X-linked congenital nephrogenic diabetes insipidus (CNDI) in the Q3 family consists of a T to C transition in codon 113, causing the change of Arg-113 to Trp. Arg-113 is located in the putative first extracellular loop of the V2R next to a frequently conserved Cys thought to interact via a disulfide bridge with a Cys of the second extracellular loop. The present study explored whether this mutation may account for the CNDI phenotype. The mutation was excised from the genomic DNA of a Q3 patient and introduced into the V2R cDNA, which was then placed into an expression plasmid and transfected into COS cells for transient expression and murine L cells for stable expression. Studies with L cells expressing similar levels of wild type and Q3 receptors showed that the mutant receptor has a 20-fold reduced affinity for arginine vasopressin (AVP) and stimulates adenylyl cyclase with an EC50 that is increased by a factor of about 60-fold. The same shift in the EC50 for adenylyl cyclase stimulation was obtained when deamino[8-D-Arg]vasopressin was substituted for AVP. Studies with COS cells revealed that at equal levels of transfected DNA, the mutant receptor is expressed at lower levels (about 20%) than the wild type receptor, indicating that the mutation hinders the transport of the receptor to the cell membrane.(ABSTRACT TRUNCATED AT 250 WORDS)