Characterization of a functional V1B vasopressin receptor in the male rat kidney: evidence for cross talk between V1B and V2 receptor signaling pathways.

Although vasopressin V1B receptor (V1BR) mRNA has been detected in the kidney, the precise renal localization as well as pharmacological and physiological properties of this receptor remain unknown. Using the selective V1B agonist d[Leu4, Lys8]VP, either fluorescent or radioactive, we showed that V1BR is mainly present in principal cells of the inner medullary collecting duct (IMCD) in the male rat kidney. Protein and mRNA expression of V1BR were very low compared with the V2 receptor (V2R). On the microdissected IMCD, d[Leu4, Lys8]VP had no effect on cAMP production but induced a dose-dependent and saturable intracellular Ca2 + concentration increase mobilization with an EC50 value in the nanomolar range. This effect involved both intracellular Ca2 + mobilization and extracellular Ca2 + influx. The selective V1B antagonist SSR149415 strongly reduced the ability of vasopressin to increase intracellular Ca2+ concentration but also cAMP, suggesting a cooperation between V1BR and V2R in IMCD cells expressing both receptors. This cooperation arises from a cross talk between second messenger cascade involving PKC rather than receptor heterodimerization, as supported by potentiation of arginine vasopressin-stimulated cAMP production in human embryonic kidney-293 cells coexpressing the two receptor isoforms and negative results obtained by bioluminescence resonance energy transfer experiments. In vivo, only acute administration of high doses of V1B agonist triggered significant diuretic effects, in contrast with injection of selective V2 agonist. This study brings new data on the localization and signaling pathways of V1BR in the kidney, highlights a cross talk between V1BR and V2R in the IMCD, and suggests that V1BR may counterbalance in some pathophysiological conditions the antidiuretic effect triggered by V2R activation. [ABSTRACT FROM AUTHOR]