Characterization of a functional V 1B vasopressin receptor in the male rat kidney: evidence for cross talk between V 1B and V 2 receptor signaling pathways

Although V 1B R mRNA has been detected in the kidney, the precise renal localization as well as pharmacological and physiological properties of this receptor remain unknown. Using original pharmaceutical tools, this study brings new data on the localization and signaling pathways of V 1B R, highlights a cross talk between V 1B R and V 2 receptor (V 2 R) in the inner medullary collecting duct, and suggests that V 1B R may counterbalance in some pathophysiological conditions the antidiuretic effect triggered by V 2 R activation. Although vasopressin V 1B receptor (V 1B R) 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 V 1B agonist d[Leu 4 , Lys 8 ]VP, either fluorescent or radioactive, we showed that V 1B R is mainly present in principal cells of the inner medullary collecting duct (IMCD) in the male rat kidney. Protein and mRNA expression of V 1B R were very low compared with the V 2 receptor (V 2 R). On the microdissected IMCD, d[Leu 4 , Lys 8 ]VP had no effect on cAMP production but induced a dose-dependent and saturable intracellular Ca 2+ concentration increase mobilization with an EC 50 value in the nanomolar range. This effect involved both intracellular Ca 2+ mobilization and extracellular Ca 2+ influx. The selective V 1B antagonist SSR149415 strongly reduced the ability of vasopressin to increase intracellular Ca 2+ concentration but also cAMP, suggesting a cooperation between V 1B R and V 2 R 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 V 1B agonist triggered significant diuretic effects, in contrast with injection of selective V 2 agonist. This study brings new data on the localization and signaling pathways of V 1B R in the kidney, highlights a cross talk between V 1B R and V 2 R in the IMCD, and suggests that V 1B R may counterbalance in some pathophysiological conditions the antidiuretic effect triggered by V 2 R activation. NEW & NOTEWORTHY Although V 1B R mRNA has been detected in the kidney, the prec