Differential coupling of the vasopressin V1b receptor through compartmentalization within the plasma membranes

Abstract

We show here that the rat vasopressin V1b receptor simultaneously activates both the Gq/11-inositol phosphate (IP) and Gs-cAMP pathways when transiently expressed in Chinese hamster ovary, human embryonic kidney (HEK) 293, and COS-7 cells and stimulated with arginine-vasopressin. Higher concentrations of the hormone, however, were needed to trigger the cAMP pathway. The nonmammalian analog argininevasotocin and the selective V1b agonist d[Cha4]vasopressin also activated the cAMP and IP pathways, although d[Cha4]-vasopressin elicited the two responses with equivalent potencies. We determined that the V1b receptor is present as a homodimer at the plasma membrane. Treatment of V 1b-transfected HEK-293 cells with methyl-β-cyclodextrin, a drug known to dissociate cholesterol-rich domains of the plasma membrane, shifted the EC50 of the vasopressin-induced cAMP accumulation to lower concentrations and, remarkably, increased the hormone efficacy related to the activation of this second messenger system. In parallel, the vasopressin-mediated activation of the IP pathway was slightly reduced without modification of its EC50. These results suggest that, as with many other G protein-coupled receptors, when trans-fected in heterologous cell systems, the V1b receptor forms dimers that signal differentially through the Gq/11 and Gs proteins depending on the nature of the ligand as well as on its localization within specialized compartments of the plasma membrane. The present study thus illustrates how signal transduction associated with the activation of a G protein-coupled receptor can be versatile and highly dependent on both the cell context and the chemical nature of the extracellular signaling messenger. © 2009 The American Society for Pharmacology and Experimental Therapeutics.