Na+ ions binding to the bradykinin B2 receptor suppress agonist-independent receptor activation

Biochemistry. 1996 Oct 15;35(41):13368-77. doi: 10.1021/bi961163w.


Control of the balance between receptor activation and inactivation is a prerequisite for seven transmembrane domain (7TM) receptor function. We asked for a mechanism to stabilize the inactive receptor conformation which prevents agonist-independent receptor activation. Na+ ions have reciprocal effects on agonist versus antagonist interaction with various 7TM receptors. To investigate the Na+ dependence of receptor activation we chose the bradykinin B2 receptor as a prototypic 7TM receptor. Decrease of the intracellular Na+ content from 40 mM to 10 mM of COS-1 cells transiently expressing rat B2 receptors activated the B2 receptor in the absence of agonist as shown by a 3-fold increase in the basal release of inositolphosphates and increased the intrinsic activity of bradykinin to 1.2. In contrast, under increased intracellular Na+ (148 mM) the intrinsic activity of bradykinin decreased to 0.72. When the interaction of Na+ with the B2 receptor was prevented by exchanging a conserved aspartate in transmembrane domain II for asparagine the B2 receptor was also constitutively-activated in the absence of agonist. Agonist-independence B2 receptor activation under decreased intracellular Na+ was similarly observed with primary human fibroblasts endogenously expressing human B2 receptors by a 2.5-fold increase in basal inositolphosphates. Activation of human B2 receptors in the absence of agonist under decreased intracellular Na+ was further evident by an increased basal phosphorylation of the B2 receptor protein. Thus our data suggest that the interaction of Na+ ions with the B2 receptor stabilizes or induces an inactive receptor conformation thereby providing a mechanism to suppress agonist-independent receptor activation in vivo.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bradykinin / analogs & derivatives
  • Bradykinin / metabolism
  • COS Cells
  • Cell Line
  • Humans
  • In Vitro Techniques
  • Inositol Phosphates / metabolism
  • Intracellular Fluid / metabolism
  • Ligands
  • Mutagenesis, Site-Directed
  • Phosphorylation
  • Point Mutation
  • Rats
  • Receptor, Bradykinin B2
  • Receptors, Bradykinin / agonists
  • Receptors, Bradykinin / genetics
  • Receptors, Bradykinin / metabolism*
  • Sodium / metabolism*


  • Inositol Phosphates
  • Ligands
  • Receptor, Bradykinin B2
  • Receptors, Bradykinin
  • icatibant
  • Sodium
  • Bradykinin