The bradykinin receptor family is a group of G-protein coupled receptors whose principal ligand

Ligand

In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...

 is the protein bradykinin

Bradykinin

Bradykinin is a peptide that causes blood vessels to dilate , and therefore causes blood pressure to lower. A class of drugs called ACE inhibitors, which are used to lower blood pressure, increase bradykinin further lowering blood pressure...

.

There are two Bradykinin receptors: the B₁ receptor

Bradykinin receptor B1

Bradykinin receptor B1 is a G-protein coupled receptor encoded by the BDKRB1 gene in humans. Its principal ligand is bradykinin, a 9 amino acid peptide generated in pathophysiologic conditions such as inflammation, trauma, burns, shock, and allergy...

 and the B₂ receptor

Bradykinin receptor B2

Bradykinin receptor B2 is a G-protein coupled receptor for bradykinin, encoded by the BDKRB2 gene in humans.-Mechanism:The B2 receptor is a G protein-coupled receptor, probably coupled to Gq and Gi. Gq stimulates phospholipase C to increase intracellular free calcium and Gi inhibits adenylate cyclase...

.

B₁ receptor

Bradykinin receptor B1 (B₁) is a G-protein coupled receptor encoded by the BDKRB1 gene in humans. Its principal ligand is bradykinin, a 9 amino acid peptide generated in pathophysiologic conditions such as inflammation, trauma, burns, shock, and allergy. The B₁ receptor is one of two of G protein-coupled receptors that have been found which bind bradykinin and mediate responses to these pathophysiologic conditions.

B1 protein is synthesized de novo following tissue injury and receptor binding leads to an increase in the cytosolic calcium ion concentration, ultimately resulting in chronic and acute inflammatory responses.

B₂ receptor

The B₂ receptor is a G protein-coupled receptor

G protein-coupled receptor

G protein-coupled receptors , also known as seven-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptor, and G protein-linked receptors , comprise a large protein family of transmembrane receptors that sense molecules outside the cell and activate inside signal...

, coupled to G_q

Gq alpha subunit

Gq protein or Gq/11 is a heterotrimeric G protein subunit that activates phospholipase C . PLC in turn hydrolyzes Phosphatidylinositol 4,5-bisphosphate to diacyl glycerol and inositol triphosphate signal transduction pathway...

 and G_i

Gi alpha subunit

Gi alpha subunit is a heterotrimeric G protein subunit that inhibits the production of cAMP from ATP.- Receptors :The following G protein-coupled receptors couple to the Gi subunit:* Acetylcholine M2 & M4 receptors...

. G_q stimulates phospholipase C

Phospholipase C

Phosphoinositide phospholipase C is a family of eukaryotic intracellular enzymes that play an important role in signal transduction processes. In general, this enzyme is denoted as Phospholipase C, although three other families of phospholipase C enzymes have been identified in bacteria and in...

 to increase intracellular

Intracellular

Not to be confused with intercellular, meaning "between cells".In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".It is used in contrast to extracellular...

 free calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 and G_i inhibits adenylate cyclase

Adenylate cyclase

Adenylate cyclase is part of the G protein signalling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell ....

. Furthermore, the receptor stimulates the mitogen-activated protein kinase

Mitogen-activated protein kinase

Mitogen-activated protein kinases are serine/threonine-specific protein kinases that respond to extracellular stimuli and regulate various cellular activities, such as gene expression, mitosis, differentiation, proliferation, and cell survival/apoptosis.-Activation:MAP kinases are activated...

 pathways. It is ubiquitously and constitutively expressed in healthy tissues.

The B₂ receptor forms a complex with angiotensin converting enzyme (ACE), and this is thought to play a role in cross-talk between the renin-angiotensin system (RAS) and the kinin-kallikrein system (KKS). The heptapeptide angiotensin 1-7 (A1-7) also potentiates bradykinin action on B₂ receptors.

Icatibant

Icatibant

Icatibant is a peptidomimetic drug consisting of ten amino acids, which is a selective and specific antagonist of bradykinin B2 receptors...

 is a second generation B₂ receptor antagonist which has undergone limited clinical trials in pain and inflammation. FR 173657 is another orally active non-peptide B2 antagonist that has undergone limited trials as analgesic

Analgesic

An analgesic is any member of the group of drugs used to relieve pain . The word analgesic derives from Greek an- and algos ....

 and antiinflammatory drug.

Kallidin

Kallidin

Kallidin is a bioactive kinin formed in response to injury from kininogen precursors through the action of kallikreins.Kallidin is a decapeptide that can be converted to bradykinin by the aminopeptidase enzyme....

also signals through the B₂ receptor.

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