Bitter taste receptors are part of which receptor family?

• A. G-protein coupled receptors.
• B. Ligand-gated ion channels.
• C. Receptor tyrosine kinases.
• D. Nuclear hormone receptors.

Answer: (A)

Bitter taste receptors are G-protein coupled receptors, a family of seven-transmembrane domain receptors that sense diverse chemicals and signal through heterotrimeric G proteins. In taste cells, bitter compounds bind to TAS2R receptors, which are GPCRs, and activate G proteins such as gustducin. This triggers a cascade involving phospholipase Cβ2, IP3 production, calcium release, opening of TRPM5, and neurotransmitter (ATP) release to gustatory afferents. This GPCR signaling is distinct from ligand-gated ion channels (which open an ion pore directly), receptor tyrosine kinases (which initiate phosphorylation cascades), and nuclear hormone receptors (which act as transcription factors). So bitter taste receptors belong to the G-protein coupled receptor family.