Figure 2.

Diagrammatic representation of taste GPCRs (top panel) and downstream signaling effectors (bottom panel). Receptor binding leads to Gβγ activation of PLCβ2, production of IP₃, release of Ca²⁺ from intracellular stores, Ca²⁺ dependent activation of TrpM5, depolarization, activation of voltage-gated Na⁺ channels (VGNC), and release of ATP through pannexin-1 hemichannels. The released ATP activates purinergic receptors on afferent nerve fibers. Alpha gustducin tonically regulates cAMP levels via activation of a phosphodiesterase (PDE), which subsequently prevents phosphorylation and desensitization of Ca²⁺ signaling effectors.