Figure 1.

Signal transduction molecules involved in 5 taste qualities. Sweet, umami, and bitter compounds are detected by 2 distinct families of G-protein-coupled receptors (GPCRs), T1Rs and T2Rs, expressed in type II taste cells. These signals are relayed via the common downstream components, including G-proteins, PLC-b2, IP₃R3. and TRPM5, resulting in ATP release. In contrast, sour compounds are potentially detected by PKD1L3/PKD2L1 heteromers expressed in type III taste cells. Type III cells are supposed to transmit the gustatory information by the neurotransmitter, serotonin.