Gustducin - Sweet Transduction

Sweet Transduction

There are currently two models proposed for sweet taste transduction. The first pathway is a GPCRG_s-cAMP pathway. This pathway starts with sucrose and other sugars activating G_s through GPCR. The activated G_as activates adenylyl cyclase to generate cAMP. From this point, one of two pathways can be taken. cAMP may act directly to cause an influx of cations through camp gated channels or cAMP can activate protein kinase A, which cases phosphorylation of K+ channels, closing the channels, depolarizing the taste cell causing, voltage-gated Ca2+ channels to open and causing neurotransmitter release. The second pathway is a GPCR-G_q/Gβγ-IP₃ pathway which is used with artificial sweeteners. Artificial sweeteners bind and activate GPCRs coupled to PLCβ₂ by either α-G_q or Gβγ. The activated subunits activate PLCβ₂ to generate IP₃ and DAG. IP₃ and DAG elicit Ca2+ release and cause cellular depolarization. In influx of Ca2+ trigger neurotransmitter release. While these two pathways coexist in the same TRCs, it is unclear how the receptors selectively mediate cAMP responses to sugars and IP₃ responses to artificial sweeteners.