Synaptic transmission in Type III taste cells

Type III taste cells are the primary taste receptor cells that form conventional chemical synapses with gustatory nerve fibers. Since the first ultrastructural identification of synaptic vesicles in Type III cells, numerous studies have demonstrated that these cells have synapse-associated proteins and vesicular release machinery that is similar to that in the central nervous system.

This review summarizes historical and ultrastructural studies describing synaptic vesicles in taste bud cells across a range of animal species. The classical mechanisms of chemical synaptic transmission in the central nervous system are then outlined, followed by review studies demonstrating the expression of synapse-associated proteins in taste bud cells, with particular emphasis on the putative mechanisms of synaptic transmission in Type III taste cells. Finally, the current evidence for candidate neurotransmitters, including 5-hydroxytryptamine, gamma-aminobutyric acid, noradrenaline, acetylcholine, and ATP, is discussed.

Although several proteins related to conventional chemical synapses in the central nervous system and some candidate neurotransmitters have been identified in Type III cells, their contributions to sour taste transmission have not been fully elucidated. Further molecular and physiological studies are required to establish their roles in the synaptic transmission of sour taste signals from Type III cells.