Robert F. Margolskee

CHAPTER 229 – G Proteins Mediating Taste Transduction

Based on electrophysiological, genetic, and biochemical studies, several mechanisms have been identified for signal transduction by taste cells. For salty and sour compounds, the main signaling pathway is initiated by passive diffusion of ions through apical ion channels, amiloride-sensitive sodium channels, and acid-sensing channels. For bitter, sweet, and umami compounds, the main signaling mechanisms depend on seven transmembrane-helix receptors, their coupled G proteins, and downstream effector enzymes. The sense of taste in humans is comprised of five primary qualities: sweet, bitter, sour, salty, and umami (the taste of glutamate). Taste sensation is initiated in primary taste sensory cells located in papillae at the surface of the tongue and in the soft palate. The papillae contain one to several taste buds, each comprising approximately 100 cells, including taste receptor cells (TRCs), precursor, and support cells. TRCs are specialized epithelial cells that typically respond to one or more tastants by undergoing depolarization, elevating intracellular calcium, releasing a neurotransmitter, and activating the afferent neurons that they synapse upon.