What are the five basic taste modalities and their primary transduction mechanisms?

What are the five basic taste modalities and their primary transduction mechanisms?

• A. Sweet and umami via GPCRs; salty via Na+ influx; sour via protons; bitter via GPCRs; all depolarize receptor cells and release ATP.
• B. Sweet via Na+; sour via GPCR; salty via proton channel; bitter via direct Ca2+ influx; all use glutamate release.
• C. Sweet via GPCR; sour via TRP channels; salty via voltage-gated K+ channels; bitter via mechanosensitive channels; all produce action potentials directly.
• D. Sweet and umami via receptor tyrosine kinases; salty via Cl- efflux; sour via water channel; bitter via GPCR; all release GABA.

Answer: (A)

Taste signals rely on two main transduction pathways. Sweet and umami and bitter use G-protein–coupled receptors (GPCRs). When these receptors are activated, they trigger a G-protein cascade that raises intracellular Ca2+, opens the TRPM5 channel, depolarizes the cell, and leads to release of the transmitter ATP onto the gustatory nerve fibers. Salty is detected by Na+ influx through epithelial Na+ channels, directly depolarizing the receptor cell. Sour is detected by proton-related channels that let H+ in (or affect other ion channels), also causing depolarization. The common end result is depolarization of the taste receptor cell and transmitter release to the afferent nerves, with ATP acting as a primary transmitter in many taste cells. So this grouping aligns with the established mechanisms (GPCRs for Sweet/Umami/Bitter; Na+ for Salty; protons for Sour) and the idea that the depolarized cells release transmitter to activate the gustatory nerves.

Taste signals rely on two main transduction pathways. Sweet and umami and bitter use G-protein–coupled receptors (GPCRs). When these receptors are activated, they trigger a G-protein cascade that raises intracellular Ca2+, opens the TRPM5 channel, depolarizes the cell, and leads to release of the transmitter ATP onto the gustatory nerve fibers. Salty is detected by Na+ influx through epithelial Na+ channels, directly depolarizing the receptor cell. Sour is detected by proton-related channels that let H+ in (or affect other ion channels), also causing depolarization. The common end result is depolarization of the taste receptor cell and transmitter release to the afferent nerves, with ATP acting as a primary transmitter in many taste cells.

So this grouping aligns with the established mechanisms (GPCRs for Sweet/Umami/Bitter; Na+ for Salty; protons for Sour) and the idea that the depolarized cells release transmitter to activate the gustatory nerves.