Taste Receptor CellsTaste cells are transformed epithelial cells that reside in taste buds in the papillae of the tongue, palate, pharynx, epiglottis, and esophagus

Circumvallate Papillae Fungiform papillae Filliform papillae

Saliva contacts the microvilli through the taste pore The solubility of a substance affects the response time

Salty EnAC Sodium Channel NaCl – Ion channel allows Na⁺ to enter the cell Depolarization occurs and voltage-gated Ca²⁺

channels open Ultimately leads to neurotransmitter release

SourEnAC proteinH⁺ blocks K⁺ channels increasing intracellular [K⁺] via the MDEG1 receptorH⁺ also binds to yet another protein which allows Na⁺ ions to flow down the concentration gradient into the cell

BitterG protein coupled receptor (GCPR) - gustducinActivated phosphodiesterase leads to conversion of cAMP to AMPcAMP holds K⁺ ions open – so intracellular K⁺ concentration ↑

SweetGPCRs coupled with gustducinAdenylate cyclase becomes active increasing [cAMP]Ca²⁺ channels open inreasing intracellular [Ca²⁺] K⁺ channels close

Umami (Savory)Similar to the bitter and sweet pathwaysL-glutamate binds to mGluR4 (a GPCR)

mGluR4 is thought to close a cation channel which causes depolarization

Fats?Spicy … ???

Spicy is not a taste receptor cellTemperature sensitive receptors respond to spicy foodsTactile receptors also present information about a substance’s texture

Drosophila melanogaster has taste bristles containing gustatory receptor neurons at the end of the proboscis as well as on the legs and anterior wing margins Internal taste organs line the walls of the pharynx

Sensation of harmful substances regurgitate responseSensation of pleasurable substances sucking reflexes

So why do different people have different food preferences?