poruš gustatoríus
chuťová
buňka —
chuťové látky
nervová zakončeni
nerv
relativní koncentrace dráždivých látek __________________(podle Pfaffmanna)
E. Chuťový pohárek          (podle Andrese)     F. Hodnocení chuťových podnětů
to Salt "Extracellular
Som-
it '  Sw eet
Closed K*
díti nud
Taste bud cell membrane
Depolarization
Cytoplasm
fit) ümami
I h'pol.-u-i/dtinn
Depolarization
Receptor^       ,G1 u to m r( li-
fe» Bitter
Closed K+ channel \
Bitter substance
Phospholipase C
gure 13.34 Taste-transduction mechanisms differ for different ste qualities    All transduction mechanisms except the IP3 action in ! lead to depolarization, which spreads to the basal end of the cell id opens voltage-gated Ca2+ channels to allow Ca2- entry and transfer release, (a) For salt taste, sodium ions enter a taste bud cell rough amiloride-sensitive cation channels, directly depolarizing the >\\,(h) In sour taste, either H^ ions enter the cell through amiloride-msitive cation channels, or they close K* channels to produce depo-rization, (c) Sweet taste is most commonly mediated by the binding sugars to a G protein-coupled receptor, which acts via a G protein to tiyate adenylyl cyclase and produce cyclic AMP. Cyclic AMP then acti-*■•"• nrnt"'" Lwata n (SUCuXtei t&asa a l/~ ebaonal <^" afaasofajaadatina
it), producing depolarization, (djThe amino acid glutamate (monosodi-urn glutamate, MSG) stimulates the taste quality umami (a savory or meaty quality). Glutamate binds to a G protein-coupled receptor (related to synaptic metabotropic glutamate receptors) to activate a phosphodiesterase (PDE) and decrease the concentration of cAMP.The decrease in cAMP leads to an increase in intracellular Cai+ concentration, (e) Bitter taste mechanisms can involve a G protein-coupled receptor for bitter substances that acts via a G protein and phospholi-pase C to produce IP3. IP3 liberates Cai+ ions from intracellular stores, eliciting transmitter release without requiring depolarization.Other bitter substances bind to K" channels and close them to depolarize
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