<prompt> The bitter taste is mediated by the action ofGuanyl cyclaseG proteinTyrosine kinaseEpithelial Na chain  <response>: Sweet- G protein coupled increased in cAMP causing closure of K channels.Salt- Opening of amiloride sensitive Na channelsSour- Increased intracellular H concentration causing closure of K channelsBitter- G protein-coupled increase in intracellular Ca triggering neurotransmitter release. 