Two categories of taste receptors
1. Sweet, umami, and bitter receptors are GPCR. Tastant binding to receptor triggers signal transduction pathway involving G protein, phospholipase C, and second messengers Ca2+, which causes opening of channel resulting in Na+ influx.
2. Sour receptor. Part of the transient receptor potential family. Formed from pair of TRP proteins. Similar to capsaicin receptor. In taste buds, TRP sour receptors assemble into a channel in plasma membrane of taste cell, binding of an acid to receptor triggers change in ion channel resulting in depolarization.