Figure 1.

A. Diagrammatic illustration of a taste bud, showing the 3 types of taste cells and a renewing population of basal (B) cells. Type II cells contain the GPCRs signaling effectors for bitter, sweet, and umami stimuli, and are the focus of this review. Type I cells are generally considered to have a support function, while Type III cells respond to sour stimuli and form prominent synapses with afferent nerve fibers. Type II cells also associate closely with afferent nerve fibers, but do not form conventional synapses.

B. Image of two taste buds, showing Type II cells stained with an antibody against the Type III IP3 receptor, and nerve fibers stained with an antibody against the purinergic receptor P2X2. Apical staining of P2X2 may represent non-specific binding. (Image courtesy of A. Montoya and J. Kinnamon, University of Denver).