TABLE 2.

Summary of taste receptor cell characteristics.

Taste receptor cells	Type I	Type II	Type III
Cell type	50% of the total population	20–30%	5–10%
Taste responses	Low salt taste amiloride sensitive response	Sweet, biiter, umami and probably kokumi flavor response (?) via GPCRs	Sour response via otopterin 1
Morphology	Spindle shaped with long brush like microvilli (1–2 mm), no synapse	Long and slender short microvilli, no synapse	Single large microvillus, have synaptic contact with afferent nerve
Other functions	Support function, ion redistribution, neurotransmitter clearance	High salt taste amiloride insensitive response?	Probable salt response?
Marker proteins	GLAST, K+ channel (ROMK)	CALHM1, CALHM3, pannexin, connexins	Kir2.1, PDK2L1, SNAP25, synapsinII, NCAM

GLAST, glutamate aspartate transporter; ROMK, renal outer medullary potassium channel; PDK2L1, polycystin 2 like 1, transient receptor potential cation channel; CALHM, calcium homeostasis modulator; Kir2.1, inward rectifier K(+) channel; NCAM, neural cell adhesion molecule; SNAP25, synaptosome associated protein 25 kDa.