Why Is Type 1 Cells Important

Type I Cells: Type I taste cells are most abundant in number but least understood. Ultrastructural studies of taste buds show that these cells have a spindle shaped structure, contain dark granules, and irregularly shaped nucleus. These cells are characterized by numerous cytoplasmic processes that wrap other cells, thus are thought to have a glial-like function (Finger, 2005). Type I cells extend a microvillus into the taste pore where taste molecules can come in contact with the cell.

Type I cells express some specific markers proteins like an ecto-ATPase NTPDase 2 and a Glutamate aspartate transporter or GLAST (Bartel et al., 2006; Pumplin et al., 1999). Both of these proteins are involved in terminating neurotransmitter action hence further

These cells have round oval nuclei and have an elongated structure. These cells are mainly located at the periphery of the taste buds and are often found at the upper part of a taste bud. In addition, they do not always extend to the basal part of the taste buds. These cells contain several short microvilli that extend into the taste pore. Type II cells are also called receptor cells because they express receptors for sweet, bitter and umami compound (DeFazio et al., 2006). Several studies suggest that the receptors for each of the taste quality are expressed in mutually exclusive fashion, thus forming three function subsets of sweet sensitive, bitter sensitive, and umami sensitive Type II cells (Nelson et al., 2001; Tomchik et al., 2007; Zhang et al., 2003). However some physiological and molecular studies suggest that at least in a subset of type II cells, receptors of different taste qualities may be expressed in the same cell

Moreover, Type III cells are also involved in the detection of carbonation (Graber and Kelleher, 1988; Simons et al., 1999; Chandrashekar et al., 2009). Genetic knockout studies have identified carbonic anhydrase 4, an enzyme attached to the cell surface of Type III cells through a glycosylphosphatidylinositol anchor, which at least in part functions as a carbonation detector. Additionally, synaptic transmission in Type III taste cells is also critical for taste responses to carbonation (Chandashekar et al., 2009). However, the complete transduction mechanism for sour or carbonation is not yet understood.

Type IV Cells: Type IV cells have a shape similar to that of epithelial cells in the stratified squamous epithelium, and are generally present at the base of the taste buds. Unlike the TSCs, Type IV cells do not possess any microvilli or reach to the taste pore. These cells are also known as progenitor cell for other cell types and express the developmental signaling protein sonic hedgehog (Miura et al.,