title: Morphologic characterization of rat taste receptor cells that express components of the phospholipase C signaling pathway.
abstract: Rat taste buds contain three morphologically distinct cell types that are candidates for taste transduction. The physiologic roles of these cells are, however, not clear. Inositol 1,4,5-triphosphate (IP(3)) has been implicated as an important second messenger in bitter, sweet, and umami taste transductions. Previously, we identified the type III IP(3) receptor (IP(3)R3) as the dominant isoform in taste receptor cells. In addition, a recent study showed that phospholipase Cbeta(2) (PLCbeta(2)) is essential for the transduction of bitter, sweet, and umami stimuli. IP(3)R3 and PLCbeta(2) are expressed in the same subset of cells. To identify the taste cell types that express proteins involved in PLC signal transduction, we used 3,3'diaminobenzidine tetrahydrochloride immunoelectron microscopy and fluorescence microscopy to identify cells with IP(3)R3. Confocal microscopy was used to compare IP(3)R3 or PLCbeta(2) immunoreactivity with that of some known cell type markers such as serotonin, protein gene-regulated product 9.5, and neural cell adhesion molecule. Here we show that a large subset of type II cells and a small subset of type III cells display IP(3)R3 immunoreactivity within their cytoplasm. These data suggest that type II cells are the principal transducers of bitter, sweet, and umami taste transduction. However, we did not observe synapses between type II taste cells and nerve fibers. Interestingly, we observed subsurface cisternae of smooth endoplasmic reticulum at the close appositions between the plasma membrane of type II taste cells and nerve processes. We speculate that some type II cells may communicate to the nervous system via subsurface cisternae of smooth endoplasmic reticulum in lieu of conventional synapses.
authors.affiliation: Department of Biomedical Sciences, Anatomy and Neurobiology Section, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: Tod R
authors.initials: TR
authors.lastname: Clapp
authors.forename: Ruibiao
authors.initials: R
authors.lastname: Yang
authors.forename: Cristi L
authors.initials: CL
authors.lastname: Stoick
authors.forename: Sue C
authors.initials: SC
authors.lastname: Kinnamon
authors.forename: John C
authors.initials: JC
authors.lastname: Kinnamon
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000032:analysis* / Q000378:metabolism; D018871:Endoplasmic Reticulum, Smooth / Q000648:ultrastructure; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007527:Isoenzymes / Q000032:analysis* / Q000378:metabolism; D008297:Male; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D019006:Neural Cell Adhesion Molecules / Q000032:analysis; D054799:Phospholipase C beta; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000032:analysis* / Q000378:metabolism; D012701:Serotonin / Q000032:analysis; D015398:Signal Transduction; D013569:Synapses / Q000648:ultrastructure; D013649:Taste; D013650:Taste Buds / Q000737:chemistry* / Q000166:cytology* / Q000648:ultrastructure; D010738:Type C Phospholipases / Q000032:analysis* / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007527:Isoenzymes; D019006:Neural Cell Adhesion Molecules; D018160:Receptors, Cytoplasmic and Nuclear; D012701:Serotonin; D015544:Inositol 1,4,5-Trisphosphate; D010738:Type C Phospholipases; D054799:Phospholipase C beta