Type II and III Taste Bud Cells Preferentially Expressed Kainate Glutamate Receptors in Rats

Abstract

Glutamate-induced cobalt uptake reveals that non-NMDA glutamate receptors (GluRs) are present in rat taste bud cells. Previous studies involving glutamate induced cobalt staining suggest this uptake mainly occurs via kainate type GluRs. It is not known which of the 4 types of taste bud cells express subunits of kainate GluR. Circumvallate and foliate papillae of Sprague-Dawley rats (45~60 days old) were used to search for the mRNAs of subunits of non-NMDA GluRs using RT-PCR with specific primers for GluR1-7, KA1 and KA2. We also performed RT-PCR for GluR5, KA1, PLCbeta2, and NCAM/SNAP 25 in isolated single cells from taste buds. Taste epithelium, including circumvallate or foliate papilla, express mRNAs of GluR5 and KA1. However, non-taste tongue epithelium expresses no subunits of non-NMDA GluRs. Isolated single cell RT-PCR reveals that the mRNAs of GluR5 and KA1 are preferentially expressed in Type II and Type III cells over Type I cells.

Keywords: Kainate receptor; RT-PCR; Single isolated cell; Taste bud.

Fig. 1

Results of tissue RT-PCR of mRNA obtained from tongue epithelium and hippocampus. N, non-taste epithelium; F, epithelium including foliate papilla; CV, epithelium including circumvallate papilla; H, hippocampus as positive control; -, no tissue as negative control; M, size marker.

Fig. 2

Representative isolated single cell RT-PCR results. Data is from 15 cells obtained from a single rat. Data from lanes 11 and 15 were discarded because both PLCβ2 and SNAP25 are expressed. Two cells express PLCβ2, another 2 cells express SNAP 25, 6 cell express GluR5, and 2 cells express KA1. Even cells in lanes 11 and 15 do not express KA1. However, GAPDH is expressed in all lanes except the negative control.

Fig. 3

Results of isolated single cell RT-PCR for taste bud cells. Each column represents data from an individual taste cell. Each row indicates expression of different mRNAs.