TASTE-BUDS HAVE A CYCLIC NUCLEOTIDE-ACTIVATED CHANNEL, CNGGUST

Cyclic nucleotide-gated (CNG) channels have been characterized as impo rtant factors involved in physiological processes including sensory re ception for vision and olfaction. The possibility thus exists that a c ertain CNG channel functions in gustation as well. In the present stud y, we carried out reverse transcription-polymerase chain reaction and genomic DNA cloning and characterized a CNG channel (CNGgust) as a cyc lic nucleotide-activated species expressed in rat tongue epithelial ti ssues where taste reception takes place. Several types of 5'-rapid amp lification of cDNA ends clones of CNGgust cDNA were obtained with vari ous 5'-terminal sequences. As the CNGgust gene was a single copy, the formation of such CNGgust variants should result from alternative spli cing. The encoded protein was homologous to known vertebrate CNG chann els with 50-80% similarities in amino acid sequence, and particularly homologous to bovine testis CNG channel and human cone CNG channel wit h 82% similarities, CNGgust was functional when expressed in human emb ryonic kidney cells, where it opened upon the addition of cGMP or cAMP . Immunohistochemical analysis using an antibody raised against a CNGg ust peptide demonstrated the channel to be localized on the pore side of each taste bud in the circumvallate papillae, with no signal observ ed for degenerated taste buds after denervation of the glossopharyngea l nerve. All these results, together with the indication that cyclic n ucleotides play a role gustatory signaling pathway(s), strongly sugges t the involvement of CNGgust in taste signal transduction.