Taste Buds Have a Cyclic Nucleotide-activated Channel, CNGgust

Abstract

Cyclic nucleotide-gated (CNG) channels have been characterized as important factors involved in physiological processes including sensory reception for vision and olfaction. The possibility thus exists that a certain CNG channel functions in gustation as well. In the present study, we carried out reverse transcription-polymerase chain reaction and genomic DNA cloning and characterized a CNG channel (CNGgust) as a cyclic nucleotide-activated species expressed in rat tongue epithelial tissues where taste reception takes place. Several types of 5-rapid amplification of cDNA ends clones of CNGgust cDNA were obtained with various 5-terminal sequences. As the CNGgust gene was a single copy, the formation of such CNGgust variants should result from alternative splicing. The encoded protein was homologous to known vertebrate CNG channels with 50 -80% similarities in amino acid sequence, and particularly homologous to bovine testis CNG channel and human cone CNG channel with 82% similarities. CNGgust was functional when expressed in human embryonic kidney cells, where it opened upon the addition of cGMP or cAMP. Immunohistochemical analysis using an antibody raised against a CNGgust peptide demonstrated the channel to be localized on the pore side of each taste bud in the circumvallate papillae, with no signal observed for degenerated taste buds after denervation of the glossopharyngeal nerve. All these results, together with the indication that cyclic nucleotides play a role gustatory signaling pathway(s), strongly suggest the involvement of CNGgust in taste signal transduction.

The Transduction Channel TRPM5 Is Gated by Intracellular Calcium in Taste Cells

“…However, it was subsequently determined by patch-clamp recording that vertebrate phototransduction depends on changes in a cyclic-nucleotide gated (CNG) conductance (Fesenko et al, 1985;Haynes and Yau, 1985). CNG-regulated ion channels have been noted in taste cells (Kolesnikov and Margolskee, 1995;Misaka et al, 1997), but the Figure 9. Properties of a TRPM5-independent Ca 2ϩ -activated channels in TRPM5 Ϫ/Ϫ taste cells.…”

Characterization of a Plasma Membrane Calcium Oscillator in Rat Pituitary Somatotrophs

“…After heat inactivation of DNase I by incubating at 70°C for 15 min, first strand cDNA was synthesized from 5 g of total RNA, using Superscript II reverse transcriptase and oligo(dT) [12][13][14][15][16][17][18] primers (Life Technologies, Inc.) in a reaction volume of 20 l. Aliquot (1 l) of the resulting single-strand cDNA was used for the PCRs, which were performed in 25-l volume, containing 200 M each of four deoxynucleotide triphosphates, 50 mM KCl, 10 mM Tris-HCl, pH 8.3, 2 mM MgCl 2 , and 0.5 units of Ex Taq polymerase (Panvera Corp., Madison, WI). Nucleotide sequences for the PCR primers correspond to cytoplasmic carboxyl regions of rat rod CNG1 (28), cone CNGgust (29), and olfactory CNG2 (30) and have the following sequences: CNG1U (sense), 5Ј-TGCGAATTTGGGCAGTG-ACC-3Ј, CNG1L (antisense), 5Ј-TCTCCTCCGGGTTCCTCAAG-3Ј; CNGgustU (sense), 5Ј-AGGGCAGATGCCAGGAACAT-3Ј, CNGgustL (antisense), 5Ј-CGAGGCTGTAAAGTGTCTCA-3Ј; CNG2U (sense), 5Ј-GGAGGTAGATGTTCAGGAGA-3Ј, and CNG2L (antisense), 5Ј-CTTTGGGGAGAGTTCAGAGG-3Ј.…”

The carboxyl-terminal region of cyclic nucleotide-modulated channels is a gating ring, not a permeation path

“…They generate the primary electrical signals of vertebrate phototransduction, olfaction, and gustation (15)(16)(17). These channels are also found in other neural and nonneuronal tissues, in which their function is less clearly understood (18).…”