title: Extracellular proton sensing of the rat gustatory cyclic nucleotide-gated channel.
abstract: Elevations of the intracellular levels of cyclic nucleotides appear to cause the cation influx through gustatory cyclic nucleotide-gated (CNGgust) channels expressed in taste cells. Although changes in the oral pH may directly regulate the activity of the CNGgust channel, the mechanism of pH-dependent control of the channel is not understood. In the present study, we combined the whole-cell patch-clamp recording and the site-directed mutagenesis to investigate the effect of extracellular pH on the ion permeation through CNGgust channels expressed in HEK293 cells. Extracellular acidification strongly inhibited ion permeation through open CNGgust channels. Mutation of Glu(289) remarkably attenuated the pH-dependence of the channel, suggesting that Glu(289) in the pore-forming region is a major proton acceptor site. However, the mutant E289A-CNGgust channel possesses the other residual protonation/deprotonation site. The channel activity, tightly regulated by pH(o) and [cNMP](i), suggests the involvement of its pH(o)-dependent ion permeation in taste signal transduction events.
authors.affiliation: Department of Oral Physiology, Graduate School of Biomedical Sciences, Hiroshima University, Kasumi 1-2-3, Minami-ku, Hiroshima 734-8553, Japan. sugisan@hiroshima-u.ac.jp
authors.forename: Makoto
authors.initials: M
authors.lastname: Sugita
authors.forename: Hiroe
authors.initials: H
authors.lastname: Ohishi
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Iwasa
authors.forename: Chikara
authors.initials: C
authors.lastname: Hirono
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Shiba
mesh_terms: D000818:Animals; D002460:Cell Line; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating; D007473:Ion Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009711:Nucleotides / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011522:Protons; D051381:Rats; D013650:Taste Buds / Q000378:metabolism*
chemical_list: D007473:Ion Channels; D009711:Nucleotides; D011522:Protons