Kyoichi Takao

A region of the muscarinic-gated atrial K+ channel critical for activation by G protein βγ subunits

Abstract Complementary DNAs encoding two types of inwardly rectifying K + channels, GIRK1 and IRK1, have been cloned from rat atrium and mouse macrophage, respectively. GIRK1 expressed in Xenopus oocytes was activated by acetylcholine when m2 muscarinic acetylcholine receptor was coexpressed. The acetylcholine-induced activation of GIRK1 was enhanced by coexpression with the G protein β1γ2 subunit but not the β1γ1 or a subunits. Deletion of the C-terminus of GIRK1 impaired the channel activation associated with the β1γ2 subunit. Moreover, replacement of the C-terminus of IRK1 with that of GIRK1 produced a chimera channel that was activated by the β1γ2 subunit, whereas intact IRK1 was not activated by the S1γ2 subunit. These findings define the C-terminus of GIRK1 as a regulatory region for the G protein βγ subunit.

A region of the sulfonylurea receptor critical for a modulation of ATP-sensitive K+ channels by G-protein βγ-subunits

To determine the interaction site(s) of ATP‐sensitive K+ (KATP) channels for G‐proteins, sulfonylurea receptor (SUR2A or SUR1) and pore‐forming (Kir6.2) subunits were reconstituted in the mammalian cell line, COS‐7. Intracellular application of the G‐protein βγ2‐subunits (Gβγ2) caused a reduction of ATP‐induced inhibition of Kir6.2/SUR channel activities by lessening the ATP sensitivity of the channels. Gβγ2 bound in vitro to both intracellular (loop‐NBD) and C‐terminal segments of SUR2A, each containing a nucleotide‐binding domain (NBD). Furthermore, a single amino acid substitution in the loop‐NBD of SUR (Arg656Ala in SUR2A or Arg665Ala in SUR1) abolished the Gβγ2‐dependent alteration of the channel activities. These findings provide evidence that Gβγ modulates KATP channels through a direct interaction with the loop‐NBD of SUR.

Lower expressions of the human bitter taste receptor TAS2R in smokers: reverse transcriptase-polymerase chain reaction analysis

BackgroundDespite the fact that smokers have deficit in detecting taste, particularly bitter taste, no study has investigated its biological correlate.MethodsIn this context, we compared the expression of the bitter taste receptor gene, taste 2 receptor (TAS2R) in the tongues of smokers and non-smokers. Tissue samples were collected from the lateral portion of the tongues of 22 smokers and 22 age- and gender-matched healthy volunteers (19 males and three females) with no history of smoking. Reverse transcriptase-polymerase chain reaction was used to examine the expression of TAS2R in the two groups, and the effect of aging on TAS2R expression was also assessed.ResultsTAS2R expression was significantly lower among smokers than non-smokers (t = 6.525, P < .0001, 11.36 ± 6.0 vs. 2.09 ± 2.8, mean ± SD, non-smokers vs. smokers). Further, a positive correlation between age and expression of TAS2R was observed in non-smokers (r = .642, P = .001), but not smokers (r = .124, P = .584). This correlation difference was significant (Z = 1.96, P = .0496).ConclusionsSmokers showed a significantly lower expression of the bitter taste receptor gene than non-smokers, which is potentially caused by their inability to acquire such receptors with age because of cigarette smoking, in contrast to non-smokers.

Patients with phantogeusia show increased expression of T2R taste receptor genes in their tongues.

Objectives: The taste receptor gene family T2R has been implicated in the sensation of bitter taste. Phantogeusia is a spontaneous abnormal taste with no external stimulus. We analyzed the expression of T2R taste receptor genes in the tongues of patients with phantogeusia to assess their role in the pathogenesis of phantogeusia. Methods: We obtained specimens from 43 patients with phantogeusia and 24 normal volunteers by scraping the foliate papillae and examined these specimens for the expression of 10 T2R taste receptor genes using reverse transcription–polymerase chain reaction and electrophoresis. Results: The expression rate (subjects with detectable expression) of the 10 taste receptor genes in the healthy subjects ranged from 16.7% to 100%; 3 receptor genes were found in 50% or fewer of these subjects. In the patients with phantogeusia, the expression rate was increased significantly compared to that in the healthy control subjects for 3 of the 10 receptor genes examined. Conclusions: Our results show that the expression rate of some of the T2R taste receptor genes was increased significantly in patients with phantogeusia. These results suggest that increased expression of taste receptor genes is involved in the pathogenesis of phantogeusia; this finding may contribute to elucidation of the mechanism of this disorder.

Patients with hypogeusia show changes in expression of T2R taste receptor genes in their tongues

Taste receptor genes associated with bitterness belong to the T2R gene family. In this study, we compared the expression of genes of the T2R family in the tongues of patients with hypogeusia to those in healthy subjects and examined the possibility that T2R genes are involved in the pathogenesis of hypogeusia.

Effects of zinc deficiency and supplementation on gene expression of bitter taste receptors (TAS2Rs) on the tongue in rats.

We examined the effect of zinc deficiency and supplementation on the expression of bitter taste receptor (TAS2R) and epithelial sodium ion channel (ENaC) genes on the tongue in rats.

Expression and localization of taste receptor genes in the vallate papillae of rats: effect of zinc deficiency.

Abstract Conclusion: We found a difference in expression sites between TAS2Rs and ENaC (epithelial sodium channels). The number of TAS2R-positive cells and ENaC-positive cells were decreased in zinc-deficient diet rats. These findings suggest that decreased expression of taste receptor genes may play an important role in the onset of zinc deficiency-associated taste disorder. Objective: The present study was aimed at histologically investigating the expression and localization of TAS2Rs and ENaC in the vallate taste buds of rats. Changes in expression of the taste receptor genes in zinc-deficient rats were also investigated. Methods: The vallate papillae of five rats fed a normal diet and five rats fed a zinc-deficient diet were used. In situ hybridization was performed to investigate the expression and localization of TAS2Rs and ENaC. TAS2R-positive cells per taste bud were counted, and differences in number between the normal and zinc-deficient diet rats were investigated. Results: In the normal rats, expression of TAS2Rs was observed specifically in the taste bud cells. In contrast, ENaC-positive cells were observed in a part of the taste bud cells and a large number of epithelial cells. Fewer cells were positive for TAS2Rs and ENaC in the zinc-deficient diet rats.