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Pure Appl. Chem., 2002, Vol. 74, No. 7, pp. 1141-1151

http://dx.doi.org/10.1351/pac200274071141

Ion channels and second messengers involved in transduction and modulation of sweet taste in mouse taste cells

Kumiko Sugimoto1*, Noriatsu Shigemura2, Keiko Yasumatsu2, Rie Ohta2, Kiyohito Nakashima3, Kirio Kawai4 and Yuzo Ninomiya2

1 Section of Molecular Neurobiology, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan
2 Section of Oral Neuroscience, Graduate School of Dental Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
3 Department of Chemistry, Asahi University School of Dentistry, 1851-1 Hozumi, Motosu-gun, Gifu 501-0296, Japan
4 Department of Anatomy (Division II), School of Dental Medicine, Tsurumi University, 2-1-3 Tsurumi, Tsurumi-ku, Yokohama 230-8501, Japan

Abstract: Leptin, a hormone released from the adipose tissue, inhibits food intake and increases energy expenditure. We have found a novel function of leptin as a modulator of sweet taste sensitivity in mice. In lean normal mice, the gustatory nerve responses to sweet stimuli were selectively suppressed depending on plasma leptin level after an intraperitoneal injection of recombinant leptin. Patch-clamp studies using isolated taste cells of lean mice showed that extracellular leptin enhanced K+ currents of sweet-responsive taste cells, which led to membrane hyperpolarization and a reduction of sweetener-induced depolarization. Reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization analyses demonstrated specific expression of mRNA of the long-form functional leptin receptor (Ob-Rb) in taste tissue and cells of lean mice. The genetically diabetic db/db mice, which have defects in Ob-Rb, demonstrated neither a suppression of gustatory neural responses to sweeteners nor an increment of whole-cell K+ conductance of taste cells even with high doses of leptin. These results suggest that Ob-Rb is specifically expressed in sweet-responsive taste cells of lean mice and that leptin suppresses sweetener-induced depolarization via activation of K+ channels, leading to a decrease in impulses of sweet-best fibers. The enhanced sweet responses of db/db mice may result from the lack of inhibitory modulation by leptin.