Chemical Senses Vol. 29 No. 8 © Oxford University Press
2004; all rights reserved
A Specific Receptor Site for Glycerol, a New Sweet Tastant for Drosophila: Structure–Taste Relationship of Glycerol in the Labellar Sugar Receptor Cell
1 Department of Developmental Biology and Neuroscience, Graduate School of Life Sciences, Tohoku University, Sendai 980-8578, Japan and 2 Laboratory of Information Biology, Graduate School of Information Science, Tohoku University, Sendai 980-8578, Japan
Correspondence to be sent to: Ichiro Shimada, Department of Developmental Biology and Neuroscience, Graduate School of Life Sciences, Tohoku University, Sendai 980-8578, Japan. e-mail: ishimada{at}mail.tains.tohoku.ac.jp
Glycerol, a linear triol, is a sweet tastant for mammals but it has not previously
been recognized to stimulate the sense of taste in insects. Here we show by
electrophysiological experimentation that it effectively stimulates the labellar sugar
receptor cell of Drosophila. We also show that in accord with the
electrophysiological observations, the behavioral feeding response to glycerol is dose
dependent. 3-Amino-1,2-propanediol inhibited the response of the sugar receptor cell to
glycerol, specifically and competitively, while it had almost no effect on responses to
sucrose, D-glucose, D-fructose and trehalose. In the null
Drosophila mutant for the trehalose receptor (
EP19), the
response to glycerol showed no change, in sharp contrast with a characteristic drastic
decrease in the response to trehalose. The glycerol concentration–response curves
for I-type and L-type labellar hairs were statistically indistinguishable, while those
for sucrose, D-glucose, D-fructose and trehalose were clearly
different. These all indicate the presence of a specific receptor site for glycerol. The
glycerol site was characterized by comparing the effectiveness of various derivatives of
glycerol. Based on this structure–taste relationship of glycerol, a model is
proposed for the glycerol site including three subsites and two steric barriers, which
cannot accommodate carbon-ring containing sugars such as D-glucose.
Key words: chemoreception, electrophysiology, fly, inhibitor, mutant, receptor model
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