Chemical Senses Advance Access originally published online on June 8, 2005
Chemical Senses 2005 30(6):497-504; doi:10.1093/chemse/bji042
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Biochemical and Physiological Evidence that Calmodulin Is Involved in the Taste Response of the Sugar Receptor Cells of the Blowfly, Phormia regina
1 Department of Applied Biology, Faculty of Textile Science, Kyoto Institute of Technology, Kyoto, Japan and 2 Department of Applied Physics and Chemistry, The University of Electro-Communications, Tokyo, Japan
Correspondence to be sent to: Mamiko Ozaki, Department of Applied Biology, Faculty of Textile Science, Kyoto Institute of Technology, Kyoto, Japan. e-mail: mamiko{at}ipc.kit.ac.jp
The gustatory system is essential for almost all animals. However, the signal transduction mechanisms have not yet been fully elucidated. We isolated labellar chemosensilla from blowfly, Phormia regina, and purified calcium binding proteins from the water soluble fraction. The most abundant calcium-binding protein was calmodulin. To investigate the role of calmodulin in taste transduction, electrophysiological responses were recorded with the calmodulin inhibitor, W-7. When we stimulated the labellar chemosensillum with sucrose plus W-7, a dose-dependent decrease of impulse frequency was observed when the concentration was <50 µM. In addition, when W-7 at 50 µM or higher concentration was added, an initial short-term impulse generation from the sugar receptor cell was observed, but this was followed by a silent period. When the sensillum was stimulated with W-7 plus a membrane-permeable cGMP analog, dibtyryl-cGMP or 8-bromo-cGMP, impulses of the sugar receptor cell were induced but the frequency was decreased. By the sidewall-recording method, we observed that the receptor potential induced by sucrose stimulation was decreased by W-7 in the sugar receptor cell, and corresponded with a disappearance of impulses. These data strongly suggest that the cGMP-gated channel generating receptor potential in the sugar receptor cell requires calmodulin for its gating.
Key words: CNG channel, contact chemoreceptor, electrophysiology, gustatory, insect, transduction
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