Water taste transduction pathway is calcium dependent in Drosophila.
In mammals, detection of osmolarity by the gustatory system was overlooked until recently. In insects, specific taste receptor neurons detect hypoosmotic stimuli and are commonly called "W" (water) cells. W cells are easy to access in vivo and represent a good model to study the transduction of hypoosmotic stimuli. Using pharmacological and genetic approaches in Drosophila, we show that tarsal W cell firing activity depends on the concentration of external calcium bathing the dendrite. This dependence was confirmed by the strong inhibition of W cell responses to hypoosmotic stimuli by lanthanum (IC(50) = 8 nM), an ion known to inhibit calcium-permeable channels. Downstream, the transduction pathway likely involves calmodulin because calmodulin antagonists such as W-7 (IC(50) = 2 microM) and fluphenazine (IC(50) = 30 microM) prevented the activation of the W cell by hypoosmotic stimuli. A protein kinase C (PKC) may also be involved as W cell responses were blocked by PKC inhibitors, chelerythrine (IC(50) = 20 microM) and staurosporine (IC(50) = 30 microM). It was also reduced when expressing an inhibitory pseudosubstrate of PKC in gustatory receptor neurons. In the rat, the transduction pathway underlying low osmolarity detection involves aquaporin and swelling-activated ion channels. Our study suggests that the transduction pathway of hypoosmotic stimuli in insects differs from mammals.
Meunier
Nicolas
N
Institut National de Recherche Agronomique, Unité Mixte de Recherche, 1272 Physiologie de l'Insecte-Signalisation et Communication, Versailles, France. nicolas.meunier@jouy.inra.fr
Marion-Poll
Frédéric
F
Lucas
Philippe
P
D000818:Animals; D053119:Benzophenanthridines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism; D018118:Chloride Channels / Q000187:drug effects; D004330:Drosophila / Q000502:physiology*; D029721:Drosophila Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005476:Fluphenazine / Q000494:pharmacology; D007811:Lanthanum / Q000494:pharmacology; D009994:Osmolar Concentration; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction; D019311:Staurosporine / Q000494:pharmacology; D013449:Sulfonamides / Q000494:pharmacology
D053119:Benzophenanthridines; D002147:Calmodulin; D018118:Chloride Channels; D029721:Drosophila Proteins; D011956:Receptors, Cell Surface; D013449:Sulfonamides; C405956:gustatory receptor, Drosophila; C017967:W 7; D007811:Lanthanum; C016299:chelerythrine; D011493:Protein Kinase C; D019311:Staurosporine; D005476:Fluphenazine; D002118:Calcium