, 2007 and Volgraf et al., 2006), this class of ion channel has been surprisingly underexploited as a tool to couple recognition of different types this website of chemicals with cellular physiological responses. The existence of many hundreds of divergent IRs of presumed distinct specificity reveals a natural exploitation of this ligand-gated ion channel for chemical sensing (Croset et al., 2010 and Liu et al., 2010). The molecular properties of IRs uncovered here provide a basis for their rational modification to generate custom-designed chemoreceptors of

desired specificity. Such sensors could offer invaluable tools as genetically encoded neuronal activators or inhibitors as well as have broad practical applications, for click here example, in environmental pollutant detection or clinical diagnosis. Standard methods were used for Drosophila genetics, as described together with a

list of strains used, in the Supplemental Experimental Procedures. Standard methods were used in construction of all plasmids; details are provided in the Supplemental Experimental Procedures. Standard methods were employed for immunofluorescence as described, together with all antibodies used, in the Supplemental Experimental Procedures. Extracellular recordings in single sensilla of 2- to 14-day-old flies were performed and quantified essentially as described (Benton et al., 2007 and Benton et al., 2009); details are provided, together with odor sources, in the Supplemental Experimental Procedures. Oocyte preparation and injection was carried out essentially as described (Vukicevic et al., 2006); details are provided in the Supplemental Experimental Procedures. Solutions containing agonists were applied once every minute for 10 s; between applications, the recording chamber was perfused with standard bath solution (110 mM NaCl, 2 mM BaCl2, 10 mM HEPES-NaOH, pH adjusted to 7.4 with NaOH) without agonist.

For current/voltage (IV) curves in the presence of different ions, NaCl was replaced 17-DMAG (Alvespimycin) HCl by 110 mM KCl or 40 mM CaCl2 and the osmolarity was adjusted with sucrose. The Na+ and K+ solutions contained 2 mM Ba2+ as divalent cation. Kaleidagraph (Synergy Software) was used to fit the inhibition curves to the Hill equation: I = I0/[1+([inh]/IC50)nH], where I0 is the current in the absence of inhibitor (inh), IC50 is the inhibitor concentration that induces 50% inhibition, and nH is the Hill coefficient. For IV curve measurements in high extracellular Ca2+, we injected 50 nl of 40 mM BAPTA 1-2 hr prior to the electrophysiological measurements to test the contribution of the Ca2+ currents by endogenous Ca2+-dependent chloride currents. Phenylacetaldehyde and propionic acid were prepared as 1 M stock solutions in DMSO and diluted in bath solution to the desired final concentration. Philanthotoxin 433 tris(trifluoroacetate) (Sigma) was diluted to 1 mM in standard bath solution containing 0.