Mutants in Drosophila TRPC Channels Reduce Olfactory Sensitivity to Carbon Dioxide

Background: Members of the canonical Transient Receptor Potential (TRPC) class of cationic channels function downstream of Gaq and PLC beta in Drosophila photoreceptors for transducing visual stimuli. Gaq has recently been implicated in olfactory sensing of carbon dioxide (CO2) and other odorants. Here we investigated the role of PLC beta and TRPC channels for sensing CO2 in Drosophila. Methodology/Principal Findings: Through behavioral assays it was demonstrated that Drosophila mutants for plc21c, trp and trpl have a reduced sensitivity for CO2. Immuno-histochemical staining for TRP, TRPL and TRP gamma indicates that all three channels are expressed in Drosophila antennae including the sensory neurons that express CO2 receptors. Electrophysiological recordings obtained from the antennae of protein null alleles of TRP (trp(343)) and TRPL (trpl(302)), showed that the sensory response to multiple concentrations of CO2 was reduced. However, trpl(302); trp(343) double mutants still have a residual response to CO2. Down-regulation of TRPC channels specifically in CO2 sensing olfactory neurons reduced the response to CO2 and this reduction was obtained even upon down-regulation of the TRPCs in adult olfactory sensory neurons. Thus the reduced response to CO2 obtained from the antennae of TRPC RNAi strains is not due to a developmental defect. Conclusion: These observations show that reduction in TRPC channel function significantly reduces the sensitivity of the olfactory response to CO2 concentrations of 5% or less in adult Drosophila. It is possible that the CO2 receptors Gr63a and Gr21a activate the TRPC channels through Gaq and PLC21C.