National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, Karnataka, India.
PLoS One. 2012;7(11):e49848. doi: 10.1371/journal.pone.0049848. Epub 2012 Nov 19.
Members of the canonical Transient Receptor Potential (TRPC) class of cationic channels function downstream of Gαq and PLCβ in Drosophila photoreceptors for transducing visual stimuli. Gαq has recently been implicated in olfactory sensing of carbon dioxide (CO(2)) and other odorants. Here we investigated the role of PLCβ and TRPC channels for sensing CO(2) in Drosophila.
METHODOLOGY/PRINCIPAL FINDINGS: Through behavioral assays it was demonstrated that Drosophila mutants for plc21c, trp and trpl have a reduced sensitivity for CO(2). Immuno-histochemical staining for TRP, TRPL and TRPγ indicates that all three channels are expressed in Drosophila antennae including the sensory neurons that express CO(2) 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 CO(2) was reduced. However, trpl(302); trp(343) double mutants still have a residual response to CO(2). Down-regulation of TRPC channels specifically in CO(2) sensing olfactory neurons reduced the response to CO(2) and this reduction was obtained even upon down-regulation of the TRPCs in adult olfactory sensory neurons. Thus the reduced response to CO(2) obtained from the antennae of TRPC RNAi strains is not due to a developmental defect.
These observations show that reduction in TRPC channel function significantly reduces the sensitivity of the olfactory response to CO(2) concentrations of 5% or less in adult Drosophila. It is possible that the CO(2) receptors Gr63a and Gr21a activate the TRPC channels through Gαq and PLC21C.
经典的瞬时受体电位（TRPC）阳离子通道家族的成员在果蝇光感受器中充当 Gαq 和 PLCβ 的下游，用于将视觉刺激转化为电信号。Gαq 最近被牵连到二氧化碳（CO2）和其他气味剂的嗅觉感知中。在这里，我们研究了 PLCβ 和 TRPC 通道在果蝇 CO2 感知中的作用。
方法/主要发现：通过行为测定，证明了 plc21c、trp 和 trpl 的果蝇突变体对 CO2 的敏感性降低。TRP、TRPL 和 TRPγ 的免疫组织化学染色表明，这三种通道都在果蝇触角中表达，包括表达 CO2 受体的感觉神经元。从 TRP（trp(343)) 和 TRPL（trpl(302))的蛋白质缺失等位基因的触角中获得的电生理记录显示，对多种浓度 CO2 的感觉反应都降低了。然而，trpl(302); trp(343)双突变体对 CO2 仍有残留反应。特异性下调 CO2 感知嗅觉神经元中的 TRPC 通道会降低对 CO2 的反应，即使在成年嗅觉感觉神经元中下调 TRPCs 也能获得这种降低。因此，从 TRPC RNAi 株的触角获得的对 CO2 的反应降低并不是由于发育缺陷引起的。
这些观察结果表明，TRPC 通道功能的降低显著降低了成年果蝇对 5%或更低浓度 CO2 的嗅觉反应的敏感性。可能是 CO2 受体 Gr63a 和 Gr21a 通过 Gαq 和 PLC21C 激活 TRPC 通道。
