gene silencing of selected calciumsignalling molecules in a drosophila cell line using doublestranded rna interference using the drosophila melanogaster s2 cell line stably expressing a cloned muscarinic acetylcholine receptor achr dm1 we have applied gene silencing by doublestranded rna interference rnai to knock down gene products involved in dm1mediated calcium signalling we have shown that rnai knock down of either the inositol 145trisphosphate receptor ins145p3r or the serca calcium pump in the s2dm1 cells blocks the increase in intracellular calcium concentration ca2i resulting from activation of the dm1 receptor by 100 microm carbamylcholine cch when rnai designed to knock down the ryanodine receptor ryr was tested there was no change in the calcium increase detected in response to cch consistent with a failure to detect ryrs in s2dm1 cells using rtpcr a combination of rnai and calcium imaging has provided a direct demonstration of key roles for the ins145p3r and the serca pump in the response to dm1 receptor activationthus we show that silencing of individual genes by rnai in a well characterised drosophila s2 cell line offers experimental opportunities for cellsignalling studies future investigations with rnai libraries taking full advantage of the wealth of new information available from sequencing the drosophila genome may help identify novel components of cellsignalling pathways and functionally linked gene products