Phototransduction in Is Compromised by Gal4 Expression but not by InsP Receptor Knockdown or Mutation.

phototransduction is mediated by phospholipase C, leading to activation of transient receptor potential (TRP) and TRP-like (TRPL) channels by mechanisms that are unresolved. A role for InsP receptors (IPRs) had been excluded because IPR mutants () appeared to have normal light responses; however, this was recently challenged by Kohn et al. ("Functional cooperation between the IP3 receptor and phospholipase C secures the high sensitivity to light of photoreceptors in vivo," 35:2530), who reported defects in phototransduction after IPR-RNAi knockdown. They concluded that InsP-induced Ca release plays a critical role in facilitating channel activation, and that previous failure to detect phenotypes resulted from trace Ca in electrodes substituting for InsP-induced Ca release. In an attempt to confirm this, we performed electroretinograms, whole-cell recordings, and GCaMP6f Ca imaging from both IPR-RNAi flies and -null mutants. Like Kohn et al., we used to drive expression of , but we also used controls expressing alone. We describe several phenotypes suggestive of compromised development, including reductions in sensitivity, dark noise, potassium currents, and cell size and capacitance, as well as extreme variations in sensitivity between cells. However, we found no effect of IPR RNAi or mutation on photoreceptor responses or Ca signals, indicating that the IPR plays little or no role in phototransduction.