Constitutive activity of the light-sensitive channels TRP and TRPL in the Drosophila diacylglycerol kinase mutant, rdgA

Mutations in the Drosophila retinal degeneration A (rdgA) gene, which encod es diacylglycerol kinase (DGK), result in early onset retinal degeneration and blindness. Whole-cell recordings revealed that light-sensitive Ca2+ cha nnels encoded by the trp gene were constitutively active in rdgA photorecep tors. Early degeneration was rescued in rdgA;trp double mutants, lacking TR P channels; however, the less Ca2+-permeable light-sensitive channels (TRPL ) were constitutively active instead. No constitutive activity was seen in rdgA;trpl;trp mutants lacking both classes of channel, although, like rdgA; trp, these still showed a residual slow degeneration. Responses to light we re restored in rdgA;frp but deactivated abnormally slowly, indicating that DGK is required for response termination. The findings suggest that early d egeneration in rdgA is caused by uncontrolled Ca2+ influx and support the p roposal that diacylglycerol or its metabolites are messengers of excitation in Drosophila photoreceptors.