Phototransduction in Drosophila melanogaster.
As in most invertebrate microvillar photoreceptors, phototransduction in Drosophila melanogaster uses a G-protein-coupled phosphoinositide pathway, whereby hydrolysis of phosphatidyl inositol 4,5-bisphosphate (PIP(2)) by phospholipase C generates inositol 1,4,5-trisphosphate (InsP(3)) and diacyl glycerol (DAG), leading to activation of two classes of Ca(2+)-permeable light-sensitive channel, encoded by the trp and trpl genes. In some invertebrate photoreceptors, excitation is mediated by release of Ca(2+) from intracellular stores by InsP(3); however, in Drosophila melanogaster, recent evidence suggests instead that a lipid messenger, such as DAG, its metabolites and/or the reduction in PIP(2) levels, may mediate excitation. Like vertebrate rods, Drosophila melanogaster photoreceptors generate quantum bumps in response to single photons, but their kinetics is approximately 10-100 times faster, and this reflects a fundamentally different strategy incorporating a threshold, positive and negative feedback by Ca(2+) acting downstream of phospholipase C and a refractory period.
Hardie
R C
RC
Cambridge University, Department of Anatomy, Downing Street, Cambridge CB2 3DY, UK. rch14@hermes.cam.ac.uk
D000818:Animals; D001426:Bacterial Proteins / Q000502:physiology; D015220:Calcium Channels / Q000502:physiology; D002148:Calmodulin-Binding Proteins / Q000502:physiology; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology; D008565:Membrane Proteins / Q000502:physiology; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D010786:Photoreceptor Cells / Q000502:physiology; D015398:Signal Transduction; D050052:TRPC Cation Channels; D015534:Trans-Activators; D050051:Transient Receptor Potential Channels; D010738:Type C Phospholipases / Q000378:metabolism; D014785:Vision, Ocular
D001426:Bacterial Proteins; D015220:Calcium Channels; D002148:Calmodulin-Binding Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D008565:Membrane Proteins; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols; D050052:TRPC Cation Channels; D015534:Trans-Activators; D050051:Transient Receptor Potential Channels; C074192:trpl protein, Drosophila; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins