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J Exp Biol. 2001 Oct;204(Pt 20):3403-9.

Phototransduction in Drosophila melanogaster.

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Cambridge University, Department of Anatomy, Downing Street, Cambridge CB2 3DY, UK.


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.

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