PMID:16005297

Citation	Gu, Y, Oberwinkler, J, Postma, M and Hardie, RC (2005) Mechanisms of light adaptation in Drosophila photoreceptors. Curr. Biol. 15:1228-34
Abstract	Phototransduction in Drosophila is mediated by a phospholipase C (PLC) cascade culminating in activation of transient receptor potential (TRP) channels. Ca(2+) influx via these channels is required for light adaptation, but although several molecular targets of Ca(2+)-dependent feedback have been identified, their contribution to adaptation is unclear. By manipulating cytosolic Ca(2+) via the Na(+)/Ca(2+) exchange equilibrium, we found that Ca(2+) inhibited the light-induced current (LIC) over a range corresponding to steady-state light-adapted Ca(2+) levels (0.1-10 microM Ca(2+)) and accurately mimicked light adaptation. However, PLC activity monitored with genetically targeted PIP(2)-sensitive ion channels (Kir2.1) was first inhibited by much higher (>/= approximately 50 microM) Ca(2+) levels, which occur only transiently in vivo. Ca(2+)-dependent inhibition of PLC, but not the LIC, was impaired in mutants (inaC) of protein kinase C (PKC). The results indicate that light adaptation is primarily mediated downstream of PLC and independently of PKC by Ca(2+)-dependent inhibition of TRP channels. This is interpreted as a strategy to prevent inhibition of PLC by global steady-state light-adapted Ca(2+) levels, whereas rapid inhibition of PLC by local Ca(2+) transients is required to terminate the response and ensures that PIP(2) reserves are not depleted during stimulation.
Links	PubMed Online version:10.1016/j.cub.2005.05.058
Keywords	Adaptation, Ocular/physiology; Animals; Calcium/metabolism; Calcium Channels/metabolism; Drosophila/physiology; Drosophila Proteins/metabolism; Electrophysiology; Mutation/genetics; Phosphatidylinositol 4,5-Diphosphate/metabolism; Photoreceptor Cells, Invertebrate/physiology; Potassium Channels, Inwardly Rectifying/metabolism; Protein Kinase C/genetics; Protein Kinase C/metabolism; Sodium/metabolism; Transient Receptor Potential Channels; Type C Phospholipases/metabolism; Vision, Ocular/physiology
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