Neuron
Volume 59, Issue 5, 11 September 2008, Pages 778-789
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Article
Ca2+-Dependent Metarhodopsin Inactivation Mediated by Calmodulin and NINAC Myosin III

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Summary

Phototransduction in flies is the fastest known G protein-coupled signaling cascade, but how this performance is achieved remains unclear. Here, we investigate the mechanism and role of rhodopsin inactivation. We determined the lifetime of activated rhodopsin (metarhodopsin = M) in whole-cell recordings from Drosophila photoreceptors by measuring the time window within which inactivating M by photoreisomerization to rhodopsin could suppress responses to prior illumination. M was inactivated rapidly (τ ∼20 ms) under control conditions, but ∼10-fold more slowly in Ca2+-free solutions. This pronounced Ca2+ dependence of M inactivation was unaffected by mutations affecting phosphorylation of rhodopsin or arrestin but was abolished in mutants of calmodulin (CaM) or the CaM-binding myosin III, NINAC. This suggests a mechanism whereby Ca2+ influx acting via CaM and NINAC accelerates the binding of arrestin to M. Our results indicate that this strategy promotes quantum efficiency, temporal resolution, and fidelity of visual signaling.

MOLNEURO
SYSNEURO

Cited by (0)

3

Present address: Section Computational Science, Faculty of Science, University of Amsterdam, Kruislaan 403,1098 SJ Amsterdam, The Netherlands

4

Present address: Division of Biological Sciences, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, Japan 466-8601