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Calcium signalling in $\textit{Drosophila}$ photoreceptors measured with GCaMP6f

Published version
Peer-reviewed

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Authors

Asteriti, S 
Liu, C-H 
Hardie, RC 

Abstract

Drosophila phototransduction is mediated by phospholipase C leading to activation of cation channels (TRP and TRPL) in the 30000 microvilli forming the light-absorbing rhabdomere. The channels mediate massive Ca2+ influx in response to light, but whether Ca2+ is released from internal stores remains controversial. We generated flies expressing GCaMP6f in their photoreceptors and measured Ca2+ signals from dissociated cells, as well as in vivo by imaging rhabdomeres in intact flies. In response to brief flashes, GCaMP6f signals had latencies of 10–25 ms, reached 50% Fmax with 1200 effectively absorbed photons and saturated (ΔF/F0 10–20) with 10000–30000 photons. In Ca2+ free bath, smaller (ΔF/F0 4), long latency ( 200 ms) light-induced Ca2+ rises were still detectable. These were unaffected in InsP3 receptor mutants, but virtually eliminated when Na+ was also omitted from the bath, or in trpl;trp mutants lacking light-sensitive channels. Ca2+ free rises were also eliminated in Na+/Ca2+ exchanger mutants, but greatly accelerated in flies over-expressing the exchanger. These results show that Ca2+ free rises are strictly dependent on Na+ influx and activity of the exchanger, suggesting they reflect re-equilibration of Na+/Ca2+ exchange across plasma or intracellular membranes following massive Na+ influx. Any tiny Ca2+ free rise remaining without exchanger activity was equivalent to <10 nM (ΔF/F0 0.1), and unlikely to play any role in phototransduction.

Description

Keywords

Calcium imaging, genetically encoded calcium indicators, InsP(3), Na/Ca exchanger, phospholipase C, phototransduction, TRP channels

Journal Title

Cell Calcium

Conference Name

Journal ISSN

0143-4160
1532-1991

Volume Title

Publisher

Elsevier
Sponsorship
Biotechnology and Biological Sciences Research Council (BB/M007006/1)
Biotechnology and Biological Sciences Research Council (BB/J009253/1)
European Commission Horizon 2020 (H2020) Marie Sk?odowska-Curie actions (658818)
The authors thank Dr Marten Postma for comments on the MS. This project received funding from the Biotechnology and Biological Sciences Research Council (BB/M00706/1 and BB/J009253/1; RCH, C-HL) and Horizon 2020 “European Union’s Horizon 2020 research and innovation programme under grant agreement No (658818-FLYghtCaRe RCH, SA).