Calcium signalling in Drosophila photoreceptors measured with GCaMP6f.

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 10-25ms, reached 50% F_max with ?1200 effectively absorbed photons and saturated (?F/F₀?10-20) with 10000-30000 photons. In Ca²⁺ free bath, smaller (?F/F₀ ?4), long latency (?200ms) 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 <10nM (?F/F₀ ?0.1), and unlikely to play any role in phototransduction.

SUBMITTER: Asteriti S 

PROVIDER: S-EPMC5472182 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature