Periodic Reporting for period 1 - FLYghtCaRe (Ca2+ feedback control of TRP/TRPL channels in Drosophila photoreceptors)
Período documentado: 2015-11-01 hasta 2017-10-31
We also measured the dynamic changes in Ca2+ underlying these processes using genetically encoded fluorescent Ca2+ indicators (GECIs) expressed in the photoreceptors. Fluorescent signals were measured both from dissociated cells and also in vivo in intact flies by imaging the rhabdomeres through the fly’s own optics. We thus provided the first quantitative measurements of Ca2+ in Drosophila photoreceptors in both wild-type flies and in a range of mutants in which Ca2+ homeostasis is altered.
Most of the Ca2+ signal derives from influx through the TRP and TRPL ion channels; however, in Ca2+ free bath, smaller and slower light-induced Ca2+ rises are still detectable in dissociated photoreceptors. The source of this has been debated for years and was recently proposed to be due to light-induced release from internal Ca2+ stores. By expressing our GECIs in different mutants we showed conclusively that this was not the case. Instead, we found it was due to a membrane transporter (“sodium/calcium exchanger”) which normally protects the cells from Ca2+ overload by extruding Ca2+ in exchange for sodium, (usually highest outside the cell). However, in Ca2+ free bath the lack of negative feedback results in a massive influx of sodium ions, which drives the transporter in reverse and paradoxically increases Ca2+.