Abstract
Phototransduction in Drosophila's microvillar photoreceptors is mediated by phospholipase C (PLC) resulting in activation of two distinct Ca(2+)-permeable channels, TRP and TRPL. Here we review recent evidence on the unresolved mechanism of their activation, including the hypothesis that the channels are mechanically activated by physical effects of PIP2 depletion on the membrane, in combination with protons released by PLC. We also review molecularly explicit models indicating how Ca(2+)-dependent positive and negative feedback along with the ultracompartmentalization provided by the microvillar design can account for the ability of fly photoreceptors to respond to single photons 10-100× more rapidly than vertebrate rods, yet still signal under full sunlight.
