Calcium Transients in the Rhabdomeres of Dark- and Light-Adapted Fly Photoreceptor Cells

The light response of fly photoreceptor cells is modulated by changes in free Ca2+ concentration. Fly phototransduction and most processes regulating it take place in or very close to the rhabdomere. We therefore measured the kinetics and the absolute values of the free Ca2+ concentration in the rhabdomere of fly photoreceptor cells in vivo by making use of the natural optics of the fly’s eye. We show that Ca2+ flowing into the rhabdomere after light stimulation of dark-adapted cells causes fast Ca2+ transients that reach peak values higher than 200 µM in