In Drosophila photoreceptor cells, Ca2+ exerts regulatory functions that control the shape, duration, and amplitude of the light response. Ca2+ also orchestrates light adaptation allowing Drosophila to see in light intensity regimes that span several orders of magnitude ranging from single photons to bright sunlight. The prime source for Ca2+ elevation in the cytosol is Ca2+ influx from the extracellular space through light-activated TRP channels. This Ca2+ influx is counterbalanced by constitutive Ca2+ extrusion via the Na+/Ca2+ exchanger, CalX. The light-triggered rise in intracellular Ca2+ exerts its regulatory functions through interaction with about a dozen well-characterized Ca2+ and Ca2+/CaM binding proteins. In this review we will discuss the dynamic changes in Ca2+ concentration upon illumination of photoreceptor cells. We will present the proteins that are known to interact with Ca2+ (/CaM) and elucidate the physiological functions of these interactions.
Keywords: Arrestin; Calcium signaling; Drosophila; Light adaptation; Phospholipase C; Phototransduction; Protein kinase C; Rhodopsin; TRP channel; Vision.