CALMODULIN REGULATION OF CALCIUM STORES IN PHOTOTRANSDUCTION OF DROSOPHILA

Phototransduction in Drosophila occurs through the ubiquitous phosphoi nositide-mediated signal transduction system. Major unresolved questio ns in this pathway are the identity and role of the internal calcium s tores in light excitation and the mechanism underlying regulation of C a2+ release from internal stores. Treatment of Drosophila photorecepto rs with ryanodine and caffeine disrupted the current induced by light, whereas subsequent application of calcium-calmodulin (Ca-CaM) rescued the inactivated photoresponse. In calcium-deprived wild-type Drosophi la and in calmodulin-deficient transgenic flies, the current induced b y light was disrupted by a specific inhibitor of Ca-CaM. Furthermore, inhibition of Ca-CaM revealed light-induced release of calcium from in tracellular stores. It appears that functional ryanodine-sensitive sto res are essential for the photoresponse. Moreover, calcium release fro m these stores appears to be a component of Drosophila phototransducti on, and Ca-CaM regulates this process.