A photoreceptor cell responds to light in a series of steps. In the vertebrate eye, cyclic GMP is a compound in the photoreceptors that increases in internal concentration when the cell is illuminated. The increased concentration of cGMP then triggers opening of channels in the cell membrane that allow ions to cross it. Since the ions carry electrical charge, their movement produces the electrical event called the receptor potential. Very little is known about the light-dependent cation channel in photoreceptors of invertebrates, although invertebrates offer the promise of understanding the genetic basis for the development and regulation of this important feature. The fruit fly, Drosophila, is well-known for its use in genetic studies, and a wide variety of mutant strains are available. This project will study light-dependent cation channel in flies, using a newly developed preparation in vitro that allows access to cell membranes for the electrophysiological technique of patch-clamp recording. The properties of channel opening and closing will be established and compared with those for vertebrate photoreceptors. Biochemical compounds will identified that control the opening of the channel to compare to the cGMP role in the vertebrate photoreceptors. Visual mutants of Drosophila will be screened to identify possible genes that determine the structure or function of the genes controlling this important membrane component. This work will lead directly to the promise of genetic manipulation allowing structural analysis of these channels; such analysis of proteins important in sensory transduction will have substantial impact on all sensory science.
