Light is detected by photoreceptor cells in the retina of the eye. Phototransduction is the process of converting the light energy into a neural signal for relay to the brain, and generally depends on activation of a phosphate-containing compound as an agent to trigger release of intracellular calcium; the free calcium in turn triggers changes in the membrane to initiate the neural signal. Biochemical mechanisms in the photoreceptors initiate and control light adaptation, which is necessary to keep the eye sensitive over a huge range of light intensities, from darkest night to brightest day. Recently some invertebrate eyes have been found to utilize phosphate compounds incorporating the inositol molecule, rather than the guanine molecule as in the vertebrate eye, and these inositol phosphates have been implicated in light adaptation. This project will use squid for a model invertebrate eye providing abundant material for biochemistry. The aims are to measure the spectral sensitivity and determine the rate and formation ratios of the inositol phosphates; to identify the subcellular location of the precursor molecules; and to study enzymes related to activity of these inositol compounds and calcium release, particularly protein kinase C that is important in many cellular activities. Results will be very important for visual physiology, other sensory transduction systems, and for other aspects of cell biology related to intracellular signalling.
