Richard Payne
Professor, Dept. Biology. 
Left: A photoreceptor cell from the ventral eye of the horseshoe crab, Limulus polyphemus. Right:  This is a movie of a Limulus ventral photoreceptor releasing calcium during a flash of light. A red color means a high calcium ion concentration, blue means less. On the left is an image of the cell and on the right is a profile of calcium dye fluorescence along the length of the cell. The light flash begins at the time of the first frame, when the cell's image first appears.
Dr. Payne investigates mechanisms of visual excitation in photoreceptors. The research concentrates on messenger molecules released by light inside photoreceptor cells. These messengers mediate and modulate the electrical response of the photoreceptor to light. One messenger under investigation is inositol trisphosphate, which releases calcium from internal stores within a wide range of animal and plant cells. When injected into the giant photoreceptors of the horseshoe crab, inositol trisphosphate mimics excitation of the cell by light. Biochemical studies have shown that light releases inositol trisphosphate from the photoreceptor's membrane into the cell interior. These giant photoreceptors are one of the few living cells in which the actions of this important messenger can be easily studied. 

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