Meeting Abstract

61.1  Thursday, Jan. 6  Biochemical responses of Limulus photoreceptors to darkness with and without circadian clock input BATTELLE, B-A*; PARKER, A; GADDIE, C; KEMPLER, K; Whitney Laboratory , Univ. of Florida; Whitney Laboratory, Univ. of Florida; Whitney Labortory, Univ. of Florida; Whitney Laboratory, Univ of Florida battelle@whitney.ufl.edu

Limulus lateral eyes (LEs) are more sensitive to light at night due, in part, to signals from a central circadian clock that reach LEs via a neural projection through the optic nerves. Clock input is silent during the day, activates at dusk and remains active until dawn. LE sensitivity increases at dusk, is maximum about 30min after sunset and remains high throughout the night. Increased sensitivity is thought largely caused by clock driven changes in ommatidial structure. But photoreceptor biochemistry also changes day to night in ways anticipated to increase sensitivity and responsiveness. Opsin levels in the rhabdom (RhOps) increase day to night, and clock input is required to achieve normal nighttime RhOps levels. Testing further the role of clock in regulating RhOps, we asked whether darkness during the day, when clock input to LEs is silent, changed RhOps as does darkness during the night when clock input is active. We found that RhOps increased following 4hr of darkness during the day, but only to the extent observed during the night in clockless eyes. These findings confirm that the clock regulates RhOps and indicate that for RhOps, dark-adaptation during the day is not equivalent to dark-adaptation during the night. However, we also found that at dusk the normal rise in RhOps is not sufficiently rapid to contribute to the rapid rise in retinal sensitivity. Levels of rhabdomeral arrestin (RhArr), the protein which terminates phototransduction, also change day to night. RhArr is high during the day and low during the night. During the day in the dark, RhArr falls rapidly to near nighttime levels, and it falls rapidly during dusk to near nighttime levels by 30 min after sunset whether or not the eye received clock input. Thus, while clock input influences RhOps levels, it does not influence RhArr levels. Supported by NSF-REU Site grant to Whitney Lab