The unicellular protozoan ciliate, Stentor coeruleus, is able to sense differences in light intensity and wavelength, being most sensitive to red light (610 nm). Stentor also senses the direction of light propagation, as evidenced by their light-avoiding and negative phototactic swimming behaviors. This aneural photosensory phenomenon is triggered by the photoreceptor, and the proposed work involves the elucidation of how the organism perceives the light signal and processes it for subsequent sensory transduction of the light energy into behavioral responses. In particular, we propose to study the possible involvement of a light-induced proton release from the photoreceptor as a primary mechanism of light-signal processing. The primary sensory signal, in the form of proton release, triggers subsequent transduction steps that include calcium ion influx from the extracellular medium. It is proposed that the calcium ion influx causes the Stentor cell to reverse its ciliary beating and subsequently turn away from the light source. The present project is aimed at elucidating the mechanisms of these various transduction steps and their functional network in the photoresponse of Stentor coeruleus. For this aim, the photoreceptor protein will be further characterized, and its primary photoprocess will be elucidated spectroscopically in both H20 and D20. The nature of calcium channel(s) and Ca2+-pump involved in the ciliary reversal will also be characterized.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
Project #
Application #
Study Section
Biophysics and Biophysical Chemistry A Study Section (BBCA)
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Texas Tech University
Schools of Arts and Sciences
United States
Zip Code
Dai, R; Yamazaki, T; Yamazaki, I et al. (1995) Initial spectroscopic characterization of the ciliate photoreceptor stentorin. Biochim Biophys Acta 1231:58-68
Fabczak, H; Park, P B; Fabczak, S et al. (1993) Photosensory transduction in ciliates. II. Possible role of G-protein and cGMP in Stentor coeruleus. Photochem Photobiol 57:702-6
Fabczak, S; Fabczak, H; Tao, N et al. (1993) Photosensory transduction in ciliates. I. An analysis of light-induced electrical and motile responses in Stentor coeruleus. Photochem Photobiol 57:696-701
Fabczak, H; Fabczak, S; Song, P S et al. (1993) Photosensory transduction in ciliates. Role of intracellular pH and comparison between Stentor coeruleus and Blepharisma japonicum. J Photochem Photobiol B 21:47-52
Fabczak, H; Tao, N; Fabczak, S et al. (1993) Photosensory transduction in ciliates. IV. Modulation of the photomovement response of Blepharisma japonicum by cGMP. Photochem Photobiol 57:889-92
Yamazaki, T; Yamazaki, I; Nishimura, Y et al. (1993) Time-resolved fluorescence spectroscopy and photolysis of the photoreceptor blepharismin. Biochim Biophys Acta 1143:319-26
Song, P S; Kim, I H; Florell, S et al. (1990) Structure and function of the photoreceptor stentorins in Stentor coeruleus. II. Primary photoprocess and picosecond time-resolved fluorescence. Biochim Biophys Acta 1040:58-65
Kim, I H; Rhee, J S; Huh, J W et al. (1990) Structure and function of the photoreceptor stentorins in Stentor coeruleus. I. Partial characterization of the photoreceptor organelle and stentorins. Biochim Biophys Acta 1040:43-57
Iwatsuki, K; Song, P S (1989) The ratio of extracellular Ca2+ to K+ ions affects the photoresponses in Stentor coeruleus. Comp Biochem Physiol A Comp Physiol 92:101-6
Hong, C B; Prusti, R K; Song, P S (1987) Light-adaptation in the photophobic response by Stentor coeruleus. Arch Microbiol 147:117-20

Showing the most recent 10 out of 13 publications