Stentor coeruleus, a unicellular hetrotrich,possesses both light intensity-and color (wavelength)-sensory """"""""visions"""""""", representing the first clearly identifiable """"""""visual sensory system"""""""" based on stentorin as the photoreceptor,as an alternative to the well established rhodospin-based visual sensory system in higher animals. This aneural organism is also able to perceive the direction of light propagation. Light sensing is manifested in the form of ciliary beat reversal by the organism. The photosensory process in this cell can be described schematically as follows: Light signal to Absorption by photoreceptor to Signal generation and amplification to Response (ciliary stroke reversal) We propose to study the possible involvement of a light-induced proton release (ph change) from the photoreceptor as a primary mechanism for the generation of a light signal. The initial signal in the form of proton release from the photoreceptor complexes has been suggested to trigger subsequent transduction steps that include calcium ion influx from the extracellular medium,thus amplifying the initial light signal. It is proposed that the calcium ion influx causes stentor cell to reverse the ciliary beat direction and subsequently steer away from the harmful light source. Specifically, we plan to elucidate the mechanisms of the key sensory transduction steps. The photoreceptor stentorin will be isolated and further characterized,and its primary photoprocesses in solution and in the photoreceptor organelle (pigment granule) as well as in the intact cell will be investigated. The role of proton release from the excited state of stentorin as an initial sensory signal (a ph change-evoked receptor potential) will be illustrated by using ph probes in the pigment granule-entrapped liposomes and in vivo. We propose that a transient intracellular ph drop resulting from the proton release from pigment granules serves as an electrical signal to open calcium in the cell/ciliary membranes. The influx of calcium ions then trigger a ciliary beat reversal. This hypothesis will be further tested in the present study.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS015426-14
Application #
3396242
Study Section
Visual Sciences A Study Section (VISA)
Project Start
1987-12-01
Project End
1994-11-30
Budget Start
1992-12-01
Budget End
1993-11-30
Support Year
14
Fiscal Year
1993
Total Cost
Indirect Cost
Name
University of Nebraska Lincoln
Department
Type
Schools of Arts and Sciences
DUNS #
555456995
City
Lincoln
State
NE
Country
United States
Zip Code
68588
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

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