Photosensory transduction in unicellular eukaryote Blepharisma |
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Authors: | Matsuoka T Kotsuki H |
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Affiliation: | Department of Biology, Kochi University, Kochi 780-8520, Japan. tmatsuok@cc.kochi-u.ac.jp |
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Abstract: | In the ciliated protozoan Blepharisma, step-up photophobic response is mediated by a novel type of photosensory complex of pink-colored pigment "blepharismins" and 200-kDa membrane protein contained in the pigment granules located just beneath the plasma membrane. We found that the fluorescence intensity of isolated blepharismins decreased prominently with a decrease of H(+) concentration in the surrounding medium. In the present study, therefore, we utilized the endogenous pigment blepharismins as the pH indicator. Light stimulation evoked a sudden decrease in fluorescence intensity in a photosensitive anterior portion of the cell, suggesting that a drop in H(+) concentration occurred in the anterior region. The result indicates that the photosignal is transduced into cytoplasmic signaling of H(+) translocation across the outer membrane surrounding the pigment granules, so that cytosolic H(+) concentration in the vicinity of plasma membrane might be increased. |
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