Stimulus Perception and Membrane Excitation in Unicellular Alga Chlamydomonas
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Chlamydomonas cells display various Ca2+-dependent behavioral responses against environmental stimuli to find a better place for proliferation. The cells show phototaxis to move toward a light condition suitable for photosynthesis and also display photophobic response to avoid excessive light. The flagellar motility during phototaxis and photophobic response is controlled by changes in intraflagellar Ca2+ concentration. Ca2+ influx on photophobic response is brought about by voltage-dependent calcium channel, CAV2. Avoiding reaction, which occurs on collision to obstacles, is triggered by mechanosensitive channel TRP11, a member of transient receptor potential channels, subfamily V. Elimination of the CAV2 localization in the flagellar proximal region prevents untimely activation of Ca2+-dependent flagellar excision machinery at flagellar base. By contrast, false activation TRP11 by the flagellar bending motion is kept to minimum by targeting TRP11 to the proximal region of flagella. A set of Ca2+-dependent processes performed by flagella is coordinated by various ion channels that show specific distribution along the length of flagella.
KeywordsTransient Receptor Potential Channel Transmembrane Segment TRPV Channel Mechanosensitive Channel Swimming Direction
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