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Journal of Experimental Biology 137,477-485 (1988)
Published by Company of Biologists 1988

Photoreceptor Potential Causing Phototaxis of Paramecium Bursaria

Kohji Matsuoka ¹ and Yasuo Nakaoka ¹

¹ Department of Biophysical Engineering, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka, Japan 560

To whom reprint requests should be addressed.

Paramecium bursaria shows phototaxis by accumulating in a lighted region. Intracellular recordings from both chlorella-containing and chlorella-free cells showed that a step-increase in the light intensity induced a steady depolarization of membrane potential, and a step-down caused recovery to the original level. The action spectrum of the depolarization corresponded to that for phototaxis, and showed two peaks at 420 and 560 nm. The amplitude of the depolarization became larger as light intensity was increased. Cells which accumulated in a lighted spot decreased their swimming velocity or stayed in the same place. As the light intensity was increased from dark, swimming velocity decreased and became zero at the intensity at which the cell showed the most noticeable photoaccumulation. Further increase in light intensity produced an increase in swimming velocity. The degree of photoaccumulation was inversely proportional to the swimming velocity. These results suggest that a step-increase in light intensity induces the steady depolarization and causes the decrease in swimming velocity, resulting in accumulation of cells in the lighted region.

Key words: Paramecium bursaria, photoreceptor, membrane potential, action spectrum, phototaxis.

Accepted on February 3, 1988

This article has been cited by other articles:

				C. H. Johnson, I. Miwa, T. Kondo, and J. W. Hastings Circadian Rhythm of Photoaccumulation in Paramecium bursaria J Biol Rhythms, December 1, 1989; 4(4): 405 - 415. [Abstract] [PDF]