POL: P&P Abstract VOL 65:PG 902

The Photodynamic Action of Methylene Blue on the Ion Channels of Paramecium Causes Cell Damage

Fumihito Saitow¹,² and Yasuo Nakaoka*¹

¹Department of Biophysical Engineering, Osaka University, Osaka, Japan
²International Institute for Advanced Research, Matsushita Electric Industrial Co., Ltd., Kyoto, Japan

*To whom correspondence should be addressed at: Department of Biophysical Engineering, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560, Japan. Fax: 81 6 850 6557; e-mail: nakaoka@bpe.es.osaka-u.ac.jp.


The photodynamic effects of methylene blue (MB) on wild-type and mutant strains of Paramecium were studied. From measurements of survival and cell motility under the continuous application of light in the presence of MB, the mutant strains remained alive for about three times longer than the wild-type strain. Although the resting potential of the mutant cells was similar to that of wild-type cells, the continuous photodynamic action shifted the membrane potentials of the mutant and wild-type cells to a depolarized level and a hyperpolarized level, respectively, from that before light application. Under voltage clamping, the mutant cells reduced not only the outward current elicited by the photodynamic action but also the outward tail current elicited by the preceding pulse of hyperpolarization. We conclude that the mutant strain is defective in the activation of Ca2+-dependent K+ channels. This defect might cause a reduction in the Ca2+ influx because of the suppression of the membrane hyperpolarization, which results in the elongation of survival time under the photodynamic action.

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