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First published online August 30, 2006
Journal of Experimental Biology 209, 3580-3586 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02426
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Correlation between thermotolerance and membrane properties in Paramecium aurelia

Toshiaki Sasaki1, Yoshimi Konoha2, Taichi Toyoda2, Yuta Yasaka3, Eva Przybos4 and Yasuo Nakaoka1,*

1 Biophysical Dynamics Laboratories, Graduate School of Frontier Bioscience, Osaka University, Toyonaka, Osaka 560-8531, Japan
2 Division of Biophysical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
3 Research Center for Environmental Preservation, Osaka University, Suita, Osaka 565-0871, Japan
4 Department of Experimental Zoology, Institute of Systematics and Evolution of Animals, Polish Academy of Sciences, Slawkowska 17, 31-016 Krakow, Poland

* Author for correspondence (e-mail: nakaoka{at}bpe.es.osaka-u.ac.jp)

Accepted 3 July 2006

The relationship between thermotolerance and membrane properties was studied by using a ciliated protozoan, Paramecium aurelia. P. aurelia is a complex of sibling species termed `syngens' whose cell morphology appear similar on microscopic examination. From the comparison of tolerance to increasing temperature among 14 syngens of P. aurelia, we selected syngens 2 and 3 as low thermotolerant examples, and syngens 8 and 10 as high thermotolerant examples. The membrane resistance of high thermotolerant syngens measured by injection of a constant inward current was greater than that of low thermotolerant syngens. Membrane fluidity measurements of living cells using the fluorescent dye, 6-lauroyl-2-dimethylaminonaphtalene (laurdan) showed that the fluidity at the cultured temperature was decreased in high thermotolerant syngens compared to that of low thermotolerant syngens. However, when the temperature was increased to the killing temperature of each syngens, the fluidity was increased to almost the same level irrespective of syngen. Furthermore, analysis of fatty acids extracted from whole cells showed that the ratios of unsaturated to saturated fatty acids was smaller in high thermotolerant syngens than in low thermotolerant syngens. These results suggest that the thermotolerance of P. aurelia syngens is determined by the membrane fluidity which is related to the fatty acids composition.

Key words: thermotolerance, tonic permeability, fatty acids, membrane fluidity, laurdan fluorescence, Paramecium aurelia






© The Company of Biologists Ltd 2006