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Inhibition of Mg2+ current by single-gene mutation in Paramecium

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Abstract

“Eccentric” is a newly-isolated mutant of Paramecium tetraurelia that fails to swim backwards in response to Mg2+. In the wild type, this backward swimming results from Mg2+ influx via a Mg2+-specific ion conductance (I Mg. Voltage-clamp analysis confirmed that, as suspected, step changes in membrane potential over a physiological range fail to elicit I Mg from eccentric.

Further electrophysiological investigation revealed a number of additional ion-current defects in eccentric: (i) The Ca2+ current activated upon depolarization inactivates more slowly in eccentric than in the wild type, and it requires longer to recover from this inactivation. (ii) The Ca2+-dependent Na+ current deactivates significantly faster in the mutant, (iii) The two K+ currents observed upon hyperpolarization are reduced by >60% in eccentric.

It is difficult to envision how these varied pleiotropic effects could result from loss of a single ion current. Rather, they suggest that the eccentric mutation affects a global regulatory system. Two plausible hypotheses are discussed.

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Authors and Affiliations

  1. Laboratory of Molecular Biology, University of Wisconsin-Madison, 53706, Madison, Wisconsin

    R. R. Preston & C. Kung

  2. Department of Genetics, University of Wisconsin-Madison, 53706, Madison, Wisconsin

    C. Kung

Authors
  1. R. R. Preston
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  2. C. Kung
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We are grateful to Dr. Yoshiro Saimi for his comments and suggestions on this work, and for the support of the Lucille P. Markey Charitable trust and the National Institutes of Health (GM22714 and GM38646).

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Preston, R.R., Kung, C. Inhibition of Mg2+ current by single-gene mutation in Paramecium . J. Membarin Biol. 139, 203–212 (1994). https://doi.org/10.1007/BF00232624

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