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Genetics, Vol 146, 871-880, Copyright © 1997
INVESTIGATIONS |
Phenotypic and Genetic Analysis of ``Chameleon,'' a Paramecium Mutant With an Enhanced Sensitivity to Magnesium
R. R. Preston and J. A. Hammond
Department of Physiology, Allegheny University of the Health Sciences, Philadelphia, Pennsylvania 19129
Three mutant strains of Paramecium tetraurelia with an enhanced sensitivity to magnesium have been isolated. These new ``Chameleon'' mutants result from partial- or codominant mutations at a single locus, Cha. Whereas the wild type responded to 5 mM Mg(2+) by swimming backward for 10-15 sec, Cha mutants responded with ~30 sec backward swimming. Electrophysiological analysis suggested that this behavior may be caused by slowing in the rate at which a Mg(2+)-specific ion conductance deactivates following membrane excitation. This would be consistent with an observed increase in the sensitivity of Cha mutants to nickel poisoning, since Ni(2+) is also able to enter the cell via this pathway. More extensive behavioral analysis showed that Cha cells also overresponded to Na(+), but there was no evidence for a defect in intracellular Ca(2+) homeostasis that might account for a simultaneous enhancement of both the Mg(2+) and Na(+) conductances. The possibility that the Cha locus may encode a specific regulator of the Mg(2+)- and Na(+)-permeabilities is considered.
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  J. A. Hammond and R. R. Preston Isolation and Characterization of Magbane, a Magnesium-Lethal Mutant of Paramecium Genetics, July 1, 2001; 158(3): 1061 - 1069. [Abstract] [Full Text] [PDF]
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