Phenotypic and genetic analysis of "Chameleon," a paramecium mutant with an enhanced sensitivity to magnesium.
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 Mg2+ by swimming backward for 10-15 sec, Cha mutants responded with approximately 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 Ni2+ 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 Ca2+ homeostasis that might account for a simultaneous enhancement of both the Mg2+ and Na+ conductances. The possibility that the Cha locus may encode a specific regulator of the Mg(2+)- and Na(+)-permeabilities is considered.
Preston
R R
RR
Department of Physiology, Allegheny University of the Health Sciences, Philadelphia, Pennsylvania 19129, USA. preston@allegheny.edu
Hammond
J A
JA
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004351:Drug Resistance; D004594:Electrophysiology; D008274:Magnesium / Q000494:pharmacology*; D009154:Mutation; D009532:Nickel / Q000494:pharmacology; D016805:Paramecium tetraurelia / Q000187:drug effects / Q000235:genetics* / Q000502:physiology; D010641:Phenotype
D009532:Nickel; D008274:Magnesium; D002118:Calcium