Preston R R, Hammond J A
Department of Physiology, Allegheny University of the Health Sciences, Philadelphia, Pennsylvania 19129, USA.
Genetics. 1997 Jul;146(3):871-80. doi: 10.1093/genetics/146.3.871.
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.
已分离出三株对镁敏感性增强的四膜虫突变株。这些新的“变色龙”突变体是由单个基因座Cha上的部分或共显性突变产生的。野生型在5 mM Mg2+作用下会向后游动10 - 15秒，而Cha突变体则会向后游动约30秒。电生理分析表明，这种行为可能是由于膜兴奋后Mg(2+)特异性离子电导失活速率减慢所致。这与观察到的Cha突变体对镍中毒敏感性增加是一致的，因为Ni2+也能够通过该途径进入细胞。更广泛的行为分析表明，Cha细胞对Na+也有过度反应，但没有证据表明细胞内Ca2+稳态存在缺陷，而这种缺陷可能解释Mg2+和Na+电导的同时增强。文中考虑了Cha基因座可能编码Mg(2+)和Na(+)通透性的特定调节因子的可能性。
