Wright M V, Frantz M, Van Houten J L
Department of Zoology, University of Vermont, Burlington 05405.
Biochim Biophys Acta. 1992 Jun 30;1107(2):223-30. doi: 10.1016/0005-2736(92)90408-e.
Paramecia respond to environmental stimuli by altering swimming behavior to disperse from or accumulate in the vicinity of the stimulus. We have found, using the T-maze assay, that treatment of paramecia with LiCl in a time- and concentration-dependent manner modifies the normal response to folate, acetate, and lactate from attraction to no response or even repulsion. Responses to NH4Cl were unaffected and to cAMP were variably affected by LiCl. Cells incubated in the presence of K+, or both Na+ and K+, but not Na+ alone reliably recovered attraction to folate. Treatment of cells with 4 mM LiCl for 1 h dramatically slowed swimming speed from about 1 mm/s in NaCl or KCl (control) to 0.18 mm/s in LiCl. Li-treated cells subsequently incubated in 4 mM NaCl, KCl or sequentially in KCl and NaCl for a total of 20 min increased their swimming speed to 0.35, 0.45 and 0.67 mm/s, respectively. Paramecia readily took up Li+ in Na(+)- and K(+)-free media reaching intracellular concentrations of 5-10 mM in 10 mM extracellular Li+. Efflux of intracellular Li+ was stimulated 35% by extracellular 10 mM NaCl and 185% by 10 mM KCl over 10 mM choline chloride. Incubation of cells in 10 mM LiCl for 1 h inhibited the rate of Ca2+ efflux by 44% compared to cells in 10 mM NaCl. This may relate to the mechanism by which Li+ perturbs chemoresponse. A mutant with defects in Ca homeostasis responds normally to NH4Cl, but not to any of the stimuli that are affected by LiCl.
草履虫通过改变游动行为对环境刺激做出反应，以从刺激源附近分散或聚集在其附近。我们使用T迷宫试验发现，用氯化锂处理草履虫时，其对叶酸、乙酸盐和乳酸盐的正常反应会随时间和浓度而改变，从吸引变为无反应甚至排斥。对氯化铵的反应不受影响，对环磷酸腺苷（cAMP）的反应则受到氯化锂不同程度的影响。在钾离子或钠离子与钾离子同时存在的情况下孵育的细胞能可靠地恢复对叶酸的吸引力，而仅在钠离子存在下孵育的细胞则不能。用4 mM氯化锂处理细胞1小时会使游动速度从氯化钠或氯化钾（对照）中的约1毫米/秒显著减慢至氯化锂中的0.18毫米/秒。随后在4 mM氯化钠、氯化钾中或依次在氯化钾和氯化钠中孵育20分钟的经锂处理的细胞，其游动速度分别提高到0.35、0.45和0.67毫米/秒。草履虫在无钠和无钾的培养基中很容易摄取锂离子，在细胞外10 mM锂离子的情况下，细胞内浓度可达5 - 10 mM。与10 mM氯化胆碱相比，细胞外10 mM氯化钠刺激细胞内锂离子外流35%，10 mM氯化钾刺激185%。与在10 mM氯化钠中的细胞相比，在10 mM氯化锂中孵育1小时的细胞，其钙离子外流速率被抑制了44%。这可能与锂离子扰乱化学感受反应的机制有关。一个钙稳态存在缺陷的突变体对氯化铵反应正常，但对任何受氯化锂影响的刺激都无反应。
