Varecka L, Smigán P, Greksák M
Department of Biochemistry and Microbiology, Slovak Technical University, Bratislava, Slovak Republic.
FEBS Lett. 1996 Dec 9;399(1-2):171-4. doi: 10.1016/s0014-5793(96)01297-5.
The effects of monovalent cations (Na+, K+ and choline+) and the uncoupler 3,3',4',5-tetrachlorosalicylanilide (TCS) were tested on 45Ca2+ uptake by non-energized cells of Methanobacterium thermoautotrophicum. 45Ca2+ uptake was stimulated by the addition of K+ and (less) by choline+ while Na+ slowed down and even reversed it, thereby mimicking the energization of cells. The uncoupler agent, TCS, suppressed 45Ca2+ uptake in non-energized cells in the presence or absence of Na+ but in cells energized in an atmosphere of CO2+H2 it exerted a stimulating effect. Uncoupled 45Ca2+ efflux was measured in cells pre-loaded with 45Ca2+ by means of the divalent ionophore A23187 following its washing out by buffer containing serum albumin. The efflux was temperature-dependent and was stimulated by external 40Ca2+ and Na+. In the absence of Na+, the uncoupled efflux was completely inhibited by TCS, whereas in the presence of Na+, TCS was without any effect. The results are in agreement with the model in which the Ca2+ influx pathway is represented by a membrane potential-driven uniport whereas Ca2+ efflux is mediated by two transport systems - Na+/Ca2+ and H+/Ca2+ antiporters - whose participation in the total efflux is dependent on the energy of the corresponding gradients of driving ions.
测试了单价阳离子（Na⁺、K⁺和胆碱⁺）以及解偶联剂3,3',4',5-四氯水杨酰苯胺（TCS）对嗜热自养甲烷杆菌非活性细胞摄取⁴⁵Ca²⁺的影响。添加K⁺刺激了⁴⁵Ca²⁺的摄取，胆碱⁺的刺激作用较小，而Na⁺则减缓甚至逆转了这种摄取，从而模拟了细胞的能量化过程。解偶联剂TCS在有无Na⁺的情况下均抑制非活性细胞摄取⁴⁵Ca²⁺，但在CO₂ + H₂气氛中能量化的细胞中，它发挥了刺激作用。在通过含血清白蛋白的缓冲液洗脱出预加载有⁴⁵Ca²⁺的细胞后，借助二价离子载体A23187测量了非偶联的⁴⁵Ca²⁺外流。外流是温度依赖性的，并且受到外部⁴⁰Ca²⁺和Na⁺的刺激。在没有Na⁺的情况下，非偶联外流被TCS完全抑制，而在有Na⁺的情况下，TCS没有任何作用。这些结果与以下模型一致：Ca²⁺内流途径由膜电位驱动的单向转运体代表，而Ca²⁺外流由两个转运系统介导——Na⁺/Ca²⁺和H⁺/Ca²⁺反向转运体——它们在总外流中的参与取决于驱动离子相应梯度的能量。
