Condrescu M, Rojas H, Gerardi A, DiPolo R, Beaugé L
Centro de Biofisica y Bioquímica, IVIC, Caracas, Venezuela.
Biochim Biophys Acta. 1990 May 9;1024(1):198-202. doi: 10.1016/0005-2736(90)90226-e.
Squid axons display a high activity of Na+/Ca2+ exchange which is largely increased by the presence of external K+, Li+, Rb+ and NH+4. In this work we have investigated whether this effect is associated with the cotransport of the monovalent cation along with Ca2+ ions. 86Rb+ influx and efflux have been measured in dialyzed squid axons during the activation (presence of Ca2+i) of Ca2+o/Na+i and Ca2+i/Ca2+o exchanges, while 86Rb+ uptake was determined in squid optic nerve membrane vesicles under equilibrium Ca2+/Ca2+ exchange conditions. Our results show that although K+o significantly increases Na+i-dependent Ca2+ influx (reverse Na+/Ca2+ exchange) and Rb+i stimulates Ca2+o-dependent Ca2+ efflux (Ca2+/Ca2+ exchange), no sizable transport of rubidium ions is coupled to calcium movement through the exchanger. Moreover, in the isolated membrane preparation no 86Rb+ uptake was associated with Ca2+/Ca2+ exchange. We conclude that in squid axons although monovalent cations activate the Na+/Ca2+ exchange they are not cotransported.
鱿鱼轴突表现出较高的Na⁺/Ca²⁺交换活性，外部K⁺、Li⁺、Rb⁺和NH₄⁺的存在会使其大幅增加。在这项工作中，我们研究了这种效应是否与单价阳离子和Ca²⁺离子的协同转运有关。在Ca²⁺外/Na⁺内和Ca²⁺内/Ca²⁺外交换激活（存在细胞内Ca²⁺）期间，测量了透析鱿鱼轴突中的⁸⁶Rb⁺流入和流出，而在平衡Ca²⁺/Ca²⁺交换条件下，测定了鱿鱼视神经膜囊泡中的⁸⁶Rb⁺摄取。我们的结果表明，尽管细胞外K⁺显著增加了依赖Na⁺内的Ca²⁺流入（反向Na⁺/Ca²⁺交换），且Rb⁺内刺激了依赖Ca²⁺外的Ca²⁺流出（Ca²⁺/Ca²⁺交换），但铷离子没有大量的转运与通过交换器的钙移动偶联。此外，在分离的膜制剂中，没有⁸⁶Rb⁺摄取与Ca²⁺/Ca²⁺交换相关。我们得出结论，在鱿鱼轴突中，尽管单价阳离子激活了Na⁺/Ca²⁺交换，但它们不是协同转运的。
