细胞外低钠对胞质游离钙的影响。钠钙交换作为肾细胞主要的钙内流途径。
Effects of low extracellular sodium on cytosolic ionized calcium. Na+-Ca2+ exchange as a major calcium influx pathway in kidney cells.
作者信息
Snowdowne K W, Borle A B
出版信息
J Biol Chem. 1985 Dec 5;260(28):14998-507.
The effects of extracellular Na+ (Na+o) on cytosolic ionized calcium (Ca2+i) and on calcium and sodium fluxes were measured in monkey kidney cells (LLC-MK2). Ca2+i was measured with aequorin and the ion fluxes with 45Ca and 22Na. Na+-free media rapidly increased Ca2+i from 60 to a maximum of about 700 nM in 2-3 min. After the peak, Ca2+i declined and reached a plateau of about twice the resting Ca2+i. The peak Ca2+i was inversely proportional to Na+o and directly proportional to the extracellular calcium concentration (Ca2+o). On the other hand, a pH of 6.8 reduced and Ca2+o substitution with Sr2+ completely blocked the Ca2+i response to low Na+o. A Na+-free medium stimulated calcium efflux from the cells 4-5-fold, a response which was abolished in the absence of extracellular Ca2+. Na+-free media also stimulated calcium influx and sodium efflux. The cell calcium content, however, was not increased. These results indicate that removal of extracellular Na+ increases Ca2+i by stimulating calcium influx and not by inhibiting calcium efflux; the increased calcium influx takes place on the Na+-Ca2+ antiporter operating in the reverse mode in exchange for sodium efflux. The increased calcium efflux occurs as a consequence of the rise in Ca2+i and presumably takes place on the (Ca2+-Mg2+) ATPase-dependent calcium pump.
在猴肾细胞（LLC-MK2）中测量了细胞外钠离子（Na⁺ₒ）对胞质游离钙离子（Ca²⁺ᵢ）以及钙和钠通量的影响。用水母发光蛋白测量Ca²⁺ᵢ，用⁴⁵Ca和²²Na测量离子通量。无钠培养基在2 - 3分钟内迅速将Ca²⁺ᵢ从60 nM增加到最大约700 nM。达到峰值后，Ca²⁺ᵢ下降并达到约为静息Ca²⁺ᵢ两倍的平台期。峰值Ca²⁺ᵢ与Na⁺ₒ成反比，与细胞外钙浓度（Ca²⁺ₒ）成正比。另一方面，pH值为6.8会降低Ca²⁺ᵢ反应，用Sr²⁺替代Ca²⁺ₒ会完全阻断Ca²⁺ᵢ对低Na⁺ₒ的反应。无钠培养基刺激细胞的钙外流增加4 - 5倍，在没有细胞外Ca²⁺的情况下该反应消失。无钠培养基还刺激钙内流和钠外流。然而，细胞钙含量并未增加。这些结果表明，去除细胞外Na⁺通过刺激钙内流而非抑制钙外流来增加Ca²⁺ᵢ；增加的钙内流发生在以反向模式运行的Na⁺-Ca²⁺反向转运体上，以交换钠外流。钙外流增加是Ca²⁺ᵢ升高的结果，可能发生在依赖（Ca²⁺-Mg²⁺）ATP酶的钙泵上。
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