Addition of 3.5 mM ATP to mouse neuroblastoma Neuro-2A cells results in a selective enhancement of the plasma membrane permeability for Na+ relative to K+, as measured by cation flux measurements and electro-physiological techniques. 2. Addition of 3.5 mM ATP to Neuro-2A cells results in a 70% stimulation of the rate of active K+ -uptake by these cells, partly because of the enhanced plasma membrane permeability for Na+. Under these conditions the pumping activity of the Neuro-2A (Na+ +K+)-ATPase is optimally stimulated with respect to its various substrate ions. 3. External ATP significantly enhances the affinity of the Neuro-2A (Na+ +K+)-ATPase for ouabain, as measured by direct [3H]ouabain-binding studies and by inhibition studies of active K+ uptake. In the presence of 3.5 mM ATP and the absence of external K+ both techniques indicate an apparent dissociation constant for ouabain of 2 X 10(-6)M. Neuro-2A cells contain (3.5 +/- 0.7) X 10(5) ouabain-binding sites per cell, giving rise to an optimal pumping activity of (1.7 +/- 0.4) X 10(-20) mol K+/min per copy of (Na+ +K+)-ATPase at room temperature.
摘要
向小鼠神经母细胞瘤Neuro-2A细胞中添加3.5 mM三磷酸腺苷（ATP），通过阳离子通量测量和电生理技术测定，结果显示相对于钾离子（K+），钠离子（Na+）的质膜通透性有选择性增强。2. 向Neuro-2A细胞中添加3.5 mM ATP会使这些细胞主动摄取钾离子的速率提高70%，部分原因是质膜对钠离子的通透性增强。在这些条件下，Neuro-2A（Na+ +K+）-ATP酶的泵浦活性相对于其各种底物离子得到了最佳刺激。3. 通过直接的[3H]哇巴因结合研究以及主动摄取钾离子的抑制研究测定，细胞外ATP显著增强了Neuro-2A（Na+ +K+）-ATP酶对哇巴因的亲和力。在存在3.5 mM ATP且不存在细胞外钾离子的情况下，两种技术均表明哇巴因的表观解离常数为2×10^(-6)M。Neuro-2A细胞每个细胞含有（3.5±0.7）×10^5个哇巴因结合位点，在室温下每个（Na+ +K+）-ATP酶分子产生的最佳泵浦活性为（1.7±0.4）×10^(-20) mol K+/min。
