Morrill G A, Robbins E
J Gen Physiol. 1967 Mar;50(4):781-92. doi: 10.1085/jgp.50.4.781.
Studies on HeLa cells in spinner culture at pH 7.0 and 37 degrees have shown that Na decreased and K increased with increasing Ca. In Na-free (choline) medium K remained high whether or not Ca was present in the medium. Na and K approached a new steady state within 1 min after transfer to Ca-free medium and returned to the initial values within 15 min upon readdition of Ca. 40% of the cell Ca exchanged within 1 min followed by a slow exchange of the remaining Ca over several hours. Ca increased with decreasing Na but was independent of K. Equimolar Mg did not substitute for Ca in maintaining low Na and high K. Under steady-state conditions about 50% of the cell Na exchanged in accordance with a single rate constant. The initial Na influx was 270, 100, and 2.5 microM/liter of cell water/sec for 0, 0.10, and 1.0 mM Ca, respectively. When Na transport was inhibited with strophanthidin and Na and K allowed to reach a steady state, Na influx was more rapid for cells incubated in Ca-free medium than for cells incubated in medium containing 1.0 mM Ca. These results suggest that Ca competes with Na at the cell membrane and thus controls the passive diffusion of Na into the cell.
对处于pH 7.0和37摄氏度旋转培养的海拉细胞的研究表明，随着细胞外钙浓度（Ca）升高，细胞内钠浓度（Na）降低，细胞内钾浓度（K）升高。在无钠（胆碱）培养基中，无论培养基中是否存在钙，细胞内钾浓度都保持在较高水平。细胞转移至无钙培养基后1分钟内，细胞内钠和钾浓度接近新的稳态，重新添加钙后15分钟内恢复到初始值。40%的细胞内钙在1分钟内发生交换，随后剩余的钙在数小时内缓慢交换。细胞内钙浓度随细胞外钠浓度（Na）降低而升高，但与细胞外钾浓度（K）无关。等摩尔的镁不能替代钙来维持低细胞内钠浓度和高细胞内钾浓度。在稳态条件下，约50%的细胞内钠按照单一速率常数进行交换。对于细胞外钙浓度分别为0、0.10和1.0 mM的情况，初始钠内流速率分别为270、100和2.5微摩尔/升细胞水/秒。当用毒毛花苷抑制钠转运，使细胞内钠和钾浓度达到稳态时，在无钙培养基中培养的细胞的钠内流比在含有1.0 mM钙的培养基中培养的细胞更快。这些结果表明，钙在细胞膜上与钠竞争，从而控制钠向细胞内的被动扩散。
