Savineau J P, Mironneau J, Mironneau C
Laboratoire de Physiologie Cellulaire, Institut de Biochimie Cellulaire et Neurochimie du C.N.R.S., Bordeaux, France.
Gen Physiol Biophys. 1987 Dec;6(6):535-59.
The effects of varying the sodium gradient-either by lowering [Na+]o or by increasing [Na+]i on the electromechanical properties of pregnant rat uterine smooth muscle were studied. In normal tissues, complete removal of external sodium ions (choline, Tris or sucrose as substitutes) induced a strong and maintained contraction which was dependent on the presence of extracellular calcium ions, and was sensitive to Ca2+-antagonist drugs (Nifedipine; D 600, Mn2+). Electrical recordings showed that the membrane was transiently hyperpolarized (-10 +/- 2.4 mV, n = 20); after 1 minute depolarization accompanied by a spontaneous spike discharge occurred. Partial withdrawal of external sodium ions resulted in following changes in twitch contractions evoked by electrical stimulation: a linear relationship was found between the time constant of twitch relaxation and the external Na-concentration. In Na-rich tissues, where the Na/K pump was blocked, or in the presence of monensin, Na-free solutions (whatever the substitute, even K+ ions) again triggered strong contractions entirely dependent on external calcium but rather insensitive to Ca-antagonists. The Na-free (K+) induced contraction was larger than the Na-free (choline or Tris)-induced contraction. It was concluded that the sodium gradient was an important factor for the regulation of contractile activity of uterine smooth muscle. Na-Ca exchange appeared to mediate twitch relaxation in normal tissues and was responsible for Ca-influx in Na-rich tissues.
研究了通过降低细胞外钠离子浓度（[Na⁺]ₒ）或增加细胞内钠离子浓度（[Na⁺]ᵢ）来改变钠梯度对妊娠大鼠子宫平滑肌电机械特性的影响。在正常组织中，完全去除细胞外钠离子（用胆碱、三羟甲基氨基甲烷或蔗糖替代）会诱导强烈且持续的收缩，这种收缩依赖于细胞外钙离子的存在，并且对钙离子拮抗剂药物（硝苯地平；D 600、锰离子）敏感。电记录显示，细胞膜会短暂超极化（-10 ± 2.4 mV，n = 20）；1分钟后会出现去极化并伴有自发的锋电位发放。部分去除细胞外钠离子会导致电刺激诱发的抽搐收缩发生以下变化：抽搐舒张的时间常数与细胞外钠浓度之间存在线性关系。在富含钠离子的组织中，钠钾泵被阻断，或者在存在莫能菌素的情况下，无钠溶液（无论替代物是什么，即使是钾离子）再次引发完全依赖于细胞外钙离子的强烈收缩，但对钙拮抗剂不太敏感。无钠（钾离子）诱导的收缩大于无钠（胆碱或三羟甲基氨基甲烷）诱导的收缩。得出的结论是，钠梯度是调节子宫平滑肌收缩活性的重要因素。钠钙交换似乎在正常组织中介导抽搐舒张，并在富含钠离子的组织中负责钙离子内流。
