Matsuo K, Uchida M K
Department of Molecular Pharmacology, Meiji College of Pharmacy, Tokyo, Japan.
Eur J Pharmacol. 1987 Aug 21;140(3):295-301. doi: 10.1016/0014-2999(87)90286-x.
The effect of Ca2+ on the oxytocin-induced, sustained contraction of rat uterine muscle in Ca-free medium after prolonged incubation with 3 mM EGTA (Ca-free contraction) was investigated. A micromolar concentration of Ca2+ caused phasic contraction followed by relaxation while a submicromolar concentration caused relaxation only. Cumulative addition of Ca2+ (10(-8)-3 X 10(-6) M) caused dose-dependent relaxation (Ca reversal). This relaxation was inhibited by nicardipine and enhanced by Bay k 8644, and the effects of these two drugs were potentiated in 45.6 mM K+ medium. It is concluded that the inhibitory effect of Ca2+ on Ca-free contraction is caused by the influx of a minute amount of Ca2+. Thus, Ca2+ has dual actions in the cell: activation at concentrations higher than 10(-6) M, and inhibition alone at concentrations lower than 10(-7) M.
研究了在无钙培养基中，经3 mM乙二醇双四乙酸（EGTA）长时间孵育后，Ca2+对大鼠子宫肌催产素诱导的持续性收缩（无钙收缩）的影响。微摩尔浓度的Ca2+引起阶段性收缩，随后松弛，而亚微摩尔浓度仅引起松弛。累积添加Ca2+（10(-8)-3×10(-6)M）引起剂量依赖性松弛（Ca逆转）。这种松弛被尼卡地平抑制，被Bay k 8644增强，并且这两种药物的作用在45.6 mM K+培养基中增强。得出结论，Ca2+对无钙收缩的抑制作用是由微量Ca2+的内流引起的。因此，Ca2+在细胞中具有双重作用：浓度高于10(-6)M时激活，浓度低于10(-7)M时单独抑制。
