Nifedipine induced concentration-dependent relaxations in segments of human placental arteries precontracted with 40 mM K+. 2. Preincubation of segments with nifedipine induced concentration-dependent inhibition of contractions elicited by 40 mM K+ (IC50, 2.5 x 10(-9) M) and 10(-7) M 5-HT (5.9 x 10(-8) M). 3. The time-course of contractions elicited by K+ and 5-HT (responses not sustained) in the absence and in the presence of nifedipine was different. 4. Nifedipine inhibited Ca addition-evoked contractions in Ca-free medium containing 40 mM K+ or 10(-7) M 5-HT, mainly those obtained in depolarized segments. 5. These results indicate that these arteries are very sensitive to nifedipine and that the voltage-operated Ca channels are more affected by the Ca antagonist than receptor-operated ones.
摘要
硝苯地平可使预先用40 mM钾离子预收缩的人胎盘动脉节段产生浓度依赖性舒张。2. 用硝苯地平对节段进行预孵育可引起对40 mM钾离子（半数抑制浓度，2.5×10⁻⁹ M）和10⁻⁷ M 5-羟色胺（5.9×10⁻⁸ M）诱发的收缩的浓度依赖性抑制。3. 在不存在和存在硝苯地平的情况下，钾离子和5-羟色胺诱发的收缩（反应不持续）的时间进程不同。4. 硝苯地平抑制在含有40 mM钾离子或10⁻⁷ M 5-羟色胺的无钙培养基中钙添加诱发的收缩，主要是在去极化节段中获得的收缩。5. 这些结果表明这些动脉对硝苯地平非常敏感，且电压门控钙通道比受体操纵性钙通道更易受钙拮抗剂的影响。
