Standard microelectrode techniques were used to investigate the influence of N-ethylmaleimide on the action potential, slow response action potential and force of contraction of guinea-pig papillary muscles. 2. N-ethylmaleimide, 3 x 10(-5) to 10(-4) mol l-1, concentration-dependently increased the force of contraction. The positive inotropic effect developed quickly and, with the largest drug concentration, was followed by a progressive decline of the contractile force. The action potential duration was progressively shortened by N-ethylmaleimide. 3. The effects of N-ethylmaleimide were not prevented in the presence of tetrodotoxin 3 x 10(-8) mol l-1 and propranolol 4 x 10(-6) mol l-1 or by a reduction of the Na(+)-concentration to 70 mmol l-1. 4. Verapamil, 10(-6) mol l-1, reduced the positive inotropic, but not the action potential shortening effect of N-ethylmaleimide. 5. In K(+)-depolarized muscles in the presence of propranolol and tetrodotoxin, N-ethylmaleimide 10(-4) mol l-1 increased the maximum depolarization velocity and the duration of the slow response action potential. The latter effect was transient and was followed by a progressive reduction of the action potential duration. 6. The most likely explanation for the action potential shortening effect of N-ethylmaleimide seems to be an increase of an outward potassium current while the transient inotropic effect of the drug may be caused, at least in part, by an increase of the slow inward calcium current.
摘要
采用标准微电极技术研究N - 乙基马来酰亚胺对豚鼠乳头肌动作电位、慢反应动作电位和收缩力的影响。2. N - 乙基马来酰亚胺浓度在3×10⁻⁵至10⁻⁴mol/L时，可浓度依赖性地增强收缩力。正性肌力作用起效迅速，在最大药物浓度时，随后收缩力逐渐下降。N - 乙基马来酰亚胺可使动作电位时程逐渐缩短。3. 在存在3×10⁻⁸mol/L河豚毒素和4×10⁻⁶mol/L普萘洛尔时，或把Na⁺浓度降至70mmol/L时，N - 乙基马来酰亚胺的作用并未被阻断。4. 10⁻⁶mol/L维拉帕米可减弱N - 乙基马来酰亚胺的正性肌力作用，但不影响其缩短动作电位的作用。5. 在存在普萘洛尔和河豚毒素的K⁺去极化肌肉中，10⁻⁴mol/L N - 乙基马来酰亚胺可增加最大去极化速度和慢反应动作电位时程。后一种作用是短暂的，随后动作电位时程逐渐缩短。6. N - 乙基马来酰亚胺缩短动作电位的作用最可能的解释似乎是外向钾电流增加，而该药物短暂的正性肌力作用可能至少部分是由慢内向钙电流增加引起的。
