Rakotonirina A, Soustre H
Laboratoire de Physiologie Générale, CNRS U.R.A. 290, Université de Poitiers, France.
Gen Physiol Biophys. 1989 Aug;8(4):313-26.
The action of isoprenaline, a purely beta-agonist, was investigated on frog atrial fibres under voltage clamp conditions; tonic tension was induced by long depolarizing pulses and the outward delayed current simultaneously developed. The cumulative dose-response curves showed that isoprenaline increased the peak of tonic tension in the concentration range 10(-8) to 3. 10(-6) mol.l-1, with a maximum effect for 10(-6) mol.l-1. The positive inotropic action of isoprenaline was associated with an increase in the rates of tension rise and of relaxation. Isoprenaline also increased the amplitude of the outward delayed current in a dose-dependent manner. The effects of isoprenaline (10(-6) mol.l-1) on tonic tension and outward delayed current were not observed in the presence of propranolol (10(-7) mol.l-1). Experiments carried out in low-sodium solution demonstrated that the action of isoprenaline on tonic tension can be explained by activation of Na-Ca exchange; the enhanced relaxation might result from the same process. These results suggested that the positive inotropic action of isoprenaline is mediated not only by the well-known increase in the slow inward current but also by activation of the Na-Ca exchange mechanism.
在电压钳制条件下，研究了纯β-肾上腺素能激动剂异丙肾上腺素对蛙心房纤维的作用；通过长时间去极化脉冲诱导张力，并同时产生外向延迟电流。累积剂量-反应曲线表明，异丙肾上腺素在10^(-8)至3×10^(-6) mol·l^(-1)的浓度范围内增加了张力峰值，在10^(-6) mol·l^(-1)时达到最大效应。异丙肾上腺素的正性肌力作用与张力上升速率和松弛速率的增加有关。异丙肾上腺素还以剂量依赖性方式增加外向延迟电流的幅度。在存在普萘洛尔（10^(-7) mol·l^(-1)）的情况下，未观察到异丙肾上腺素（10^(-6) mol·l^(-1)）对张力和外向延迟电流的影响。在低钠溶液中进行的实验表明，异丙肾上腺素对张力的作用可通过钠-钙交换的激活来解释；增强的松弛可能源于相同的过程。这些结果表明，异丙肾上腺素的正性肌力作用不仅由众所周知的慢内向电流增加介导，还由钠-钙交换机制的激活介导。
