Freer R J, Smith A B
Am J Physiol. 1976 Apr;230(4):1132-7. doi: 10.1152/ajplegacy.1976.230.4.1132.
Studies were carried out to investigate the effect of Na+ deprivation on the response of rat uterine smooth muscle to angiotensin II (AII). Replacement of Na+ with Li+ in a low-Ca2+-, Mg2+-free solution resulted in a concentration-dependent inhibition of both AII and acetylcholine (ACh)-induced contractions. Inhibition was noted at 10% Li+ substitution and was usually complete when 50% of the Na+ was replaced by Li+. The inhibition was not observed when an equivalent amount of tris(hyroxymethyl)aminomethand (Tris+) or sucrose was used to replace Na+. However, elevation of Ca2+ concentration from 0.2 to 0.5 mM did prevent full expression of the Li+ inhibition of AII. The Li+ effect was rapid in onset (60% inhibition after 5 min preincubation) and readily reversible following removal of the Li+. If, however, the tissue was placed in a depolarizing solution (151 mM KCL), Li+ inhibition of AII WAS NO LONGER OBSERVED. These results are interpreted to mean that Li+ interferes with an essential Ca2+-dependent step involved in membrane excitation following agonist-receptor interaction. The results are discussed in relation to a previously suggested model for AII-induced contractions in this tissue.
开展了多项研究以调查钠缺乏对大鼠子宫平滑肌对血管紧张素II（AII）反应的影响。在低钙、无镁溶液中用锂替代钠导致对AII和乙酰胆碱（ACh）诱导的收缩产生浓度依赖性抑制。在10%锂替代时即观察到抑制作用，当50%的钠被锂替代时通常完全抑制。当用等量的三（羟甲基）氨基甲烷（Tris+）或蔗糖替代钠时未观察到抑制作用。然而，将钙浓度从0.2 mM提高到0.5 mM确实可防止锂对AII抑制作用的完全表现。锂的作用起效迅速（预孵育5分钟后抑制60%），去除锂后易于逆转。然而，如果将组织置于去极化溶液（151 mM KCl）中，则不再观察到锂对AII的抑制作用。这些结果被解释为意味着锂干扰了激动剂 - 受体相互作用后膜兴奋所涉及的一个必需的钙依赖性步骤。结合该组织中先前提出的AII诱导收缩模型对结果进行了讨论。
