Ikenouchi H, Kangawa K, Matsuo H, Hirata Y
Second Department of Internal Medicine, University of Tokyo, Japan.
Circulation. 1997 May 6;95(9):2318-24. doi: 10.1161/01.cir.95.9.2318.
Adrenomedullin (AM) is a potent vasodilator peptide. AM-induced vasodilatation is mediated by an increase of NO as well as cAMP. Both AM and binding sites for this peptide have been found in cardiac tissue, indicating the possible existence of an autocrine or paracrine system of AM in the heart.
Myocytes were isolated by use of retrograde coronary perfusion with physiological solution containing collagenase and hyaluronidase from adult rabbit ventricles. Contraction of cardiac myocytes was traced with a video motion detector, and [Ca2+]i was measured with indo 1 at 37 degrees C. The Ica was measured with a whole-cell patch clamp at 23 degrees C. AM and calcitonin gene-related peptide (CGRP), another member of the same peptide family, showed a concentration-dependent negative inotropic effect (10(-7) mol/L AM: contraction amplitude, 64 +/- 7% of control; [Ca2+]i, 52 +/- 5% of control; n = 10; 10(-6) mol/L CGRP: contraction amplitude, 64 +/- 25%; [Ca2+]i, 70 +/- 3%; n = 5; mean +/- SD). Ica was decreased to 60 +/- 39% by superfusion with AM after the cessation of NG-monomethyl-L-arginine (L-NMMA), an NO synthase inhibitor. Pretreatment with L-NMMA (10 mumol/L) abolished the negative inotropic effect of AM, whereas switching from AM+L-NMMA to AM+L-arginine (1 mmol/L) restored it. Superfusion with 8-bromo-cGMP also showed a negative inotropic effect. AM significantly increased the intracellular content of cGMP, a second messenger of NO, but not that of cAMP. AM (10 nmol/L) blunted the effect of 1 mumol/L forskolin.
AM has a negative inotropic effect and decreased both [Ca2+]i and Ica, with these effects being at least party mediated via the L-arginine-NO pathway in adult rabbit ventricular myocytes.
肾上腺髓质素（AM）是一种强效血管舒张肽。AM诱导的血管舒张由一氧化氮（NO）和环磷酸腺苷（cAMP）增加介导。在心脏组织中已发现AM及其该肽的结合位点，提示心脏中可能存在AM的自分泌或旁分泌系统。
采用含胶原酶和透明质酸酶的生理溶液逆行冠状动脉灌注法，从成年兔心室分离心肌细胞。用视频运动检测器记录心肌细胞收缩情况，并于37℃用indo 1测量细胞内钙离子浓度（[Ca2+]i）。于23℃用全细胞膜片钳测量L型钙电流（Ica）。AM和降钙素基因相关肽（CGRP，同一肽家族的另一个成员）呈浓度依赖性负性肌力作用（10⁻⁷mol/L AM：收缩幅度为对照的64±7%；[Ca2+]i为对照的52±5%；n = 10；10⁻⁶mol/L CGRP：收缩幅度为64±25%；[Ca2+]i为70±3%；n = 5；均值±标准差）。一氧化氮合酶抑制剂NG-单甲基-L-精氨酸（L-NMMA）停用后，用AM灌流使Ica降至60±39%。用10μmol/L L-NMMA预处理可消除AM的负性肌力作用，而从AM+L-NMMA转换为AM+L-精氨酸（1mmol/L）可恢复该作用。用8-溴-cGMP灌流也显示负性肌力作用。AM显著增加NO的第二信使cGMP的细胞内含量，但不增加cAMP的含量。10nmol/L AM可减弱1μmol/L福斯可林的作用。
在成年兔心室肌细胞中，AM具有负性肌力作用，降低[Ca2+]i和Ica，这些作用至少部分通过L-精氨酸-NO途径介导。
