Bell D, McDermott B J
Department of Therapeutics and Pharmacology, Queen's University of Belfast, Northern Ireland.
J Cardiovasc Pharmacol. 1994 Jun;23(6):1011-21. doi: 10.1097/00005344-199406000-00021.
Calcitonin gene-related peptide (CGRP) elicits marked positive inotropic and chronotropic actions in the atria of several mammals. The second-messenger substance cyclic AMP and activation of L-type calcium channels have been implicated in these actions, but CGRP failed consistently to stimulate a contractile response in ventricular tissue obtained from various mammals. We assessed the actions of CGRP using isolated ventricular cardiomyocytes obtained from adult rats. Maximum changes in cell length (dL) of isolated cardiomyocytes during electrically stimulated (0.5 Hz) contractions were determined with adenosine deaminase (2.5 U/ml). In these conditions, CGRP produced a potent concentration-dependent positive contractile response that became maximal 4 min after initial stimulation. CGRP increased amplitude of cellular contractions maximally at a 1-nM concentration to a value 21.4% greater than that obtained without peptide. The EC50 value for the response was 31 pM. At concentrations greater than 1 nM, amplitude of the cellular contractile response decreased rapidly. The CGRP2-selective agonist, [cys ACM2,7] CGRP, increased the amplitude of cellular contractions maximally at 500 nM to a value 19.8% greater than that obtained without peptide. EC50 for this response was 6 nM. Salmon calcitonin (< or = 100 nM) did not elicit a significant contractile response. The fragment, CGRP8-37, a selective antagonist at the CGRP1 receptor subtype, while devoid of agonist activity, was a potent competitive antagonist of the positive contractile action of CGRP (pA2 value = 7.95). CGRP, present at maximally effective concentration (1 nM), when combined with isoprenaline ISO 100 pM-1 microM, elicited a greater increase in contractile amplitude than that elicited by ISO 100 pM-1 microM without CGRP. CGRP 1 nM combined with low concentrations of extracellular calcium ion < or = 4 mM produced a greater increase in contractile amplitude than that elicited by calcium ion < or = 4 mM without CGRP, but this additive effect was abolished in the presence of higher concentrations of extracellular calcium ion (> 4 mM). The cyclic AMP antagonist, Rp-cyclic AMPS (< or = 200 microM), did not inhibit the contractile response to CGRP 1 nM, but inhibited the contractile responses to ISO 100 nM and secretin 20 nM significantly and in a concentration-dependent manner. Diltiazem < or = 1 microM, a selective antagonist of L-type calcium channels, also failed to inhibit the contractile response to CGRP 1 nM but inhibited the contractile responses to ISO 100 nM and secretin 20 nM significantly and in a concentration-dependent manner.(ABSTRACT TRUNCATED AT 400 WORDS)
降钙素基因相关肽（CGRP）在多种哺乳动物的心房中可引发显著的正性变力和变时作用。第二信使物质环磷酸腺苷（cAMP）以及L型钙通道的激活与这些作用有关，但CGRP始终未能在从各种哺乳动物获取的心室组织中刺激出收缩反应。我们使用从成年大鼠分离出的心室心肌细胞评估了CGRP的作用。通过腺苷脱氨酶（2.5 U/ml）测定电刺激（0.5 Hz）收缩过程中分离心肌细胞的最大细胞长度变化（dL）。在这些条件下，CGRP产生了强大的浓度依赖性正性收缩反应，在初始刺激后4分钟达到最大值。CGRP在1 nM浓度时最大程度地增加了细胞收缩幅度，比未添加肽时的值高21.4%。该反应的半数有效浓度（EC50）值为31 pM。在浓度大于1 nM时，细胞收缩反应幅度迅速下降。CGRP2选择性激动剂[cys ACM2,7]CGRP在500 nM时最大程度地增加了细胞收缩幅度，比未添加肽时的值高19.8%。此反应的EC50为6 nM。鲑鱼降钙素（≤100 nM）未引发显著的收缩反应。片段CGRP8 - 37是CGRP1受体亚型的选择性拮抗剂，虽无激动剂活性，但却是CGRP正性收缩作用的强效竞争性拮抗剂（pA2值 = 7.95）。以最大有效浓度（1 nM）存在的CGRP与100 pM - 1 μM的异丙肾上腺素（ISO）联合使用时，引发的收缩幅度增加比单独使用100 pM - 1 μM的ISO更大。1 nM的CGRP与低浓度（≤4 mM）的细胞外钙离子联合使用时，引发的收缩幅度增加比单独使用≤4 mM的钙离子更大，但在存在较高浓度（> 4 mM）的细胞外钙离子时，这种相加作用消失。环磷酸腺苷拮抗剂Rp - 环磷腺苷酸（≤200 μM）未抑制对1 nM CGRP的收缩反应，但显著且呈浓度依赖性地抑制了对100 nM ISO和20 nM促胰液素的收缩反应。1 μM以下的地尔硫䓬，一种L型钙通道的选择性拮抗剂，也未能抑制对1 nM CGRP的收缩反应，但显著且呈浓度依赖性地抑制了对100 nM ISO和20 nM促胰液素的收缩反应。（摘要截断于400字）
