Sun L S, Vulliemoz Y, Huber F, Bilezikian J P, Robinson R B
Department of Anesthesiology, College of Physicians and Surgeons, Columbia University, New York 10032.
J Mol Cell Cardiol. 1994 Jun;26(6):779-87. doi: 10.1006/jmcc.1994.1092.
Previously, we demonstrated that low concentrations of acetylcholine (< or = 10(-9) M) increased automaticity in neonatal but not in adult rat ventricular myocardium. In the present study, we used cultured neonatal rat ventricular myocytes grown alone or in the presence of dissociated sympathetic neurons as an experimental model to study the ontogeny of the muscarinic response. McN A343 (< or = 10(-9) M), an M1 selective agonist, increased spontaneous rate from 51 +/- 4 to 56 +/- 5 beats per minute (bpm), and this excitatory response was blocked by 10(-9) M pirenzepine, an M1 selective antagonist, but not by the M2 selective antagonist AFDX-116, nor by the alpha 1 adrenergic antagonist prazosin and the beta adrenergic antagonist propranolol (all 10(-7) M) In innervated myocytes, McN A343 also increased rate from 48 +/- 6 to 55 +/- 6 bpm. However, this effect was blocked by either 10(-9) M pirenzepine or 10(-7) M propranolol. After pretreatment with 10 ng/ml of pertussis toxin, the McN A343-induced excitatory response in non-innervated myocytes was absent, thus suggesting that this response involved a pertussis toxin-sensitive G protein dependent pathway. McN A343 failed to stimulate inositol phosphate or cAMP accumulation in non-innervated myocytes. These results demonstrate the following. (1) The muscarinic excitatory response is mediated via direct stimulation of a post-synaptic M1 receptor in non-innervated myocytes. (2) The excitatory response after innervation is related to the release of catecholamines, possibly through activation of muscarinic receptors located at the pre-synaptic sympathetic nerve terminals. (3) Sympathetic innervation prevents the functional expression of the post-synaptic myocardial M1 receptor. (4) The intracellular pathway for the post-synaptic M1 excitatory response involves a pertussis toxin-sensitive G protein, but does not depend on obvious changes in cAMP or phosphoinositide hydrolysis.
此前，我们证明低浓度的乙酰胆碱（≤10⁻⁹ M）可增加新生大鼠而非成年大鼠心室肌的自律性。在本研究中，我们使用单独培养或在解离的交感神经元存在下培养的新生大鼠心室肌细胞作为实验模型，来研究毒蕈碱反应的个体发生。M₁选择性激动剂 McN A343（≤10⁻⁹ M）使自发频率从每分钟51±4次增加到56±5次搏动（bpm），并且这种兴奋反应被M₁选择性拮抗剂10⁻⁹ M哌仑西平阻断，但未被M₂选择性拮抗剂AFDX - 116阻断，也未被α₁肾上腺素能拮抗剂哌唑嗪和β肾上腺素能拮抗剂普萘洛尔（均为10⁻⁷ M）阻断。在有神经支配的心肌细胞中，McN A343也使频率从48±6次增加到55±6次bpm。然而，这种效应被10⁻⁹ M哌仑西平或10⁻⁷ M普萘洛尔阻断。用10 ng/ml百日咳毒素预处理后，非神经支配心肌细胞中McN A343诱导的兴奋反应消失，因此表明这种反应涉及百日咳毒素敏感的G蛋白依赖性途径。McN A343未能刺激非神经支配心肌细胞中肌醇磷酸酯或环磷酸腺苷（cAMP）积累。这些结果表明如下几点。（1）毒蕈碱兴奋反应是通过直接刺激非神经支配心肌细胞中的突触后M₁受体介导的。（2）神经支配后的兴奋反应与儿茶酚胺的释放有关，可能是通过位于突触前交感神经末梢的毒蕈碱受体的激活。（3）交感神经支配阻止了突触后心肌M₁受体的功能表达。（4）突触后M₁兴奋反应的细胞内途径涉及百日咳毒素敏感的G蛋白，但不依赖于cAMP或磷酸肌醇水解的明显变化。
