Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA.
J Physiol. 2011 May 15;589(Pt 10):2559-68. doi: 10.1113/jphysiol.2010.204768. Epub 2011 Mar 21.
M-type (KCNQ) K⁺ channels are known to regulate excitability and firing properties of sympathetic neurons (SNs), but their role in regulating neurotransmitter release is unclear, requiring further study. We sought to use a physiological preparation in which SNs innervate primary cardiomyocytes to evaluate the direct role of M-channels in the release of noradrenaline (NA) from SNs. Co-cultures of rat SNs and mouse cardiomyocytes were prepared, and the contraction rate (CR) of the cardiomyocyte syncytium monitored by video microscopy. We excited the SNs with nicotine, acting on nicotinic acetylcholine receptors, and monitored the increase in CR in the presence or absence of the specific M-channel opener retigabine, or agonists of bradykinin B2 or purinergic P2Y receptors on the SNs. The maximal adrenergic effect on the CR was determined by application of isoproterenol (isoprenaline). To isolate the actions of B2 or P2Y receptor stimulation to the neurons, we prepared cardiomyocytes from B2 receptor or P2Y2 receptor knock-out mice, respectively. We found that co-application of retigabine strongly decreased the nicotine-induced increase in CR. Conversely, co-application of bradykinin or the P2Y-receptor agonist UTP augmented the nicotine-induced increase in CR to about half of the level produced by isoproterenol. All effects on the CR were wholly blocked by propranolol. Our data support the role of M-type K⁺ channels in the control of NA release by SNs at functional adrenergic synapses on cardiomyocytes.We conclude that physiological receptor agonists control the heart rate via the regulation of M-current in SNs.
M 型（KCNQ）钾通道已知可调节交感神经元 (SN) 的兴奋性和发放特性，但它们在调节神经递质释放中的作用尚不清楚，需要进一步研究。我们试图使用一种生理制剂，其中 SN 支配原代心肌细胞，以评估 M 通道在 SN 中去甲肾上腺素 (NA) 释放中的直接作用。我们制备了大鼠 SN 和小鼠心肌细胞的共培养物，并通过视频显微镜监测心肌细胞合胞体的收缩率 (CR)。我们用尼古丁刺激 SN，作用于烟碱型乙酰胆碱受体，并在存在或不存在特定 M 通道 opener 瑞替加滨或 SN 上的缓激肽 B2 或嘌呤能 P2Y 受体激动剂的情况下监测 CR 的增加。通过应用异丙肾上腺素（异丙肾上腺素）确定对 CR 的最大肾上腺素作用。为了分离 B2 或 P2Y 受体刺激对神经元的作用，我们分别从小鼠 B2 受体或 P2Y2 受体敲除小鼠制备心肌细胞。我们发现，瑞替加滨的共同应用强烈降低了尼古丁诱导的 CR 增加。相反，缓激肽或 P2Y 受体激动剂 UTP 的共同应用增强了尼古丁诱导的 CR 增加，达到异丙肾上腺素产生的水平的一半左右。所有对 CR 的影响均被普萘洛尔完全阻断。我们的数据支持 M 型钾通道在功能性肾上腺素能突触上控制 SN 中去甲肾上腺素释放的作用。我们得出结论，生理受体激动剂通过调节 SN 中的 M 电流来控制心率。
