Verkerk Arie O, Geuzebroek Guillaume S C, Veldkamp Marieke W, Wilders Ronald
Department of Anatomy, Embryology and Physiology, Academic Medical Center, University of Amsterdam Amsterdam, Netherlands.
Front Physiol. 2012 May 31;3:174. doi: 10.3389/fphys.2012.00174. eCollection 2012.
The autonomic nervous system controls heart rate and contractility through sympathetic and parasympathetic inputs to the cardiac tissue, with acetylcholine (ACh) and noradrenalin (NA) as the chemical transmitters. In recent years, it has become clear that specific Regulators of G protein Signaling proteins (RGS proteins) suppress muscarinic sensitivity and parasympathetic tone, identifying RGS proteins as intriguing potential therapeutic targets. In the present study, we have identified the effects of 1 μM ACh and 1 μM NA on the intrinsic action potentials of sinoatrial (SA) nodal and atrial myocytes. Single cells were enzymatically isolated from the SA node or from the left atrium of rabbit hearts. Action potentials were recorded using the amphotericin-perforated patch-clamp technique in the absence and presence of ACh, NA, or a combination of both. In SA nodal myocytes, ACh increased cycle length and decreased diastolic depolarization rate, whereas NA decreased cycle length and increased diastolic depolarization rate. Both ACh and NA increased maximum upstroke velocity. Furthermore, ACh hyperpolarized the maximum diastolic potential. In atrial myocytes stimulated at 2 Hz, both ACh and NA hyperpolarized the maximum diastolic potential, increased the action potential amplitude, and increased the maximum upstroke velocity. Action potential duration at 50 and 90% repolarization was decreased by ACh, but increased by NA. The effects of both ACh and NA on action potential duration showed a dose dependence in the range of 1-1000 nM, while a clear-cut frequency dependence in the range of 1-4 Hz was absent. Intermediate results were obtained in the combined presence of ACh and NA in both SA nodal and atrial myocytes. Our data uncover the extent to which SA nodal and atrial action potentials are intrinsically dependent on ACh, NA, or a combination of both and may thus guide further experiments with RGS proteins.
自主神经系统通过对心脏组织的交感和副交感神经输入来控制心率和心肌收缩力，乙酰胆碱（ACh）和去甲肾上腺素（NA）作为化学递质。近年来，已经明确特定的G蛋白信号调节蛋白（RGS蛋白）可抑制毒蕈碱敏感性和副交感神经张力，这表明RGS蛋白是潜在的有趣治疗靶点。在本研究中，我们确定了1μM ACh和1μM NA对窦房（SA）结和心房肌细胞内在动作电位的影响。从兔心脏的窦房结或左心房中酶解分离出单细胞。在不存在和存在ACh、NA或两者组合的情况下，使用两性霉素穿孔膜片钳技术记录动作电位。在窦房结肌细胞中，ACh增加周期长度并降低舒张期去极化速率，而NA降低周期长度并增加舒张期去极化速率。ACh和NA均增加最大上升速度。此外，ACh使最大舒张电位超极化。在以2Hz刺激的心房肌细胞中，ACh和NA均使最大舒张电位超极化，增加动作电位幅度，并增加最大上升速度。ACh使复极化50%和90%时的动作电位持续时间缩短，但NA使其延长。ACh和NA对动作电位持续时间的影响在1-1000 nM范围内呈剂量依赖性，而在1-4Hz范围内未观察到明显的频率依赖性。在窦房结和心房肌细胞中同时存在ACh和NA时获得了中间结果。我们的数据揭示了窦房结和心房动作电位在多大程度上内在地依赖于ACh、NA或两者的组合，从而可能为进一步研究RGS蛋白的实验提供指导。
