Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada.
Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada; School of Biomedical Engineering, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada.
J Mol Cell Cardiol. 2015 May;82:125-35. doi: 10.1016/j.yjmcc.2015.02.024. Epub 2015 Mar 6.
Cardiovascular autonomic neuropathy (CAN) is a serious complication of diabetes mellitus that impairs autonomic regulation of heart rate (HR). This has been attributed to damage to the nerves that modulate spontaneous pacemaker activity in the sinoatrial node (SAN). Our objective was to test the hypothesis that impaired parasympathetic regulation of HR in diabetes is due to reduced responsiveness of the SAN to parasympathetic agonists. We used the Akita mouse model of type 1 diabetes to study the effects of the parasympathetic agonist carbachol (CCh) on SAN function using intracardiac programmed stimulation, high resolution optical mapping and patch-clamping of SAN myocytes. CCh decreased HR by 30% and increased corrected SAN recovery time (cSNRT) by 123% in wildtype mice. In contrast, CCh only decreased HR by 12%, and only increased cSNRT by 37% in Akita mice. These alterations were due to smaller effects of CCh on SAN electrical conduction and spontaneous action potential firing in isolated SAN myocytes. Voltage clamp experiments demonstrate that the acetylcholine-activated K(+) current (IKACh) is reduced in Akita SAN myocytes due to enhanced desensitization and faster deactivation kinetics. These IKACh alterations were normalized by treating Akita SAN myocytes with PI(3,4,5)P3 or an inhibitor of regulator of G-protein signaling 4 (RGS4). There was no difference in the effects of CCh on the hyperpolarization-activated current (If) between wildtype and Akita mice. Our study demonstrates that Akita diabetic mice demonstrate impaired parasympathetic regulation of HR and SAN function due to reduced responses of the SAN to parasympathetic agonists. Our experiments demonstrate a key role for insulin-dependent phosphoinositide 3-kinase (PI3K) signaling in the parasympathetic dysfunction seen in the SAN in diabetes.
心血管自主神经病变（CAN）是糖尿病的一种严重并发症，会损害心率（HR）的自主调节。这归因于调节窦房结（SAN）自发性起搏活动的神经受损。我们的目的是检验这样一个假设，即糖尿病中 HR 副交感神经调节受损是由于 SAN 对副交感神经激动剂的反应性降低所致。我们使用 Akita 糖尿病小鼠模型，通过心脏内程控刺激、高分辨率光学映射和 SAN 心肌细胞膜片钳技术，研究副交感神经激动剂卡巴胆碱（CCh）对 SAN 功能的影响。CCh 使野生型小鼠的 HR 降低 30%，校正 SAN 恢复时间（cSNRT）增加 123%。相比之下，CCh 仅使 Akita 小鼠的 HR 降低 12%，仅使 cSNRT 增加 37%。这些变化归因于 CCh 对分离的 SAN 心肌细胞的电传导和自发性动作电位发放的影响较小。电压钳实验表明，由于脱敏增强和更快的失活动力学，Akita SAN 心肌细胞中的乙酰胆碱激活的 K(+)电流（IKACh）减少。用 PI(3,4,5)P3 或 G 蛋白信号调节因子 4（RGS4）抑制剂处理 Akita SAN 心肌细胞可使 IKACh 改变正常化。野生型和 Akita 小鼠之间 CCh 对超极化激活电流（If）的影响没有差异。我们的研究表明，Akita 糖尿病小鼠由于 SAN 对副交感神经激动剂的反应性降低，表现出 HR 和 SAN 功能的副交感神经调节受损。我们的实验证明了胰岛素依赖性磷酯酰肌醇 3-激酶（PI3K）信号在糖尿病中 SAN 副交感神经功能障碍中的关键作用。
