Mihalevich M, Neff R A, Mendelowitz D
Department of Physiology and Biophysics, University of Tennessee, Memphis 38163, USA.
Brain Res. 1996 Nov 11;739(1-2):258-62. doi: 10.1016/s0006-8993(96)00868-2.
Heart rate is normally dominated by the activity of the cardioinhibitory parasympathetic nervous system, while abnormally low levels of parasympathetic cardiac activity have been implicated in many cardiovascular diseases including hypertension, heart failure and sudden cardiac death. In this study we have examined the voltage-gated currents in parasympathetic cardiac neurons that were identified with a retrograde fluorescent tracer in visualized sections (250 microns) of nucleus ambiguus. Depolarization of parasympathetic cardiac neurons to potentials more positive than -50 mV evoked a rapidly activating and inactivating inward current which could be blocked by tetrodotoxin (TTX), although in some neurons up to 10 microM was required for complete block. The voltage-dependent inactivation properties of this Na current showed relatively broad inactivation characteristics, a characteristic of TTX-resistant Na channels. Depolarization also elicited biphasic outward currents, which were separated into a transient IA type K current using the specific channel antagonist 4-aminopyridine and a long-lasting delayed rectified K current. These voltage-gated Na and K currents define the action potential firing patterns of parasympathetic cardiac neurons, such as frequency adaptation and spike delay, and also determine the activity of these neurons in response to depolarizing and hyperpolarizing synaptic innervation.
心率通常受心脏抑制性副交感神经系统活动的支配，而副交感神经心脏活动水平异常低下与包括高血压、心力衰竭和心源性猝死在内的许多心血管疾病有关。在本研究中，我们检测了在疑核可视化切片（250微米）中用逆行荧光示踪剂鉴定的副交感神经心脏神经元中的电压门控电流。将副交感神经心脏神经元去极化至比 -50 mV更正的电位会诱发一种快速激活和失活的内向电流，该电流可被河豚毒素（TTX）阻断，尽管在一些神经元中完全阻断需要高达10 microM的TTX。这种钠电流的电压依赖性失活特性表现出相对较宽的失活特征，这是耐TTX钠通道的一个特征。去极化还会引发双相外向电流，使用特异性通道拮抗剂4-氨基吡啶可将其分离为瞬时IA型钾电流和持久的延迟整流钾电流。这些电压门控钠电流和钾电流决定了副交感神经心脏神经元的动作电位发放模式，如频率适应性和动作电位延迟，也决定了这些神经元对去极化和超极化突触支配的反应活性。
