Particulate Matter Exposure: Cardiovascular Mechanisms

描述(由申请人提供)：流行病学研究表明，暴露于空气动力学直径为2.5？m的颗粒物(PM2.5)与心血管相关疾病，包括室性心律失常和心源性猝死之间存在显著的相关性。虽然PM2.5暴露对心血管健康构成重大风险似乎是毋庸置疑的，但其根本原因却鲜为人知。与PM2.5暴露相关的心率变异性(HRV)降低尤其重要，因为HRV降低已被证明是心脏迷走神经调节的一个指标，并与室性心律失常的易感性和心血管相关猝死的风险增加有关。更不清楚的是心率变异性降低的机制(S)，因此心血管相关的发病率。利用小鼠，我们建议使用最先进的吸入设备从真实的燃烧源释放与环境相关的颗粒污染物(铁/烟尘)，以捕获环境中普遍存在的碳基颗粒和过渡金属，以测试短期(3天)暴露于PM2.5会导致心率变异性降低的假设，这是由于调节心率变异性的解剖和功能识别的中枢神经系统迷走神经(NA)的固有膜属性和/或突触兴奋性降低。我们将在暴露于两种浓度的铁/烟尘颗粒和过滤空气(FA)的小鼠身上测试这一假设，作为对照，具体目的如下。1.通过量化总体24小时心率变异性、心率变异性的日变化和急性应激源(运动)后心率的恢复，确定短期(3天)暴露于以铁/煤烟颗粒形式存在的PM2.5是否会导致心脏迷走神经对心率的调节减弱的表型。2.通过测量静息膜电位、膜电导和对去极化电流的放电反应，确定PM2.5暴露引起的心率变异性降低是否与NA心脏迷走神经元内在兴奋性降低有关。3.为了确定PM2.5暴露引起的NA心脏迷走神经元内源性兴奋性降低是否由NA神经元上存在的三个主要钾通道的钾电流增加、激活动力学左移和/或失活动力学右移所介导。4.通过测定兴奋性GABA介导的抑制性突触后电流(GABA IPSCs)的频率和幅度，以确定PM2.5暴露引起的心率变异性降低是否通过增强抑制作用而导致的突触兴奋性降低。5.通过测量紧张性兴奋性突触后电流(GLU EpSCs)的频率和幅度以及诱发的GLU EpSCs的幅度，以确定PM2.5暴露引起的HRV降低是否是通过抑制的谷氨酸(GLU)兴奋机制在NA心脏迷走神经神经元的突触兴奋性降低所介导的。

DESCRIPTION (provided by applicant): Epidemiological studies show significant associations between exposure to particulate matter with particles of aerodynamic diameter of <_2.5 ¿m (PM2.5) and cardiovascular-related morbidity including ventricular arrhythmias and sudden cardiac death. While there appears to be little doubt that PM2.5 exposure poses a significant cardiovascular health risk, the underlying causes are poorly understood. The decreased heart rate variability (HRV) associated with PM2.5 exposure is particularly important since decreased HRV has been shown to be an index of cardiac vagal regulation and is associated with increased susceptibility to ventricular arrhythmias and risk for cardiovascular-related sudden death. Even less understood is the mechanism(s) mediating the reduced HRV and hence the cardiovascular-related morbidity. Using the mouse we propose to use state-of-the-art inhalation facilities to deliver environmentally relevant particulate pollutants (iron/soot) from a true combustion source that captures the carbon-based particles and a transition metal ubiquitous in the environment to test the Hypothesis that short-term (3-day) exposure to PM2.5 results in a reduced HRV due to decreases in the intrinsic membrane properties and/or synaptic excitability of anatomically- and functionally-identified CNS cardiac vagal neurons in the nucleus ambiguous (NA) that regulate HRV. We will test the hypothesis in mice exposed to two concentrations of iron/soot particles and filtered air (FA) as a control by the following Specific Aims. 1. To determine whether short-term (3-day) exposure to PM2.5 in the form of iron/soot particles produces the phenotype of a reduced cardiac vagal regulation of heart rate, by quantifying overall 24-h HRV, diurnal changes in HRV, and heart rate recovery following an acute stressor (exercise). 2. To determine whether the PM2.5 exposure-induced decrease in HRV is mediated by decreased intrinsic excitability of the NA cardiac vagal neurons by measuring resting membrane potential, membrane conductance and spiking responses to depolarizing current injections. 3. To determine whether the PM2.5 exposure-induced decreased intrinsic excitability of NA cardiac vagal neurons is mediated by increased potassium currents, left shift in activation kinetics, and/or right shift in inactivation kinetics of three major potassium channels present in NA neurons. 4. To determine whether the PM2.5 exposure-induced decrease in HRV is mediated by decreased synaptic excitability by enhanced inhibitory ;?-aminobutyric acid (GABA) mechanisms at the NA cardiac vagal neurons, by measuring the frequency and amplitude of tonic GABA-mediated inhibitory postsynaptic currents (GABA IPSCs). 5. To determine whether the PM2.5 exposure-induced decrease in HRV is mediated by decreased synaptic excitability by depressed glutamatergic (GLU) excitatory mechanisms at the NA cardiac vagal neurons, by measuring the frequency and amplitude of tonic excitatory postsynaptic currents (GLU EPSCs) and the amplitude of evoked GLU EPSCs.