Particulate Matter Exposure: Cardiovascular Mechanisms

描述（由申请方提供）：流行病学研究表明，空气动力学直径<2.5 μ m（PM2.5）的颗粒物暴露与心血管相关发病率（包括室性心律失常和心源性猝死）之间存在显著相关性。虽然PM2.5暴露对心血管健康构成重大风险似乎毫无疑问，但其根本原因却知之甚少。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指标，并与室性心律失常易感性增加和心血管相关猝死风险相关。更不了解的是介导HRV降低的机制，从而导致心血管相关的发病率。使用鼠标，我们建议使用国家的最先进的吸入设施，以提供环境相关的颗粒污染物（铁/烟灰），以测试以下假设：短期（3天）暴露于PM2.5导致HRV降低，这是由于固有膜特性和/或或突触兴奋性的解剖学和功能上确定的中枢神经系统心脏迷走神经元在模糊核（NA），调节HRV。我们将通过以下特定目的在暴露于两种浓度的铁/烟灰颗粒和过滤空气（FA）的小鼠中测试该假设。1.通过量化总体24小时HRV、HRV的昼夜变化和急性应激源（运动）后的心率恢复，确定短期（3天）暴露于铁/烟灰颗粒形式的PM2.5是否会产生心脏迷走神经心率调节降低的表型。2.通过测量静息膜电位、膜电导和对去极化电流注射的尖峰反应，确定PM2.5暴露诱导的HRV降低是否由NA心脏迷走神经元的固有兴奋性降低介导。3.确定PM2.5暴露诱导的NA心脏迷走神经元内在兴奋性降低是否由NA神经元中存在的三种主要钾通道的钾电流增加、激活动力学左移和/或失活动力学右移介导。4.确定PM2.5暴露诱导的HRV降低是否通过增强抑制性降低突触兴奋性介导;通过测量紧张性GABA介导的抑制性突触后电流（GABA IPSC）的频率和振幅，研究了NA心脏迷走神经元的GABA机制。5.通过测量强直性兴奋性突触后电流（GLU EPSC）的频率和振幅以及诱发的GLU EPSC的振幅，确定PM2.5暴露诱导的HRV降低是否由NA心脏迷走神经元上抑制的谷氨酸能（GLU）兴奋机制引起的突触兴奋性降低介导。

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.