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< 2.5¿m （PM2.5）的颗粒物与心血管相关发病率（包括室性心律失常和心源性猝死）之间存在显著关联。虽然PM2.5暴露无疑会对心血管健康造成重大风险，但人们对其根本原因知之甚少。与PM2.5暴露相关的心率变异性（HRV）降低尤为重要，因为HRV降低已被证明是心脏迷走神经调节的一个指标，并与室性心律失常易感性增加和心血管相关猝死风险增加有关。更少了解的是介导HRV降低的机制，从而导致心血管相关的发病率。使用小鼠，我们建议使用最先进的吸入设备，从真正的燃烧源输送与环境相关的颗粒污染物（铁/烟灰），该燃烧源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导致HRV降低的假设，原因是解剖和功能鉴定的中枢神经系统心脏的固有膜特性和/或突触兴奋性降低迷走神经神经元在核模糊（NA）调节HRV。我们将在暴露于两种浓度的铁/煤烟颗粒和过滤空气（FA）作为对照的小鼠中验证这一假设，具体目的如下：为了确定短期（3天）暴露于铁/煤烟颗粒形式的PM2.5是否会产生心脏迷走神经调节心率降低的表型，通过量化24小时HRV、HRV的日变化和急性应激源（运动）后的心率恢复。2. 通过测量静息膜电位、膜电导和去极化电流注射的尖峰反应，确定PM2.5暴露诱导的HRV下降是否由NA心脏迷走神经元的内在兴奋性下降介导。3. 为了确定PM2.5暴露引起的NA心脏迷走神经元内在兴奋性下降是否由钾电流增加介导，NA神经元中存在的三个主要钾通道的激活动力学左移和/或失活动力学右移。4. 确定PM2.5暴露引起的HRV下降是否通过增强抑制突触兴奋性降低介导；通过测量强直性GABA介导的抑制性突触后电流（GABA IPSCs）的频率和振幅，研究-氨基丁酸（GABA）在NA心脏迷走神经元中的作用机制。5. 通过测量紧张性兴奋性突触后电流（GLU EPSCs）的频率和振幅以及诱发GLU EPSCs的振幅，确定PM2.5暴露诱导的HRV下降是否由NA心脏迷走神经元抑制性谷氨酸能（GLU）兴奋机制导致的突触兴奋性下降介导。

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.