TRANSMURAL REGULATION Na/K PUMP ACTIVITY IN HEART

描述(申请人提供)：高等人。(2005)发现Na/K泵的最大周转率(Vmax)在整个犬室壁上是空间调节的，其中Vmax在心外膜最大(Epi)，在中层心肌(Mid)居中，在心内膜(Endo)最小。此外，本研究报告了Vmax的跨壁梯度在[Na]j中产生的梯度，该梯度在Endo最高，在中部居中，在Epi最低。我们的初步数据表明，[Na]j的梯度改变了Na/Ca交换(NCX)，从而产生了[Ca2](和收缩)的跨壁梯度。初步数据还表明，这种跨壁梯度是通过血管紧张素II(A2)产生的，血管紧张素II(A2)似乎受到机械反馈的调节，可能受肌动蛋白激酶(Tik)的调节，Tik是一种机械传感器。我们建立了Na/K泵电流(IP)、lNCx、[Ca~(2+)]_j与收缩之间的定量模型。该模型成功地预测了Endo和Epi心肌细胞记录的收缩和钙瞬变的差异。基于这些数据，我们假设：1)Vmax跨壁梯度的目的是在Endo产生最大的收缩和心率反应，在每个动作电位(AP)中，Endo首先收缩并对抗最大的压力负荷。2)这是一个反馈控制系统，其中传感器是Tik。压力依赖的Tik激活导致自分泌肾素血管紧张素系统(RAS)上调，该系统设置最大IP的梯度，从而使[Ca~(2+)]j和收缩性能抵消负荷中的跨室壁梯度。这项提议的目的是检验这两个假设。我们将使用电生理、钠和钙成像、收缩和生化测量的组合来实现这些目标。

DESCRIPTION (provided by applicant): Gao et al. (2005) found the max turn over rate (Vmax) of the Na/K pumps is spatially regulated across the canine ventricular wall, with Vmax being largest in the epicardium (Epi), intermediate in the midmyocardium (Mid) and smallest in the endocardium (Endo). Moreover, this study reported the transmural gradient in Vmax creates a gradient in [Na+]j, which is highest in Endo, intermediate in mid and lowest in Epi. Our preliminary data suggest the gradient in [Na+]j alters Na/Ca exchange (NCX) to generate a transmural gradient in [Ca2+]( and contraction. Preliminary data also suggest this transmural gradient is generated through angiotensin II (A2), which appears to be regulated by mechanical feedback, possible by the titin kinase (TiK), which is a mechanical sensor. We have created a quantitative model relating Na/K pump current (IP), lNCx, [Ca2*]j and contraction. The model successfully predicts differences in contraction and Ca-transients recorded in myocytes from Endo and Epi. Based on these data, we hypothesize: 1) The purpose of the transmural gradient in Vmax is to generate maximum contractility and rate responsiveness in Endo, which contracts first and against the greatest pressure load during each action potential (AP). 2) This is a feedback control system in which the sensor is the TiK. Pressure dependent activation of TiK causes up regulation of an autocrine renin angiotensin system (RAS) that sets the gradient in max IP such that [Ca2+]j and hence contractility offsets transmural gradients in load. The aims of this proposal are to test these two hypotheses. We will use a combination of electrophysiological, Na- and Ca-imaging, contraction, and biochemical measurements to accomplish these aims.