TRANSMURAL REGULATION Na/K PUMP ACTIVITY IN HEART

描述（由申请人提供）：Gao等人（2005）发现Na/K泵的最大周转率（Vmax）在犬心室壁受到空间调节，其中Vmax在心外膜（Epi）最大，在中心肌（Mid）中等，在心内膜（Endo）最小。此外，本研究还报道了Vmax的跨壁梯度在[Na+]j中产生梯度，该梯度在Endo中最高，在mid中居中，在Epi中最低。我们的初步数据表明，[Na+]j的梯度改变Na/Ca交换（NCX），从而产生[Ca2+]的跨壁梯度（和收缩）。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，它似乎是由机械反馈调节的，可能是由titin激酶（TiK），这是一种机械传感器。我们建立了Na/K泵电流（IP）、lNCx、[Ca2*]j和收缩的定量模型。该模型成功地预测了Endo和Epi肌细胞中记录的收缩和钙瞬态的差异。基于这些数据，我们假设：1)Vmax跨壁梯度的目的是产生最大的远道收缩力和速率响应性，远道在每次动作电位（AP）期间首先收缩并承受最大的压力负荷。2)这是一个反馈控制系统，其中传感器是TiK。TiK的压力依赖性激活导致自分泌肾素血管紧张素系统（RAS）的上调，该系统设置最大IP梯度，使[Ca2+]j和收缩性抵消负载的跨壁梯度。这个提议的目的是检验这两个假设。我们将结合电生理、钠钙成像、收缩和生化测量来实现这些目标。

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.