Suppression of cardiac calcium channels by acute hypoxia

描述（由申请人提供）：在工作心肌中，急性血流阻塞后，氧张力迅速下降，几分钟内引起不可逆的组织损伤。缺血性梗死的发生以细胞水平的一系列事件为标志，包括能量产生减少（- amp, / ATP， -糖酵解，/pH, - ros），离子通道活性改变（/ICa, -[K+]o, -[Na+]i）和Ca2+信号受损（/ICa， -舒张[Ca2+]i），最终导致心律失常，心肌病和心力衰竭。我们假设心肌缺氧的发作（<60 s）首先被Ca2+通道调节机制检测到，导致快速通道电流抑制，远早于全局细胞代谢表现（/ATP, /pH， -ROS等）。为了验证这一假设，我们将对暴露于氧张力阶跃变化的单个心肌细胞进行实验，同时使用电压钳和Ca2+成像技术监测ICa和[Ca2+]i。pO2的变化将通过快速灌注系统（<50 ms）来实现，并将在细胞附近进行监测。具体目的是：1)表征急性缺氧时ICa抑制的离子依赖性、电压依赖性和磷酸化依赖性；2)确定检测氧损失的分子实体和导致Ca2+通道调节的信号通路。意义与影响：本研究可能与心脏缺氧缺血期患者的治疗直接相关。结果可能建立缺氧诱导的ICa抑制作为保留代谢能量和延迟Ca2+过载的固有第一道防线。从更广泛的角度来看，整理由缺氧触发和/或汇聚控制ICa、收缩力和ATP消耗的各种调节途径是很重要的。反过来，认识到这些途径的独立性或相互依赖性可能有助于确定与急性和慢性心源性缺氧所有阶段相关的预防和治疗选择，包括例如，在临床上已经使用抑制ICa来预防随后的心律失常的再灌注发作。如果提出的O2传感器确实对Ca2+通道的控制有重要贡献，它可能会导致心脏损伤治疗新类别的发展。创新点：在细胞能量代谢、离子梯度和氧化还原状态发生显著变化之前，急性缺氧对ICa的抑制可以通过快速调控途径触发，这是一种新颖的观点。为了验证这一想法，我们使用了一系列电生理、光学和分子技术，这些技术提供了关键信号参数的同时测量，适合于动力学研究。为了探索临床意义，我们将扩大实验范围，从标准动物模型扩展到可用的人类心脏细胞和左右心室细胞。

DESCRIPTION (provided by applicant): In working myocardium, acute blockage of blood flow is followed by a rapid drop in oxygen tension that within minutes causes irreversible tissue damage. The onset of ischemic infarction is marked by a cascade of events that at the cellular level includes reduced energy production (-AMP, / ATP, -gycolysis, /pH, -ROS), altered ion channel activity (/ICa, -[K+]o, -[Na+]i), and impaired Ca2+ signaling (/ICa, -diastolic [Ca2+]i) leading eventually to arrhythmia, cardiomyopathy, and heart failure. We hypothesize that the onset of cardiac hypoxia (<60 s) is first detected by a Ca2+ channel regulatory mechanisms leading to rapid channel current suppression long before the global cellular metabolic manifestations (/ATP, /pH, -ROS etc.). To test this hypothesis, we shall perform experiments on single cardiomyocytes exposed to step changes in oxygen tension while ICa and [Ca2+]i are monitored using voltage-clamp and Ca2+-imaging techniques. The changes in pO2 will be implemented with a rapid perfusion system (<50 ms), and will be monitored in the immediate vicinity of the cells. The specific aims are: 1) To characterize the ionic-, voltage-, and phosphorylation- dependence of suppression of ICa in response to acute hypoxia, and 2) To identify the molecular entity that detects the loss of oxygen and the signaling pathway that leads to the modulation of the Ca2+ channel. Significance and Impact: The proposed research might be directly relevant to the management of patients who suffer periods of cardiac hypoxic ischemia. The results may establish hypoxia-induced suppression of ICa as an inherent first line of defense that preserves metabolic energy and delays Ca2+ overload. In a wider perspective, it is important to sort out the various regulatory pathways that are triggered by hypoxia and/or converge to control ICa, force of contraction, and expenditure of ATP. In turn, recognition of the independence or interdependence of these pathways may serve to identify prophylactic and therapeutic options that are relevant to all stages of acute and chronic cardiac hypoxia including e.g. the onset of reperfusion where suppression of ICa is already clinically used to prevent ensuing arrhythmias. If the proposed O2 sensor does indeed contribute significantly to the control of the Ca2+ channel, it may lead to development of new class of therapeutics for treatment of cardiac injury in general. Innovation: It is a novel idea that the suppression of ICa by acute hypoxia can be triggered by a rapid regulatory pathway long before significant occurrence of changes in the cellular energy metabolism, ionic gradients and redox state. To test this idea, we use an array of electrophysiological, optical, and molecular technique that provide simultaneous measurements of key signaling parameters and are suited for kinetic studies. To explore clinical relevance we shall expand the experimental scope from standard animal models to also include available human cardiac cells and cells from the right and left ventricles.