Suppression of cardiac calcium channels by acute hypoxia

描述（由申请人提供）：在工作心肌中，血流急性阻塞后氧分压迅速下降，在几分钟内导致不可逆的组织损伤。缺血性梗塞的发作以级联事件为标志，所述级联事件在细胞水平上包括能量产生减少（-AMP、-ATP、-糖酵解、-pH、-ROS）、离子通道活性改变（/伊卡、-[K+]o、-[Na+]i）和Ca 2+信号传导受损（/伊卡、-舒张[Ca 2 +]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（<60 s）的发生首先是由Ca 2+通道调节机制检测到的，导致快速通道电流抑制，早于整体细胞代谢表现（/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Ca 2+成像技术监测伊卡和[Ca 2 +]i。将使用快速灌注系统（<50 ms）实现pO 2的变化，并在细胞附近进行监测。具体目标是：1）表征响应于急性缺氧的伊卡抑制的离子依赖性、电压依赖性和磷酸化依赖性，和2）鉴定检测氧损失的分子实体和导致Ca 2+通道调节的信号传导途径。意义和影响：拟议的研究可能直接相关的患者谁遭受心脏缺氧缺血时期的管理。结果可能建立缺氧诱导的抑制伊卡作为一个固有的第一道防线，保持代谢能量和延迟Ca 2+超载。从更广泛的角度来看，重要的是要整理出由缺氧触发和/或汇聚到控制伊卡，收缩力和ATP消耗的各种调节途径。反过来，认识到这些途径的独立性或相互依赖性可以用于确定与急性和慢性心脏缺氧的所有阶段相关的预防和治疗选择，包括例如再灌注的开始，其中抑制伊卡已经在临床上用于预防随后的心律失常。如果所提出的O2传感器确实对Ca 2+通道的控制有显著贡献，则它可能导致开发用于治疗心脏损伤的新类别的治疗剂。创新：这是一个新的想法，抑制伊卡的急性缺氧可以触发一个快速的调节途径，在细胞的能量代谢，离子梯度和氧化还原状态的显着发生变化之前很久。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，并适用于动力学研究。为了探索临床相关性，我们将从标准动物模型扩大实验范围，以包括可用的人心脏细胞和来自右心室和左心室的细胞。 公共卫生相关性：当人体心脏的含氧血液供应因冠状动脉血栓形成而中断时，即使是短暂的中断，也会造成不可逆的损害。我们将探索一种内在的、潜在的保护机制，使心脏细胞感受到缺氧，并通过下调钙通道迅速做出反应，以节省能量，钙通道对维持心跳的节奏和强度至关重要。该项目可能提供对心脏关键蛋白之一的多方面功能的洞察，并帮助我们识别心脏的氧传感器，并开发新的治疗策略用于治疗患病的心脏。

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. PUBLIC HEALTH RELEVANCE: The human heart suffers irreversible damage when its supply of oxygenated blood is interrupted even briefly by coronary thrombosis. We shall explore an inherent, potentially protective, mechanism whereby heart cells sense oxygen deprivation and respond rapidly to husband their energy resources by down-regulating their calcium channels, which are essential in maintaining the rhythm and strength of the heart beat. This project may provide insight into the multi-faceted function of one of the key proteins of the heart, and help us identify the oxygen sensor of the heart and develop new therapeutic strategies for treatment of the diseased heart.