MYOCARDIAL CALCIUM HANDLING DURING AND AFTER HYPOTHERMIA

低温期间和之后的心肌钙处理

• 批准号: 2752395
• 负责人: DAVID F STOWE
• 金额: $ 36.31万
• 依托单位: MEDICAL COLLEGE OF WISCONSIN
• 依托单位国家: 美国
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-01-15 至 2002-12-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/2752395
• 关键词: action potentials; calcium flux; fluorimetry; guinea pigs; heart contraction; heart metabolism; induced hypothermia; ion transport; myocardium; potassium ion; reperfusion; sodium ion; voltage /patch clamp

Mild (27 degrees C) to moderate (17 degrees C) hypothermia is used to reduce myocardial energy consumption and function by slowing metabolism during valve, coronary vessel, and ascending aortic surgery; severe (3 degrees C) hypothermia is used to protect donor hearts prior to transplant. But cardiac function on reperfusion after hypothermia often remains impaired. It is known that mild to moderate hypothermia increases myocardial contractility per beat and severe hypothermia causes arrest with diastolic contracture and results in impaired contractility and relaxation on warm reperfusion. Altered Ca2+ handling by Ca2+ pumps, voltage-regulated Ca2+ conductance, Ca2+ linked exchanger activity, and altered Ca2+ sensitivity ultimately underlie these contractile effects. It is not known how disturbances in overall cation homeostasis during cooling lead to altered Ca2+. The mechanisms underlying Ca2+ deregulation and poor reperfusion function are likely temperature dependent. The aim is to investigate the mechanisms of interaction of specific cations responsible for changes in cardiac action potential and contractility during 4 hrs of graded hypothermia, and particularly during 2 hrs of reperfusion. It is proposed that hypothermia alters Ca2+ homeostasis via mechanisms linked to regulation of a) [Na+]i, via the Na+ K+ pump, Na+ influx, and Na+ H+ and Na+ Ca2+ exchangers, b) [Ca2+]i, mediated via the Ca2+ pump, c) myofilament Ca2+ sensitivity, and d) K+ efflux. The objectives are to discover how cation equilibrium and contractile function are altered by hypothermia; to find if mild and moderate hypothermia alter cation equilibrium and contractile function differently than severe hypo-thermia; to find if low-flow cold perfusion is better than cold storage, and to determine which treatment strategies are best to counteract deleterious contractile effects during reperfusion. Three guinea pig cardiac models will be used to measure: intracellular concentrations of Na+ and H+ mitochondrial Ca2+, and phasic diastolic and systolic myoplasmic Ca+ fluorometrically, with left ventricular pressure (LVP) and other functional and metabolic variables in intact beating hearts; whole cell voltage-clamped Na+, Ca+, and K+ATP channel currents in isolated cardio myocytes, and; AP's in sub endocardial cells. Hypothermia and rewarming effects on Ca2+ sensitivity will be assessed by plotting LVP vs diastolic and systolic [Ca2+] at increasing external Ca. These studies will lead to a better understanding of Ca2+ loading and therapies to protect hypothermic hearts.

轻度（27 摄氏度）至中度（17 摄氏度）低温用于 通过减慢新陈代谢来减少心肌能量消耗和功能 在瓣膜、冠状血管和升主动脉手术期间；严重（3 C 度）低温用于在捐赠心脏之前保护心脏 移植。 但低温后再灌注的心功能常常受到影响 仍然受损。 众所周知，轻度至中度体温过低 增加每次心跳的心肌收缩力和严重低温 导致舒张性挛缩停止并导致功能受损 热再灌注时的收缩和舒张。 改变 Ca2+ 处理 通过 Ca2+ 泵、电压调节 Ca2+ 电导、Ca2+ 连接交换器 活性和改变的 Ca2+ 敏感性最终是这些的基础 收缩效应。 目前尚不清楚总体阳离子的干扰如何 冷却过程中的稳态导致 Ca2+ 发生变化。 机制 可能存在潜在的 Ca2+ 失调和再灌注功能不良 温度依赖性。 目的是研究特定相互作用的机制 负责心脏动作电位变化的阳离子和 4 小时分级低温期间的收缩力，特别是 再灌注2小时期间。 据建议，体温过低会改变 Ca2+ 稳态通过与 a) [Na+]i 的调节相关的机制实现，通过 Na+ K+ 泵、Na+ 流入以及 Na+ H+ 和 Na+ Ca2+ 交换器，b) [Ca2+]i，通过 Ca2+ 泵介导，c) 肌丝 Ca2+ 敏感性， d) K+ 流出。 目标是发现阳离子平衡如何 体温过低会改变收缩功能；找出是否温和 中度低温改变阳离子平衡和收缩功能 与严重低温不同；寻找是否低流量冷灌注 优于冷藏，并确定采用何种处理策略 最好抵消期间的有害收缩效应 再灌注。 将使用三个豚鼠心脏模型来测量： Na+ 和 H+ 线粒体 Ca2+ 的细胞内浓度，以及 阶段性舒张期和收缩期肌浆 Ca+ 荧光测定，左 心室压力 (LVP) 和其他功能和代谢变量 完整跳动的心脏；全细胞电压钳位 Na+、Ca+ 和 K+ATP 分离心肌细胞中的通道电流，以及； AP 位于 sub 心内膜细胞。 低温和复温对 Ca2+ 的影响 通过绘制 LVP 与舒张压和收缩压的关系来评估敏感性 [Ca2+] 增加外部 Ca。 这些研究将带来更好的结果 了解 Ca2+ 负荷和保护体温过低的疗法 心。