CARDIAC CELL VOLUME REGULATION IN CARDIOPLEGIA

细胞水肿是心肌损伤的一个重要方面。 细胞缺陷 容量调节与细胞损伤和收缩有关， 心脏停搏期间的电功能障碍（选择性心脏停搏）， 缺血和再流。 尽管其重要性，心脏容量调节 细胞还不太了解。 这是一个严重的问题， 因为灌注心脏的溶液必须设计成 在停搏期间提供心肌保护。 这些研究的目的是了解调节 心脏停搏和生理条件下的心脏细胞体积。 细胞体积控制的基本过程将从 测量细胞体积和细胞内离子的决定因素 离子选择性微电极测定K~+、Na~+、Cl~-和H~+的活性 在成人和成人的离体心室肌细胞和乳头肌中， 新生兔心脏 细胞体积的测量将使用 三种独立的方法：（1）视频显微镜将“光学切片” 肌细胞;（2）体积将根据对电流的阻力确定 在一个特殊设计的移液器中保持的单个肌细胞周围;以及（3） 细胞质隔室体积的变化将通过加载 用四甲基铵（TMA+）处理乳头肌或肌细胞，并测量 用ISE捕获TMA+。 我们将：（1）检验等渗心脏停搏液是 等渗并引起细胞体积改变。 (2)评价的作用 Na +/K +/2Cl-共转运，Na +/Cl-共转运，Na +-K+泵，Na +-H+交换， Cl--HCO3-交换和Na +-Ca2+交换维持细胞体积 在生理和心脏停搏条件下以及在渗透应激期间。 运输过程将从运输的影响来识别 抑制剂和选择性地从浸浴中排除被运输的离子 培养基对细胞体积和细胞内离子活性的影响。 (3)评估 移动的阴离子和[K +][Cl-]产物在设定细胞体积中的作用。 (3)检验新生儿细胞体积控制不同的假设 成人细胞 (4)确定改变pHi和代谢的影响 对细胞体积的抑制。 (5)在工作心脏模型中，比较 标准心脏停搏液对"改良"心脏停搏液的有效性 旨在更好地调节细胞体积。 细胞内离子活性测量与新的 用于测定分离的肌细胞和乳头状肌中的细胞体积的技术 肌肉可以提供关于心脏细胞反应的独特信息 改变细胞体积并允许识别溶质的扰动 有助于调节细胞体积的转运途径， 最终影响到细胞膜的完整性。 的意义 这些实验将提供一个基本的，关键的， 这些生理过程在心脏中几乎是未被探索的。 知识 的因素负责细胞体积控制是必要的 了解细胞病理生理紊乱的先决条件 体积，如心脏停搏和梗死期间发生的体积。

Cellular edema is a critical aspect of myocardial injury. Defects in cell volume regulation are associated with cell damage and contractile and electrical dysfunction during cardioplegia (elective cardiac arrest), ischemia and reflow. Despite its importance, volume regulation by cardiac cells is not well understood. This presents an acute problem for cardioplegia because the solution perfusing the heart must be designed provide myocardial protection during arrest. The goal of these studies is to understand the mechanisms that regulate cardiac cell volume under cardioplegic and physiologic conditions. Processes underlying cell volume control will be identified from measurements of cell volume and determinants of the intracellular ion activities of K+, Na+, Cl- and H+ with ion-selective microelectrodes (ISE) in both isolated ventricular myocytes and papillary muscles from adult and neonatal rabbit hearts. Measurements of cell volume will be made with three independent methods: (1) video microscopy will 'optically section' myocytes; (2) volume will be determined from the resistance to current flow around a single myocyte held in a specially designed pipette; and (3) changes in cytoplasmic compartment volume will be determined by loading papillary muscles or myocytes with tetramethylammonium (TMA+) and measuring the trapped TMA+ with an ISE. We will: (1) Test the hypothesis that isosmotic cardioplegic solutions are anisotonic and cause cell volume to change. (2) Evaluate the role of Na+/K+/2Cl- cotransport, Na+/Cl- cotransport, Na+-K+ pump, Na+-H+ exchange, Cl--HCO3- exchange, and Na+-Ca2+ exchange in the maintenance of cell volume under physiologic and cardioplegic conditions and during osmotic stress. Transport processes will be identified from the effects of transport inhibitors and selective omission of transported ions from the bathing media on both cell volume and intracellular ion activities. (3) Assess the role of mobile anions and the [K+] [Cl-] product in setting cell volume. (3) Test the hypothesis that cell volume control is different in neonatal and adult cells. (4) Determine the effect of altering pHi and metabolic inhibition on cell volume. (5) In a working heart model, compare the efficacy of standard cardioplegic solutions to that of 'improved' solutions designed to better regulate cell volume. The combination of intracellular ion activity measurements with novel techniques for determining cell volume in isolated myocytes and papillary muscles can provide unique information about the response of cardiac cells to perturbations that alter cell volume and allow identification of solute transport pathways that contribute to regulation of cell volume and, ultimately, to the integrity of the cell membrane. The significance of these experiments is that they will provide insight into a basic, critical, physiological processes that are virtually unexplored in heart. Knowledge of the factors responsible for cell volume control is a necessary prerequisite for understanding pathophysiological disturbances of cell volume, such as those occurring during cardioplegia and infarction.