PH AND MYOCARDIAL CONTRACTILITY

细胞内pH值的变化发生在病理生理条件下， 例如心肌缺血、缺氧或酸中毒的病症， 与心肌功能低下有关。 研究 为进一步了解这些机制， 参与心肌酸碱平衡和pH诱导 心肌收缩力的变化。 完整培养和新鲜 这些研究将使用分离的心肌细胞 因为它们允许精确的连续测量 跨肌膜离子通量、pHi、胞质游离钙（Ca）和 收缩状态 代谢性或呼吸性酸中毒 将使用具有pH值的HEPES缓冲培养基生产 范围从5.0到9.0，具有不同HCO 3或CO2含量的培养基， 或NH 4Cl。 使用45 Ca通量测量，我们将首先测试 pHo或pHi变化影响跨肌膜Ca ~（2+）的假说 运动在培养的心肌细胞。 我们将在 与收缩反应的关系，1）上pHo或pHi的变化 钙通道单向流动，钠钙交换 和肌膜钙泵; 2）净钙流量; 3）细胞钙 池. 我们还将检验Ca-H相互作用 发生在心肌细胞内，并检查其特性， 互动 细胞内的钙-氢相互作用将被研究 通过监测（Ca）i随pHi变化，反之亦然，最近使用 开发的pH和Ca敏感的荧光染料（BCECF和 Fura-2）。 (Ca)i将通过暴露于低Nao、Ko或Cao而改变 培养基、强心苷或Ca通道激动剂或拮抗剂。 使用NH 4Cl或通过改变CO2含量来改变pHi， 调整（HCO 3）。 Na-H交换是否起重要作用 在pH值介导的变化，钙通量和（钙）i也将 使用乙基异丙基氨氯吡咪（一种有效的Na- H交换，并通过Na-H直接测量24 Na通量 交易所 肌浆网和 线粒体在Ca-H相互作用将检查使用特定的 改变这些细胞器中Ca运动的试剂。 额外 使用实验条件单独改变pHo或pHi的研究 单独将检验pHo和pHi决定的假设 心肌细胞的正性肌力状态 酸碱平衡 预计这些研究将提供重要的补充资料， 了解pH值对钙稳态的影响， 酸中毒或水肿介导的 心肌收缩力的变化。

Changes in intracellular pH occur under pathophysiologic conditions such as myocardial ischemia, hypoxia or acidosis that are associated with depressed myocardial function. The studies proposed seek to gain further understanding of the mechanisms involved in myocardial acid-base homeostasis and pH-induced changes in myocardial contractility. Intact cultured and freshly dissociated cardiac myocytes will be used for these studies because they allow accurate sequential measurements of transsarcolemmal ion fluxes, pHi, cytosolic free (Ca) and contractile state. Metabolic or respiratory acidosis or alkalosis will be produced using HEPES-buffered media with pH values ranging from 5.0 to 9.0, media with varied HCO3 or CO2 content, or NH4Cl. Using 45Ca flux measurements, we will first test the hypothesis that changes in pHo or pHi affect transsarcolemmal Ca movement in cultured cardiac myocytes. We will examine in relation to contractile responses, changes in pHo or pHi on 1) unidirectional Ca fluxes via slow Ca channels, Na-Ca exchange and the sarcolemmal Ca pump; 2) net Ca fluxes; and 3) cellular Ca pools. We will also test the hypothesis that Ca-H interactions occur within cardiac myocytes and examine the properties of this interaction. The Ca-H interaction within the cells will be studied by monitoring (Ca)i as pHi is varied and vice versa, using recently developed pH- and Ca-sensitive fluorescent dyes (BCECF and Fura-2). (Ca)i will be altered by exposure to low Nao, Ko, or Cao media, cardiac glycosides, or Ca channel agonists or antagonists. pHi will be altered using NH4Cl, or by varying CO2 content with adjusted (HCO3). Whether Na-H exchange plays a significant role in pH-mediated changes in Ca fluxes and (Ca)i will also be examined using ethylisopropylamiloride, a potent inhibitor of Na- H exchange, and by direct measurement of 24Na flux via Na-H exchange. The potential roles of sarcoplasmic reticulum and mitochondria in Ca-H interaction will be examined using specific agents that alter Ca movements in these organelles. Additional studies using experimental conditions to alter pHo alone or pHi alone will test the hypothesis that both pHo and pHi determine the inotropic state of cardiac myocytes during disturbances of acid-base balance. These studies are expected to provide important additional knowledge on the effect of pH on Ca homeostasis and the underlying mechanisms involved in acidosis- or alkalosis-mediated changes in myocardial contractility.