PH AND MYOCARDIAL CONTRACTILITY

病理生理条件下细胞内pH的变化 心肌缺血、缺氧或酸中毒等情况 与心肌功能受抑有关。这些研究 提议寻求进一步了解这些机制 参与心肌酸碱平衡和pH诱导 心肌收缩能力的改变。完好无损，有教养，新鲜的 分离的心肌细胞将用于这些研究 因为它们允许精确的顺序测量 跨肌膜离子通量、phi、胞浆游离(Ca)和 收缩状态。代谢性或呼吸性酸中毒或碱中毒 将使用具有PH值的HEPES缓冲介质生产 范围从5.0到9.0，具有不同HCO3或CO2含量的介质， 或NH4Cl。使用45Ca通量测量，我们将首先测试 Pho或phi变化影响跨肌膜钙离子的假说 培养的心肌细胞的运动。我们将在 与收缩反应的关系，pho或phi的变化(1) 通过慢钙通道、钠钙交换进行的单向钙流动 和肌膜钙泵；2)净钙通量；3)细胞内钙 泳池。我们还将测试钙-氢相互作用的假设 在心肌细胞内发生，并检查这一特性 互动。将研究细胞内的钙-氢相互作用 通过监测(Ca)i，因为Phi是变化的，反之亦然，使用最近 开发的pH和钙敏感荧光染料(BCECF和 福拉-2)。(CA)暴露于低NaO、Ko或CaO时，I会发生改变 介质、强心苷、钙通道激动剂或拮抗剂。 PHI将使用NH4Cl改变，或通过改变二氧化碳含量与 已调整(HCO3)。钠氢交换是否起着重要作用 在pH介导的钙通量和(钙)i的变化中也将 用钠离子的有效抑制剂乙基异丙基阿米洛利进行检测 H交换，通过Na-H直接测量~(24)Na通量 交换。肌浆网和肌浆网的潜在作用 线粒体在钙-氢相互作用中将使用特定的 改变这些细胞器中钙运动的药剂。其他内容 利用实验条件单独改变pho或phi的研究 将单独测试pho和phi共同决定的假设 心肌细胞在收缩功能紊乱时的变力状态 酸碱平衡。 这些研究预计将提供重要的补充 PH对钙动态平衡的影响及其机制的认识 酸中毒--或碱中毒--的潜在机制 心肌收缩能力的改变。

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.