CALCIUM AND SODIUM TRANSPORT IN VASCULAR SMOOTH MUSCLE

在"主动"（上坡）挤出的机制， 钙从肌肉细胞，并在稳定钙的调节 平衡，不完全理解。 许多类型的细胞， 包括无脊椎动物的肌肉和脊椎动物的平滑肌和心肌 肌肉，采用钙转运机制，其中钠离子 Ca交换（"Na/Ca交换"）。 因此， 电化学梯度可以提供至少一些能量 此外，Na/Ca交换也可能介导Ca 当Na电化学梯度降低时进入。 atp也 起作用，部分是通过对Na/Ca交换动力学的影响， 并且部分作为并行Ca-ATP酶驱动的"Ca泵"的燃料。 内部灌注的单个巨大藤壶肌细胞是 作为模型系统来研究Ca的运输， 肌肉的新陈代谢。 在即将到来的项目期间， 藤壶Na/Ca交换系统的表征 肌肉应该完成，包括直接测定 交换化学计量，和比较性质的 正向（Na进入/Ca退出）和反向（Ca进入/Na退出）模式 交换器的操作以及"无效模式" (Ca/Ca和Na/Na）交换。 特别令人感兴趣的是 内部Ca和Na在调节交换器周转中的作用。 的 从该模型系统获得的信息将被应用于 动脉平滑肌钙转运和代谢研究 肌细胞（ASM）。 牛尾环的初步研究 动脉（进展报告）表明，Na/Ca交换起着重要作用， 在调节（Ca2+）i，细胞内游离 钙浓度，在这个组织中。 在实验中，A 钙敏感荧光染料（Fura-2）和数字成像方法 将用于测量单个解离牛尾中的（Ca2+）i ASM细胞。 (Ca2+）i将在静息和活化细胞中测量， 以及随后的Na电化学梯度还原。 的 后者应提供有关Na/Ca的直接信息 这些细胞中的交换系统。 膜片钳方法，在 结合成像方法，将用于测量 与Na/Ca交换相关的离子电流，以及 确定调节ASM中Na/Ca交换的因素。 的 这些实验的结果应该提供新的信息 Na/Ca交换和其他相对重要性（平行） Ca~（2+）i的调节。 结果可能适用于病理生理过程 例如与高血压相关的那些。

The mechanisms involved in the "active" (uphill) extrusion of calcium from muscle cells, and in the regulation of steady Ca balance, are incompletely understood. Many types of cells, including invertebrate muscle and vertebrate smooth and cardiac muscle, employ a Ca transport mechanism in which Na ions exchange for Ca ("Na/Ca exchange"). Thus, the Na electrochemical gradient may provide at least some of the energy for Ca extrusion; moreover, Na/Ca exchange may also mediate Ca entry when Na electrochemical gradient is reduced. ATP also plays a role, in part via an effect on the Na/Ca exchange kinetics, and in part as fuel for a parallel Ca-ATPase driven "Ca pump". Internally perfused single giant barnacle muscle cells are employed as a model system to study Ca transport and metabolism in muscle. During the forthcoming project period, characterization of the Na/Ca exchange system in barnacle muscle should be completed, including direct determination of the exchange stoichiometry, and the comparative properties of the forward (Na entry/Ca exit) and reverse (Ca entry/Na exit) modes of operation of the exchanger as well as the "futile modes" (Ca/Ca and Na/Na) exchange. Of particular interest is the role of internal Ca and Na in the regulation of exchanger turnover. The information obtained from this model system will be applied to the study of Ca transport and metabolism in arterial smooth muscle (ASM) cells. Preliminary studies on rings of bovine tail artery (Progress Report) indicate that Na/Ca exchange plays a prominent role in the regulation of (Ca2+)i, the intracellular free Ca concentration, in this tissue. In the proposed experiments, a Ca-sensitive fluorescent dye (fura-2) and digital imaging methods will be used to measure (Ca2+)i in single, dissociated bovine tail ASM cells. (Ca2+)i will be measured in resting and activated cells, and following reduction of Na electrochemical gradient. The latter should provide direct information about the Na/Ca exchange system in these cells. Patch clamp methods, in conjunction with the imaging methods, will be used to measure the ionic currents associated with Na/Ca exchange, and to determine the factors that regulate Na/Ca exchange in ASM. The results of these experiments should provide new information about the relative importance of Na/Ca exchange and other (parallel) Ca transport systems in the regulation of (Ca2+)i in these cells. The results may be applicable to pathophysiological processes such as those associated with hypertension.