Study on ion transport of cardiac Na^+-K^+ pump and Na^+-Ca^<2+> exchnage

1.我们成功地建立了一种完整的心肌细胞大片切除方法，并记录了Na~+-Ca~(2+)交换和Na~+-K~+泵电流(心肌细胞大片法)。我们用心肌细胞宏观斑片法，通过测定Na~+-Ca~(2+)-Ca~(2+)和Gt~(2+)的翻转电位，研究了Na~+-Ca~(2+)&Gt~(2+)交换的化学计量学。化学计量比约为4Na^+：1Ca^&lt；2+&gt；，与目前公认的3Na^+：1Ca^&lt；2+&gt；有所不同。结果表明，当细胞质Na~(2+)降至5 mM以下时，其化学计量比接近3Na~+：1Ca~(2+)&gt~(2+)。我们在宏观膜片上研究了细胞质Na~(2+)和Ca~(2+)对I_&lt；Na/Ca&gt；的调节。Na~+依赖的失活动力学比水泡和卵母细胞中表达的交换器快约一倍。CA^lt；2+&gt；激活速度大约快十倍。我们提出，在跳动的细胞中，钙离子的调节是以节拍的方式进行的。我们建立了数学上的Na~(++)-Ca~(2+)交换模型…更多的是基于宏观补丁数据。该模型能很好地模拟Na~(2+)和Ca~(2+)的依赖关系、Na~+依赖的失活和Ca~(2+)的激活过程。用计算机模拟的方法研究了Na~(++)-Ca~(2+)~(2+)和Gt~(2+)交换在跳动心肌细胞中的作用。在静止膜电位下，大部分Na~+-Ca~(2+)&Gt~(2+)交换处于非激活状态，不起作用。当细胞内钙瞬变发生时，交换器返回到激活状态，并以正向模式工作。随着细胞内Ca~(2+)浓度的降低，交换器进入失活状态。在电压钳制的心室肌细胞中，我们通过快速的胞外Na~+浓度跃升，成功地记录到与Na~(++)-K~(++)泵的Na~(++)转运相关的电荷运动。与钙离子转运相关的电荷运动也可以通过胞外K^+跃迁来记录。K+转运的总电荷约为Na+转运的1/4。结果表明，K+转运步骤与Na+转运步骤一样，都是电压敏感的。较少

1. We successfully developed a method to excise macro-patch from intact cardiac ventricular cells and recorded Na^+-Ca^<2+> exchange (I_<Na/Ca>) and Na^+-K^+ pump currents (cardiac cell macro-patch method).2. We studied stoichiometry of Na^+-Ca^<2+> exchange using the cardiac cell macro-patch method by determining reversal potentials of I_<Na/Ca>. The stoichiometry was approximately 4Na^+ : 1Ca^<2+>, which was different from currently-accepted 3Na^+ : 1Ca^<2+>. It was suggested that the stoichiometry gets close to 3Na^+ : 1Ca^<2+> as cytoplasmic Na^+ decreases to less than 5 mM.3. We studied regulation by cytoplasmic Na^+ and Ca^<2+> of I_<Na/Ca> in the macro-patch. Kinetics of Na^+ dependent inactivation was about two-fold faster than the exchanger in blebs and the one expressed in oocytes. Ca^<2+> activation was about ten times faster. We proposed that the Ca^<2+> regulation functions in a beat-to-beat manner in beating cells.4. We developed a mathematical Na^+-Ca^<2+> exchange model … More , based on the macro-patch data. The model can well simulate Na^+ and Ca^<2+> dependences, the Na^+ dependent inactivation and the activation by Ca^<2+>.5. We studied contribution of Na^+-Ca^<2+> exchange in a beating heart cell by computer simulation. At resting membrane potential, the majority of Na^+-Ca^<2+> exchange was in inactive states and does not function. The exchanger returns to the active state as intracellular Ca^<2+> transient occurs and functions in a forward mode. The exchanger enters the inactive states as intracellular Ca^<2+> concentration declines.6. In voltage-clamped ventricular cells, we successfully recorded charge movement associated with the Na^+ translocation of Na^+-K^+ pump by a rapid extracellular Na^+ concentration jump. Charge movement associated with the Ca^<2+> translocation could also be recorded by an extracellular K^+ jump. The total charge of K^+ translocation was about 1/4 of the one of Na^+ translocation. It was indicated that the K^+ translocation step is voltage sensitive as well as Na^+ translocation step. Less