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从完整心室肌细胞上切取大膜片的方法，并记录了Na^+-Ca^<2+>交换（I_<Na/Ca>）和Na^+-K^+泵电流（心肌细胞大膜片法）.我们用心肌细胞大斑片法，通过测定I_<Na/Ca>的逆转电位，研究了Na^+-Ca^<2+>交换的化学计量学。化学计量比约为4 Na ^+：1 Ca ^<2+>，这与目前公认的3 Na ^+：1 Ca ^<2+>不同。研究表明，当细胞质Na^+浓度降至5 mM以下时，化学计量比接近3 Na ^+：1 Ca ^<2+>。我们研究了细胞质Na^+和Ca^<2+>对巨斑I_<Na/Ca>的调节。Na^+依赖性失活的动力学比泡中的交换器和卵母细胞中表达的交换器快两倍左右。Ca^2+的激活速度大约快了10倍。我们认为，在搏动细胞中，Ca^<2+>的调节是以逐拍的方式进行的.我们建立了Na^+-Ca^<2+>交换的数学模型 ...更多信息 基于宏块数据。该模型能很好地模拟Na^+和Ca^<2+>依赖性、Na^+依赖性失活和Ca^<2+激活。我们用计算机模拟研究了心脏细胞在跳动过程中Na^+-Ca^<2+>交换的贡献.在静息膜电位下，大部分Na^+-Ca^<2+>交换处于失活状态，不起作用。当细胞内Ca^2+瞬变发生时，交换器恢复到活性状态，并以正向模式发挥作用。随着细胞内Ca^<2+>浓度的降低，交换剂进入失活状态.在电压钳制的心室肌细胞中，我们通过细胞外Na^+浓度的快速跳跃，成功地记录到了与Na^+-K^+泵的Na^+移位相关的电荷运动。与Ca^2+易位相关的电荷运动也可以通过细胞外K^+跳跃记录下来。K^+转运的总电荷量约为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。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