Intracellular Calcium Homeostasis in the Heart

细胞内钙离子浓度的调节是维持各种细胞功能的重要过程。在心肌细胞中，Ca~(2+)的内流主要通过电压门控的Ca~(2+)通道进行，外流主要通过Na~(+)-Ca~(2+)交换器进行。也就是说，动作电位的去极化打开了L式的钙通道，触发了肌肉的收缩。在舒张期，Na~(++)-Ca~(2+)~(2+)~(2+)交换利用Na~(++)的电化学驱动力将Ca~(2+)~(2+)泵出。在各种病理条件下，细胞内钙离子泵出受到干扰，导致细胞内钙超载。为了研究Na~(++)-Ca~(2+)交换器的功能，我们测定了Na~(++)-Ca~(2+)交换器产生的膜电流(Na~(++)-Ca~(2+)交换电流)，同时测定了细胞内游离Ca~(2+)。通过处理豚鼠Hea-…获得单个心肌细胞。用全细胞膜片钳技术测定胶原酶作用下的RT及其膜电流。钙离子指示剂Indo-1通过全细胞膜片钳电极被负载到细胞内。结果发现，膜去极化使外向Na~(++)-Ca~(2+)~(2+)交换电流的幅度增大，同时细胞内Ca~(2+)&Gt~(2+)浓度升高。Na~(++)-Ca~(2+)和~(2+)&gt~(2+)交换电流的整合与胞内Ca~(2+)和~(2+)浓度的升高相对应。在另一系列单独的实验中，使用耐光性化合物Nitr-5瞬间提高了细胞质中的Ca~(2+)浓度。笼状Ca~(2+)的闪光光解以单指数时间过程激活了Na~(++)-Ca~(2+)的内向交换电流。这一发现与安娜^+-Ca^&lt；2+&gt；交换模型在Na~+转运步骤中具有电生步骤是一致的。基于传统的交换模型，我们得出结论：在26ﾟC-80 mV下，成交率至少为125100%S^-1；站点密度大于2000/亩m^2。

The regulation of the cytosolic Ca^<2+> concentration is a essential process to maintain the cellular function in every type of cells. In the cardiac myocytes the influx of Ca^<2+> is conducted mainly through the Voltage-gated Ca^<2+> channel, and the efflux via the Na^+-Ca^<2+> exchanger. Namely, the depolarization of the action potential opens the L-type Ca^<2+> channels, which triggers the contraction of the muscle. During the diastole, the Na^+-Ca^<2+> exchange pump out the Ca^<2+> using the electrochemical driving force for Na^+. Under various types of pathological conditions, pumping out of Ca^<2+> is disturbed, so that the cell become overloaded with Ca^<2+>. To investigate the function of the Na^+-Ca^<2+> exchanger, we measured the membrane current, which is produced by the Na^+-Ca^<2+> exchanger (the Na^+-Ca^<2+> exchange current), simultaneously with the measurement of the intracellular free Ca^<2+>. The single ventricular myocytes were obtained by treating the guinea-pig hea … More rt with collagenase, and its membrane currents were measured using the whole cell patch clamp technique. The Ca^<2+>-indicator, Indo-1 was loaded within the cell through the whole cell patch clamp electrode. It was found that the depolarization of the membrane increased the amplitude of the outward Na^+-Ca^<2+> exchange current, and simultaneously the intracellular Ca^<2+> concentration increased. The integration of the Na^+-Ca^<2+> exchange current well corresponded to the increase of the intracellular Ca^<2+> concentration. In a separate series of experiments, the cytosolic Ca^<2+> concentration was raised instantaneously using the photolabile compound, Nitr-5. The flash photolysis of this caged Ca^<2+> activated the inward Na^+-Ca^<2+> exchange current in a single exponential time course. This finding is consistent with an Na^+-Ca^<2+> exchange model having the electrogenic step in the Na^+ transporting step. Based on the conventional exchanger model, we conclude that the turnover rate is at least 125 s^<-1> at 26 ﾟC -80 mv, and the site density is more than 2000/ mu m^2. Less