IDENTIFICATION OF SODIUM CALCIUM EXCHANGE CURRENT IN SINGLE VENTRICULAR CELLS OF GUINEA-PIG
IDENTIFICATION OF SODIUM CALCIUM EXCHANGE CURRENT IN SINGLE VENTRICULAR CELLS OF GUINEA-PIG
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DOI：
10.1113/jphysiol.1987.sp016450
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发表时间：
1987-03-01
影响因子：
5.5
通讯作者：
NOMA, A
中科院分区：
文献类型：
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作者：
KIMURA, J;MIYAMAE, S;NOMA, A
1. 采用全细胞电压箝位和细胞内灌注相结合的方法研究了豚鼠心脏单心室细胞的Na-Ca交换电流。2. 通过阻断Ca和K通道以及Na-K泵，使膜电导最小化。在这些条件下，当Ca2+被含有430 nM-Ca2+的移液管溶液内部加载时，将富含Li+的外部溶液改变为富含Na+的外部溶液会诱导显着的内向电流。在没有内部Ca2+的情况下施加外部Na+并没有明显改变电流。相比之下，在内部Na+存在的情况下灌注1 mm -外部Ca2+，由20 mM-Na+移液管溶液加载，诱导明显的向外电流。在没有内部Na+的情况下，Ca2+的过剩只引起很小的电流变化。4. 外部Ca2+-和外部na +-感应电流的电流-电压关系几乎呈指数电压依赖关系，由等式i = a exp （rEF/RT）给出，其中a是决定电流大小的比例因子，r是速率理论中使用的分配参数，表示能量势垒在电场中的位置，这表明电流的电压依赖关系的陡峭性。E， F， R和T有它们通常的含义。a的值为1-2 .mu. a /.mu。Ca2+诱导的向外电流F和r约为0.35。在非常正或负的电位下，电流的大小比指数关系所期望的要小。5. 电流被La3+、Cd2+、Mn2+、Ni2+等重金属阳离子阻断，被amiloride和D600部分阻断。6. Ca2+诱导的外向电流的温度系数（Q10）为3.6 +-。0.4 （n = 4）在0 mV和4.0。0.9在50毫伏，范围在21和36度之间。c . 7。向外电流大小与外部Ca2+浓度呈s型关系，最大浓度为一半，K1/2为1.38 mM， Hill系数为0.9 +-。0.2 （n = 5）。Sr2+能以7 mM的K1/2取代Ca2+，而Mg2+和Ba2+不能取代Ca2+。9. 向内电流分量也表现出与外部Na+呈s型关系，K1/2为87.5 +-。10.7 mM，希尔系数2.9±。0.4 （n = 6）。电流的反转电位接近3na +: 1ca2 +交换的预期值。11. Ca2+和Na+诱导电流瞬态衰减。这种现象很可能是由于膜下Ca2+浓度立即发生变化引起的。12. 上述结果与离子通量测量在鱿鱼轴突和心脏肌鞘囊泡中所研究的Na-Ca交换特性基本一致。因此，我们认为Na+-和Ca2+感应电流是由电致Na- ca交换产生的。
1. The Na-Ca exchange current was investigated in single ventricular cells from guinea-pig hearts by combining the techniques of whole-cell voltage clamp and intracellular perfusion. 2. The membrane conductance was minimized by blocking Ca and K channels as well as the Na-K pump. Under these conditions, when Ca2+ was loaded internally by a pipette solution containing 430 nM-Ca2+, changing the Li+-rich external solution to a Na+-rich one induced a significant inward current. Applying external Na+ in the absence of internal Ca2+ did not appreciably change the current. In contrast, perfusing 1 mM-external Ca2+ in the presence of internal Na+ which was loaded by a 20 mM-Na+ pipette solution, induced a marked outward current. Ca2+ superfusion in the absence of internal Na+ caused only a small current change. 4. The current-voltage relation of external Ca2+- and external-Na+-induced current showed almost exponential voltage dependence as given by the equation i = a exp (rEF/RT), where a is a scaling factor that determines the magnitude of the current and r is a partition parameter used in the rate theory and represents the position of the energy barrier in the electrical field, which indicates the steepness of the voltage dependence of the current. E, F, R and T have their usual meanings. The value of a was 1-2 .mu.A/.mu.F and r about 0.35 for the Ca2+-induced outward current. At very positive or negative potentials, the current magnitude became smaller than expected from an exponential relation. 5. The current was blocked by heavy metal cations, such as La3+, Cd2+, Mn2+ and Ni2+ and partially blocked by amiloride and D600. 6. The temperature coefficient (Q10) value of the Ca2+-induced outward current was 3.6 .+-. 0.4 (n = 4) at 0 mV and 4.0 .+-. 0.9 at 50 mV in the range between 21 and 36.degree. C. 7. The outward current magnitude showed a sigmoidal dependence upon the external Ca2+ concentration with a half-maximum concentration, K1/2 of 1.38 mM and a Hill coefficient of 0.9 .+-. 0.2 (n = 5). 8. Sr2+ could replace Ca2+ with K1/2 of 7 mM. Mg2+ and Ba2+, however, did not replace Ca2+. 9. The inward current component also showed as sigmoidal external Na+ dependence with K1/2 of 87.5 .+-. 10.7 mM and a Hill coefficient of 2.9 .+-. 0.4 (n = 6). 10. The reversal potential of the current was obtained near the values expected for 3 Na+:1 Ca2+ exchange. 11. The Ca2+- and Na+-induced currents decayed transiently. This phenomenon is most likely caused by Ca2+ concentration change immediately under the membrane. 12. The above findings largely agree with the properties of the Na-Ca exchange studied by ionic flux measurements in squid axon and cardiac sarcolemmal vesicles. Thus we conclude that the Na+- and Ca2+-induced currents were generated by electrogenic Na-Ca exchange.