Swandulla D, Armstrong C M
Department of Neurophysiology, Max Planck Institute for Psychiatry, Martinsried-Planegg, Federal Republic of Germany.
J Gen Physiol. 1988 Aug;92(2):197-218. doi: 10.1085/jgp.92.2.197.
Whole-cell Ca and Ba currents were studied in chick dorsal root ganglion (DRG) cells kept 6-10 in culture. Voltage steps with a 15-microseconds rise time were imposed on the membrane using an improved patch-clamp circuit. Changes in membrane current could be measured 30 microseconds after the initiation of the test pulse. Currents through Ca channels were recorded under conditions that eliminate Na and K currents. Tail currents, associated with Ca channel closing, decayed in two distinct phases that were very well fitted by the sum of two exponentials. The time constants tau f and tau s were near 160 microseconds and 1.5 ms at -80 mV, 20 degrees C. The tail current components, called FD and SD (fast-deactivating and slowly deactivating), are Ca channel currents. They were greatly reduced when Mg2+ replaced all other divalent cations in the bath. The SD component inactivated almost completely as the test pulse duration was increased to 100 ms. It was suppressed when the cell was held at membrane potentials positive to -50 mV and was blocked by 100-200 microM Ni2+. This behavior indicates that the SD component was due to the closing of the low-voltage-activated (LVA) Ca channels previously described in this preparation. The FD component was fully activated with 10-ms test pulses to +20 mV at 20 degrees C, and inactivated to approximately 30% during 500-ms test pulses. It was reduced in amplitude by holding at -40 mV, but was only slightly reduced by micromolar concentrations of Ni2+. Replacement of Ca2+ with Ba2+ increased the FD tail current amplitudes by a factor of approximately 1.5. The deactivation kinetics did not change (a) as channels inactivated during progressively longer pulses or (b) when the degree of activation was varied. Further, tau f was affected neither by changing the holding potential nor by varying the test pulse amplitude. Lowering the temperature from 20 to 10 degrees C decreased tau f by a factor of 2.5. In all cases, the FD component was very well fitted by a single exponential. There was no indication of an additional tail component of significant size. Our findings indicate that the FD component is due to closing of a single class of Ca channels that coexist with the LVA Ca channel type in chick DRG neurons.
在体外培养6 - 10天的鸡背根神经节（DRG）细胞中研究了全细胞钙电流和钡电流。使用改进的膜片钳电路，向细胞膜施加上升时间为15微秒的电压阶跃。在测试脉冲开始30微秒后可测量膜电流的变化。在消除钠电流和钾电流的条件下记录通过钙通道的电流。与钙通道关闭相关的尾电流以两个不同的阶段衰减，这两个阶段可以很好地用两个指数之和拟合。在-80 mV、20℃时，时间常数τf和τs分别接近160微秒和1.5毫秒。尾电流成分，称为FD和SD（快速失活和缓慢失活），是钙通道电流。当浴液中的Mg2+取代所有其他二价阳离子时，它们会大幅降低。随着测试脉冲持续时间增加到100毫秒，SD成分几乎完全失活。当细胞保持在高于-50 mV的膜电位时，它受到抑制，并被100 - 200 μM Ni2+阻断。这种行为表明，SD成分是由于在此制剂中先前描述的低电压激活（LVA）钙通道关闭所致。在20℃时，用10毫秒的测试脉冲到+20 mV可使FD成分完全激活，在500毫秒的测试脉冲期间失活至约30%。通过保持在-40 mV，其幅度减小，但仅被微摩尔浓度的Ni2+略微降低。用Ba2+取代Ca2+使FD尾电流幅度增加约1.5倍。失活动力学在以下情况不会改变：（a）随着通道在逐渐延长的脉冲期间失活；（b）当激活程度改变时。此外，τf既不受改变钳制电位的影响，也不受改变测试脉冲幅度的影响。将温度从20℃降至10℃使τf降低2.5倍。在所有情况下，FD成分都能很好地用单个指数拟合。没有迹象表明存在显著大小的额外尾电流成分。我们的研究结果表明，FD成分是由于在鸡DRG神经元中与LVA钙通道类型共存的一类单一钙通道关闭所致。
