Doroshenko P A, Kostyuk P G, Martynyuk A E
Gen Physiol Biophys. 1984 Feb;3(1):1-17.
The decline of calcium inward currents evoked by a long-lasting membrane depolarization was studied on isolated snail neurons internally perfused with a K+-free solution. Two exponential components superimposed on a steady inward current could be distinguished, a slow decline with a time constant of several hundreds of milliseconds, observed at all the testing potentials used, and a fast one with a time constant of several dozens of milliseconds, which appeared at depolarizations to about -10 mV and above. When the calcium current was blocked by extracellular Cd2+ or verapamil, an outward current could be recorded at the same depolarizations. Subtraction of the latter current from the total current, recorded prior to the blockage, largely reduced the fast component of the decline of the total current. An increase in pHi from 7.3 to 8.1 led to the elimination of both the outward current and the fast component of the calcium current decline. The slow component remained practically unchanged, with its rate depending upon the current amplitude. It was slowed following intracellular administration of EDTA, and after equimolar substitution of Ba2+ for Ca2+. It is concluded that the fast component of the calcium inward current decline is mainly due to the superposition of the outward current produced by low selective channels. Only the slow component represents an actual decline of the inward current through calcium channels; it is due to ion accumulation at the inner surface of the cell membrane.
在内部灌注无钾溶液的分离蜗牛神经元上，研究了由长时间膜去极化引起的钙内向电流的衰减。叠加在稳定内向电流上的两个指数成分可以区分，一个是在所有测试电位下都观察到的具有数百毫秒时间常数的缓慢衰减，另一个是在去极化至约-10 mV及以上时出现的具有几十毫秒时间常数的快速衰减。当钙电流被细胞外Cd2+或维拉帕米阻断时，在相同的去极化情况下可以记录到外向电流。从阻断前记录的总电流中减去后一种电流，大大减少了总电流衰减的快速成分。细胞内pH值从7.3增加到8.1导致外向电流和钙电流衰减的快速成分都消失。缓慢成分实际上保持不变，其速率取决于电流幅度。在细胞内给予EDTA后以及用Ba2+等摩尔替代Ca2+后，它会减慢。结论是，钙内向电流衰减的快速成分主要是由于低选择性通道产生的外向电流的叠加。只有缓慢成分代表通过钙通道的内向电流的实际衰减；这是由于离子在细胞膜内表面的积累。
