Stanley E F, Russell J T
Laboratory of Biophysics, NINCDS, Bethesda, MD 20892.
Brain Res. 1988 Dec 13;475(1):64-72. doi: 10.1016/0006-8993(88)90199-0.
The voltage-dependent inactivation of Ca currents was explored in dissociated intermediate lobe (IL) cells from the rat pituitary. On the basis of current-voltage relations two main inward currents could be identified in this cell, a transient current, (I-t), and a sustained current, (I-s). Inactivation was explored either by changing the holding potential and testing the change in the inward currents during a brief test pulse, or, by depolarizing the membrane and following the decay of the evoked inward current. Three current decay rates were identified, each with a characteristic dependence on membrane potential. The fastest decay rate (tau 1), was attributed to the inactivation of the I-t current and had a value of 57 ms at -40 mV, decreasing to 10 ms at -10 mV (extrapolated value of 6 ms at 0 mV). The other two decay rates, tau 2 and tau 3, decreased monotonically with depolarization of the membrane potential and reflected the inactivation of the I-s current with values of 1.8 and 20 s at 0 mV. I-s inactivation and reactivation was found to occur even in the normal resting potential range of this cell. These properties of the calcium channels can explain the voltage-dependent inactivation of secretion that has been observed previously in this and other secretory cells. In addition, they suggest that calcium currents, and hence secretion, may be modulated by external factors that cause small, but sustained, changes in the resting potential of the IL cell.
在大鼠垂体中间叶（IL）的解离细胞中研究了钙电流的电压依赖性失活。根据电流-电压关系，在这种细胞中可识别出两种主要的内向电流，一种瞬时电流（I-t）和一种持续电流（I-s）。通过改变保持电位并在短暂测试脉冲期间测试内向电流的变化，或者通过使膜去极化并跟踪诱发的内向电流的衰减来研究失活。确定了三种电流衰减速率，每种速率对膜电位都有特征性的依赖性。最快的衰减速率（tau 1）归因于I-t电流的失活，在-40 mV时的值为57 ms，在-10 mV时降至10 ms（在0 mV时的外推值为6 ms）。另外两种衰减速率tau 2和tau 3随着膜电位的去极化而单调下降，反映了I-s电流的失活，在0 mV时的值分别为1.8秒和20秒。发现即使在该细胞的正常静息电位范围内，I-s也会发生失活和再激活。钙通道的这些特性可以解释先前在该细胞和其他分泌细胞中观察到的分泌的电压依赖性失活。此外，它们表明钙电流以及因此的分泌可能受到外部因素的调节，这些外部因素会导致IL细胞静息电位发生小的但持续的变化。
