Larsen E H, Gabriei S E, Stutts M J, Fullton J, Price E M, Boucher R C
Department of Medicine, University of North Carolina at Chapel Hill 27599-7020, USA.
J Gen Physiol. 1996 Jun;107(6):695-714. doi: 10.1085/jgp.107.6.695.
The endogenous Cl- conductance of Spodoptera frugiperda (Sf9) cells was studied 20-35 h after plating out of either uninfected cells or cells infected by a baculovirus vector carrying the cloned beta-galactosidase gene (beta-Gal cells). With the cation Tris+ in the pipette and Na+ in the bath, the reversal potential of whole-cell currents was governed by the prevailing Cl- equilibrium potential and could be fitted by the Goldman-Hodgkin-Katz equation with similar permeabilities for uninfected and beta-Gal cells. In the frequency range 0.12 < f < 300 Hz, the power density spectrum of whole-cell Cl- currents could be fitted by three Lorentzians. Independent of membrane potential, >50% of the total variance of whole-cell current fluctuations was accounted for by the low frequency Lorentzian (fc = 0.40 +/- 0.03 Hz, n = 6). Single-Cl- channels showed complex gating kinetics with long lasting (seconds) openings interrupted by similar long closures. In the open state, channels exhibited fast burst-like closures. Since the patches normally contained more than a single channel, it was not possible to measure open and closed dwell-time distributions for comparing single-Cl- channel activity with the kinetic features of whole-cell currents. However, the power density spectrum of Cl- currents of cell-attached and excised outside-out patches contained both high and low frequency Lorentzian components, with the corner frequency of the slow component (fc = 0.40 +/- 0.02 Hz, n = 4) similar to that of whole-cell current fluctuations. Chloride channels exhibited multiple conductance states with similar Goldman-Hodgkin-Katz-type rectification. Single-channel permeabilities covered the range from approximately 0.6.10(-14) cm5/s to approximately 6.10(-14) cm3/s, corresponding to a limiting conductance (gamma 150/150) of approximately 3.5 pS and approximately 35 pS, respectively. All states reversed near the same membrane potential, and they exhibited similar halide ion selectivity, P1 > PCl approximately PBr. Accordingly, Cl- current amplitudes larger than current flow through the smallest channel unit resolved seem to result from simultaneous open/shut events of two or more channel units.
在接种未感染细胞或感染携带克隆β-半乳糖苷酶基因的杆状病毒载体的细胞（β-Gal细胞）20 - 35小时后，对草地贪夜蛾（Sf9）细胞的内源性氯离子电导进行了研究。移液器中为阳离子Tris⁺，浴槽中为Na⁺时，全细胞电流的反转电位由当时的氯离子平衡电位决定，并且未感染细胞和β-Gal细胞的渗透率相似，可通过戈德曼-霍奇金- Katz方程拟合。在0.12 < f < 300 Hz频率范围内，全细胞氯离子电流的功率密度谱可用三个洛伦兹曲线拟合。与膜电位无关，全细胞电流波动总方差的>50%由低频洛伦兹曲线解释（fc = 0.40 ± 0.03 Hz，n = 6）。单氯离子通道显示出复杂的门控动力学，具有持续较长时间（数秒）的开放，其间穿插着类似的长时间关闭。在开放状态下，通道表现出快速的爆发式关闭。由于膜片通常包含多个以上通道，因此无法测量开放和关闭停留时间分布以比较单氯离子通道活性与全细胞电流的动力学特征。然而，细胞贴附式和切除的外翻膜片的氯离子电流功率密度谱包含高频和低频洛伦兹分量，慢分量的转折频率（fc = 0.40 ± 0.02 Hz，n = 4）与全细胞电流波动的相似。氯离子通道表现出多种电导状态，具有类似戈德曼-霍奇金- Katz型整流。单通道渗透率范围从约0.6×10⁻¹⁴ cm⁵/s到约6×10⁻¹⁴ cm³/s，分别对应于约3.5 pS和约35 pS的极限电导（γ 150/150）。所有状态在接近相同的膜电位处反转，并且它们表现出相似的卤离子选择性，P⁻ > PCl ≈ PBr。因此，大于通过分辨出的最小通道单元的电流的氯离子电流幅度似乎是由两个或更多通道单元的同时开放/关闭事件导致的。
