DeCoursey T E, Hutter O F
J Physiol. 1984 Apr;349:329-51. doi: 10.1113/jphysiol.1984.sp015159.
Ba2+ was used to introduce K+ current fluctuations in addition to those arising from the intrinsic 'gating' mechanism studied in the preceding paper. In the presence of 0.5 to 2.0 mM-Ba2+, Lorentzian spectra were observed at potentials between -10 and -63 mV. The amplitude and corner frequency of these Lorentzian spectra varied with voltage in the general manner to be expected from the voltage- and time-dependent blocking action of Ba2+, but the microscopically determined time constant was consistently faster than that determined from the intensification of block upon hyperpolarization. The variance of the Ba2+-induced fluctuations could be used to calculate the limiting single-channel conductance, gamma, without the need to assume a specific model for inward rectification. The value of gamma obtained for preparations in symmetrical 120 mM-K+ was about 8 pS (20-24 degrees), in good agreement with that found in the preceding paper. Some fibres underwent a spontaneous, large increase in membrane conductance. This conductance showed inward rectification in the positive quadrant. At negative potentials this high conductance was blocked by 1 mM-Ba2+ in a voltage- and time-dependent manner. The block became faster and more complete at more negative potentials. Analysis of current noise in the high conductance state in the presence of Ba2+ gave Lorentzian spectra with corner frequencies in general agreement with the time constant of macroscopic current relaxations. The unitary conductance in that state was estimated to be at least 70 pS.
除了前一篇论文中研究的由内在“门控”机制引起的钾离子电流波动外，钡离子（Ba2+）也被用于引入钾离子电流波动。在存在0.5至2.0 mM - Ba2+的情况下，在 - 10至 - 63 mV的电位之间观察到洛伦兹光谱。这些洛伦兹光谱的幅度和转角频率随电压变化，其变化方式符合Ba2+的电压和时间依赖性阻断作用所预期的一般模式，但微观测定的时间常数始终比通过超极化时阻断增强所确定的时间常数更快。Ba2+诱导的波动的方差可用于计算极限单通道电导γ，而无需假设内向整流的特定模型。在对称的120 mM - K+中制备物获得的γ值约为8 pS（20 - 24摄氏度），与前一篇论文中发现的值非常一致。一些纤维的膜电导自发大幅增加。这种电导在正象限显示内向整流。在负电位下，这种高电导被1 mM - Ba2+以电压和时间依赖性方式阻断。在更负的电位下，阻断变得更快且更完全。在存在Ba2+的情况下，对高电导状态下的电流噪声分析得到的洛伦兹光谱的转角频率与宏观电流弛豫的时间常数总体一致。该状态下的单通道电导估计至少为70 pS。
