Fiekers J F
J Neurosci. 1985 Feb;5(2):502-14. doi: 10.1523/JNEUROSCI.05-02-00502.1985.
The concentration-dependent actions of neostigmine, a carbamate anticholinesterase agent, were studied on the acetylcholine receptor channel complex in voltage-clamped twitch fibers of costocutaneous muscles of garter snakes. Low concentrations of neostigmine (10(-6) or 10(-5) M) increased miniature endplate current (MEPC) amplitude and the time constant of MEPC decay without changing the relationship between the MEPC decay time constant and membrane potential. Acetylcholine- or carbachol-induced endplate current fluctuation spectra were well fitted by a single Lorentzian curve with a characteristic frequency and single-channel conductance unaltered by low concentrations of neostigmine. Concentrations of neostigmine greater than 5 X 10(-5) M decreased MEPC amplitude and split the decay of MEPCs into two components, one faster and one slower than the control rate. These effects were both voltage and concentration dependent. Spectra of current fluctuations recorded in concentrations greater than or equal to 5 X 10(-5) M neostigmine required two time constants, one faster and one slower than the control. Two component spectra were also obtained with carbachol-induced current fluctuation spectra, indicating that these effects of neostigmine were direct and not a consequence of acetylcholinesterase inhibition. Similar results were also obtained in muscles pretreated with collagenase to remove junctional acetylcholinesterase. The fast and slow time constants obtained from current fluctuation spectra decreased and increased, respectively, with either increases in the concentration of neostigmine or membrane hyperpolarization when analyzed in the same fiber. The effects of neostigmine on channel lifetime were reversible with washing. These results indicate that the effects of neostigmine are concentration dependent. Concentrations greater than 2.5 X 10(-5) M exhibit direct effects on the endplate receptor channel complex which are unrelated to acetylcholinesterase inhibition. These actions include: a prolongation of the gating kinetics of the endplate receptor channel complex, the production of an altered state of the receptor channel complex evidenced by a high frequency component to current fluctuation spectra, and a direct action to block the acetylcholine receptor.
研究了氨基甲酸酯类抗胆碱酯酶药物新斯的明对束带蛇肋皮肌电压钳制的抽搐纤维中乙酰胆碱受体通道复合物的浓度依赖性作用。低浓度的新斯的明（10^(-6) 或 10^(-5) M）增加了微小终板电流（MEPC）幅度和 MEPC 衰减的时间常数，而不改变 MEPC 衰减时间常数与膜电位之间的关系。乙酰胆碱或卡巴胆碱诱导的终板电流波动谱能很好地拟合为具有特征频率的单洛伦兹曲线，且低浓度新斯的明不改变单通道电导。浓度大于 5×10^(-5) M 的新斯的明降低了 MEPC 幅度，并将 MEPC 的衰减分为两个成分，一个比对照速率快，一个比对照速率慢。这些效应均依赖于电压和浓度。在浓度大于或等于 5×10^(-5) M 的新斯的明中记录的电流波动谱需要两个时间常数，一个比对照快，一个比对照慢。卡巴胆碱诱导的电流波动谱也得到了双成分谱，表明新斯的明的这些效应是直接的，而非乙酰胆碱酯酶抑制的结果。在用胶原酶预处理以去除接头处乙酰胆碱酯酶的肌肉中也得到了类似结果。当在同一纤维中分析时，从电流波动谱获得的快时间常数和慢时间常数分别随新斯的明浓度增加或膜超极化而减小和增加。新斯的明对通道寿命的影响经冲洗后是可逆的。这些结果表明新斯的明的效应是浓度依赖性的。浓度大于 2.5×10^(-5) M 时对终板受体通道复合物表现出直接作用，这与乙酰胆碱酯酶抑制无关。这些作用包括：延长终板受体通道复合物的门控动力学，通过电流波动谱中的高频成分证明受体通道复合物状态改变，以及直接作用阻断乙酰胆碱受体。
