Haws C M, Winegar B D, Lansman J B
Department of Cellular and Molecular Pharmacology, University of California, San Francisco 94143-0450, USA.
J Gen Physiol. 1996 Mar;107(3):421-32. doi: 10.1085/jgp.107.3.421.
The activity of single L-type Ca2+ channels was recorded from cell-attached patches on acutely isolated skeletal muscle fibers from the mouse. The experiments were concerned with the mechanism by which aminoglycoside antibiotics inhibit ion flow through the channel. Aminoglycosides produced discrete fluctuations in the single-channel current when added to the external solution. The blocking kinetics could be described as a simple bimolecular reaction between an aminoglycoside molecule and the open channel. The blocking rate was found to be increased when either the membrane potential was made more negative or the concentration of external permeant ion was reduced. Both of these effects are consistent with a blocking site that is located within the channel pore. Other features of block, however, were incompatible with a simple pore blocking mechanism. Hyperpolarization enhanced the rate of unblocking, even though an aminoglycoside molecule must dissociate from its binding site in the channel toward the external solution against the membrane field. Raising the external permeant ion concentration also enhanced the rate of unblocking. This latter finding suggests that aminglycoside affinity is modified by repulsive interactions that arise when the pore is simultaneously occupied by a permeant ion and an aminoglycoside molecule.
从小鼠急性分离的骨骼肌纤维上的细胞贴附式膜片记录单个L型Ca2+通道的活性。这些实验关注氨基糖苷类抗生素抑制离子通过该通道流动的机制。当将氨基糖苷类添加到外部溶液中时，它们会使单通道电流产生离散波动。阻断动力学可以描述为氨基糖苷类分子与开放通道之间的简单双分子反应。发现当膜电位变得更负或外部渗透离子浓度降低时，阻断速率会增加。这两种效应都与位于通道孔内的阻断位点一致。然而，阻断的其他特征与简单的孔阻断机制不相符。超极化增强了解阻断速率，尽管氨基糖苷类分子必须逆着膜电场从其在通道中的结合位点朝着外部溶液解离。提高外部渗透离子浓度也增强了解阻断速率。后一发现表明，当孔同时被一个渗透离子和一个氨基糖苷类分子占据时，由于排斥相互作用，氨基糖苷类的亲和力会发生改变。
